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12-03-2010, 05:04 AM   #1
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Quality of 645 2x teleconverter

Guys,
can anybody comment on 645 2x teleconverter? Is it worth the hassle?

I mean, 645 system was bought for a top-notch quality; if the converter would visibly affect it, it defies the purpose, and I can get extreme tele much more easily with digital bodies. On the other hand, if I can double the reach of 200/4 and especially 300/4 for low cost and weight, it sounds very tempting...

Thank you,
Maxim

12-03-2010, 08:20 AM   #2
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I had one, sold it. It really didn't stand up to critical film use, and I suspect it might be worse with digital. In all fairness, I had other options as well (longer 67 lenses); less convenient, but higher quality. The 1.4x or a K5 might be a better choice.
12-03-2010, 08:29 AM   #3
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In general, any teleconverter for any camera will do three or four things:

1. extend the length of the lens by the magnification factor (like 2 times in this case).
2. degrade to some extent the image quality of the original lens. This is because t/c's whether high quality or not, are not going to be as good as a lens designed to function in a specific way.
3. will loose some f-stops on the original lens, I don't have a good explanation for that, but that is a side effect.
4. very likely change the functionality of the lens (like loosing the AF functions of the lens or eliminating the lens information connection to the camera).

Anyway, that's what one may expect with t/c's in general. I don't know this specific t/c but if it's like this one Rear Converter-A 645 2X Lens Reviews - Pentax Lens Reviews & Pentax Lens Database, I'd expect that you will get the magnification you want but at some degraded image quality over that of a dedicated lens at the equivalent length. T/c's are useful IMHO, and I carry one (a 1.5x) for my k-mount cameras in my photo bag for times when I want more reach. It gives me that but it's not ever as good as a dedicated lens as I've said.
12-04-2010, 11:01 AM   #4
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QuoteOriginally posted by mnovikov Quote
Guys,
can anybody comment on 645 2x teleconverter? Is it worth the hassle?

I mean, 645 system was bought for a top-notch quality; if the converter would visibly affect it, it defies the purpose, and I can get extreme tele much more easily with digital bodies. On the other hand, if I can double the reach of 200/4 and especially 300/4 for low cost and weight, it sounds very tempting...

Thank you,
Maxim
The 1.4 is the better converter but it is 1.4X. So the 2x is a compromise - I only use it with the 300/4 when I absolutely need the extra reach

12-04-2010, 04:03 PM   #5
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I have one and tried to use it on the 300/4 EDIF but either due to my poor technique, wiggly tripod, wind or whatever, it wasn't that sharp. Instead I have a Pentacon 500/5.6, which is the size of a large drainpipe, but works much better than the 300 + 2x combo.
12-04-2010, 07:45 PM   #6
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On 67/67II I could almost never get great results on film through either the 1.4x or 2x, even I use the heavy Gitzo 1548 tripod and hung 30lb+ backpacks through a custom mechanism securely on the center column. Images were never critically sharp (through 8x and 22x loupes). Camera itself on the tripod (Arca-Swiss B2G Giant ball head) was better than the lens on the tripod and camera hanging.

However, through an adapter on a Canon 5DII (camera hanging), my P67 300mm/f4 ED IF resolved almost to the 5um pitch 21MP sensor limit (i.e., 70lpr/mm) through the either extenders.

Thus the conclusion: it is not only optics but still body/shutter shake, wind, supporting and stabilization technique, and other mechanical instabilities. I read people used two tripods for the long lenses with P67.
12-05-2010, 10:47 AM   #7
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Leping:

I use the 67 and 645 bodies. Unlike the 67, the 645 has virtually no shutter (or mirror for that matter) vibration. Consequently, under certain conditions, I find I get better results using the 645, despite the smaller film size (macro, long telephoto). Years ago, I did a casual study of the 67 500mm f5.6 vs. the 300mm ED with a 2x. I was trying to determine if the 500mm was really worth carrying. The 500 was better (although not by much) than the 300mm + 2x.; although it did exhibit some purple fringing absent in the ED 2x combo. The test was performed using a 6MP Pentax DS
(10s timer, heavy tripod, ball head). I donít know the pixel size in the DS, but I suspect itís larger than a 5D II. I was involved in a discussion forum at the time and the tests are posted here:
P67 500mm f5.6 vs 300mm ED with and w/o 2x: Photo Images by Thomas Janik Photography - photo.net
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