Real-time vs post-production blurs, what's the difference?

Question

I've always been a huge fan of blurry photos, guess in part because almost any camera is able to take blurry photos, though some better than others.

That said, getting to the point of the question, what's the difference between real-time vs post-production blurs?

Asked by blunders

Answer

In general: "real" blur, either due to optical characteristics (including depth of field, chromatic aberation, spherical aberation, and more) or due to movement, is based on more information. It includes the three-dimensional and time aspects of the scene, and the different reflection and refraction of different wavelengths of light.

In post-processing, there's only a flat, projected rendering to work with. Smart algorithms can try to figure out what was going on and simulate the effect, but they're always at a disadvantage. It's hard to know if something is small because it's far away or because it's just tiny to start with, or if something was moving or just naturally fuzzy — or which direction and how quickly. If you're directing the blur process by hand as an artistic work, you'll get better results because you can apply your own knowledge and scene recognition engine (in, you know, your brain), but even then, it's a lot of work and you'll to approximate distance and differing motion for different objects in the scene — or intentionally start with a photograph where these things are simple.

In the World of Tomorrow, cameras will gather much more information in both time and space. The current Lytro camera is a toy preview of this. With a better 3D model, the effects of different optical configurations can be better simulated — and of course motion blur can be constructed from a recording over time.

Answered by mattdm

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What is causing the cyan outline in the building in the background of this image?

Question

I took this picture the other day. It's a JPEG from the Fujifilm X-Pro1. The sky is overexposed as was necessary to light Anya brightly — and because I was playing with shooting wide open, and that plus the high base ISO plus max shutter of ¹⁄₄₀₀₀th meant this went beyond what the metering really wanted to do. Maybe a bit much, as we've lost the top corner of her head.

But, never mind that. What I'm interested in here is the cyan blur outlining the Prudential building in the background. A one-for-one pixel-level crop is below the full image....

_{Anya on the Esplanade; photo by me and CC-BY-SA 3.0 in this size only.}

What is causing that blue outline? Is it just a matter of the out-of-focus blur interacting with the overexposed sky? Is chromatic aberration to blame? Or, is it because of the larger-than-normal color matrix used by this camera's unique sensor, and basically an artifact of RAW decoding?

Camera make  : FUJIFILM
Camera model : X-Pro1
Focal length : 35.0mm  (35mm equivalent: 53mm)
Exposure time: 0.0003 s  (1/4000)
Aperture     : f/1.4
ISO equiv.   : 200
Whitebalance : Auto
Metering Mode: pattern
Exposure     : aperture priority (semi-auto)

Asked by mattdm

Answer

The sky on a sunny day is cyan (primarily green and blue with some red). Where the intake of light is really bright, all three color components (red, green, blue) on the sensor chip are fully saturated (at their maximum counter values), which results in overexposure, or pure white in this case.

What you're seeing as a cyan outline is actually the result of that section of the image not being pegged to pure white, because the darkness of the gray building is interfering with (blurring) the ligthness of the sky, and thus preventing the sensor counters from attaining their maximum (e.g, overexposed) values in that region.

If you were to shoot the image again with the same exposure values, but this time with the building in sharp focus instead of the subject, then you would see a sharp line where the building is solid gray-ish and the sky is overexposed to pure white, but no more cyan fringing.

This effect is very similar to the laser bolts in the some of the space battles in Star Wars — where light green or light red charged-particle beams are a white line in the center, surrounded by a beautiful pure color fading out to black. The pure white in the center is simply an artifact of over-exposure; there is no actual white light there.

Note that if you had a light source that was pure red, pure blue, or pure green (such that it perfectly matched the receptor frequencies of your sensor), then you would not see over-exposure toward white, but instead over-exposure to a single color component only.

Answered by Todd Lehman

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Which Lensbaby Sweet 35 or Edge 80 effects are harder to reproduce post-processing?

Question

I want some suggestions from Lensbaby users.

I have the plastic optic, double glass and fisheye optic. I use the composer.

