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09-23-2009, 05:38 AM   #1
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Setting up focal point for manual lenses. consider crop factor?


I am a little confused. I just got a 90mm vivitar 2.8 macro, and i am not sure where to the set the focal point it. First of all, there isnt a 90. Then, i wonder if i should multiply it by 1.5 crop factor and come up with 135mm....what should i do, and why does this matter anyway? What does this setting really do in terms of my image taking?


09-23-2009, 06:00 AM   #2

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The setting is for shake reduction, just set it to the closest number.
09-23-2009, 06:11 AM   #3
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Use the closest number to the physical focal length of the lens. Do not count the "crop factor".
09-23-2009, 07:46 AM   #4
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QuoteOriginally posted by RBellavance Quote
Use the closest number to the physical focal length of the lens. Do not count the "crop factor".
What's a crop factor?

09-23-2009, 11:04 AM   #5
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QuoteOriginally posted by Wheatfield Quote
What's a crop factor?
Did i mistake the meaning of crop factor? Sometimes i am not sure whether i know what things meant or whether i am just throwing words around
09-23-2009, 11:35 AM   #6
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You are correct in your usage of crop factor. As the previous posters stated, just use the physical focal length of the lens. Well, I guess you could always perform a Shake Reduction test for the forum by taking a series of shots at various focal length settings in-camera and comparing the results to see which work best for that lens. But the easiest method is probably just to enter the closest number, probably rounding up if you're unsure of which one to use.
09-23-2009, 12:38 PM   #7
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Wheatfield was being facetious. His point is that unless you have a specific reason that you know you need to think in those terms, then you can safely pretend you had never heard of it, and pretty much be better off for it.

Basically, the only time you ever need to think in those terms if you're trying to compare the behavior of a lens on your DSLR to the behavior of a lens on a film camera. If you don't have a film camera in your hand while asking the question, then chances are, you don't need to ask it. My analogy: unless you're actually packing your bags for a trip to the moon, you don't need to be asking how much you'd weigh there. Similarly, if you don't plan on using the lens on a film camera, there is no point in worrying about crop factors.

BTW, the term you are looking for is "focal length", not "focal point". 90mm is the focal length of the lens. If that's not an option in the SR menu, enter whatever's closest - most would say it's better to be a little under than to be over. It matters because the SR system needs to know the focal length of the lens to know how much to move the sensor to counteract shake. If it doesn't move the sensor enough, then you don't get the full advantage of SR. If it moves the sensor too much, it ends up overcompensating and *potentially* make things worse than not having SR in the first place. But you'd have to have *way* too high a number entered. Entering 100 instead of 90 wouldn't be a big problem - but it would be better to go with 85.

Last edited by Marc Sabatella; 09-23-2009 at 05:48 PM.
09-23-2009, 01:00 PM   #8
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I see. That made it clear for me. Also on crop factor - i wasn't quite sure why it was mentioned in a lot of older lens listing, but now i understand. I guess what you are saying is that it doesn't mean anything for me who comes straight to digital SLR, but would mean something to someone who owns and works a film camera. It actually is a relieve, it always confuses me.

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