Can a new focusing screen affect exposure metering?

Question

After i replaced original focusing screen with a split one, it seems that every picture i take is overexposed now. Can it affect on exposure? Or i damaged something while replacing it? I own Nikon d7000.

Asked by Overdose

Answer

It can and it does. The metering sensors are placed up in the top of the prism housing, in other words it reads the light AFTER the light has passed through the focusing screen.

If you are using a camera that is designed to have different mattes replaced (bad news: You are not) and the screen is one the camera is designed for, the necessary adjustments that have to be made to the metering to compensate for the screen will be pre-programmed into the camera and all you have to do is tell the camera exactly what screen you are using. But, alas, this does not apply to you.

If the effect of the screen was constant, ie "this screen eats one and one third of a stop of light", you could simply dial in this as the exposure adjustment and be happy. Alas, it is most problably not so, matte screens tend to have variable effect on the exposure readings depending on aperture.

This means that all auto and semi-auto modes on the camera will be affected by misleading meter readings. Which leaves you the option of shooting the camera in M mode... which is a lot easier than it sounds actually. I've been doing it for years. As long as the light is not rapidly changing, you can take a peek at the histogram every once in a while and adjust exposure so that the exposure is where you want it to be.

Answered by Staale S

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Is over-exposure preferable than under-exposure?

Question

I am learning the world of Photography and always attempt to get the best possible shot but there are times when getting the exposure just right can be tricky depending on the situation. (I can tell experience will be a big factor here in learning how to get the correct exposure quickly.)

Assuming you are shooting in RAW and the exposure is not correct is it better to have the shot a bit underexposed and increase the exposure in raw, have it a bit overexposed and decrease the exposure or is it the same regardless of being over or under exposed.

Asked by Lynda

Answer

What you usually want to avoid is over-exposure. When you clip the highlights (i.e. your image has blown-out whites), you won't be able to recover any detail in these areas from the RAW file. So most of the time it is better to boost the darks with an underexposed RAW file.

Sometimes clipping is unavoidable though, depending on what you're trying to achieve with your photograph. So as a photographer you have to decide whether what you gain by over-exposure (more detail in the shadows) is worth what you lose (less detail in the highlights). Situations like: 'I don't mind that that streetlight is blown-out, because now I can clearly see the bicycle leaning against the wall in the alley'.

Answered by Nix

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What is “exposure safety shift”?

Question

I ran into the term "exposure safety shift" in this answer. What is exposure safety shift, and what is its intended purpose?

Asked by DragonLord

Answer

Exposure safety shift is a feature that overrides the set aperture or shutter speed (in aperture or shutter-speed priority, respectively) in the event said aperture or shutter speed causes the other exposure determinants required to achieve a correct exposure to exceed the camera's limits.

For example, if you are attempting to shoot wide open on an f/1.4 prime lens in an outdoor environment, and the required shutter speed exceeds the camera's limits, the camera will override the f/1.4 setting you entered, changing it to a value that will permit correct exposure within the camera's limits, such as f/2.0 if the shutter speed otherwise required is one stop faster than supported by the camera.

It helps prevent images from inadvertently being exposed incorrectly when the set exposure determinant results in other exposure values that are outside of the limits of the camera, but it may also result in unexpected changes in exposure settings.

On Canon EOS cameras, it is available in the two-digit series (...40D, 50D, 60D) and higher models. It is not available in Rebels (...500D/T1i, 550D/T2i, 600D/T3i; 1000D/XS, 1100D/T3). On Pentax, it is called "Auto EV Compensation" and is available in the higher models (eg. K-7, K-5), but is not available in the entry-level cameras (eg. K-x, K-r).

Answered by DragonLord

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What's the difference between holding a half-pressed shutter button and pressing the AE lock?

Question

As I have been looking around today the AE lock button is supposed to lock in the focus and exposure settings (aperture and shutter) so that the picture can be recomposed before taken. I also believe that holding my shutter button half pressed does the same thing.

As I type this I realize that there's a multiple successive shot consideration as well as the ability to release the shutter button while pressing the AE lock button, but I wonder if it is otherwise still the same?

Rebel XS (1000D)

Thanks!

Asked by tenmiles

Answer

It's mainly about using the camera as a tool in extreme situations where user experience and preference and circumstance mean that very fine differences in operation may make all the difference to achieving the desired shot. Use or non-use of AE lock may be appropriate for different users and differing situations.

The effect on exposure and focusing is identical as long as the camera is set to lock both of these on half pressure. With many DSLRs, having either or both or neither lock on shutter half press is an option. Similarly, the AE button can usually be set to affect focus and/or exposure and to lock or to toggle.

AE can usually be set to lock only on pressure or to toggle the controlled parameter(s) on/off alternately and focus and or exposure may be able to be controlled. This adds to theaspects needing to be considered.

I'll use "shutter operated" for actual operation of the shutter mechanism below to avoid confusion of the term shutter-released and button-released.

The differences are minor but significant. To some extent it is a matter of preference and personal experience and both have their place. The differences probably only matter at all under extreme pressure at the outside edge of user and camera shooting ability.

