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03-24-2016, 12:27 AM   #1
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KA mount lens on a K5II

Hello everybody! I just received my Lester A.Dine 105mm Macro lens and started to play with this beauty. One thing puzzles me - when I switch on the camera with the lens attached, I'm asked to dial in the focal length of the lens. Should I dial 100mm (full frame focal length) or 150mm (cropped sensor equivalent)? Tried both and don't see any difference in images so far.

03-24-2016, 12:34 AM   #2
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Enter the actual focal length of the lens or the closest of available choices.

03-24-2016, 12:49 AM   #3
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QuoteOriginally posted by Buruny Quote
One thing puzzles me - when I switch on the camera with the lens attached, I'm asked to dial in the focal length of the lens

Hi Buruny. Because your camera doesn't recognize your lens, you must tell it the focal length so the camera will know how much " Shake Reduction " to use. If you dial in 100, that will be close enough. Good luck.
03-24-2016, 10:29 AM   #4
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Unless you've used 35mm film for years or plan to switch to the full frame K-1, you can completely forget about 'equivalence'.

A lenses focal length and aperture do not change, regardless of the sensor, so you should dial in the actual focal length marked on the lens. The resulting image would be different since the crop sensor covers a smaller area, but the whole idea of equivalence was so people who were used to thinking in terms of 35mm full frame could quickly get an idea of how something would perform on a crop sensor, mostly in relation to field of view and depth of field. If you have no frame of reference, worrying about the equivalence calculation is just wasted thought process.

Think of it like inches and centimeters. If you grew up thinking in inches, you might convert lengths from centimeters to inches to help you picture them in your head. If you've grown up thinking in centimeters there's no reason to consider the equivalent in inches, so you just stick with centimeters. The only time 'equivalence' comes in is when you have to move between the two systems and want to understand the relation, the same with full frame and crop sensors.

Honestly, equivalence is most useful for knowing what focal length on a crop camera gives approximately the same field of view as a certain focal length on a full frame or vice versa. There are more technical details and comparisons beyond that, but if you're just starting out and only use APS-C then that's more than you need to know.

03-25-2016, 10:56 AM   #5
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Thank you! All is clear now.

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