Category Archives: Photography Equipment

Lens Compression and Lens Distortion

(Originally published 2016-03-16 as /archives/10930)

This lens-compression-thing: we all agree on it correct?

Lens Compression

The definition of lens compression is this: if you use a longer focal length, then the background will appear to be closer to the subject. There are numerous examples of images that “prove” this out there (including the GIF below), but guess what? Lens compression doesn’t actually exist.

Here’s how the prove-it examples work:

  1. First the photographer makes a photo of a subject, standing in front of a background object, with a short focal length lens (wide angle, less magnification).
  2. Then the photographer takes the same picture, of the same subject, at the same distance from the camera, but with a longer focal length lens (telephoto, more magnification).
  3. Then we compare the two images, and note that the background object appears to be closer to the subject in image #2.Here’s the kicker:
  4. If we then crop image #1, so that the subject takes up the same amount of space in each image, we will note that the subject now looks to be the same exact distance from the background object as in image #2.

In other words: lens compression is just an optical illusion.

Lens distortion

Barrel Distortion, Pincushioning, Bokeh, etc., may be different with each of the two lenses. Generally the wider angle lens (shorter focal length, less magnification) will distort the image more and cause more foreshortening relative to the telephoto lens (longer focal length, more magnification), but not always. A lot depends on lens design, and post processing software is really good at removing distortion these days.

The following GIF was shared at “reddit /r/educationalgifs How different lenses affect portraits“. It shows the foreshortening issue and the so-called-lens-compression-issue at various focal lengths of a telephoto super zoom lens. For many people this will be proof that lens compression is real. It still isn’t real, and not all wide angle lenses will cause such drastic foreshortening.

OK: so if the focal length is changing, then why is the subject’s head mostly the same size? Because the photographer is moving physically closer to the subject, for the wider angle shots, and farther away for the telephoto shots.

Here’s the GIF:
XBIOEvZ - Imgur

Back to the Lens Compression Example

OK, so Paul must be wrong about lens compression. I mean look at how that tree in the background of that GIF moves closer to the subject: right?

In the following video, Dieter Schneider does the steps (from above) to prove that lens compression does not exist.

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White Balance Does Not Work The Way That They Say, Maybe Not For You, Definitely Not For Me

(Original posting date: 2016-07-27)

Spiritia [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons
It’s quite common for photography writers to write something like, “The human eye… adjusts the colors you see,” whenever discussing white balance. I never encountered one of these articles that also referred to scientific research, and I am unsatisfied with the explanation.

For one thing: it’s not consistent with anything that I learned in physiological psychology or psychophysics regarding vision.

For another thing: it is extremely common for scientific-thinking people to disprove much of what photographers teach.

By Håkan Bergknut (Own work) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons

For another: it’s not consistent with my personal experience, which is more like this:

I don’t believe that my “human eye… adjusts the colours [I] see.” I am very aware of color temperature. I suspect that most photographers develop this awareness, and some people have always had it.

When I am in an environment with soft white light, that’s what I see, but it’s everywhere. It’s even affecting the color of the photos on my wall. If those were white balanced, then the light from the too-warm bulbs is affecting the colors of those photos exactly the same way that it’s affecting everything else in the room, so it’s tolerably similar, but not changed by my eyes.

I left that as a comment on a Picture Correct article on white balance, and Wendy disagreed, but her rebuttal is not actually inconsistent with my comment above. She wrote:

Some say it’s the “eye” that adjusts, some say it’s in the “brain,” point is, you DO adjust to a “normal” WB. If you’ve been inside with a bunch of tungsten–especially low-light, like in a theater–and then suddenly go outside, the world will be blue-shifted for a few seconds while you adjust.

I make temari (embroidered thread balls), and I’ve got one that’s got a design in blue and three shades of purple. Thing is, in dim light, your eyes will try to convince you it’s red, yellow, green and blue–that you’re just seeing it in a different “white balance” than you really are.

She gives an example of an adjustment here, but I am not convinced it is. To me it looks like an example of becoming aware of the different colors of light, but I am always aware of them, and people that think about light will be too.

The “human eye adjusts” isn’t a scientific explanation, it’s an expectation. Photographers think about white balance this way, because that’s what they have been taught, but in reality, they do see three shades of purple as non-purple, because there’s no real adjusting going on.

That said: adjusting white balance in your image is important, because the colors in your photo are affected by the light that you are viewing it in, exactly as much as every other color that’s in that same light. Your photos won’t look “right”.

On the other hand, by all means: monkey with white balance in order to meet your artistic goals.

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How To Use DSLRs To Create Stereo Images

PetaPixel posted an image of David Klutho making 3D images of the Olympics.

  • You can see what looks like a two cable shutter release on top. That can be made by adding a second cable to an existing shutter release.
  • He is probably using manual settings to sync the camera settings.
  • You can see how he physically keeps the cameras held together.
  • You can also see a band in front that might be for syncing zoom.

OK, so now we know see how the Sports Illustrated 3D Pro David Klutho does it!

peta

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