The following modes are "denied to you" by using the AE lock feature:

• With respect to multiple shots with the settings locked, this is also generally possible using shutter half-pressure but can take some getting used to. To do this the shutter is operated by full shutter button pressure, but the shutter-button pressure is then returned to half pressure rather than being released fully. This holds the locked settings and allows the next photo to be taken with the same focus and exposure settings. I find this immensely useful when you want a variable multi shot mode but slower than the auto repeat rate or at variable timing. This is to some extent an alternative to using tracking focus with the exposure locked and which is better is a matter of preference and circumstance.

• If you like to work in "one armed wallpaper hanger mode" you may wish to set the shutter button to lock only one of the two functions, allowing the other to release after the shot when the shutter button is held and then using AE or some other option to reset and relock the second function. For example you could lock and hold focus with the shutter button but not exposure, allowing the latter to be altered and then locked with AE button or some other button. This requires the brain to coordinate several fingers with he shutter finger needing to be partial-travel controlled and would not be usual (but, you did ask :-) ).

  Why would you want to do that? One reason MAY be to allow tracking something that held focus position but was moving through a zone of variable lighting. This would be a rather extreme case and not usually preferred.

• If you use AE lock it takes an extra finger operation to release it, which is one more factor (amongst many) setting the outside edge of what you can achieve in a given time in utterly extreme shooting situations.

Camera stability and ability to hold user-attention on the job at hand and to track a "target" (especially a fast moving one such as an animal or surfer or gymnast) is affected by using either AE lock or half pressure. Which way it is affected is again a matter of preference. I much prefer using shutter half pressure as it allows all control in the index finger without extra time or thought to access the AE button, to the extent that I never use AE lock, whereas others may value the lack of need to hold button tension in absolute extreme situations. (Time i a vanishingly small consideration once the preferred functionality becomes burned into the brain).

In a tripod situation of a fixed scene, or where a scene is not going to change for some seconds until a critical moment arrives (head turns, bird flaps, diver dives, ...) and a shot will be taken, perhaps with a "cable release", use of AE lock may be preferred to maintaining half pressure for an extend period. An alternative is to swap focus to manual mode and to accept the minimal penalty of exposure 'calculation' at exposure time, ot to use AE toggle, but this too is a preference.

Other similar and subtle considerations could be thought of.

Answered by Russell McMahon

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How do you photograph sand dunes?

Question

In 2010 I was lucky enough to visit Death Valley. While we were there we went to the sand dunes.

I took this shot

Its not how I remembered the scene, It seems as if a lot of the detail has been washed out, e.g. the shadows.

The heat was unbearable so that didn't help either. I have seen some stunning sand dune shots on flickr - some have the sand flying off the dune, some look dramatic with nice shadows.

Asked by Rob

Answer

I have also been lucky enough to visit Death Valley on two occasions and getting good shots of the dunes can take some planning ...

• Best time is sunrise as the low temperature helps to reduce heat haze that can rob your image of detail.
• Also sunrise is good due to the angle of the light, with it being low in the sky you get lots of shadows which create contrast enabling you to photograph the detail in the dunes.
• Try to shoot the dunes at 90 degrees to the rising sun so that you get maximum effect of the shadows.
• Yet another reason for sunrise is the golden light on the dunes turns them to a beautiful golden colour.
• You can use ridges of the dunes to lead the viewer in to your image, or get closeups of the abstract patterns of the sand on the dunes.
• Try to not include too much of the surrounding mountains or the viewer's eye may loose focus on the sand dunes in the foreground.

Get to the dunes at least an hour before sunrise and park on the edge of the road about 1km west of the car park, this enables you to hike in to the west end of the dunes. I went in winter when the sun was rising to the south east so we we able to get to the far side of the dunes and get that angle to see the shadows & contrast.

Ensure you have a headlamp as it is very dark indeed once you leave the car. There is some risk as the desert wildlife are certainly about at that time of the day, but if you walk heavy the vibrations help to scatter them.

Walk up on to the top of the dunes at the edge of the collection of dunes, ensuring you do NOT walk in front of where you want to shoot. There are often strong winds over night in Death Valley that help to erase footsteps from the previous day (I was unlucky to get a morning with no winds the previous night so had to try and find "man free" views).

Don't forget to shoot from very low down as well as from eye-level standing as both have a different view of the same stretch of wind patterned sand. Of course always shoot with a tripod, it can be more difficult than people realise to keep steady on the edge of a dune for example.

It can mean an extremely early start, a slightly scary hike in the dark for about 40 minutes, and hard work getting up some of the taller dunes, BUT the results can certainly be worthwhile ... http://www.thetrueshot.com/Death_Valley_National_Park.html#10

Answered by Barry Semple

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How do I effectively photograph when the sun is in the frame?

Question

I have been trying to get a good shot out of direct sunlight but my shots just turn out dark, even if I set my shutter speed to the 1000-4000 range at ISO 200. Another odd thing is that even if my shutter speed is below the thousands range, they still turn out dark when sunlight is involved.

What settings can I use to remedy this? I am using a Canon EOS 50 film camera, and I usually use ISO 200 films. I am in Manual Mode. What shutter speed-aperture combination can you suggest. What about ISO, or even lenses?

