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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The Fastest Woman On Earth Attempt -and- Where Will Our Future Pilots Come From?

(Originally posted Aug 1, 2015 on as /archives/10506)

Here’s a video about becoming the fastest woman on Earth

I dig land speed record videos.

What’s with the fighter-pilot-oxygen-mask?

Is it for cooling (not oxygen) like on a racing helmet?

Pilots use oxygen to fly unpressurized planes at high altitudes. Why do that? If there’s a stronger tailwind up there, then they can save time and fuel. I read a story about a check-delivery-pilot that did this, but became oxygen-deprived by mistake. Most military flying requires oxygen masks too.

A commercial pilot is not what many people think it is.

(The rest of this post is USA-centric.)

The people that fly for the airlines, need an Air Transport Pilot License (ATPL). The ATPL requires 750 to 1500 hours (depending on your training) of flying. The people that we usually call “commercial pilots”, are actually ATPs. The commercial pilots license is different.

Where will our future pilots come from?

That check-delivery-story reminded me of my concerns about where the USA will get its future pilots.

How does a pilot get 750 to 1500 hours of experience, which is just one of the requirements for the ATPL?

  • Delivering our checking-acount-checks from bank-to-bank at night. The “Check 21 Act” of 2003, made it legal to send scans of checks. So no more “flying checks”. Two-billion dollars of flights (per year?) are now gone: “poof”.
  • Fly as an airline co-pilot, but now they also need an ATPL (as-of July 15, 2013).
  • As a flight instructor
  • Charters
  • Corporate aviation
  • Plane rental, but that’s expensive; 1500 hours costs $112,500 to $600,000. (at $75 to $400 per hour for small non-turbine planes).
  • The military
  • Etc.

Without check deliveries, and non-ATP co-pilots, where will get enough pilots with enough hours? I have no idea, but it will become a problem without some future change.

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How To REALLY Drive on Ice

(Originally posted on 2016-05-22)

How much to turn? Which way to turn? Opposite lock: really? The point of this post is to provide a simple 100% accurate answer. My child is now learning how to drive, so this is timely information in my life.

What do you do if your car skids out (ice, water, mud)? You simply point your tires where you want to go. (In non-ABS cars, you also release your brake.)

This says, “turn into the slide,” and “turn your wheels in the direction that the rear of your car is sliding.” In other words: if the back of the car is sliding to the left, and the front of the car is pointing to the right, then you steer left. OK, but how much? Simply point your tires where you want to go.

TexasDex at the English language Wikipedia [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
Please pay attention to where the tires point. It’s where the driver wants to go. (CC-BY-SA-3.0 via Wikimedia Commons)
At 1:30 minutes into this video Doc Hudson shows how to steer in a skid. This is on dirt, but ice is the same thing, both are low traction oversteer conditions. Notice how he points his tires where he wants to go. Simple.

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The Price of Atheism

(Originally posted on 2007-08-07 as /archives/73)

If this bigotry had occurred in [insert arbitrary name of state here], then I wouldn’t think twice about posting it without an explanation, but it occurred in Oklahoma, and I used to live there.  I met some good people in Oklahoma.  Have no doubt that I respect them.

When people say things like, “This is a Christian nation.  92% of Americans believe in God, so atheists should be quiet” they are saying a hateful thing.  If you don’t recognize that as hate speech, then try this version on for size: “This is a [insert arbitrary skin color here] nation…”

“Now the argument that America is a ‘Christian nation’, created by Christians for Christians and traditionally, therefore rightly, dominated by a Christian majority, could just as easily be extended to calling America a ‘white male nation’ and a demand to once again disenfranchise women and minorities. I’m sure we could find a biblical basis for that, as was done in the past, as well as plenty of precedent in law, so long as we went back before the 20th century for our rhetoric” … “No difference in the basic bigoted impulse, or the structure of the argument.” – Bruce Springsteen, Lawrence KS,

SOMA listserv, 2007-08-06

My interest in this video is not religious; if it inspires anyone to recognize and confront their own prejudices, then that is a very good thing.

So, with all that out of the way, “enjoy” the film.

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