What can go wrong with extreme long term exposure?

Question

Ok, maybe I'm crazy, but I'm curious what will happen when I combine a ND400 filter (9 stops) with a zone plate or zone sieve "lens."

If I'm shooting a sunset, it I might get a 30 second exposure with the zone sieve in place. (I have two, they are about f50 and f100). So if I tape the ND400 in front of it, do I multiply the 30 seconds by 512? (2 to the 9 is 512). This will yield about a 4 hour exposure.

With a 4 hour exposure, what can go wrong? I expect some overheating on the sensor, but how bad will it be?

And yes, I know I need to experiment but at hours per shot, a bit of advance planning will go a long way.

(Note, I have a power adapter for the camera, so I could use a car battery and an inverter to give me 4 hours of power in the field.)

Asked by Paul Cezanne

Answer

I really like the idea but in my opinion anything can go wrong with a 4 hour exposure.

Firstly, you may be right about the sensor. It might overheat, although opinions are divided on this issue. CMOS sensors are really energy efficient and I've never experienced sensor overheating while taking pictures or recording videos. However, my longest exposures were 3 consecutive 30min exposures, captured with a Nikon D7000. Some people claim that the reason why you can only capture 20min videos on most DSLR cameras relates to sensor overheating. I personally believe that this isn't really a problem. Most advanced DSLR cameras are probably equipped with a thermal cut-off system that simply turns the sensor off when it reaches critical temperatures (please don't quote me on that). Besides, overheating also depends on a variety of outside factors like the weather.

Secondly, with a 4 hour exposure it would be difficult to determine the light conditions and calculate other settings such as ISO and aperture. I realise that you want to use the zone sieve so the aperture is already determined. However, with such 'extreme' setup, your built-in light meter will become inaccurate or even unusable. Therefore, if you are wrong with your calculations, your pictures can be either overexposed or underexposed. I personally think that a 4 hour exposure is just like a stab in the dark. You never know what to expect as the light conditions can drastically change in 4 hours.

Next, the images may be completely unusable due to the amount of noise. My experience is limited to APS-C sensors but I can tell you that a 30min exposure I took was very noisy. It took me a long time and effort to reduce the noise and the image quality wasn't great.

Finally, you have to think about image stabilisation. Like I said, anything can happen during 4 hours so you have to stabilise your tripod and protect it from outside influences such as a strong wind or even rain.

I hope I managed to answer your question and I'm looking forward to seeing your 4 hour exposure soon.

Best Greg

Answered by Greg

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What is the effect of Long Exposure on file size

Question

Is it a rule that long exposure will produce a larger size file compared to a shorter exposure? It seems logical (you are writing more data to the memory card when you expose more time).

What about shooting long exposure at night and at day? I believe that shooting in a day light will produce a larger file than shooting at night for the same exposure time (I've no idea why I believe so)

Asked by Akram Mellice

Answer

No, it doesn't work that way. The image file isn't built up as the exposure goes on, but rather is made from a full read of the sensor when the exposure is complete. So, you're not writing more data to the memory card when you expose for a longer time.

Each photosite — one "pixel" on the sensor — is a counter that goes up as it's hit by more photons. It's actually an analog device, but when read at the end of exposure, a single digital value is produced (usually 12 or 14 bits). This value is simply the total amount of light that site received. If the particular pixel is all dark, it'll be 000000000000, and if it's all light, it'll be 111111111111. There's no record of how long it took that all-full sensor to get to that state — it could be very, very bright with a wide aperture, so you could get that value in ¹⁄₁₀₀₀th of a second. Or, it could be so dark out that it takes 30 minutes to get the same result.

In the end, though, it's the same single value. And all together, there's no more or fewer values no matter how long the exposure is.

There is another factor, though. Some files will compress better than others. Patterns compress well, and of course large identical areas compress best of all. Arbitrary detail compresses poorly, and random data worst of all. Since noise is by definition random, very noisy images produce the largest files. There isn't a direct correlation to exposure length here, but longer exposures may have more noise as the sensor heats up. So, that may be a practical consideration, but it isn't because of the accumulation of data per se.

Answered by mattdm

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Will stacked ND filters perform as well as a single 10 stop ND filter?

Question

I have the Tiffen 0.9 ND filter which gives me approximately 3f stops reduction. I like to really slow things down and although it's sufficient in low light it just won't do in daylight.

Should I get a pair of 2 more 0.9 ND filters to stack or should I would a single say 10 stop filter be a better solution? Will the stacked ND filters perform as well as a single 10 stop filter?

