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03-07-2011, 12:43 PM   #1
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An extender

Is having a 200mm F4 lens vs a 400mm f5.6 better if I add an extender to it?
Can someone give me the quality difference of a 200mm F4 lens with a 2x teleconverter (names of both would be nice to) vs a 300-400mm f5.6 lens?
Also is the sharpness still good with the extender?

03-07-2011, 01:12 PM   #2
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A lens by itself (e.g., 400mm) will beat another lens plus a teleconverter to match the first lens's focal length (e.g., 200mm + 2X TC). With some combinations of lens and TC, the quality is close enough so the difference outweighs the advantages (cost, weight, size, optional focal length). With the Pentax system, neither option really gives you many choices. Do you have a budget in mind?
03-07-2011, 01:58 PM   #3
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there have been lots of different discussions about this, specifically when comparing perhaps either a good 200F4 cropped to the same siae as a cheap 400F5.6, and also a really good lens like the early SIGMA APO 70-200F2.8 EX with a Sigma 2x TC which combined produce stellar results at the full focal length

It really depends on the 200mm lens, and the teleconverter, as well as what you are comparing it to at 400mm.

From my experience it is hard to top the sigma pair (lens plus TC) at 400mm with any other combo, except maybe the A 400F5.6 all by itself, although I think the sigma manages CA better.
03-07-2011, 09:43 PM   #4
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I think in general a single lens will have better IQ than a lens and TC combination assuming both lenses are of equal quality. I have heard there are some matched sets with the TC designed for use with that lens that produce good quality but the average TC bought on eBay or where ever is not going to match that IQ.

The other thing to remember is that an f/4 lens with a 2x TC is going to lose two stops so it becomes a 400mm f/8 as opposed to the 400mm f/5.6.

Assuming the lens is auto focus you lose that ability as well with TC usually. Of course if we are talking all manual lenses that is not a problem.


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