I have no means to scan the photos, so I guess I will just describe one of them in detail:

The picture is composed such that the camera is pointed at the sunlight, and a person is at the left side of the photo. The sun has just risen, about 7 am, and a little above the horizon. The output image is dark, so is the person, but the sunlight is beaming radiantly, forming some sort of a huge ball of light, and everything that's near the camera (the person, the plants around the person) is dark, and the sky is a bit dark too.

Asked by Ygam

Answer

How are you metering the photograph? There is no one aperture/shutter-speed/iso combo for any situation, you either need to get an accurate meter reading or 'guess'. When I say 'guess' I mean use the Sunny 16 rule which is:

In daylight, the appropriate shutter speed at f16 is 1/ISO

So if your ISO is 200 and your aperture is f16 then your shutter speed is 1/200 (or 1/250), from this you can figure out any other aperture/shutter-speed combo 'guess': f11 would be 1/400, f8 would be 1/800 etc.

Given this starting point you can hold the camera up and get a meter reading to see how far off the guess is and adjust accordingly by looking at the meter in the view finder and changing your aperture/shutter-speed until it reads a good exposure. You may also want to try changing metering modes to be tighter (spot) or wider (matrix) which has a pretty good discussion going here:

Rule of thumb for metering? When best to use Multi-Zone/Matrix, Spot, or Center-Weight?

EDIT (given the OP's edit):

The problem most certainly is metering. The camera is metering for the scene which sounds like its 90% The Sun and 10% your subject, you need to meter for your subject. You can accomplish this in a variety of ways:

-You could switch to spot metering and take a meter reading off your subject first and then use that for the photograph

-You could get really close to your subject and meter their chest/face such that they fill up most of the frame for metering and then go back to your original position and use that reading.

-You could look around near you for something in a similar amount of light (the ground in front of or behind your feet) and take a reading and use that

-Get more light on your subject somehow

-etc

Answered by Shizam

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Why does the exposure vary in these Nikon flash photos?

Question

The following 4 photos were all taken with a Nikon D300 at 1/250s, f/5.3, ISO-400, in shutter priority mode, with the on-camera pop-up flash. The only difference between them is the exposure bias, which varies from -4EV to +2EV. You can clearly see that the four pictures get brighter, despite having the same exposure settings.

Can you explain how/why this is happening? I have come up with a few possibilities, but I don't know which (if any) is actually correct:

• Is the camera adjusting the output of the flash to compensate for the exposure bias? This seems like the most likely solution to me, based on how the images look, but my understanding is that exposure bias was supposed to control the amount of ambient light in the scene, while leaving the flash alone, whereas flash exposure compensation is supposed to control the power output from the flash. (Flash exposure compensation remained constant for the four images).
• Alternately, is the camera applying some sort of automatic lighting correction in post-processing after the images were shot? (These images were all taken in JPEG mode, not as Raw).
• Is there some other effect at play here that I don't understand?

Edit I've copied-and-pasted the relevant exif data, extracted by exiftool, for the photos. The data is identical in all important fields (I checked using diff), except for the Exposure Compensation and Exposure Difference fields (I don't know what the latter means):

Camera Model Name               : NIKON D300
Exposure Time                   : 1/250
F Number                        : 5.3
Exposure Program                : Shutter speed priority AE
ISO                             : 400
Flash                           : On, Return not detected
Flash Type                      : Built-in,TTL
Flash Exposure Compensation     : +2/3
Active D-Lighting               : Normal

The Exposure Compensation and Exposure Difference fields for each image, from top to bottom is as follows:

Exposure Compensation           : -4
Exposure Difference             : -0.3Exposure Compensation           : -2
Exposure Difference             : -2.5Exposure Compensation           : 0
Exposure Difference             : -4.4Exposure Compensation           : +2
Exposure Difference             : -6.6

Asked by David

Answer

With Nikon, Exposure Compensation affects the overall exposure, including any automatically metered flash, while Flash Exposure Compensation (when available) affects only the flash's contribution to the overall exposure.

If the scene weren't essentially a flat plane (there isn't much depth to the scene at all), you could use Exposure Compensation to bring down the entire exposure, then boost the flash exposure to correctly expose your main subject. That would isolate the subject from the background. (The opposite can be set in theory, but it won't work unless and until somebody invents a "flash" that subtracts light from the ambient exposure.) More often, though, you'd use the Exposure compensation to compensate for the tonality of the scene (bumping it up for scenes consisting mostly of lighter tones or lowering it for predominantly dark scenes), then independently adjust the flash (usually downward) to add the desired amount of fill.

Note that with these pictures, there isn't much contribution to the exposure from ambient light at all, so if you had set the Exposure compensation to -1 EV and the Flash Exposure Compensation to +1 EV, you would have gotten pretty much the same picture as the normal exposure.

Answered by Stan Rogers

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What is T-number / T-stop?

Question

Usually, when discussing aperture of a lens, F-stop and F-number are used for quantifying. But some photographers, and especially videographers, also mention T-stop. The concept and numbering used (e.g. T/3.4) seem to be similar to F-stops.