The recent new optics: Sweet 35 and Edge 80 seem very intriguing and I want to buy one of them, but not sure which one to get. I know they have the in-built aperture which will be a lot more convenient, but will the Sweet 35 be very similar to the double glass other than the fact it's now wider? I've heard the blur is not as smooth as the blur in double glass. (updated: here is the link about the highlighted blurs: here)

Also if I could shoot on a normal SLR lens and work on post-processing, is it easier to create the effect of the Edge 80 or the Sweet 35? The Edge 80 is just tilt-shift focus with a line-focus thru the photo, am I right? If that's the case, should I be getting the Sweet 35 instead because the effect can't be reproduced? But I have the double glass already; would it be an overlap? I don't have a Canon tilt shift lens, so maybe the Edge 80 is a better choice?

Sorry for being so long winded. I really have no idea which lens I should get.

Thanks so much.

Asked by Natalie

Answer

The effect of the Edge 80 can be approximated in software, but using a tilt lens is generally considered to be both easier and better in terms of actual results. (Real lens blur is hard to fake without a 3D model.)

Whether the Sweet 35 would be too much overlap with the standard double-glass optic depends on how into all this you are. In "mundane" non-LensBaby photography, a 35mm lens and a 50mm lens usually are happy side by side — they're part of a "standard" set of prime lenses, not competitors. On an APS-C camera, the original LensBaby lenses are in the focal length range normally used for portraiture, while the Sweet 35 is a "normal" focal length. I think the less-attractive blur is not because of worse design, but simply a matter of what you get with this construction and a wider angle. Not necessarily bad, but just what it is.

So, between the two, I think the key questions are:

• Do you shoot enough with the Lensbaby that you've really come to wish you sometimes had the flexibility of a wider focal length for some photographs? If so, expand your kit with the Sweet 35 — or, if you'd like that a little bit but it's not really what you want a large portion of the time, look into the cheaper but less convenient (and probably less optically nice) wideangle conversion lens for the normal optic.
• Do you want to make tilt photograph with the miniature effect a lot? If so, the Tilt 80 is an easy choice. If you only want to do this very, very occasionally, it's probably not a good investment.

Of course, since this is an apples-to-oranges comparison, the answer very well may be yes to both. In that case, I say go with whichever is speaking to you more now, and get the other when a space in the budget opens up again.

Answered by mattdm

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Can software auto-detect image focus?

Question

I was wondering if there was any photo management software out there that could auto detect and "rate" images on how in focus they are. This comes up for me quite commonly when i am looking through a large series of macro images of the same subject.
In a perfect world, light room (or whatever program) could highlight in focus and out of focus ares the same way that it detects burned out areas of an image. Also the algorithm i am hoping exists would be smart and would not be detracted by blurred backgrounds and only seeks that some sufficient area is in enough focus.
Anything like that out there?

As another thought for people talking about pictures being in focus on the wrong spot, and that camera focus models already look into this. Another large factor for a lack of clarity in a macro image is blur from camera movement. This damages all points on an image, and is not something the camera accounted for when focusing.

Asked by Andrey

Answer

It's an interesting question. It's certainly possible for software to detect the parts of an image that is in focus, as it's the basis for focus-stacking software like Helicon Focus.

Focus stacking is a technique used by macro photographers. The depth of field in many macro shots is very shallow, so to extend this it's possible to take a set of photos of the subject, modifying the focal point in each one. Helicon Focus takes the stack of photos and detects the most in-focus parts of each image, and blends them together to produce a result where the entire subject is in focus. It's also possible to do this with some of the technology behind Hugin, but it's a bit more tricky to set up.

I think the difficulty in extending this for a general "in focus" check would be determining whether the subject is in focus - how do we automatically determine what the subject is? How much depth of field was required by the photographer?

Answered by Maynard Case

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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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How is the term gaussian blur used?

Question

Is the term Gaussian blur used strictly in post-production, or can it also be used as a term for an out-of-focus area in your image when you-re taking the picture? I'm pretty sure that bokeh is used to describe an area out-of-focus when you're taking the picture, can gaussian blur also be used when you're taking the picture?

Asked by J. Walker

Answer

It's not appropriate to use the term "Gaussian blur" for the out-of-focus parts of an image, because "Gaussian" refers to a specific blurring function. It's the same Gaussian curve that you may know from the "normal distribution" or "bell curve" in statistics. A bright point that's smoothed by a Gaussian will taper smoothly from a bright center to a dark edge.