I would like to be able to slow things down to the point where I get similar results to this photo which was shot at f4, ISO 200 and 75 seconds.

Asked by Jakub

Answer

From a functional standpoint, yes, you could essentially achieve the same effect with multiple stacked filters as a single high-density filter (say a 10-stopper.) There are a variety of concerns to be aware of, however, regarding stacking multiple filters.

1. Filter quality:
   • The Lee "Big Stopper" 10-stop ND filter is pretty high quality glass filter
   • There are two Lee ProGlass filters (0.6 and 0.9) of the same quality
   • The full range of standard Lee ND filters, (0.3, 0.45, 0.6, 0.75, 0.9) are resin
   • Many third-party filters are resin, a very few are glass
2. Color cast:
   • Stacking lots of resin filters can cause strange color casts
   • With digital, color cast is usually an easy post-process fix
3. Vignetting:
   • Stacking enough resin filters means a pretty thick hunk of junk on the end of the lens
   • At least four resin ND filters (0.3/1stop, 0.6/2, 0.9/3, 1.2/4) are needed to match a single 10-stop filter
   • On wider-angle lenses, you can barely get away with two stacked filters let alone four without vignetting
4. Flaring:
   • Any additional optical device added to the light path adds the potential for flare and ghosting
   • Stacking four ND filters adds a total of 8 additional surfaces which can reflect
   • To my knowledge, no 4x4/100mm filters are multicoated, so their chances of flaring/ghosting are high
5. Versatility:
   • A single 10-stop filter still leaves you some room to also stack on a graduated ND filter to balance contrast

If you want to do some serious ND work, such as 5 minute exposures of sunset along the coast, you should get a 10-stop filter. You'll probably also need at least one GND to normalize scene contrast if you are photographing a sunset/sunrise, which would usually require a setup like the Lee base filter kit with a tandem adapter and an additional independent filter holder (for a total of up to 8 filters)...that is pretty much guaranteed to add vignetting on anything other than a telephoto lens.

Answered by jrista

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How can I prevent blurred images when using a tripod?

Question

I'm doing panoramic HDR photography for work using one of those stupid cheap mirror balls mounted on a tripod (not my decision!) and I am noticing on my longer exposures that sometimes I'm getting blurred images. I am using mirror lock-up and a 2 second delay. SOMETIMES on my 2 or 3 longest exposures the image is blurred when I view it in Photoshop. I am using a Canon kit lens with a +2 magnifying lens mounted on the front, and I'm SURE I'm not touching the tripod at all. The only thing I can think is causing this is the image stabilizer which is pretty much kept on at all times. Can anyone think of anything else that might cause this behavior?

EDIT: I might add that it's not ALL of my longest exposures. It's one or two, sometimes 1, sometimes NONE, but usually it's the 2nd longest exposure. The tripod itself is a sturdy Manfrotto. Now that I think of it, I usually have to bring all my images into Photoshop first before merging to HDR because they all seem to be out of alignment by up to 4 or 5 pixels. The way the panorama head works on this contraption is that there is a head mounted on the tripod with a screw for mounting the camera, pointing up at the mirror lens. The plate that the camera sits against can be adjusted up or down by millimeters so that different camera/lens configurations can be used.

UPDATE: Ok, after reading all your comments/suggestions, let me give you guys some more info. For those of you wondering, the mirror ball contraption is used for when you need a 360 panorama of your subject (in my case it's a room inside a condominium) in one shot (the system is used a lot by realtors who need quick shots of a whole room using a cheap point and shoot). You get a low-res pic since you are shooting a reflected image of the image, but for quick solutions to real estate photography it does its job. What you get is a large round image that you then stick into the software for this particular mirror ball manufacturer and you can either 'roll' the image out into a panoramic cylinder image or you can use it to turn into a 'virtual tour' for showing on the web.