What is a T-stop, how is it related to F-stop, and what are the differences?

Asked by Imre

Answer

F-stops are purely geometrical, the ratio of aperture to focal length, regardless of actual light transmitted. But all lenses absorb a part of the light passing through them, and the amount being absorbed varies lens to lens. So, in situations where even the slightest change of lights being transmitted affect the output, i.e cinematography, where many images are seen in rapid succession and even small changes in exposure will be noticeable, T-Stop is used as an standard. Since all lenses absorb some light, the T-number of any given aperture on a lens will always be greater (less light transmission) than the f-number. For example, a lens with f-stop 2.8 can have a t-stop 3.2, meaning a small portion (0.4) of the transmitted light have been absorbed by the lens glass elements.

A real lens set to a particular T-stop will, by definition, transmit the same amount of light as an ideal lens with 100% transmission at the corresponding f-stop. A f/2.8 lens can have t/3.2 and another f/2.8 lens can have t/3.4, so the actual lights being transmitted are not the same though they both have the same f-stop.

Answered by ShutterBug

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How does aperture affect exposure?

Question

I've heard that aperture can change the exposure, but I would like to know if this is true, and how it does it.

P.S. I hope this question isn't dumb like my last two.

Asked by J. Walker

Answer

It depends on your definition of exposure. Exposure is the overall amount of light that falls on the film or sensor. So by that definition, if you have a fixed shutter speed, then if you use a wider aperture, you'll let in more light, so you will increase the exposure. A narrower aperture opening will let in less light, so less exposure.

Keep in mind that a camera on Auto mode will adjust, so if you narrow the aperture, the camera will slow the shutter to compensate, and you'll end up with roughly the same exposure. So for aperture to affect exposure, you have to keep other parameters constant.

People also use the term exposure as a substitute for shutter speed, as in "I took a long exposure of the stars". If you are thinking exposure = shutter speed, then I can understand your confusion. But the real definition of exposure is the overall amount of light. This is affected by the exposure triangle of ISO, aperture and shutter speed.

Answered by MikeW

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Why does a 15-second exposure on my camera actually last 16 seconds?

Question

I was doing a test and wanted the shutter to stay open for 15 seconds -- no problem, I have a 15-second exposure setting in my camera. It seemed to stay open for about an extra second, though, so I started timing it. The 15-second setting takes about 16.1 seconds (+/- about 0.2 seconds or whatever my measurement accuracy is) between the first and second set of sounds the mirror makes. I also timed the 4-second setting, and it takes exactly 4.0 seconds (+/- my measurement accuracy); I measured the 30-second setting at 31.9 seconds.

For the sake of this question, I'm assuming that the 15-second exposure is taking exactly 16 seconds and the 30-second exposure is taking exactly 32 seconds, while the 4-second exposure is taking exactly 4 seconds.

I understand why 16 seconds would be more desirable (and probably easier to implement in software) than 15 (more-precisely one stop longer than 8 seconds), and I also realize that for a 15-second exposure, 1 extra second is a fraction of a third of a stop, and I probably wouldn't be able to see the difference between two otherwise-identical pictures taken at 15 and 16 seconds. But why is the setting called "15" when it's actually 16 (and it's relatively easy to measure that delta)?

Is this common among cameras, or unique to my camera's brand (Canon) or model (30D)?

Is there a spec somewhere that calls this out?

Should I be trying to measure more shutter speeds (in the fractions-of-a-second range) to see if my camera is mis-behaving?

If this is intentional, do the shorter shutter speeds that aren't exact halves/doubles also have different shutter speeds than they claim (e.g. 1/60 - 1/125)?

Asked by drewbenn

Answer

In "classic" cameras systems exposures varied by a factor of two between adjustment steps and by a factor of 2 with standard aperture number changes. The aperture f numbers usually provided vary by a factor of square root of 2 as the aperture is proportional to the square of the diameter and stop numbers relate to the diameter.
ie aperture is an area measure which is proportional to diameter squared. Yes, that hopefully makes sense if you read it slowly a few times :-).

The important thing is that a "classic" range of exposure times would be, starting at 1 second:

• 1 2 4 8 16 32 64 128 ...

The question is more why it would be labelled 15.

They may well be wanting to match the times to fractions of a minute so eg

• 1 2 4 8 15 30 60 120 ...

BUT leaving theactual values in a true power of 2 progression from 1 second.

However, going to faster steps starting at 1 second we also "run into problems".

1 1/2 1/4 1/8 1/16 1/32 1/64 1/128 is OK in fractional form BUT when written as decimal we get

1 0.5 0.25 0.125 0.0625 0.03125 0.015... ... you get the idea. Gets messy.

SO along the way people cheated slightly. The series may end up slightly like

1 1/2 1/4 1/8 1/16 1/30 1/60 1/125 1/250 1/500 1/1000 1/2000 1/4000 1/8000 ...

The decimal values get untidy around 1/16th to 1/125th but get tidy again below 1.250th and people largely don't use these.