Example of bright points with Gaussian Blur, made in the GIMP.

The out-of-focus parts of your photograph are not smoothed in the same way. Instead, an out-of-focus bright point in your image will appear in the shape of your aperture. So if your lens isn't stopped down, it will look like a bright circle. It doesn't taper smoothly from the center to the edge like a Gaussian does. (If your lens is stopped down, you'll get a polygon instead of a circle—for example, a hexagon if your aperture has 6 blades. But the same point applies: It doesn't smoothly taper from bright to dark like a Gaussian does.)

In the above picture, notice that the out-of-focus lights are evenly filled circles, not Gaussian profiles (which would fade gradually from a bright center to a dark edge).

Answered by coneslayer

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Can this photo be considered to have bokeh?

Question

This photo was accidentally captured by me. Can it be considered to have bokeh? I am confused, because it does not have any foreground in focus.

Asked by Kaustubh P

Answer

The Japanese word Boke (ボケ) or the American spelling Bokeh, refers to the out of focus areas of a photograph. It does not necessarily mean only the background blur, it refers to foreground blur as well. Bokeh is often used to refer to the quality of out of focus blur more so than its presence. In Japanese, Boke Aji (ボケ味) is used to specifically refer to the quality of bokeh. Aji literally means "flavor", so it would be referring to the kind of bokeh...good or bad, clean or dirty, etc.

Bokeh ranges in quality from poor, where blur circles are rough and polygonal with poor uniformity to very high, where blur circles are smooth and perfectly round, with clean uniformity or a slight spheric grade from center to edge. Circular apertures with rounded diaphragm blades generally create more pleasing bokeh, and a slight amount of spherical aberration in a lens tends to create the most pleasing bokeh.

In your specific shot, you do indeed have bokeh. The quality of your bokeh appears to be lower than one would really look for in a photograph. Its a bit rough and the blur circles are not entirely uniform. Your shot is also only slightly out of focus...you might notice better results if you put it out of focus even more, however without a useful foreground subject...bokeh is largely useless.

Answered by jrista

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What's the difference between Bokeh and Gaussian Blur?

Question

I have heard multiple times in photography, the words Bokeh, and Gaussian Blur. To me, it seems that the words are used almost interchangeably, but in some instances, I have heard them contrasted. What's the difference, and what are the definitions of each of them?

Asked by J. Walker

Answer

Bokeh is the out-of-focus areas of an image. Gaussian blur is an algorithm to fog selected image areas, to hide details or make them look out of focus.

The main differences:

• bokeh is created optically, gaussian blur in post-production;
• in bokeh, the amount of how wide an out-of-focus point will be smeared is determined by its relative distance from focal plane, whereas gaussian blur is applied to a two-dimensional image where no distance information is present, thus all points are smeared equally;
• gaussian blur is always smooth, whereas in bokeh, the smearing characteristics depend on configuration and aperture shape of the lens;
• you can use one to fake another, but the result will be similar only for bokeh containing items on roughly a plane parallel to focal plane, provided the lens has a smooth bokeh.

Answered by Imre

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How can I achieve this effect, where the flower is sharp and everything else is blurry?

Question

I was wondering how it is possible to take a picture like this.

Please have a look here for some example pictures. The flower is sharp, and everything else looks like taken with a long shutter.

Is that even possible, or do you think it's Photoshop-edited?

I asked the photographer about the lens, and it's a Minolta RF Rokkor 250mm f5.6.

Answer

Looks like it's been shot with a wide aperture (low f number, like f/2.8), from a close distance, with a camera that has a large sensor -- the combined effect is a shallow depth of field, as demonstrated there.

To reproduce, put your camera in aperture priority mode (Av on a lot of cameras) and choose a wide aperture (head for f/2.8 rather than f/22) and get shooting.

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Where does the ¹/shutter speed = focal length rule for hand shake come from?

Question

The generally accepted rule of thumb is that the shutter speed must be the same or larger than the inverse of the focal length.

As is, it seems that it makes no sense as is:

1. On a 24 Mpixels full-frame camera, at 100%, the blur from camera movement will be more visible than on a 10 Mpixels full-frame camera.

2. A photo intended to be printed small can have slight blur at 100%: nobody will see it when scaled down for printing. When doing a high-quality large print, even a small blur will be noticeable.