Here is a picture of what they look like mounted to a camera (tho my setup is mounted on a tripod and looks a little different):

Here is the image that these things produce:

Here is what I get sometimes--note that it looks like camera shake:

Here is the exact same shot taken right afterwards to ensure at least one of the exposures comes out sharp:

I have mirror lockup enabled, and am using a delay before shooting, so there is no issue with me touching the camera and accidentally causing blur once the shutter opens, or the mirror causing vibrations. Because this sucker takes a picture of the WHOLE room at once, I can either choose to stick it on a 10 second delay and leave the room or sit underneath it with a smaller 2 second delay. Since an HDR series takes me about 15 pictures, it is not expedient for me to leave the room for 10+ seconds at a time, and a shutter release cable (or IR remote) isn't necessary if I'm using a timed delay (and if I used it it would be in the shot unless I was still sitting underneath the tripod). I am not using auto bracketing but manually dialing in each stop. The building is rock solid, well away from the road, and is built to withstand hurricane force winds. I am not walking around during the shot, but sitting underneath it. I make sure no part of my body is close to any element of the tripod before I press the shutter, and hold my hand away from the camera until the timed delay passes and the camera takes the picture. I have taken to taking two shots of each of my exposures that are more than 1 second as inevitably at least one of them will be completely blurred. The others will maintain their sharpness.

So, somehow, even tho the building is solid, the mirror is locked up, there is a timed delay, I'm not touching the camera or the tripod and the tripod is sturdy, I am getting camera shake. Because these mirror ball images are EXTREMELY sensitive to vibrations and I am positive I have eliminated any human reasons for shake, I gotta wonder if the only thing that's left is the IS?

Asked by Heather Walters

Answer

One of the Great Truths of photography is that for every camera/lens/tripod combination, there is a range of shutter speeds that you need to avoid. At faster shutter speeds, the exposure is completed before the system's physical resonance has a chance to blur things; at slower shutter speeds the system has damped out before the exposure is complete, and the majority of the exposure occurs when the system is essentially motionless. That is true of any lens/camera/tripod, but the problem is usually difficult to notice except on a very high-resolution system.

It's the speeds in the middle, where the system is in motion for the majority of the exposure, that you need to find and avoid. Mirror lock-up can only help a little, since the action of the shutter can be enough to initiate the resonance. Since you are experiencing this problem on only one or two exposures out of a three-shot sequence, I'd be willing to bet money that the shutter speed is what you're changing between exposures and that the problem is occurring consistently in a range of shutter speeds.

In this situation (with the one-shot 360° lens attachment), the problem is exacerbated by the inherent springiness of the mirror stalk. (There are more stable designs, but then you're generally shooting through a cylinder of polycarbonate that's a real sonofabee to keep meticulously clean and unscratched.) Just find out which shutter speeds are causing the problem, and adjust your exposure settings to avoid them. You may want to find the best (least blurry) speed and sharpest aperture, then base your bracket on a varying ISO instead.

Answered by Stan Rogers

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Why does my camera make a whirring noise during a long exposure?

Question

I have a Sony Alpha a55.

When I take a long exposure photo, while the shutter is open, the camera makes a whirring sound. What causes this noise and why is it necessary to the camera's operation? (I have interface sounds turned off — so I suppose this is some piece of the hardware physically making a noise.)

Asked by jtbandes

Answer

I'm familiar with Canon lenses featuring Image Stabilization that can emit a faint "whir" as IS operates. Your Sony body has a form of image stabilization built into the body, and if that's on during a long exposure, you might be hearing that as it operates.

If you're shooting long-exposure shots with the camera mounted on a tripod (which would be best), it's usually recommended that image stabilization be turned off (I believe this to be the case for your a55).

Answered by D. Lambert

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How do I lengthen shutter speed with out washing out the picture?

Question

I read this question, and I tried some long exposure shots myself. Every one of my shots though, is washed out. How do I achieve a long shutter speed while keeping the lighting natural?

Asked by J. Walker

Answer

You still need to expose correctly! Exposure is covered in depth in this answer. What you've done is increase one leg of the exposure, by using a longer shutter speed. Now you need to decrease the overall exposure by the same amount to get back to a properly-exposed image.

So for example, if your camera's exposure meter told you to take a picture at 1/60 s, and you carried all the settings over to manual mode but changed the shutter speed to 1/4 s, you have added four stops of light to your exposure and need to remove them.

You can reduce the exposure through in-camera settings:

• lower your ISO, as long as you weren't already shooting at the lowest ISO ("for the best quality"). If you were at 200 ISO, though, you could get one stop back by lowering the ISO to 100.
• use a smaller aperture. If you were already at f/11 to get the most depth of field for your picture, or if you're using a P&S camera without good aperture control, there's not much you can do here. But if you were shooting wide open you should be able to get several stops back.

You can also try to reduce the exposure by decreasing the amount of light coming in to your lens. There are two ways to do this:

• if you're impatient, use a filter. There are several strengths of ND filters, which are rated by how many stops of light they restrict. Polarizing filters typically cut out between 1 and 2 stops of light and also have other uses, so if you just want to buy one filter, a circular polarizer might be a better value than an ND filter.
• shoot when there's less light. Either wait for a cloudy day, or shoot at dawn/dusk, or shoot at night.

