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09-24-2009, 10:48 PM   #1
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Pentax 1,7x af adapter: is a good converter?

I want to buy a pentax 1,7x adapter (that I had for few day for lens with manual focus) , but I never used it with af lens. Is it a good choice for sigma 70-200 2.8 apo (not hsm) and for pentax F 300 4,5 or there are better converter or the af will not work? It is better of kenko 1,5x shq for example?


Last edited by mpg; 09-25-2009 at 04:51 AM.
09-24-2009, 11:03 PM   #2
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It is indeed a good converter - the converter will AF any lens the same regardless of whether it's an AF lens or a MF lens, and the converter will pass aperture information through, so the Sigma and Pentax-F lenses would be auto aperture (and the converter actually calculates the equivalent aperture and passes that to the camera). The autofocusing mechanism of the lens is not used when using this converter, and you will have to manually focus until the lens is close to the right focus, and then it will lock on with AF.

I find it to be very sharp - probably the best TC I've used... Here's a recent post I made where many of the shots used that TC...
09-25-2009, 03:55 AM   #3
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you don't need to look any further for what this can do.

see attached photos, but note you need a prime lens F4 or faster for AF to work

this is a full frame shot at 1/150 with flash, on my *istD

this is a 100% crop
09-25-2009, 04:35 AM   #4
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QuoteOriginally posted by Lowell Goudge Quote
but note you need a prime lens F4 or faster for AF to work
Actually, I've gotten it to work on slower lenses (in strong light)--but not reliably.

But the AF functionality aside, I've found it to be very good optically and I use it on a MF basis as well. As with any TC, you have to pair it with a good lens--in my experience, any tc will magnify the limitations of the lens it's used with.

09-25-2009, 04:46 AM   #5
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i've heard it is a good tc, but will it work with a 70-200 f/2.8 sigma hsm?
09-25-2009, 05:20 AM   #6
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QuoteOriginally posted by jenko Quote
i've heard it is a good tc, but will it work with a 70-200 f/2.8 sigma hsm?
the TC has some unique features.

First of all, it modifies the lens information for F-Stop so that the correct F-Stop is used by the camera for exposure including the 1 1/2 stop loss of the TC

Second, it does not have a pin for transmitting the lens focal length and focusing data to the body, so you will have to enter focal length, therefore for a zoom, you will need to enter the focal length you wish to use. This is because it needs that pin to control the movement of the internal elements in the TC which actually do the focusing function.

The TC does not have the power pins of the KAF2 mount.

So with respect to HSM lenses, it will function as it does with MF lenses, you focus close with the lens focusing collar, then let the AF elements in the TC do the rest.
09-25-2009, 05:30 AM   #7
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QuoteOriginally posted by dadipentak Quote
Actually, I've gotten it to work on slower lenses (in strong light)--but not reliably.
I hear lots of comments about this, but I prefer to ignore them for a simple reason. Saying you can get it to work with slower lenses, even if you state it is not reliable or needs strong light , can give people false hope that it will work with their specific lens, leaving them disappointed when it does not work as they had hoped.

For me, it is much better to only state things that work reliabily, For this TC, even though the manual states only for use with F2.8 or faster lenses, I have used it for over 15 years on my 300mmF4 my 100mm F4 macro and my series 1 70-210 F3.5, and can absoultely state that it will focus just as well as any other lens. This also includes use on 4 different AF camera bodies, PZ-1, *istD, K10D, and K7D. I have also stated, it simply does not work on a 400mm F5.6 because it does not!
09-25-2009, 05:52 AM   #8
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QuoteOriginally posted by Lowell Goudge Quote
I hear lots of comments about this, but I prefer to ignore them for a simple reason. Saying you can get it to work with slower lenses, even if you state it is not reliable or needs strong light , can give people false hope that it will work with their specific lens, leaving them disappointed when it does not work as they had hoped.

For me, it is much better to only state things that work reliabily, For this TC, even though the manual states only for use with F2.8 or faster lenses, I have used it for over 15 years on my 300mmF4 my 100mm F4 macro and my series 1 70-210 F3.5, and can absoultely state that it will focus just as well as any other lens. This also includes use on 4 different AF camera bodies, PZ-1, *istD, K10D, and K7D. I have also stated, it simply does not work on a 400mm F5.6 because it does not!
A reasonable approach. I was just reporting my experience.

09-25-2009, 05:57 AM   #9
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Actually it works 100% reliably on my Pentax F* 300mm f4.5 which is slower than f4

Hmm, wonder if it will work on my A* 300mm f2.8 with Pentax 1.4x-L or 2x-L converters
09-25-2009, 06:05 AM   #10
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Regarding Focal Length I find if you trun SR off , the camera registers the FL I don't remember if it is just the FL of the actual lens or 1.7 times .... either way I also have got some good shots with it.
09-25-2009, 06:21 AM   #11
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QuoteOriginally posted by Mike.P Quote
Actually it works 100% reliably on my Pentax F* 300mm f4.5 which is slower than f4

Hmm, wonder if it will work on my A* 300mm f2.8 with Pentax 1.4x-L or 2x-L converters
I would bet it will work with the 1.4x because this will give you 420mm F4, and it always seems toi work with an F4 lens, but not with the 2x because it simply does not work reliably on any F5.6 lens, aside from that, what would you do with a 1020mm F9 lens any way
09-25-2009, 06:22 AM   #12
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QuoteOriginally posted by daacon Quote
Regarding Focal Length I find if you trun SR off , the camera registers the FL I don't remember if it is just the FL of the actual lens or 1.7 times .... either way I also have got some good shots with it.
with SR off or with any lens for that matter, the camera will remember the focal length you entered when you powered up.
09-25-2009, 06:44 AM   #13
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I don't know about the 70-200mm sigma but on my 100-300mm f4 it reports f2.8 with the TC (should say f 6.7) and if I close the lens down even 1/3 stop in "A" with the camera it really closes the iris to about f8 if I look into the lens with the depth of field preview. I think it reports on the exif as the 70-200 f2.8 with the TC and the 100-300mm f4 without it, very odd. I can use the aperture ring on the lens though if I want a real f5.6 for example, so it's not a real big deal and I don't know if the 70-200mm would act this way but you might want to check if you get one.
09-25-2009, 07:05 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote
with SR off or with any lens for that matter, the camera will remember the focal length you entered when you powered up.
I did not know that .... cool
09-25-2009, 08:09 AM   #15
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QuoteOriginally posted by Lowell Goudge Quote
aside from that, what would you do with a 1020mm F9 lens any way

Move to somewhere other than the UK where they do actually have a bit of sunshine
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