3. Image stabilization (vibration reduction) affects the blur when shooting handheld.

4. The blur will not be the same on a cropped vs. full-frame sensor.

I imagine that the rule of thumb appeared first when there was no DSLRs yet, and photographers were talking about SLRs with 35mm film. Is this that fact that makes the three of four points irrelevant? If yes, what about the second point? If not, what is the origin of this rule?

Answer

I did some quick Google Books searches, and while I can't pinpoint the origin, there are a number of references to it as a rule of thumb or general guideline in the early 1970s, and none that I can find before that. There are plenty of earlier references to the idea that a longer focal length requires a faster shutter but they're all general advice.

The first reference I find is from Popular Photography in 1972:

A rule that will help you determine the slowest hand-held shutter speed to use is: place the number one over the focal length of the lens (in millimeters). For example, with a 100-mm lens, one over 100 is ¹⁄₁₀₀ (¹⁄₁₂₅ would be the closest speed to set); with a 250-mm lens, the rule gives ¹⁄₂₅₀ sec. Use this rule as a guide. You may be able to hold for somewhat slower speeds if you're steady and your camera holding technique is good. If you're shaky, you may have to shoot at a faster speed than the rule indicates. Experience will tell this. If in doubt, use a tripod or other firm support and a cable release, when possible.

A year or so later, I found this

You can minimize or completely eliminate camera movement if you remember this rule: For hand-held shooting, don't use a shutter speed any slower than the focal length of the lens. The normal lens on a 35mm camera is is 50 to 55mm. When using this lens, set the shutter at ¹⁄₆₀th second. ... — Walter Chandoha, How to Photograph Cats, Dogs, and Other Animals, Crown Publishers, 1973

I doubt that either of these is the first occurance, though. There's a whole bunch of examples from around the same time, like this:

A rule of thumb is to use a shutter speed at least as high as the focal length of the lens: a 60th for the 50mm, 125th for the 105mm, 250th for the 200mm, and so on. But experience may show you are steadier or shakier than this rule assumes. — Robert Foothorap and Vickie Golden, Independent Photography: a biased guide to 35mm technique and equipment for the beginner, the student, and the artist, Simon and Schuster, 1975

So, I don't know exactly where it came from, but it's definitely an idea for 35mm film, and it's clear that in its early form, it was seen as a general guide, not a law.

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Why doesn't the background become blurred when I change the aperture on my Fujifilm S4000?

Question

I am sorry if my question is too naive, but I am a complete beginner in photography, and I think I still need to understand well what aperture is. I have a Fujifilm S4000 camera, and I know I can't do with it everything that a professional camera does.

I wanted the background of some pictures to be blurred by changing the aperture, but I don't get the results I expected. I think it also has to do with the focal length, am I right? I took two pictures to show you what I mean.

Picture 1 Aperture: f/4 Exposure: 1/2 s Focal length: 7 mm

Picture 2 Aperture: f/10 Exposure: 2.6 s Focal length: 7 mm

I would like to know what settings I can use to get the background to be blurred. I know that with smaller aperture values, the area around the object in focus will be more blurred, but when I change from f/4 to f/10, it doesn't change much.

Answer

There is NO different at ALL because the physical aperture has not changed.

The Fuji Finepix S4000 simulates a small aperture using an ND filter. When you stop-down, the ND filter slides into the optical path. The Aperture written i the EXIF is adjusted to reflect the transmittance of the ND filter but since the size of the opening has not changed, Depth-Of-Field does not change either.

Not only do such cameras have very small sensors and extensive depth-of-field but they are also extremely prone to diffraction. If the aperture was actually stopped down to F/10, images would get quite blurry.

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Why doesn't the background become blurred when I change the aperture?

Question

I am sorry if my question is too naive, but I am a complete beginner in photography, and I think I still need to understand well what aperture is. I have a Fujifilm S4000 camera, and I know I can't do with it everything that a professional camera does.

I wanted the background of some pictures to be blurred by changing the aperture, but I don't get the results I expected. I think it also has to do with the focal length, am I right? I took two pictures to show you what I mean.

