What is the true "normal"?

Started Jul 9, 2012 | Discussions thread
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Mark Ransom
Mark Ransom Veteran Member • Posts: 4,065
What is the true "normal"?

As I understand it, the "normal" focal length is the one that delivers the same perspective as you would get with the naked eye.

A rule of thumb often quoted is that this is achieved when the focal length of the lens is the same as the diagonal of the sensor. For my K-7 at 23.4x15.6 mm this would be almost precisely 28mm.

I threw my zoom lens on the camera the other day and focused on something at a reasonable distance, then adjusted the FL until the image magnification was about the same in my right eye through the viewfinder as my left eye without it. I was even able to get stereo vision by looking through both eyes at the same time. The surprise was that this occurred at about 55mm!

I know that the viewfinder shrinks the image a little (0.95 magnification) but I wouldn't expect it to make this much difference.

Could it be because of the glasses I wear for short-sightedness?

What are your experiences?

 Mark Ransom's gear list:Mark Ransom's gear list
Pentax K-7 Pentax K-01 Pentax smc DA 15mm F4 ED AL Limited Pentax smc FA 50mm F1.4 Tamron AF 70-300mm F/4-5.6 Di LD Macro +2 more
Pentax K-7
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