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10-20-2011, 11:36 PM   #1
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Pentax AF 1.7 TC observations

Hi everyone! I just got a Pentax AF 1.7 Tele-converter for Karen, and I wanted to post my observations. A little history: Karen likes to photograpph the local Antelope on the ranch and see bought a Sigma 50-500 OS for that. It was a total disappointment. It was soft on the left 1/3 of the frame, and on the rest it was never really sharp compared to her Tamron 70-200 F2.8. She hated it and I never tried another copy. We did buy the Pentax DA*300mm F4 and that lens is just a joy: light, sharp right from F4, fast focussing. Karen wanted just a little more reach, so I took the suggestion of this forum and bought the 1.7 AF TC from Ebay(expensive!). Well, it works like a charm! It is reasonable fast at focussing on that lens, and sharper than the Sigma at any setting. It is also light enough to be used hand held. She loves the combo. It also works even better on the Tamron: Even faster AF, and a bit sharper. It gives us a lot of choices for trips and local uses. A few observations: The pics with the adapter are as sharp from corner to corner as I could want, it does not vignette at the corners on the long lenses, and is easy to use once you try it a few times. I consider it a steal because of the versatility. YMMV!

David

10-21-2011, 02:13 AM   #2
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I love the AF 1,7x combined with DFA50/2,8 macro. It practically does perform like 85/4,5 lens capable of 1,7:1 magnification. Great for very tiny critters.
10-21-2011, 03:55 AM   #3
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Agree--the DA*300/4 + AF1.7x is a very good combo.
10-21-2011, 05:29 AM   #4
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I have had the 1.7x AF TC for almost 20 years (bought it shortly after my PZ-1 and the move to AF.

I used it at the onset with my series 1 70-210 F3.5 (version 1) but later moved it to my K300/4.

I would have to agree that it is a great combo (i.e. a 300/4 and the AF TC) it is truely something you can hand hold at 500mm.

I also have a sigma APO 70-200F2.8 EX which I use with sigma TCs that is every bit as goof but falls 100mm short when you want a little more reach, (I have never tried the sigma plus stacking sigma 1.4x and the AF adaptor, but that should work too I suppose) and I also have a tamron adaptall II 200-500F5.6 but at more than 2.5 kilos, it is not a hand hold option/

10-21-2011, 06:15 PM   #5
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QuoteOriginally posted by dadipentak Quote
Agree--the DA*300/4 + AF1.7x is a very good combo.
+1 here
10-21-2011, 07:47 PM   #6
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The AFA 1.7x is probably the best converter that Pentax ever built, optically. It also focuses my 50-135 well enough to get some decent hockey pictures, even though the combined f/stop is about f/4.8 or thereabouts. I need it to AF my 50-135 now that the SDM has failed for the third time. I can hand focus for soccer using catch-in-focus, but for hockey, it just would not work for me.
10-21-2011, 08:10 PM   #7
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Sorry to hear about your 50-135.
If B&H sold the converter, I would buy it in a heart beat.
10-21-2011, 08:14 PM   #8
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David: I too use the 1.7X TC with the DA*300/4, just like Dadipentak, Lowell and SylBer.

This is the best TC I have and it works like a charm once you get used to the "magic" it does.

Since I can't afford a "real" 500mm lens, this is the best combo I've found.

Glad you found it and post some pics when you have time.

Cheers.

JP

10-22-2011, 03:57 PM   #9
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I too use the converter with a DA*300 and really like the combination. I have also used it with my DA*60-250 and like that combo too. It is really versatile
10-22-2011, 05:05 PM   #10
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I tried the AF 1.7 TC with my Voigtlander 125 Macro, I was really disappointed: noticeable loss of sharpness and a lot of chromatic aberrations appeared.
10-22-2011, 06:55 PM   #11
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Interesting, Zav. My suspicion is that some lens/TC combinations just don't work as well as one might think based on the intrinsic quality of the components. I'm not aware that there has been any systematic research on this, though.
10-23-2011, 01:35 AM   #12
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Dave, I would tend to think the same. I have a Kenko x1.5 which works very well with my Voigtlander 180, but no so well with my Sigma 300. That's another story.
10-23-2011, 09:33 AM   #13
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The AFA 1.7 and the DA*300 are probably the best combination for that lens. The Tamron and Kenko with PZ contacts seem to take forever to find focus.
10-23-2011, 11:12 PM   #14
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QuoteOriginally posted by GaryH Quote
The AFA 1.7 and the DA*300 are probably the best combination for that lens. The Tamron and Kenko with PZ contacts seem to take forever to find focus.
I now have the AFA 1.7x and DA*300 (for one week so far to still working out my technique).
In the combination, the AFA 1.7x does the focusing but it is very quick and accurate. It will only focus across a short range though. You have to manually set the lens somewhere near the range of the subject.

If you have the lens set at say 3metres and the subject is 50metres away the AFA 1.7 wont focus on the subject as it is out of its focus range.

I think that this is actually an advantage rather than a limitation. If you mis-focus on a difficult target the AFA will "zip zip" across its range in 1/2 second. Having the lens go in-out from infinity to 2m and back again is much slower.


If you are having to shoot at 510mm a bird / deer / bear / celebrity or whatever might be hiding in bushes or something so would be a tricky focus anyway. Also your hand might not be so steady if your trying to trying to focus on a Grizly bear close to the minimum. focus dist.
The last thing you want is to have the lens & TC taking forever to rack in/out.
10-24-2011, 04:12 AM - 1 Like   #15
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You're quite right Steve: the TC acts as a focus limiter--very useful in certain situations. With other lenses & TCs, I use catch-in-focus in those situations.

BTW, my suggestion for the the "grizzly closer than MFD problem" is to run like hell.
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