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05-08-2019, 08:39 AM   #1
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using AF 1.4x TC for auto-focus manual lenses?

A review recently written concerning the Samyang 135mm f2 suggests that I can use a Pentax AF 1.7x TC with this lens to achieve auto focus for portraits . I have this lens and a Pentax AF 1.4x but have not been able to nudge this lens into auto focus. I don't think it is possible.

05-08-2019, 09:03 AM - 1 Like   #2
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QuoteOriginally posted by Steve Belcoski Quote
A review recently written concerning the Samyang 135mm f2 suggests that I can use a Pentax AF 1.7x TC with this lens to achieve auto focus for portraits . I have this lens and a Pentax AF 1.4x but have not been able to nudge this lens into auto focus. I don't think it is possible.
The DA 1.4x TC supports the lens' AF capability. The AFA 1.7x adds a limited AF capability to MF lenses.
05-08-2019, 09:04 AM - 1 Like   #3
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The Pentax AF 1.7x TC is a very special teleconvertor that provides AF to manual focus lenses by moving the teleconvertor in response to the camera's screw-drive motor motions.

Most teleconvertors don't do this. The best that they can do is pass AF motion or electrical signals from the body to an AF lens.
05-08-2019, 09:06 AM   #4
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They are two totally different converters. The 1.7x converter has a built-in AF mechanism and thus converts K, M and A-series lenses to af. The 1.4x does not have this built in mechanism, so it only works on af lenses. it does not have the ability to convert a non-af lens to af.

05-09-2019, 03:20 AM   #5
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Concerning the TC 1.4x and 1.7x

Is the IQ for the 1.7x as good as the 1.4x?
05-09-2019, 03:41 AM   #6
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QuoteOriginally posted by Steve Belcoski Quote
Is the IQ for the 1.7x as good as the 1.4x?
You'll be amazed by this combo! That's all I can say

I think that the 1.7X is a superb TC and I would love it if Ricoh/Pentax released a new DFA* 1.7X TC instead of the classic 1.4X and(?) 2.0X....
05-09-2019, 05:19 AM - 1 Like   #7
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Steve, I'd like to make you aware of the Teleconverter and Adapter Club thread, if you're not acquainted with it..

Teleconverter and Adapter club - PentaxForums.com
05-09-2019, 06:22 AM - 1 Like   #8
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The difference is in the names.
HF DA 1.4 TC
F 1.7x AF adapter.

The AF adapter was designed to work with all those MF A* lenses and make them useful in the age of auto-focus. Being designed to be used with fast A* lenses, the optics are special compared to many of the TCs on the market today.

05-09-2019, 12:24 PM   #9
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QuoteOriginally posted by Steve Belcoski Quote
Is the IQ for the 1.7x as good as the 1.4x?
No, but it is close. This assumes you are starting with a high quality fast prime.
05-09-2019, 12:41 PM - 1 Like   #10
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it's focus assist... lens has to be within a reasonable range manually. it will not focus from minimum - infinity by itself.
05-09-2019, 02:02 PM   #11
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QuoteOriginally posted by Steve Belcoski Quote
Is the IQ for the 1.7x as good as the 1.4x?
It depends on how you define"better". Does it define more subject detail? Yes it's better.

Images taken from here.
Understanding folks saying a TC doesn't ad more detail. - PentaxForums.com

The 1.4 TC


1.7x


If your lens tends towards purple fringing the 1.7x will make it worse, whereas the 1.4 actually seems to correct it. But in terms of IQ I don't see a lot of difference, except the 1.7 images is bigger. In the bar codes on the Green Tea image the bar code is distinguishable on the 1.7x. On the 1.4 TC parts of it are just gray and undefined.

Im not sure why UncleV says it's not better.

Last edited by normhead; 05-09-2019 at 03:07 PM.
05-09-2019, 04:44 PM   #12
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QuoteOriginally posted by normhead Quote
Im not sure why UncleV says it's not better.
To be fair you have a lot of experience also. My experience with moon shots using the fa* 300 f4.5 cropping the 1.4x seeems slightly crisper than using the 1.7x and the same with the DA* 60-250 f4. On the other hand, the DA* 200 F2.8 results with the 1.7x seems very close or as good as the 1.4x plus crop. However I'm not super rigourous in my testing and I'm not testing it methodically.
05-09-2019, 05:08 PM   #13
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QuoteOriginally posted by UncleVanya Quote
To be fair you have a lot of experience also. My experience with moon shots using the fa* 300 f4.5 cropping the 1.4x seeems slightly crisper than using the 1.7x and the same with the DA* 60-250 f4. On the other hand, the DA* 200 F2.8 results with the 1.7x seems very close or as good as the 1.4x plus crop. However I'm not super rigourous in my testing and I'm not testing it methodically.
Fair enough. I do tend to use the 1.7 on 2.8 glass, giving me ƒ4.5. The improved AF accuracy could be the deciding factor here when comparing 2.8 glass to ƒ4 + glass. Like you, I really don't like it on the DA*60-250.
05-10-2019, 04:05 AM   #14
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Thanks to all for your helpful responses and making me aware of the TC and adapter club. I hope that Pentax will one offer a new FF TC adapter this AF assist feature in the future
05-10-2019, 08:12 AM - 2 Likes   #15
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QuoteOriginally posted by Steve Belcoski Quote
Is the IQ for the 1.7x as good as the 1.4x?
It's tough to say. Purely objectively, no, as there is more image degradation with the 1.7x vs the 1.4x. However, the 1.7x gives you more magnification. Using the 1.7x TC may require a higher ISO because of the longer focal length requiring a faster shutter speed and the aperture being darker by another 1/2 stop versus the 1.4x TC. And higher ISO will lead to more detail-destroying noise.

Also, some TC's simply work better with certain lenses and not as well with others.

Last year, I shot an osprey @ 40 yards with 2 combinations - the Pentax A 400/5.6 + A 1.4x-L TC (560mm total) and the Tamron 360B 300/2.8 + 1.7x AFA (510mm total) - and the results were basically a wash. The Tamron 300/2.8 is noticeably sharper than the Pentax 400/5.6, but the Pentax combo offers more magnification.

I guess all my blather is really to say "it depends" Like @normhead, I use my 1.7x AFA on f/2.8 glass, because I don't like the performance on slower lenses.
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