(Originally published 2016-03-16 as /archives/10930)
This lens-compression-thing: we all agree on it correct?
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:
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).
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).
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:
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.
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.
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:
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?
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.
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.
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.