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08-22-2010, 04:02 PM   #1
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Tamron-F AF 2x tele-converter


I found a like new Tamron-F AF 2x tele-converter on Craigslist.
I am using a K20D with a Pentax 50mm 2.8 Macro and a 17-70mm 4.0 AF lens.
Can you give me some tips on how to use it? ISO, shutter speed, etc. I usually shot in Apetute priority mode. The pics so far have been really bright and washed out

the converter also came with a 28-250mm Tamaron lens.

Thanks in advance!

08-22-2010, 07:15 PM   #2
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The only lens you'll want to use the TC with is the 28-250, when set around the longer end. All a teleconverter does is extend the focal length of your lens at the cost of aperture and image quality. The factor of gain in focal length is the same as that of loss in aperture.

So, if you put the TC on your Tamron, you'd have a 500mm F13 (which isn't too useful), so you'd have to use a lower shutter speed to achieve the same lighting.

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08-22-2010, 09:17 PM   #3
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The above photos were taken with my copy of that TC and a Pentax A 50mm f2.8 Macro lens. The one below was taken with the same TC and my DA*55 SDM.

The bottom image by the way is the only one I bothered to properly expose. The other two are pushed nearly two stops.

Here is what I found. My copy of this TC does not transfer lens Aperture info to the camera but it will stop the lens down, most of the time. What I mean by that, is that with either lens, in Av mode, I could dial down to f1.2. That's one point two (wouldn't it be dreamy to have a 100mm f1:1.2 lens?). When using M mode with the SDM lens, I had to dial in a proper aperture in order to get it right (1.4 or greater). With the 50mm f2.8, same thing (f2.8 or greater). Exifs are in tact.

Once in awhile, a lens mounted on this TC will shoot wide open regardless of the aperture setting and it's just like I pointed a flash right at the front of the lens. I cannot explain why as I have not investigated it very much. This TC came with a camera a couple years ago and until a few months ago, I thought I had sold it.

Interestingly enough, the SDM on the DA*55 DID try to auto-focus. I suspect because of the PZ contacts. With my test subject though (the light fixture on my ceiling fan), it would not lock. I did not try a lens with screw drive AF however.

The point being, it will work with other lenses but you may have to fiddle to find the spots where it does work (and which lenses it will work with). You will probably have to go full manual and use Manual focus. The upside of that, Focus trap (Catch in focus) works or at least with the two lenses I tried it with.


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