The 5% Solution

Started 2 months ago | Discussions thread
Stephen Barrett
Contributing MemberPosts: 514Gear list
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Re: The 5% Solution
In reply to Stephen Barrett, 2 months ago

sueanne wrote: "I just want to take the picture……."

Good point, sueanne

Brian wrote: "… but did you say in what way it matters."

I guess it doesn't matter photographically but, to me, it's a matter of curiosity why the camera does not work quite the way I think it should. Also, Bob Atkins' description of the stated focal lengths of SLR telephoto lenses is bothersome:

"As you can see, it doesn't much matter who made the lens or what the maximum focal length was, in every case the measured maximum focal length is less than the marked maximum focal length, and the average difference is about 5%. The difference is always on the short side. I didn't find any examples where the actual focal length of a telephoto was longer than marked!"
-Bob Atkins, discussing the focal lengths of SLR lenses
http://www.bobatkins.com/photography/technical/focus_breathing_focal_length_changes.html

If Bob Atkins is correct, there appears to be a deliberate policy on the part of manufacturers to overstate focal lengths. I have been trusting Canon that the full zoom of my camera is 150.5 mm as specified. Now I don't know whether it is or not. It may only be 143 mm.

When people are told that their SX50 has a maximum equivalent focal length of 1200 mm, does that mean it is only 1140 mm but that's OK because it's still equivalent because the 1200 mm SLR lens is also only 1140 mm? Or is Bob Atkins wrong and is there something wrong with my measurements and calculations too?

It is also a challenge. Here is a black box. The size of the parts inside it are deliberately kept secret. All kinds of information and misinformation is available and we don't know what is true. Is it possible to deduce what is inside just from what the black box reveals to us? Aren't you tempted to take the lens off your PowerShot camera and to remove the sensor so that you can make measurements on them? (I will probably do that if my SX30 quits working.)

That is my rant for the day.

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