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04-13-2010, 03:12 PM   #1
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To those that bought the Pentax 1.7x AFA TC

Is it worth the cash (because it is a lot of cash for a 1.7x TC)? I'm really really considering getting one, but have huge buyers regret worry.

Also, does it focus both ways - i.e if you have focus locked at 70m, will it go +/- 30m in focus or just -60m - i.e. does it front focus and back focus.

04-13-2010, 03:22 PM   #2
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QuoteOriginally posted by whelmed Quote
Is it worth the cash (because it is a lot of cash for a 1.7x TC)? I'm really really considering getting one, but have huge buyers regret worry.

Also, does it focus both ways - i.e if you have focus locked at 70m, will it go +/- 30m in focus or just -60m - i.e. does it front focus and back focus.
It's one of those things that if you buy it you don't think about the cost. You already know it's going to be expensive. The way I use mine, I put the lens on, and get focus Close and the TC AF will then take over. Keep in mind that the TC does NOT focus the lens itself (won't turn the AF drive on the lens) but adjusts it's internal elements to achieve focus. I cannot tell you what the practical range is with respect to adjustment.

I thought it was a worthwhile investment enough to sell my Bigma to cover the cost of one (and other lenses). It turns my DA*300mm into a 510mm without adding a lot of bulk and it works great.

04-13-2010, 04:19 PM - 1 Like   #3
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I have used one since the early 1990's. That's right, I am an origonal owner

I bought it when I got my PZ-1 and wanted to get AF functionality with my Series 1 70-210F3.5 and 300mm F4

It is well worth the investment as it is a very good TC. The AF is a bonus.

K7 and 300F4 plus 1.7x AF TC

and 100% crop

by the way the above is at 1/40th so you can see SR works pretty well also.

and from my *istD

Same lens and TC

or again, same combo from my PZ-1 and kodacolor 400 gold

04-13-2010, 06:06 PM   #4

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Hi whelmed,

As a TC for occasional use with a consumer grade zoom, it's not worth the money since the f5.6 max aperture of these lenses will go to f9.5 with the 1.7x multiplication factor of the AFA, and the only Pentax DSLR I know of that might AF at this aperture is the K-7 -- sometimes, -- and only if the light is good. Without the AF capability, it's way outside any semblance of reasonable, IMO

As an accessory with a top quality tele zoom or prime, it can be worth many times even the inflated current market prices. For a hobbiest, IMO, a 300/2.8 (they're all good enough) + TCs (singly, or even stacked) gives you a whole lot of versatility in FL and speed -- at a significant cost savings as ultra tele AF primes and zooms are both pricey (as in thousands of dollars ea) and big and heavy (on the order of 7-15 lbs ea).

For my use (birding mostly), the AFA adds some additional functionality besides its ability to AF internally and the 1.7x multipoier. Since the focus range is limited, and must be combined with some MF to cover the entire range of focus distances, it acts as a focus limiter, but without the multiple operations needed with normal focus limiters on lenses. It is very quick to AF lock once you get the drill, and it offers the full Quick Shift advantages of DA lenses, which is as good as it gets for AF/MF clutch. I must admit that on the negative side, it can make the bokeh busier and increase existing CA/PF, but just about any TC will do this, and the AFA (IMO) offers about the best optical performance above 1.4x other than the Rear Converter A 2x-L, which is MF only.

I use these regularly, and have 3 of them. One of them has contacts insulated for use with Sigma lenses, the other two are unmodified for my Pentax and Tamron Adaptall 2s. The highest price I've paid was about 3 months ago from KEH -- an EX grade at $228 shipped.

The reason why the questions about focusing distance can't really be answered is that the focusing range in the AFA depends on the FL of the lens. For a 50mm or shorter, I believe you can focus the lens to infinity, and let the AFA do all the focusing. For teles, the range of the AFA will shrink the longer the FL of the lens, and the longer lenses need increasing amounts of MF help.


04-13-2010, 06:25 PM   #5

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Considering that currently there is no other TC that autofocuses reliably with SDM lenses, the 1.7x AFA at $300 - $350 is a fair price.

My 60-250mm F/4 now can cover from 60mm F/4 to 425mm F/6.7. In many cases, it means I don't have to bring along the big and heavy Sigma 150-500mm F/5-6.3. I lose less than 0.5 stop and some IQ at the long end, but I can live with that.

With my 50-135mm F/2.8, I have cover from 50mm F/2.8 to 230mm F/4.8. At times it means I don't have to bring along the 60-250mm F/4.
04-13-2010, 06:52 PM   #6
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The Relevant parts of the manual

04-13-2010, 10:26 PM   #7
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I'm an original owner of the Pentax 1.7x AFA also having bought mine new from Carlisle Camera in, I think the 90's when I was using a ZX-5n. Even after I switched to the Minolta Maxxum 9 system for many years I kept the TC (I think I paid less than $100 for it new).
Unlike some I don't use it with AF lenses it was not really designed for. Nowadays I use it exclusively with Tamron Adaptall II SP lenses (90/2.5, 180/2.5, 300/2.8, 400/4) since my other lenses are AF mostly. One of my favorite uses is with the Vivitar S1 105/2.5 Macro.
Kent Gittings
04-14-2010, 12:29 AM   #8
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QuoteOriginally posted by JeffJS Quote
The Relevant parts of the manual

Ah hah - so it only pulls back. That's what I was quite curious about - i.e. if you're trying to close focus, you have to make sure to focus behind the object.

As for lenses, I've got the DA* 50-135mm, and a few other fast primes. Was considering a 80-200mm Adaptall-2 f2.8 lens if I can get one on the cheap. If I stack that with the 1.4x adaptall TC I should have a smallish 190-476mm f6.7 zoom with possibly decent IQ. The only thing is the cost...

I suppose we only live once and we can't take anything with us.

04-14-2010, 12:46 AM   #9
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Of the three K-mount TCs that I have (two 2x, one Pentax and one Tamron, plus the 1.7x Pentax AFA), the most consistently good one across a variety of lenses is the AFA.

The Auto-focus with MF lenses is a bonus, but, as others have said, it is restricted in how it functions, but there's no question that it's handy in some situations.

I bought mine from China in the past 12 months, and haven't regretted it, so far.
04-14-2010, 11:05 AM   #10
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1.7x AFA TC

Howdy All,
Hi Whelmed, Im a newb with that thing, wanted one years ago,just couldnt
justify expense. Finally bought about month and half ago.
Glass was biggest suprise, best I've seen in a TC
I use it primarily on my 200/2.5 and as sno says above AF lock is indeed,fast
Over the years I think Ive expierenced a fundamental change in my approach
to use of TC's, rather than magnifcation being primary, I use it as somewhat
of an exposure aid.Look at Heron Lowell posted, that can be a tough shot to
expose, bright background can washout detail of subject (bird) pulling in tighter
allowed for more balanced, even exposure. If I might add, equipment didnt
make that shot, Lowell did, we're talking about a very talented individual.
Can I say if its right for you? Not really, you are the ultimate judge of that.
Do hope you have a chance to try before making choice.

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