Answered by drewbenn

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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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Long exposure on Canon 60D

Question

I want to take some night shots of the sky and landscape showing up stars and cars on a distant road.

I have the option to set the shutter speed to 30s, but I want to take a 2 min (or more) exposure, so capture more movement.

I've seen that you can set it to bulb mode, and hold the shutter down, which isn't practical, as I ned the camera to be completely still.

I could buy a remote, and keep my finger on this I guess, but it still seems a bit fiddly.

Am I missing a trick ? or is the solution to buy a remote?

Thanks Rich.

Asked by Rich S

Answer

You have a couple of options, you could shoot four 30 second frames and then average them in software. This solution doesn't require any extra gear, however it requires you to reopen the shutter quickly for each exposure (which could rock the camera) and introduces the possibility of having gaps in your light trials.

Alternatively, most wired remotes offer the ability to lock the shutter button down so you can let go of the remote until you need to reopen the shutter. Combine this with bulb mode and you can get 2 minute exposures easily without rocking the camera.

Answered by Matt Grum

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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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What type of camera setup is required to take photos of luciferase?

Question

I'm working with luciferase which has a wavelength of blue 480 nm and I want to be able to take a photo of it. The trouble is, I can see the luciferase glowing in all of its glory in front of me but no matter how hard I try, I can't take a photo of the luciferase with my DSLR (Nikon D80) using a Nikon 50 mm lens and a Nikon 35 mm lens. I've tried removing the filters (Nikon L37 and Hoya UV).

I'm curious if I'm missing a certain lens/filter or if I should be shooting using a different lighting setup. I'm already exposing for 30" at f/22 on ISO 1600. Perhaps longer?

Asked by bobthejoe

Answer

That wavelength is certainly within the spectrum you can capture with any lens, with or without filters. Digital sensors capture between 350-1000nm If it is glowing, then you'd want that to be your main light source. Any additional light you throw onto it is going to dilute the glow from your subject and make it harder to see.

What aperture are you using? Unless this is incredibly dim, I can't imagine 30" not capturing something unless you're using a very small aperture.

Are you doing this in a dark room with a dark background? What do you see in your 30" exposures?

Through trial and error, you could do a range of shutter speeds (and ISO) to try to hone in on a good exposure value. If you can see it with your eyes, you should be able to photograph it without special equipment.

Answered by MikeW

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Does long exposure affect the sharpness of a picture, assuming no camera shake?

Question

Assuming that the camera does not shake during long exposure photography, How does the sharpness of the image get affected? Would it be more sharp, less sharp, or remain the same?

Answer

In a perfect camera with a perfect sensor, sharpness would remain the same. No such thing exists so you have to consider two possibilities with whichever camera you have. The long exposure causes the sensor to heat and increases image noise:

1. Your camera does not like that and therefore applies long shutter noise-reduction to clean things up and you get a less sharp image.

2. Your camera is oblivious to the increase in noise and leaves it there. Speckles caused by noise destroy some fine details but make the image appear sharper sometimes.

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Where does the noise come from in a long exposure?

Question

I created another test. This time I exposed for 36 minutes, because I wanted to test star photography. This is not meant to be a nice photo; I really just tested.

Camera was inside the house behind the window (it is too cold to go out) in dark. Minimal light from other room came from behind the camera. It is a Canon EOS D1000 set on BULB, F29, ISO800

The question is: Where do the blue and red dots (noise) come from?

Answer

Well, perhaps you should have gone out after all :)

The noise is thermal noise, which will become noticeable as your sensor heats up during a long exposure. In astrophotography, it's quite a common problem.

Some ways to reduce such noise:

• cool sensor down, e.g. by shooting in the cold weather. Note that cold also negatively affects battery life.
• set the camera to take a dark frame with same settings (to get just the noise) and subtract it from the image; this can be either done manually (taking a second frame with lens cap on) or automatically by camera (the feature is called Long Exposure Noise Reduction or something similar).
• using a stronger noise reduction setting in camera; this may also make the photo softer overall.

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What causes strange spiral pattern on my star line?

Question

Ok, so I created this test image. The camera was behind the window, I just tested long exposure photography on the single star I saw. It was about 20 minutes of expo, star was out of focus (I really just tested the principles of this kind of photography)

As you can see there is a darker spiral line on the bright line of the star. I would like to know what caused that spiral line?