Picture 1 Aperture: f/4 Exposure: 1/2 s Focal length: 7 mm

Picture 2 Aperture: f/10 Exposure: 2.6 s Focal length: 7 mm

I would like to know what settings I can use to get the background to be blurred. I know that with smaller aperture values, the area around the object in focus will be more blurred, but when I change from f/4 to f/10, it doesn't change much.

Answer

There is NO different at ALL because the physical aperture has not changed.

The Fuji Finepix S4000 simulates a small aperture using an ND filter. When you stop-down, the ND filter slides into the optical path. The Aperture written i the EXIF is adjusted to reflect the transmittance of the ND filter but since the size of the opening has not changed, Depth-Of-Field does not change either.

Not only do such cameras have very small sensors and extensive depth-of-field but they are also extremely prone to diffraction. If the aperture was actually stopped down to F/10, images would get quite blurry.

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What is the best setup for shooting sports at night with a point & shoot camera?

Question

I always try to take good photographs in soccer matches or in races at night, not using flash, and I have always the same result: too much blurred photos.

I don't have an SLR, but I'm sure that's not the problem; the problem is the setup.

What I have to do?

My camera is a Panasonic Lumix FZ18.

Thanks!

Answer

Actually, shooting with a compact camera rather than an SLR is part of the problem. Basically, shooting a game at night means that you don't have enough light for decent exposure times. As a consequence, your exposures are long and the moving objects are burred. The field's lighting are rarely enough to allow you to capture moving subjects with ISO low enough so noise is not a problem. In this case, the options are to:

1. Add lighting (e.g., use a flash - but in your specific case there are 2 problems: your camera does not support an external hot-shoe flash, which may be solved by an optical slave, and more seriously, typical compact flashes just don't have enough power to light a soccer field effectively but it may be just fine for a race track if you can get close to the action).

2. Use a lens with large maximum aperture (small F-number). Your camera offers F2.8 which is not bad for this purpose, but in the SLR world you have lenses with bigger apertures.

3. Use a camera with more sensitive sensor. P&S cameras typically have far smaller sensors compared to SLR's. In the digital world, the bigger the sensor - the better its light recording ability. Pro sports shooters use full-frame, or at least APS-C bodies for the advantage in high-ISO low noise images they have over P&S cameras. You can dial up the ISO in your camera but the images will become very noisy/grainy vary fast. Also note that your camera is pretty old (2007 model?) which means that even for this form factor, you can expect better ISO performance from newer technology.

So, as you see, SLR camera will certainly help you to achieve better images in these tough conditions.

On top of all - remember to always use a tripod there and a remote release if possible. Even if the players and the ball end up somewhat blurred, at least the field and the background will remain sharp.

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How can I use image stabilization to make a moving subject clear?

Question

Image stabilizers in digital cameras are available for shooting moving/shaking snapshots clearly. The image stabilizers try to focus the moving object and reduce the shaking. However, I have set the image stabilizer to auto, but still I cant get a proper focus on moving object.

Here's an example: In the picture there is a blurring effect. I want to reduce that.

Now in such cases, are there any other settings (like ISO) to reduce this shaking effect even further, and get clear snapshot? Or, is this the best the image stabilizers can do?

Answer

Image stabilization aims to fix the problem of a moving camera (camera shake).

Your question and example photo aim to fix the problem of a moving subject.

To reduce blur of a moving subject, you need a shorter shutter speed, or you need to freeze the motion with flash.

If you also have camera shake, then image stabilization will help some. But first make sure you take steps to reduce camera shake. For example see the question "How I could take crisp sharp shots without expensive lens?".

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Would a large aperture lens help against low light subjects being blurry?

Question

I want to get nice shots with ambient light (meaning the natural light in the room of restaurants, living room with x-mas tree lights only...) so I can catch the glow of light on people’s faces as they are illuminated.

All I have is the kit lens for the Nikon d7000 for now... looking to get a 2nd lens to help with this after I can figure out what lens that will be. This is the cornerstone of my question.

The problem I see with my current shooting is that when I shoot the shutter takes so long that picture is blurred because the subjects (people) move.

With my basic understanding of photography, I get that there needs to be sufficient light and with low light the shutter will stay open longer, especially since my aperture is not large at all with the kit lens - 18-105mm f/3.5-5.6 AF-S DX VR ED Nikkor.