The slight errors introduced are inside the margin of error in all but the most tightly controlled lighting situations and well inside what any eye-brain can guarantee they have seen (even if the eye can actually resolve it).

The first few differences are:

1/32 : 1/30 = 6.7% longer 1/64 : 1/60 = +6.6% longer 1/128 : 1/125 = +2.4% 1/256 : 1/250 = +2.4% at all settings above here

Your 15 seconds shown, 16 seconds actual is 6.7% longer than shown.

---

BUT many modern cameras blow all this away with shutter speeds in 0.3 EV or other steps that seem good to them. Worse, auto ISO or shutter speed or aperture systems may choose semi random settings so you MAY see eg 1/325th of a second. Very hard on classical system sensibilities ;-).

Answered by Russell McMahon

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How can I set an exposure time over 30 seconds with a DSLR?

Question

Most DSLRs have an exposure time limit of 30 seconds. Now I'm asking myself how is it possible to create images about over 1 hour or longer, like these two:

• http://www.flickr.com/photos/froge/3899184535/
• http://www.flickr.com/photos/_belial/481126091/

(I have a Canon 60D)

Asked by Poru

Answer

Yes it is possible with all DSLRs.

The 30s limit of all non-Olympus DSLRs is for timed exposures, meaning you dial in the time ahead of time and the exposure takes up to 30s (or 60s for Olympus).

All DSLRs also have a bulb mode which you press the shutter to start the exposure and let go when you are done. This can also be done with a remote control which is highly recommended to avoid shaking the camera during the exposure.

Bulb modes also have limits but manufacturers do not all publish what it is. For Olympus and Panasonic, this is known to be 30 minutes. Some cameras can take a single exposure of several hours. Regardless of the model you are always limited to the battery-life of your camera unless you use an AC-Adapter and have somewhere to plug it in.

Digitally you can simulate extremely long exposures using Exposure Stacking which basically adds up multiple exposures to make a longer one. A lot of astro photography is done that way, just make sure that your camera does not apply Dark-Frame subtraction between shots otherwise you will have gaps in your star trails. On some cameras you can disable Dark-Frame Subtraction but not on all.

Answered by Itai

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Define own exposure time - DSLR

Question

The most DSLRs have exposure time limit of 30 seconds. Now I'm asking myself how is it possible to create images about over 1 hour or longer like these two:

• http://www.flickr.com/photos/froge/3899184535/
• http://www.flickr.com/photos/_belial/481126091/

(I have a Canon 60D)

Asked by Poru

Answer

Yes it is possible with all DSLRs.

The 30s limit of all non-Olympus DSLRs is for timed exposures, meaning you dial in the time ahead of time and the exposure takes up to 30s (or 60s for Olympus).

All DSLRs also have a bulb mode which you press the shutter to start the exposure and let go when you are done. This can also be done with a remote control which is highly recommended to avoid shaking the camera during the exposure.

Bulb modes also have limits but manufacturers do not all publish what it is. For Olympus and Panasonic, this is known to be 30 minutes. Some cameras can take a single exposure of several hours. Regardless of the model you are always limited to the battery-life of your camera unless you use an AC-Adapter and have somewhere to plug it in.

Digitally you can simulate extremely long exposures using Exposure Stacking which basically adds up multiple exposures to make a longer one. A lot of astro photography is done that way, just make sure that your camera does not apply Dark-Frame subtraction between shots otherwise you will have gaps in your star trails. On some cameras you can disable Dark-Frame Subtraction but not on all.

Answered by Itai

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What are the advantages and disadvantages of using auto ISO on a DSLR?

Question

What are the advantages and disadvantages of using auto ISO on a DSLR?

Using manual ISO obviously gives you more control, but auto ISO may mean that you get "the shot" under quickly changing conditions (such as street photography, varying quickly between direct sunlight, shade, indoor lighting.

Is auto ISO a convenient feature or a bad habit?

Asked by Freed

Answer

Hardware ISO control exists to amplify the signal before readout to maximise the signal to noise ratio. Without read noise you wouldn't need ISO if you had a high precision ADC as you could simply shoot everything at the native sensitivity, and if the image was too dark just apply digital gain (multiply the pixel values).

It's easy to demonstrate this effect. The following two images had the same shutter speed and aperture. The top one was shot at the metered ISO 1600, the bottom one was shot at ISO 100, which resulted in underexposure which was fixed in photoshop:

The ISO 100 image is noisier, on account of read noise being amplified when the exposure is fixed. The ISO 1600 is amplified before readout so read noise is much lower.

As such ISO is not a creative control (like shutter speed and aperture) it is a practicality, required by the need to overcome noise. Contrary to popular opinion using a lower ISO wont give you less noise. Unless you also decrease shutter speed or open the aperture, both of which can result in a different looking image.

I don't consider it "lazy" to use auto-ISO, as the camera is not altering the creative controls, it's just trying to minimise read noise for you.

With auto-ISO in manual the pros and cons are pretty clear:

+ You can adapt to changeable lighting whilst sticking to your preferred aperture and shutter speed.

+ You shouldn't need to

- You're still at the mercy of the camera's light meter, you can get overexposure if the meter gets confused (which wouldn't happen if you fix the ISO to a low value).