Answer

The spiral line is caused by the pattern on curtain fabric that reflects from the window glass. You can see the darker and lighter lines continue past the start trail (crank up brightness/contrast if it's not visible otherwise). Where white fabric reflects, it adds to the intensity of the star line.

For better results, take your photo outside, so there will be no reflecting glass between your lens and the star.

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Will long exposure night shots damage my camera?

Question

I've been looking into long exposure photography for star tracking. How does it negatively (if at all) affect your camera?

Answer

There might be some repercussions, especially on very cold or hot nights. Long exposures and continuous use of the sensor does cause it to heat up. This is really not that much of a problem for most modern cameras as they have adequate heat sinks and other features to bleed off heat and prevent too much buildup. (Some newer cameras may even prevent you from starting a new shot for a while if it detects the sensor is too hot.)

On extremely cold nights, you might encounter some trouble with your batteries, as cold tends to reduce their effectiveness and life. Poor current flow can occur during extremely cold or very hot nights, which can mess with the camera's electronics itself. This sometimes manifests as funky menu behavior and the like. I have not seen any permanent damage from such a thing, but I have also never spent a truly extensive amount of time photographing in very cold weather (probably the longest was during a total lunar eclipse which spanned several hours in sub-freezing temps.)

LCD displays perform poorly in very cold environments as well, and can end up damaged due to extreme cold. Most normal cold temperatures won't be a problem, but sub-freezing temps with an added windchill can bleed off every scrap of energy held in a camera, sometimes resulting in dead LCD pixels or possibly worse damage. Normally, you'll encounter problems due to poor battery performance, however if you are doing something like taking a time-lapse sequence of shots over the duration of a whole night, and intend to sleep through much of the night...you might want to pick nights that are not extremely cold. There really is no telling what super cold temperatures might do to your equipment if its exposed for an extended duration of time.

Weather sealed gear is obviously going to hold up better in more abusive conditions, however most sealed gear is only available in the top of the line equipment. Most cheaper gear has minimal weather sealing or resistance features, if it has any at all.

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How to photograph panning with a point and shoot camera?

Question

I have recently learnt about panning photography on the internet and I was curious about capturing one myself,

But as an amateur I just own a Point and shoot camera,

I have experimented through it thoroughly and the only scene mode with longer shutter speed is Fireworks mode(4s),

But when I used this mode to take a panning photograph, all I got was an Over Exposed image,

How can I take a panning photograph with a point and shoot camera?

Answer

You still need to expose your photograph correctly. So if you're taking a panning photograph in bright light you have to either use a very narrow aperture or a filter, or both. Of course with a P&S camera, both those are difficult: you may have no control over the aperture at all, and there may be no easy way to attach a filter. If that's the case, you'll have to take your panning photographs in darker lighting.

You don't need ultra-long shutter speeds like 4 seconds, though: my picture here was only 1/15 of a second. If you are closer to your subject and it's moving faster, you can probably get away with an even faster shutter speed.

One thing you could try, although I've never tried this and it may be too awkward to pan steadily, is hold your sunglasses in front of the lens as you pan, as a makeshift neutral density filter.

Finally, if you try taking panning photographs in darker light in order to achieve the longer shutter speeds, your camera will probably increase its ISO to prevent camera shake, which is the opposite of what you want (since panning is, in one sense, controlled camera shake). If your camera has a mode that lets you force the ISO to its lowest value, you probably want to use that mode.

Of course, I hope you've also read this answer -- maybe all you need to do with your camera is leave it in Auto mode, zoom in as far as you can, and take pictures of nearby, fast-moving objects.

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Situations you might use USB remote mode?

Question

I hooked up the 50D to my MacBook Pro the other day at home and found it great to see exactly how a photo is going to turn out on the big screen before taking it and was wondering when such a setup might be used and how frequently it is used, considering it's not exactly something you can roam about with.

I guess the obvious ones such as long exposure (astronomy, landscape) etc, but are there other uses? Model photo shoots?

Is it better to simply use a remote instead of hooking it right up to a computer?

Answer

It's called tethered shooting, and is mostly used in studios; as you say, it's not exactly a portable setup. It has the advantage of letting you write photos direct to disk, bypassing the memory card, and as you said, you can see a photo preview large and on-screen before shooting, like a high-res version of live view.

Press photographers at football matches and other events can use wireless tethering, with a laptop connected to the internet, so that picture editors back in the office can access the photos directly almost as soon as they are taken.

If there's no overriding need to get your photos on disk immediately, however, then using a remote will do in most situations.

