SandyF found proof that I'm right, but thinks it proves me wrong.

Started Jul 14, 2012 | Discussions thread
Erik Magnuson
Forum ProPosts: 11,342
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Re: Same framing vs. same distance: example photos
In reply to Mostly Lurking, Jul 16, 2012

Mostly Lurking wrote:

That's why I referred to the distance distance between the 2 different focal length lenses.

What's a "distance distance?" BTW, when you refer to the "focal length" of a lens, what is it actually the length of - or in other words, what are the two ends of the length?

No, it is relevant. The point of image capture is not at the sensor, it is at the focal length distance from the sensor.

Try reading that sentence out loud "The point of image capture is not at the sensor". Why would we call it the "image plane" if it's not where the image is formed? Why are focal length and focus distance calculated relative to the image plane? What is the optical term for the point you are describing - does it have "image" in it? BTW, "focal length" is only the distance to the image plane at infinity. If you pay attention the lens moves to different distances from the image plane as you change the focus.

That the sensor plane did not move to compensate for the focal length difference is one of the problems with your photos; they were not taken at a constant 2 feet. You should have used a micro-focusing rail.

Even assuming I was off by 36mm, do you think that accounts for the results? At 2ft or 610mm, 36mm is only 6% error. There may be 6% error in the difference between the two shots taken at 2ft but that doesn't explain the rather significant difference between the 2ft and the 6" shots with the same 12mm lens. According to your theory, these should be identical, but there is far more than 6% difference.

It took me only a few moments to produce that series of photos. You are free to produce a set of photos to prove your version. You don't need a 12mm lens, any 4x difference in focal length will do -- even the same zoom lens at 25mm and 100mm.

I'm sure you're aware that the tone of your posts to me is one of nastiness. With that in mind, consider yourself lucky that i not only chose to reply to you, but did so in a civil manner.

Oh what a lucky man I am. (Somehow when I say that, a 70's synthesizer riff runs through my head.)

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Erik

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