- Some cameras don't offer exposure compensation with auto-ISO meaning if the metering is consistently off due to scene content you might not be using the optimal noise reducing ISO.

Using auto ISO in either program, shutter priority or is slightly different as there are two or three values for the camera to choose, and the ISO value is no longer simply dependent on the light reading.

+ You'll be able to sue preferable shutter speeds aperture more of the time than if ISO sensitivity was fixed.

- You're at the mercy of the auto-ISO algorithm, you're still letting the camera make creative decisions.

Answered by Matt Grum

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Can telephoto lenses cause the background to be darker than the foreground in the same light?

Question

I took this photograph yesterday afternoon at around 5:15pm EDT, about two hours before sunset:

The sky, in my perception, was bright, and my little subject is standing in the same lighting as the bushes behind her. She's well-exposed, but the sky and background foliage appear darkened — even though they were most definitely not in the shade. To my eye, everything was bright, and while I'm not unhappy with the contrast in the final result, it seems a bit strange.

This is a linear histogram of just the foreground subject (selected by hand):

and here's the same for the background:

and for completeness, the full-image histogram:

Here's an iPhone snap taken a few minutes later; she's in the shade in this, but when the above picture was taken, she was in the bright sun by the shrubs you can see in the center background, as are the shrubs themselves.

That's far from a technically-great image by any measure, but you can see the brightness of the sunny areas.

Here's the key EXIF from the image:

Date                            : 2012:03:23
Time                            : 16:12:54
Camera Model Name               : PENTAX K-7
Lens Type                       : smc PENTAX-DA* 200mm F2.8 ED [IF] SDM
Focal Length                    : 200.0 mm (35 mm equivalent: 300.0 mm)
Flash                           : Off
AF Point Selected               : Center
Metering Mode                   : Multi-segment
Effective LV                    : 13.5
Exposure Compensation           : 0
ISO                             : 160
Aperture                        : f/4.0
Shutter Speed                   : 1/1000

What's going on here? Is this somehow an effect of the 200mm focal length I used? And if so, how could that be? (I wouldn't think this to be the case, except it's not something I've really noticed with my more-typically-used shorter lenses, even in similar outdoor situations.) Or is it simply a matter of the difference in tones and reflectivity of her bright clothes and light skin as compared to the green bushes? Are my eye and brain compensating for the dynamic range such that my judgment of the scene doesn't match reality? That seems plausible, but the sky was definitely bright — we've been having uncharacteristically lovely spring weather in Boston — and it appears rather dim in the photo.

Asked by mattdm

Answer

I don't think that focal range has anything to do with it.

I think that the issue is that different materials reflect light differently. Althought the different elements of the picture are illuminated by a uniform light source, they do not reflect the light equally. The green foliage is normally about 2/3 stops darker than neutral (18%) grey. The white part of the dress is of course much brighter than neutral grey. The colors in the dress look very vibrant, so I would suspect that would also reflect more light than neutral grey. And she does look like she has bright skin, so I would think that she would also reflect more light than neutral grey.

So I think that the darkness of the background is simply due to the fact that it reflects significantly less light than your main subject that the exposure has been metered for.

When you are physically present at the scene, your brain makes up for this, and what you perceive is that they are of equivalent brightness. But when you take a photograph and look at the photograph, it will reveal the difference in light reflection.

Answered by Pete

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How to best view test shots on camera LCD in bright, outdoor photo shoot

Question

A couple weeks ago I did a basic outdoor photo shoot for a family. It was mid day, and the sun was out. I took test shots initially and when viewing the shots on my DSLR's LCD screen they appeared to look good.

After getting home and viewing the photos on the computer it was obvious that a lot of the shots were overexposed. This was not immediately obvious outdoors in the bright daylight.

How does one view test shots on your camera's LCD screen in a bright outdoor environment and know that the settings are correct?

Asked by Jakobud

Answer

Don't just look at the photo, but look at the histogram, too! Often when looking at just the photo on an LCD, you can't get a good feel for under- or over-exposure, or even color balance, but if you look at the histogram (especially the RGB histogram if your camera model supports it), it will be immediately obvious if something serious is off.

Answered by Flimzy

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Why are these light trails large blobs of light instead of nice thin lines?

Question

I'm trying to shoot a traffic light trails with my point & shoot camera (Panasonic Lumix DMC-LZ8). But the oncoming vehicle headlights are appearing as large blobs of light and not exactly thin lines like I see normally in other light trails. I set the aperture to 8.0 (thats the maximum my camera supports) and the shutter speed to 6 seconds. ISO at 100. Also the street lights are emitting a blob of light too. Anything I can do to reduce all the light?

Asked by Uday Kanth

Answer

The blobs result from the bright areas being extremely overexposed. So, quite simply, you need less light coming in. The ways to do that are:

1. shorter shutter speed (keeping ISO & aperture the same...I'm assuming you're operating in manual mode and can control those). You probably don't want to do that in this case, because it will decrease the "trail" effect.

2. smaller aperture (keeping shutter & ISO the same). But as you've said you cannot go any more on that.