Am I missing something here?

Or am I correct in looking for a lens with larger aperture to get sharp low light images of moving subjects?

Please let me know if I am off base, and if I should require a new lens, please also suggest the lens and reason to me (so I can grow my knowledge as well).

Thanks all

Answer

Unless your subjects are sitting still, slow shutter speeds are just going to have blur. As a general rule of thumb that I use, I tend to be 1/150 of a second or faster for normally moving people, but in indoor ambient light this usually means quite high ISO. Fortunately for you, the D7000 is excellent at high ISO, so the normal concerns with noise is substantially reduced. Because of that, I would suggest setting your camera to shutter priority (Tv), select a shutter speed, and let the camera pick aperture and ISO.

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How can slightly blurred photos be improved in post processing?

Question

I have heard quotes which say "If its not good, delete it."

I go by that advice, but sometimes you capture some precious moment but you see that photo is slightly blurred because of camera shake. I don't have an IS lens, and it's too late to somehow do it over.

What best one can do in post processing to improve the quality of the picture?

Ideally, I'd like to use Gimp or Picassa for this.

Edit: I came across a video regarding this -
http://www.youtube.com/watch?v=xxjiQoTp864&feature=player_embedded

Answer

I used to think that blurring was one of those things that was impossible to recover from in post. Amazingly enough it's possible to take an image that is blurred beyond recognition:

and recover all the original detail if you know the exact blurring function:

So why isn't this done all the time? Well firstly you never know the exact blurring function so you can't create a perfect inverse filter, secondly if you have noise in the blurred image:

this will totally bias the outcome, as the inverse filter is unable to replicate it:

pseudo inverse filters such as the Wiener filter can cope much better with noise but you still get ringing artifacts like the following:

image (c) MathWorks, see http://www.mathworks.de/products/image/demos.html?file=/products/demos/shipping/images/ipexwiener.html for more detail

This is a bit of a digression, but it shows that deblurring is at least possible in principal. There are some very clever algorithms that outperform the Wiener filter by guessing what parts of the original image looked like, in order to estimate and reverse the blurrig function, based on the statistical likelihoods of various light patterns existing. There are some Photoshop plugins that offer image deblurring using such advanced methods, you might want to take a look at the following (which offer free trial versions)

• http://www.focusmagic.com/
• http://www.oceansystems.com/forensic/forensic-Photoshop-Plugins/toolset.htm
• http://www.humansoftware.com/pages1200/ApertureEdit/HSapertureedit111.html

The results are never perfect but for shots that are irreplacable it's better than nothing!

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Why does a larger aperture cause more blur of the background?

Question

Why is it that a larger lens aperture produces a shorter depth of field, causing the background of a photo to be more blurred?

Answer

Why the wide aperture blurs the background more

Let me start with Wikipedia figure:

Above we have a wide open aperture. Only point 2 is in focus. Points 1 and 3 are out of focus. Due to wide aperture, the rays coming from them through different parts of the lens intersect the screen 5 (a film or a digital sensor) in different points. We may also tell that these rays form a point (intersect) before (red) or beyond (green) the screen. The corresponding cones of light intersect with the screen and form an ellipse-like image on the screen. Wider aperture allows for wider cone of light (so it allows to collect more light and blurs more).

Effectively, an out-of-focus point produces a circle of confusion. This is what we can call blur or bokeh.

For smaller aperture below, the rays too far from the center are cut off, so the circle of out-of-focus point is smaller.

If the circle of confusion is smaller than film grain or sensor subpixel, we cannot tell if it is out of focus at all, and then the point appears as in focus even if it is not. So with finite aperture, there is a range of distances which all appear as in focus. The depth of this range is called the depth of field (DoF). It is bigger for smaller apertures.

If the aperture is really, really small, then only the central rays can pass, and we have an infinite depth of field no matter what. Every point, close or far away, is represented as a point on the image. This is how pinhole camera works. Adjustable aperture allows to have anything in between.

How it looks like

At smaller aperture f/32:

At larger aperture f/5, an out-of-focus background is blured more:

(images are again from Wikipedia)

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How can wide opened aperture blur the background?

Question

I would like to know how a widely opened aperture can blur the background?

