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11-02-2012, 11:35 PM   #1
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Using "Input Focal Length" with A and M Lenses

I just bought several A and M series lenses, and everything works great, but I was wondering what value should I use on the "Input Focal Length" screen of my K-5:

= The cropped value: use 75 for a 50mm full-frame lens

or

= The uncropped value: use 50 for a 50mm full-frame lens

The value is needed for shake-reduction to work, and since that is related to apparent view angle I figure the cropped value should be used, but thought I should get some other opinions.

-------------------

Oh - my new lenses are:

SMC Pentax-A 50mm f/2

SMC Pentax-A 35-105mm f/3.5

SMC Pentax-M 200mm f/4

Promaster Spectrum 7 70-210mm F/4.0-5.6 - yeah, I know, but it was in excellent condition and so cheap I couldn't resist....

11-02-2012, 11:38 PM   #2
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Use the real value, 50mm is 50mm. For a zoom lens, like your 35-105mm, use the closest to what you plan on using. Too short of a focal length is better than too long because it might overcompensate and introduce blur to the image.

Unless you're used to 35mm format or are comparing directly with a 35mm format camera, forget crop factor exists. You don't need to think about it 99% of the time, you just need to know what it looks like on your camera.
11-02-2012, 11:58 PM   #3
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Thanks Elliot. I am used to 35mm standards. It still gets to me that my 16-45mm isn't like a fisheye at the wide end.
11-03-2012, 01:03 AM   #4
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QuoteOriginally posted by ENicolas Quote
Thanks Elliot. I am used to 35mm standards. It still gets to me that my 16-45mm isn't like a fisheye at the wide end.
I still have a hard time with the K5's sensor size. I have converted some of my old Contax lenses with the Leitax bayonet (they work great). But the crop factor or the fact that 50 mm does not look the same in the viewfinder, still troubles me after nearly one year.

Btw. I would love to have the A 35-105.

11-03-2012, 01:05 AM   #5
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Sometimes I use an A series 50mm on a reversing ring or cheapy extension tube, and never know what to select. I just go with whatever comes up (usually 50mm).

Regards
11-03-2012, 01:32 AM   #6
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QuoteOriginally posted by sam-joseph Quote
Sometimes I use an A series 50mm on a reversing ring or cheapy extension tube, and never know what to select. I just go with whatever comes up (usually 50mm).

Regards
If you're on a tripod it doesn't matter anyway, since you should have anti-shake turned off - and most of the time I'm using one. But I was testing a lens handheld and it came up, so I was wondering.
11-03-2012, 01:53 AM   #7
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QuoteOriginally posted by Pontax Quote
Btw. I would love to have the A 35-105.
There's another one available right now on EBay.
11-03-2012, 09:01 AM   #8
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QuoteOriginally posted by Pontax Quote
I still have a hard time with the K5's sensor size. I have converted some of my old Contax lenses with the Leitax bayonet (they work great). But the crop factor or the fact that 50 mm does not look the same in the viewfinder, still troubles me after nearly one year.
It does take awhile to get used the "crop factor." It's all a matter of field of view. If you like the classic 50mm view use something between 30 and 35mm. Likewise for portraits use something between 50 and 70mm. Pentax has made so many outstanding nifty fifties which would fit the bill perfectly. It's why I stay with Pentax lenses even on my C 1D Mk II N. Personally I like the crop factor because I like to 'shoot' wildlife and birds. The image of the animal or bird is no larger than it would be on full frame but it's like cropping the image in the darkroom. The disadvantage to the crop sensor is when using a wide angle. Fortunately lens makers have gotten so good at making extreme WAs now that that point is now moot. Just my ¢¢.

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