3. lower ISO (keeping aperture & shutter the same). I don't know the specifics of this camera but guessing 100 is the lowest? So probably that's out.

4. use a neutral-density (ND) filter (all other variables the same). Given the above points, I think this is the only way you're going to improve things in this image. If your lens does not accept filters, you could probably rig up something using one of the larger square/rectangular ND filters and some rubber bands or some such. A Polarizing filter might help some; not so much because of the polarizing effect but because they also generally decrease the amount of light coming in...that is the main issue in this case.

As another poster mentioned, you could possibly change your angle to the cars so that they're not coming directly into your camera, but that obviously changes your composition so that may not be a realistic option depending on what you have in mind.

Answered by djangodude

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Is this picture too dark? [closed]

Question

http://500px.com/photo/5546307

Probably some personal taste applies here too, but

1. Would be better to have things more bright in order to have some area which are at the bright end of the range?
2. Actually the border up right of the flower is white so probably rising brightnes or exposition would give some overexposed areas?

Asked by Paolo

Answer

The highlights on the flower are very close to pure white - I measure RGB(252, 252, 252), so on that basis, no.

As dpollitt says, anything else is subjective.

Answered by MikeW

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Should I shoot underexposed photos?

Question

Someone more experienced than me said that he always shoots so that his photos are underexposed (darker) and I should too. The reasoning being that you can always increase the exposure in postproduction, but you can never get the details back from overexposed parts of the photo.

But if I think about it I think that you lose the dynamic range with this technique. So I have three questions:

1. What should I do? Should I do it that way, or does it depend on the circumstances (like if I have enough time to test for proper exposure, etc.). Or should I rather try to learn to "guess" the right settings (I will fail a lot but also learn a lot)?
2. What do you do? How do you aproach a shoot?
3. How does underexposing affect dynamic range of photos? Does it effectively reduce contrast?

Asked by duality_

Answer

With underexposure, a third of a stop won't hurt you much. Two-thirds is not great, but not that bad. A whole stop means you're doubling your noise. Two stops and you're quadrupling it. So underexposure is by no means "free", but there are grades of it.

With overexposure, any amount will start to clip. Whether that is very detrimental will depend on the subject matter, but it's generally more damaging to your image than the noise of underexposure.

Now to your questions.

• What should I do? Should I do it that way, or does it depend on the circumstances (like if I have enough time to test for proper exposure, etc.). Or should I rather try to learn to "guess" the right settings (I will fail a lot but also learn a lot)?

No, don't underexpose. Aim to expose correctly. If you are not sure if you've exposed correctly, and you're using JPEG (or TIFF?) then it's better to underexpose a little than overexpose a little, that is true, though it still won't get results as good as exposing correctly. If you have the opportunity to try again if you make a mistake, it's better to aim for a correct exposure and try again later if you don't get it.

• What do you do? How do you aproach a shoot?

I try to get it spot on. I check the display on the LCD, and might check the RGB histogram, and if I've under- or over- exposed then I take another one. Of course this is not a luxury you have if you're doing photojournalism or anything like that. But that's me.

I also shoot in RAW, where you can manipulate the exposure a bit more afterwards. I don't want to say you can overexpose, or that it can work miracles, because you can't and it won't. But you can at least have a little more play in your exposure afterwards.

• How does underexposing affect dynamic range of photos? Does it effectively reduce contrast?

Underexposing reduces dynamic range of your shadows. So underexposing by one stop reduces your dynamic range in shadows by one stop (ie, by half). The noise floor raises, so the loss in dynamic range is expressed as an increase in noise.

It doesn't reduce "contrast" as such. It increases noise and you lose some detail in the blacks - I am not sure how you are using the word "contrast" but it doesn't sound like how I'd describe it.

Answered by thomasrutter

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Ways in order to achieve dramatic lighting styles?

Question

My question is more specific to the situation I am going to be shooting [with the subject being a person laying down in a hospital bed]

The photo will be taken from the ceiling above the bed and catch the entire bed in the frame.

Any tips you could offer this beginner would make me happy!

What are different ways of approaching the lighting of this subject to make it dramatic?

Asked by Graeme

Answer

If you want dramatic shadows, you obviously need to prevent light from falling on those shadow areas. There are a few obvious sources of that light:

• ambient light. Room/window light which is not coming from your main lighting source. Turn off your main light and see what other light is falling on the subject. Try to block that light (shut windows, turn off lights, close doors)

• reflected light. If you have white walls, white bed sheets, you'll get a lot of reflected light. Out of camera shot, try to use black materials to absorb the light rather than reflect it.

• main light

  • if your main light source is too large the light may wrap around the face. For more dramatic lighting use small, hard lights.

  • Light may be scattered onto ceilings and walls - if you can use snoots, grids or barn doors to concentrate and direct the light, you'll get more contrast on the face. Not sure what lamps you're using, but try to shield them so the light is directed only at your subject.

  • Light falloff - the closer you get the light to your subject, the more light falloff you'll have (due to the inverse square law), so move your light as close as you can without being in frame (or remove in post processing if you must)

• fill light. In addition to your main (key) light, you may have other lights you're using. If you don't have the lighting (contrast) ratio you want, use less fill. Turn those lights down if you can, or move them further away.