Thanks

Answer

Why the wide aperture blurs the background more

Let me start with Wikipedia figure:

Above we have a wide open aperture. Only point 2 is in focus. Points 1 and 3 are out of focus. Due to wide aperture, the rays coming from them through different parts of the lens intersect the screen 5 (a film or a digital sensor) in different points. We may also tell that these rays form a point (intersect) before (red) or beyond (green) the screen. The corresponding cones of light intersect with the screen and form an ellipse-like image on the screen. Wider aperture allows for wider cone of light (so it allows to collect more light and blurs more).

Effectively, an out-of-focus point produces a circle of confusion. This is what we can call blur or bokeh.

For smaller aperture below, the rays too far from the center are cut off, so the circle of out-of-focus point is smaller.

If the circle of confusion is smaller than film grain or sensor subpixel, we cannot tell if it is out of focus at all, and then the point appears as in focus even if it is not. So with finite aperture, there is a range of distances which all appear as in focus. The depth of this range is called the depth of field (DoF). It is bigger for smaller apertures.

If the aperture is really, really small, then only the central rays can pass, and we have an infinite depth of field no matter what. Every point, close or far away, is represented as a point on the image. This is how pinhole camera works. Adjustable aperture allows to have anything in between.

How it looks like

At smaller aperture f/32:

At larger aperture f/5, an out-of-focus background is blured more:

(images are again from Wikipedia)

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What are the benefits and costs of an image stabilized, slower lens vs a non-IS faster lens?

Question

I am going thru a trade off decision between a 24-70 f2.8 lens and a 24-105 f4 IS lens from Canon. My dilemma is that the 24-105 focal length better matches my needs, but the f2.8 would occasionally be nice indoors.

What is the board's practical experience with IS? When comparing, at the same ISO and focal length, this trade off, one can observe that at f2.8 and 1/60th, would equate to 1/30th at f/4. In this example, is it practically possible to achieve blur free results with an IS equipped lens hand-held at 1/30th? (edit: this relates to the 24-70 range both lenses share)

Since it is fairly easy to achieve blur free images with nearly any lens at 1/60th and above, how does 1/30th with IS compare? Do you end up with sharp images at these speeds?

Answer

I can speak from actual hands-on experience here, for a change :) I owned both simultaneously; I kept the 24-105 and sold the 24-70. For ME, the benefits of IS outweighed the benefits of f/2.8 and the much better lens-hood of the 24-70. Your mileage may vary though.

The 24-105 IS allows me to shoot at 1/10 second at 105mm and expect a sharp photo. Or I can go to 1/5 and take three shots of every motive, and expect at least one to be sharp. With the 24-70 I'd have to live by the 1/focal length rule, exceeding 1/50 at 70mm would be iffy. The slow shutter speeds with the 24-105 lets me stop down quite a bit for depth of field for similar exposure as the 24-70 would give me at f/2.8. Extra depth of field is a Good Thing most of the time - I use the full-frame 1DsII so I don't get any free DOF from a sensor crop.

This, of course, only applies to stationary subjects. Which, fortunately, is what I shoot with the lens. In my experience, for moving subjects, the one extra stop that f/2.8 gives over f/4 is neither here nor there; if f/4 isn't fast enough then f/2.8 probably won't really cut it either. For low-light photography of moving subjects I take out the 85mm f/1.2L which is a portable black hole which will suck up any light that is present in the room. Candlelight is more than enough.

That said... the 24-70 was a more fun lens to use than the 24-105. It had a certain something. The 24-105 is a staid, practical, useful lens without a poetic bone in its body. Ho hum. The plain sister with the good personality, if you will. But it's the lens I use the most.

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How can I achieve this effect, where the flower is sharp and everything else is blurry?

Question

I was wondering how's possible to take a picture like this.

The flower is sharp, and everything else looks like taken with a long shutter.

Is that even possible, or do you think it's Photoshop-edited?

(source: https://picasaweb.google.com/ypk82004)

Answer

Looks like it's been shot with a wide aperture (low f number, like f/2.8), from a close distance, with a camera that has a large sensor -- the combined effect is a shallow depth of field, as demonstrated there.

To reproduce, put your camera in aperture priority mode (Av on a lot of cameras) and choose a wide aperture (head for f/2.8 rather than f/22) and get shooting.

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