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10-03-2011, 03:50 AM   #16
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I've just ordered a DA* 300mm and hopefully I'll receive in 10 days time. I'm amazed with comments and samples about this lens that are published @ PF and in other platforms on internet. However, I'm very curious if I'll be able to use this lens with my SMC Pentax-F 1.7x AF Adapter. Are there anybody here ever tried this combination? I have a positive prejudice and think of that it will work as both are genuine Pentax products. But, when I tried SMC Pentax-F 1.7x AF Adapter with my SMC-DA* 50-135mm f/2.8 ED [IF] SDM I was not happy with the results tough the calculated F value for that combination is a quite acceptable one. The images were getting softer at last end of the focal length.

Now, I’m a bit afraid that the F value of the combination of DA* 300mm f/4 ED (IF) SDM and SMC Pentax-F 1.7x AF Adapter will become something like F/6.8@ 510mm focal length.

I’ll appreciate if I may see some results of such combination here.

10-03-2011, 04:11 AM   #17
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The adapter will turn the lens into a f6.8 510mm one. As for the AF it will work in a way that you will have to prefocus the lens into the vicinity of the focus distance and then let the adapter do the rest. Since the lens is a quickshift one it should be a fairly quick method. Some photos taken with such a combination can be seen in a thread I started on another forum (sorry if this contradicts any forum policies over here): DA* 300mm F4 with TC vs. Sigma 150-500mm
10-03-2011, 06:35 PM   #18
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[QUOTE
Now, Iím a bit afraid that the F value of the combination of DA* 300mm f/4 ED (IF) SDM and SMC Pentax-F 1.7x AF Adapter will become something like F/6.8@ 510mm focal length.

Iíll appreciate if I may see some results of such combination here.QUOTE]

I will say that f 6.7 is about the same as a Sigma 50-500mm and is probably the best you can do to get 500mm without spending some serious cash.
I posted some pictures of the combo for you on the other thread.

regards
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