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How can I take long exposures using a Nikon D7000 with wireless remote?

Question

I have recently tried to take pictures of stars using my wife's D7000, but I couldn't get it to expose for more than 30 sec. In my old D70 I used the wired remote to do long exposures, but now I have only the wireless one. How can I get it to work?

Answer

You need to set the shutter speed to Bulb, which can only be done in Manual mode (turn the mode dial to M).

Once you've done that, and set the camera to use the remote, simply press the remote button once to open the shutter, then again to close it.

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How can I simulate a long exposure photo using a set of shorter exposure photos?

Question

I'm shooting towards the sky to capture the stars. The exposure time is 15 seconds, so I can see the stars still, without a trace. These photos are taken continuously one after the other, because I want to make a time-lapse video showing the "movement" of the sky (it is the earth that moves actually).

For that, everything's fine. But I'd also like to do one other thing. If instead of taking all those photos, I would take just one with a exposure time that equals the sums of all those photos photos together (15 sec times the quantity of photos), I would see the trace the stars left in the sky.

Is there anyway to "create" that photo, from all the "short" exposition ones?

Answer

You can do it with a script for The GIMP. I did it a couple years ago, and got pretty good results. Remember to keep the time between exposures as short as possible, otherwise you will get visible gaps in the trails. That's why it's best to take a single dark frame at the end, and subtract that frame from the result (I had intended to incorporate that into the script, but never got around to it).

My notes for the script:

Combined with renaming the first to base.JPG, "gimp -b -" with
(let* ((filelist (cadr (file-glob "IMG*.JPG" 1)))
      (img (car (gimp-file-load RUN-NONINTERACTIVE "base.JPG" "base.JPG"))))
  (while (not (null? filelist))
    (let* ((filename (car filelist))  (layer (car (gimp-file-load-layer RUN-NONINTERACTIVE img filename)))
  )
      (gimp-image-add-layer img layer 0)
      (gimp-layer-set-mode layer LIGHTEN-ONLY-MODE)
      (gimp-image-merge-visible-layers img CLIP-TO-IMAGE)
      )
    (set! filelist (cdr filelist))
    )
  (gimp-file-save RUN-NONINTERACTIVE img (car (gimp-image-flatten img)) "test2.jpg" "test2.jpg")
)

For subtracting the dark frame, my notes say, "I opened this as a layer on the composite image (the result of my gimp script), and set the dark layer's mode to Difference."

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What are neutral density filters and how do I use them to create long exposures in daylight?

Question

I've seen a few related posts on the site but nothing specifically on this point:

I'd like to be able to take long exposure photos during daylight (like the examples in this Flickr group). I'm told that you can do this by using a neutral density filter. So my question is: what is a neutral density filter exactly, and how is it used to achieve that smooth long exposure effect?

Answer

A Neutral Density (ND) filter is a filter that reduces the amount of light captured by the camera evenly across the visible spectrum. As such, it looks grey to black (depending on the filtration power) and does not cast color on the received image (like blue or yellow, e.g., filters will do).

When using a ND filter, there is a need to compensate for the reduction in light by using longer exposures (or higher ISO, but it usually defies the intention of ND filtration). This way, one can capture long-exposure images that are not possible w/o the filter as the camera (set to its lowest ISO and possibly smallest acceptable aperture) is at its slowest speed for a good exposure.

Examples for such situation is when shooting waterfalls in a fairly lit location. Then, the speed for correct exposure is not slow enough to create the required streaming water effect. Using a ND filter, one can reach slower speeds, as if the scene lighting was dimmer.

Note that a uniform ND filter does not change the Dynamic Range of the scene, as the bright areas get darker in the same amount as the dark areas.

Another type of ND filters is the graduate ND filters. These filters usually attenuate the light only at one half of the frame and gradually get clearer on the second half. These filters are used when shooting landscapes, where the sky is much more bright than the scenery and using good exposure for the ground will overexpose the sky. A graduate ND filter lets one reduce the brightness of the sky and get it captured nicely with the ground.

ND filters are marked in multiplies or stops. An 8X ND filter is similar to ND3. Both cut 3 stops of the light. If the camera's meter tells that 1/500 sec is required for the given aperture, then using a ND3 filter will allow an exposure of 1/64 sec with similar outcome.

There are some (expensive) variable ND filters. These are made from two polarizers, where the front element rotates and thus let you set the amount of light being cut (up to virtually no light passing through).

The image below, from Wikipedia, shows the effect of an ND filter:

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