How do I prevent / fix out of square images?

Question

I took photos of a lot of different framed art pieces that I wish to sell. The frames of these art pieces are either square or rectangular. In my images, the top of the frame appears to be wider than the bottom of the frame.

How do I prevent this in the future when photographing similar objects?

Is there a way to edit the images I have to remove this affect? If so, please provide step by step directions.

I have Photoshop CS 4, and Fireworks CS 4 from adobe for the Mac, but I have very minimal experience with either of these programs. I'd be willing to spend up to $20 to avoid having to re-shoot the photos, if there is another program that would let me fix this on a Mac.

The image below illustrates the affect I am talking about. the photo was taken with a Canon Eos Rebel T21, 18-135mm f/3.5-5.6 lens ISO 320, 26mm, f/4 1/50 The displayed image was compressed from the original to conserve space here.

Asked by Scott

Answer

It sounds like this is a perspective problem, you didn't or couldn't shoot the (rectangular) subject perfectly straight on. You could correct this in the future by, obviously, shooting straight at the subject or using a perspective correcting lens (tilts and shifts) or you could correct it in software using a perspective correcting application/plugin like:

• Photoshop (CS4 Tutorial)
• DxO Optics ($290)
• Perspective Pilot ($29)

Answered by Shizam

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What does it really mean that telephoto lenses “flatten” scenes?

Question

This is another perspective distortion question. I understand that perspective distortion is primarily a function of capture and viewing distance, but I am still working on fully understanding the causes of the "flattening" of scenes that is credited to telephoto lenses. This seems to refer to the fact that our ability to discern the differences in size attributable to differences in distance from the lens for subjects beyond a certain distance from the lens. If this is correct, then is it just that with the longer distance from the subject when using a telephoto lens, this compression happens closer to the foreground, rather than in the mid- or background with a wide lens? Is it fair to say that the compression effect occurs at a certain distance from the photographer regardless of lens, but the field of view influences how close to the foreground this effect takes place? Can you share any information to help people like me understand this?

Answer

The flattening or compression effect is not caused by a particular kind of lens, it applies to all lens in the same way. Actually, this property of lenses applies to our own eyes as well. The factor that affects flattening is the distance from the camera to the subjects.

Consider the following exercise:

Place two friends 1 meter away from each other. Place yourself in line with them, so that you are 1 meter away from one of them, and 2 meters away from the other. Move a bit to the side, so that you can see both. From this position, you can easily estimate what the distance between your two friends is. Now walk 100 meters back along the imaginary line determined by your two friends. Again, move a bit to the side so that you can see both. Can you really tell now how far away from each other they are? Will you see your friends in a significantly different way if one of them moves an additional meter apart from the other? You won't, because from 100 meters away, a difference of a meter is not significant.

The thing is, our eyes have a fixed field of view, so in addition to flattening, we experience a scale reduction as we move farther away from the subjects. With a camera you can magnify the effect by using a long lens. But the compression will be exactly the same no matter what lens you use.

There are a few good examples on the Wikipedia page on Perspective Distortion.

From that page, I like this animation of a cube that goes from extreme extension to extreme compression, when changing the focal length and distance to camera:

_{Image copyright 2007 SharkD, licensed CC-BY-SA 3.0}

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Will a tilt-shift lens solve my 'leaning building' shots?

Question

I shoot primarily with a Nikon D300, and that's not likely to change soon. The camera does everything I need it to do, but this. I also use a 17-55 lens, which I know that Thom castigates as being too expensive for not enough lens, but it's worked well for me for years.

I'm on a trip in Italy at the moment, though, and having some serious problems with looking up at large buildings going to infinity. Consider Il Duomo:

It doesn't actually tilt inward like that, it's a pretty solidly built structure. For some reason, I'm really noticing on this trip that my building shots are just mangled.

Is this readily solved in post production such that the resulting image is printable and usable for something other than internet slideshows? Or should I be looking at a tilt-shift lens for this? And if I do look at the lens, I've been told that the flash overhang on the d300 means that the nikon 24mm lens won't fit-- is that true?

Answer

A tilt-shift lens is indeed the best way to correct this effect in-camera, but even then, it can look odd if the distortion is quite high. The example you have given should be OK. If you want to do it in post-processing, Lightroom 3 now has built-in perspective correction tools. When you use them, a grid overlays the photo which is updated live, so you can spot when the verticals become parallel. With a high-enough resolution image, this should produce results almost as good as with a T/S lens, for a lot less money.

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How do I take forced perspective photographs with a point & shoot camera?

Question

My teenage son needs to take some forced perspective shots this weekend as part of a camping/hiking trip. He has a Panasonic DMC-FX01 point and shoot camera.

He wants to be able to hold up something like a plastic dinosaur toy close enough to the lens that it looks kind of like it's attacking his friends standing a distance away.

We've tried a number of the presets, but the toy is always out of focus, I'm really no expert on this kind of thing but I know you can do this with manual DSLR. So my question is do you have any suggestions of how to trick this little P&S camera into letting him take this kind of shot please?

Answer

It is actually easier to do so with a small camera because the can produce a much greater-depth-of-field.

The only catch is that yours is a point-and-shoot, so you have no direct controls. Instead, you must trick it using a small aperture.

You can try landscape mode which often selects a small aperture. If that does not do it, you can increase the ISO too. That will reduce the quality of your images though.

Of course, you may be trying something impossible and it would probably be impossible with a DSLR unless equipped with a tilt-shift lens. Try to shoot at the widest angle and create as much distance between the camera and the closest object.

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