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02-16-2009, 11:19 PM   #1
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Pentax A*400mm 2.8 & the 1.7 AFTC???

Will the Pentax A* 400mm f2.8 lens work with the 1.7x autofocus teleconverter?

EDIT: I am considering getting this lens the next time one become available, but I need to know for sure if the two will work with each other.

Last edited by HawaiianOnline; 02-17-2009 at 12:13 AM. Reason: Did not want to double post
02-17-2009, 05:50 AM   #2
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I found this for you but someone here probably has some hands-on info so..... I've seen a compatability list that comes with the TC also and from memory the 400 2.8
is on it.

Good luck and shooting.
I wish I could afford something like that.
02-17-2009, 01:41 PM   #3
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There is no reason, why it would not work. Just be aware, that the focusing distance of the AF converter is limited. You have to pre-focus the lens manually to the subject distance, the AF converter will do the rest. I found this to be more noticeable with longer lenses, as they need more focusing travel (or IF movement), than short fl lenses.
02-17-2009, 03:38 PM   #4
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[QUOTE=HawaiianOnline;492023]Will the Pentax A* 400mm f2.8 lens work with the 1.7x autofocus teleconverter?

I think it would work perfect. I have the 1.7 TC, and the result are wery good at f2.8 lenses and not so good at f4 lenses
You will find some information on this site, and I dont know why he dont recomend this solution: The Pentax Big Glass Comparison Pages

02-17-2009, 03:52 PM   #5
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I have used the 1.7x AF TC on f/5.6 lenses, so I don't see why it wouldn't work on an f/2.8, no matter what the focal length is.
02-17-2009, 05:56 PM   #6
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I have the 1.7 ProMaster Spectrun 7 which I think is a tamron and it works fine on my BIG MA and K20 with decent light. jim
02-17-2009, 10:46 PM   #7
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I used the A* 400 f2.8 and 1.7x quite a bit for bird photography in the past. The combination worked very well and sharpness is great.

The AF range is very narrow – like a matter of inches. The teleconverter does snap the image into focus after you pre-focus to its working range. As you probably know, the 1.7x AF adapter only uses the center AF sensor – so that is another limitation.

The A*400 f2.8 is a sweet lens with incredible sharpness. The only complaint I’d register is that the Bokeh can be really harsh under some circumstances. A few years ago a photo I took with the A*400 was bandied about on a Leica forum as an example or a really horrible bokeh. It was pretty embarrassing but they were right about the bokeh.

To test the bokeh I focused on a stalk of grass and then slowly focused to a closer point. The idea was to see how an object would look as it moved into the background. I found that as I defocused , the sharp image split into two – like seeing double – and that these two images then quickly went soft. That’s what can make the bokeh bad – things that are at the distance where the double image is present make for a distracting background. Get a bird on a branch with nothing behind it for a few feet, and the bokeh is great. Get a bird in a field with grass stalks behind it, and the bokeh is not so great.

Nonetheless – I’ve managed to get pretty good bird shots with this lens. One advantage with it is that it has a fairly close minimum focusing distance, and even with a 400mm plus a 1.7x converter, you need to get pretty close to small birds.



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