Answered by MikeW

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How and why do you use an image histogram?

Question

I realize that an image histogram is a graphical display of an images tonal distribution (i.e. horizontal darks to lights, vertical pixel distribution), but how do YOU really use it and why? I mean, can't you determine everything you need just by looking at the image? I imagine there is no right answer, but I'm interested to hear how others use it (or don't) and why...

Asked by heavilyinvolved

Answer

While there may not be a "right" answer to this question, there are "correct" answers. A histogram is a powerful tool, and when you understand how to use it effectively, it can greatly help your photography.

As you mentioned, a histogram is a representation of tonal range and distribution in a photo. The basic mechanics are as such:

1. A histogram represents tonal range from left to right, with blacks and shades to the left, progressing through midtones in the middle, to highlights on the right.
2. The "volume" of any given tone is represented by the height of the vertical line that represents that tone.
   • A vertical line at the very left end is indicative of the volume of total black tones
   • A vertical line at the very right end is indicative of the volume of total highlight tones
   • A vertical line in the very center is indicative of the volume of 18% gray tones
3. The tones for an image are taken from the intensity of each pixel (chroma, or hue, is ignored, and only brightness/lightness/luminosity is measured)
   • The total number of tones in an image is dependent upon the bit depth of the image
   • An 8-bpp (24-bit) image has a total of 256 distinct tones
   • A 12-bpp (36-bit) RAW image has a total of 4,096 distinct tones
   • A 14-bpp (42-bit) RAW image has a total of 16,384 distinct tones
   • A 16-bpp (48-bit) RAW image has a total of 65,536 distinct tones
   • A 32-bpp (96-bit) HDR image is effectively able to represent infinite tonal range
     • As a real (float) number, its values range from 1.0 x 10^-37 through 1.0 x 10^38
     • In more real-world numbers, tonal range from black, through very dim starlight (0.00001), through indoor lighting (1-10), through the sunlit outdoors (1,000,000), to the brightness of the sun itself (100,000,000) and well beyond can be represented in a single HDR image
4. There is no technical limit to the height of a histogram.
5. Unless you have a very low-bit image, a single histogram is generally incapable of representing every single individual tone in an image, so each vertical line tends to represent a small range of similar tones.
6. A color histogram can represent a much greater range of information than a pure tonal histogram in the same space.

Given these facts about a histogram, there is a wide variety of information you can gleen from one:

• Contrast
  • Contrast is the measure of difference between the brightest tones and the darkest tones.
  • The more range a histogram covers between its left and right edges, the greater the contrast of an image.
• Key
  • Key is the rough measure of brightness in an image, with high-key being brighter, and low-key being darker
  • If the histogram is bunched up in the highlights, you have a high-key image
  • If the histogram is bunched up in the shades and shadows, you have a low-key image
• White Balance
  • When using a colored histogram, the convergence of red, green, and blue peaks is an indication of white balance
  • In particular, the offset of major blue peaks can be a strong indicator of the warmth or coolness of a photo
• Tonal Range
  • The balance and height of peaks in a histogram is an indication of tonal range and tonal balance
  • Parts of the histogram that are very low (valleys) indicate very low volume for those tones
  • Parts of the histogram that are very high (peaks) indicate very high volume for those tones
• Color Volume
  • A basic colored histogram will often show gray, red, blue, and green
  • A more advanced colored histogram may also show yellow, magenta, cyan
  • Colored peaks are an indication of the volume of those given primary colors
  • The horizontal position of a colored peak is an indication of the tone of colors of that particular primary or primaries
    • Gray indicates a balance of primary colors at those tones
    • Off-primary color peaks (or partial height lines), such as yellow, magenta, and cyan, indicate a blend of two primary colors at those tones

EDIT:

As mentioned by Jordan H., there is a trick called "expose to the right" (or ETTR) that can be useful to get you the optimal RAW data. When shooting a scene, particularly those that have a broad range of contrast that may be on the border of, or possibly slightly beyond, the 5-6 stop dynamic range of a digital camera, capturing enough tonal range in the shadows can be difficult. This is due to the the limitations of most current digital sensors, and how they are more sensitive to highlights than shadows. "Exposing to the Right", which is a technique where you slightly overexpose your shots by 1/3 to 1/2 of a stop (which, in turn, shifts your histogram to the right...toward highlights), can help mitigate these limitations. Exposing to the right can also help alleviate noise problems in the shadier parts of your images. It should be noted that exposing to the right requires that you use RAW format, as only with raw are you saving enough information to correct your overexposure during post-processing to bring your image back into normal range. The benefit of this technique is that it allows you to capture detail that would otherwise be lost, without the need to resort to ND grad filters or other more extreme measures.

This guideline is just that, a guideline. With newer camera sensors, dynamic range is improving, and capturing a greater range of contrast in a scene with a single shot is easier. However, even as digital sensor dynamic range improves, there will always be times when we need to shoot "on the edge" or what is possible, and tricks like shooting to the right will always be useful.

Answered by jrista

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