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10-30-2011, 06:26 PM   #1
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K 500mm f4.5 & F 1.7X AFA

Has anyone tried this combo and if so what was the result?

Also does anyone know the diameter of the front of this lens?


Last edited by littledrawe; 10-30-2011 at 06:33 PM.
10-30-2011, 06:50 PM   #2
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I had no luck when I tried it with the k20d back when I had them, it would just hunt around and not lock on consistently. I only tried it one time and gave up, but that was a few years ago. I was really hoping it would work for Eagles at the local dam, but ended in frustration.
10-30-2011, 07:07 PM   #3
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I've used the 1.7x AFA with a Rikenon 300mm f/4.5 and it worked, but only in good light. I am sure you would need that for any chance of it working with the longer K lens.
10-30-2011, 07:42 PM   #4
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I was playing with my Sigma 300/2.8 and 1.4xTC yesterday arvo, I popped the Pentax 1.7xAFA on the back, even as the sun was getting low, auto focus snapped in pretty quick, just got the manual focus close then let the 1.7AFA fine tune it. It was actually much better than earlier in the day when I had the Sigma APO 1.4x and kenko 1.5x stacked on there.

Oh, on my K-7 BTW.

10-30-2011, 07:55 PM   #5
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QuoteOriginally posted by borno Quote
I had no luck when I tried it with the k20d back when I had them, it would just hunt around and not lock on consistently. I only tried it one time and gave up, but that was a few years ago. I was really hoping it would work for Eagles at the local dam, but ended in frustration.
Just to clarify, it was the K500 f4.5 of which I was referring, the 1.7x worked great on f4 or faster for me.
10-30-2011, 09:42 PM   #6
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QuoteOriginally posted by littledrawe Quote
Has anyone tried this combo and if so what was the result?

Also does anyone know the diameter of the front of this lens?
The K500/4.5 does not have a front filter thread and accepts 52mm filters in a rear filter holder. The actual diameter of the front is 126.5mm.

Phil.
10-30-2011, 10:19 PM   #7
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Thanks for the info, maybe I'll just keep looking for the 1.4x-L at a reasonable price. If there is such a thing.
10-31-2011, 05:46 AM   #8
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QuoteOriginally posted by littledrawe Quote
Thanks for the info, maybe I'll just keep looking for the 1.4x-L at a reasonable price. If there is such a thing.
Maybe not the L converter, but how about another option, and one I have considered as well on my Tamron 200-500F5.6

Use a sigma APO 1.4x EX DG teleconverter.

Any lens that can take the 1.4x L converter has a sufficiently recessed rear element that you can use the sigma TCs with them.

As for the 1.7x AFA this has long been debated, where people claim that they can get AF confirmation at apertures smaller than F4 but as far as I have experienced, F4 is the practical limit. My K300/4 works fine but anything slower simply can't get AF lock unless very very sunny outside. with an F4 lens, AF lock is reliable in almost all lighting.

11-01-2011, 12:28 PM   #9
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QuoteOriginally posted by gofour3 Quote
The K500/4.5 does not have a front filter thread and accepts 52mm filters in a rear filter holder. The actual diameter of the front is 126.5mm.
Nice collection of K series lenses in your signature there!

QuoteOriginally posted by Lowell Goudge Quote
and one I have considered as well on my Tamron 200-500F5.6
Well then buy it already and test it out so you can tell me how it works with older glass
11-01-2011, 12:35 PM   #10
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QuoteOriginally posted by littledrawe Quote
Well then buy it already and test it out so you can tell me how it works with older glass
Not a question of anything other than time to try it. I use the sigma APO 1.4x and 2x EX DG teleconverters with my Sigma 70-200F2.8 already

I have tested to know they fit on the tamron 200-500, the 2x makes a 1000mm F11 but the 1.4x may be interesting to try, as I might still get focus confirmation with the resulting 700mm F8
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