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01-30-2010, 09:43 AM   #1
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? Crop Factor and Old Lenses

Hello, first post here. I just got my K-x with 18-55 lens a week ago. This is my first dSLR, but I did use a 35mm SLR back in the 1980s. I've also got a Canon S90, and I'm currently trying to wrap my brain around focal length/crop factor/35mm equivalency. So here's a real newbie question:

I understand how to calculate 35mm equivalents when using lenses rated for digital cameras. But ... say I got an old Pentax M 50mm F1.7. Do I multiply that 50mm by 1.5 for a focal length of 75 (35mm equivalent)? Unfortunately I still have to convert to 35mm equivalents to visualize the capabilities of lenses. As I shoot more, I guess I won't have to do that conversion. (I hope!)

TIA!

01-30-2010, 10:22 AM   #2
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QuoteOriginally posted by twokatmew Quote
Unfortunately I still have to convert to 35mm equivalents to visualize the capabilities of lenses.
Yup. Fortunately that's all the crop factor is really needed for. It doesn't change anything else.

Yes, any lens you put on the camera you'd just multiply by 1.5 to get an idea of the view from a full-frame camera. The lens itself, of course, is still a 50mm and will always be so.
01-30-2010, 12:25 PM   #3
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Right. Whether the lens was designed for film or digital is immaterial. All 50mm lenses have exactly the same field of view on a digital SLR. So if thinking in terms of crop factor helps you visualize the field of view of a given lens, then continue to use it, and use it precisely the same way whether a lens was originally designed for film or digital.

And yes, I'd assume at some point you won't have to keep doing that mental arithmetic, unless you end up continuing to shoot film as well.
01-30-2010, 12:55 PM   #4
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Thx!

Thanks so much! I do still have my old Fuji 35mm, but I don't plan to use it. It's more of a museum piece, like my old Olympia manual typewriter.

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