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07-15-2011, 03:39 AM   #1
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Purpose-Step-down Ring Sigma 50-500

Hi, need a little help ;-)

I have recently bought a Sigma 50-500 OS HSM: The filter size of this lens is Diameter 95mm and the lens is supplied with a step down ring enabling digital cameras with an APS-C size image sensor to use an Diameter 86mm filter.

Question: I have a Pentax K20D. What will the difference be if :

a) I use the step-down ring,
b) I do not use the step-down ring?


or, what purpose does it serve?

Thanks

07-20-2011, 04:42 AM   #2
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My guess, without actually bothering to visit a photo supply site to check, is that it allows you to save money when buying filters. Larger filters often cost more than smaller filters, especially when you get to such extreme sizes as 86mm or 95mm. It may also be that it is easier to find more variety of filters in 86mm than in 95mm.

It is possible that the step-down ring may cause some vignetting at the wider end of the zoom range, but you would need to test it to be sure. You can do that without actually using a filter. Just mount the ring and do some test shots.
07-21-2011, 12:17 AM   #3
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QuoteOriginally posted by Mike Cash Quote
My guess, without actually bothering to visit a photo supply site to check, is that it allows you to save money when buying filters. Larger filters often cost more than smaller filters, especially when you get to such extreme sizes as 86mm or 95mm. It may also be that it is easier to find more variety of filters in 86mm than in 95mm.

It is possible that the step-down ring may cause some vignetting at the wider end of the zoom range, but you would need to test it to be sure. You can do that without actually using a filter. Just mount the ring and do some test shots.
Mike, thanks, will do. But it does make sense. Will do a few test etc.
regards

Arrie
07-21-2011, 03:22 AM   #4
mel
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I have the lens and Mr. Cash is right. But its for when the lens is used on crop sensors like our Pentax DSLRs have. You don't use the ring if you have the lens on a full frame camera. Same goes for the hood extender.

07-21-2011, 04:09 AM   #5
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QuoteOriginally posted by mel Quote
I have the lens and Mr. Cash is right. But its for when the lens is used on crop sensors like our Pentax DSLRs have. You don't use the ring if you have the lens on a full frame camera. Same goes for the hood extender.
Thanks for the info!
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