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10-15-2013, 07:37 AM   #1
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Has anyone tried the Samyang 85mm f1.4 with the Pentax 1.7x AF teleconverter?

I have the Samyang 85mm f1.4 lens, and I love it... but I would love it more with autofocus. Was wondering if anyone has tried plugging it into the 1.7x teleconverter Pentax makes, which has autofocus capability. Being a nice fast lens, I'd think it would AF just fine, but I'm curious how well it works and the image quality.

Thanks!

Charles.

10-15-2013, 07:41 AM   #2
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Um, Pentax makes a teleconverter that gives manual lenses AF capability??
10-15-2013, 07:51 AM   #3
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^Yes, the 1.7X AF Adapter.
10-15-2013, 09:49 AM   #4
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QuoteOriginally posted by Mr Bassie Quote
Is it still being made? I thought it was no longer in production
it's not still being made but you can find them...not cheap though 350-400

10-15-2013, 09:54 AM   #5
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QuoteOriginally posted by Mr Bassie Quote
Is it still being made? I thought it was no longer in production
Yep, no longer in production. Sadly, Pentax currently makes no tele converters that I am aware of.


Steve
10-15-2013, 10:22 AM   #6
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Send me a 85 1.4 and I'll test it for you. We find the TC works great for macro work with the Tamron 90, and great with the Tamron 90 in general, so my guess is it would be a good match. I'd qualify that by pointing out that it doesn't seem to AF at all with my A-400 and I've taken to manual focusing that combo so, I'd try before I buy. With the A-400 I get the subject in sharp focus and the AF on the TC actually moves the image out of focus then releases the shutter. It can be annoying if you forgot to turn off AF.
10-15-2013, 10:27 AM   #7
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How about you try Catch-in-focus (aka focus trapping)? That gives you capability similar to AF. Lots of threads about it.
10-15-2013, 10:42 AM   #8
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I have tried it and it gives good results. Not sure I have any shots but for something in the 145mm combined range with an F2.5 combined aperture wit is pretty good. The astute thing would be to compare it to the K135/2.5

10-15-2013, 03:47 PM   #9
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QuoteOriginally posted by normhead Quote
Send me a 85 1.4 and I'll test it for you. We find the TC works great for macro work with the Tamron 90, and great with the Tamron 90 in general, so my guess is it would be a good match. I'd qualify that by pointing out that it doesn't seem to AF at all with my A-400 and I've taken to manual focusing that combo so, I'd try before I buy. With the A-400 I get the subject in sharp focus and the AF on the TC actually moves the image out of focus then releases the shutter. It can be annoying if you forgot to turn off AF.
Hi Norm,

I wouldn't expect the 1.7x AFA to AF with your A 400 or any other f5.6 max aperture lens since the max aperture of the combination ends up being around f9.5 -- about a half stop beyond f8 where any of the SAFOX systems become really challenged, even with relatively bright light. My FA* 300 f4.5 (f7.7 with the AFA) gives me snappy AF until the lighting gets pretty dark -- heavy overcast - so probably about EV 12 or maybe 11, but this lens is exceptionally sharp and contrasty wide open. Lenses with similar speed but lower optical performance wide open will fair less well. Significantly faster lenses should AF very reliably as they won't even come close to the aperture limitation.

Whether or not the IQ of the combo is acceptable is totally subjective. IMO, Sharpness and contrast in the central portion of the frame will not be compromised significantly (IMO), but at the edges, it really depends on the base lens, and some are better towards the edges than others -- but remember that with the 1.7x magnification, only the central portion of the image circle will be used. In my experience, bokeh can also effected, especially at some specific distances from the focal plane, and this will have a lot to do with the final judgment of the combo's IQ.

I've had four 1.7x AFAs at one time, so was able to informally test them against each other, and AFAICT, they all performed equally, so I don't know how much sample variation might weigh into this, but from my experience, not too much.

I don't think there is any way to guess how any lens will perform optically with the AFA, except that center sharpness and contrast will not be compromised very significantly. The only way I could suggest to gauge the overall IQ would be to actually try it.

Scott
10-17-2013, 05:04 PM   #10
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I've been thinking about getting the Bower / Vivitar 2x7 extender just for the Rokinon (Samyang) f/1.4 85mm myself. The 2x teleconverter is < $200 for a 'good one', and I'd actually try it out (even MF) on my cheapo 18-200mm Sigma for some shots at the moon - even with manual focus.

The nice thing with the 85mm f/1.4 is that even with a 2x, its ~170mm f/2.8
It truly in a pain to focus at f/1.4 though without a tripod, or with a moving subject, as the DoF is razor thin.
10-17-2013, 09:09 PM   #11
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QuoteOriginally posted by formercanuck Quote
as the DoF is razor thin.
And there is the rub for catch-in-focus and AF...


Steve
10-17-2013, 09:31 PM   #12
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QuoteOriginally posted by snostorm Quote
I wouldn't expect the 1.7x AFA to AF with your A 400 or any other f5.6 max aperture lens since the max aperture of the combination ends up being around f9.5 -- about a half stop beyond f8 where any of the SAFOX systems become really challenged, even with relatively bright light. My FA* 300 f4.5 (f7.7 with the AFA) gives me snappy AF until the lighting gets pretty dark -- heavy overcast - so probably about EV 12 or maybe 11, but this lens is exceptionally sharp and contrasty wide open. Lenses with similar speed but lower optical performance wide open will fair less well. Significantly faster lenses should AF very reliably as they won't even come close to the aperture limitation.
Don't want to stray too far off the original topic, but I've been wondering about this. On my K-5, the AFA 1.7x seems to do pretty ok with my Tamron SP 400/4 in most light , and even kinda works with my Tamron SP 200-500 f/5.6 in bright light (but noticeably less well with my Tamron SP 300/5.6, go figure) -- all Adaptalls. But with the enhanced AF sensitivity of the K-5 II and now the K-3, is using an f/5.6 lens with the AFA 1.7x (at least in half-decent daylight) actually a reliable combo?
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