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Forum: Pentax SLR Lens Discussion
02-13-2018, 05:06 PM
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Or use one of the crop bodies with a 24mp sensor. Using the K-1 in crop mode is kind of like using a K-5iis (albeit with better AF and better high ISO performance). Even a second-hand K-3 would be worth considering.
Opinions are divided about TC v crop. There is no single right answer. It depends on a lot of factors, including light, subject size and distance to subject. The comparison by WildMark at post #26 above is done with a K-3. It might be different with a K-1, even in good light with the same size subject. It also depends on how big an image you want to finish with. For posting on the web or viewing on a phone, 1200 x 800 pixels might be enough. But most DSLR users are probably going to want more than that (certainly if you want to print at more than 6x4).
Don't bank on it. It's not on the Pentax roadmap.
My personal view, from experience, is that a decent TC is a worthwhile tool for birding, particularly with a 300mm f4 or f4.5 lens (or faster), just as a 400mm f5.6 lens is a useful tool. In fact since I got the FA*300 f4.5 and Kenko Pz-AF 1.5x Teleplus SHQ (i.e. the one that is said to be the twin of the Tamron which Mark tested, rather than the Kenko used in Mark's test), I don't use my Sigma 400mm f5.6 tele macro very much. The IQ is better with the FA*300 + TC (effectively 420mm f6.3), even though the Sigma is quite a good lens and one-third of a stop faster.
But the returns diminish when your effective maximum aperture goes beyond f5.6 or f6.3 - from trying it, I'd need to have a compelling reason to use the Sigma with the TC again (for an effective 560mm f8). Some people have got good results with the DFA 150-450 at maximum reach with a TC (effectively 630mm f8) - good luck to them. But you'd need ideal conditions.
The Kenko works very well (on the K-3) with the DFA 100 f2.8 macro WR (effectively 140mm f4).
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Forum: Pentax SLR Lens Discussion
12-30-2015, 05:42 PM
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Thanks Mark. You've answered what I thought was a rhetorical question. :)
Of course there are several variables:
- quality of the lens
- quality of the TC
- as @MarcusBMG points out, good light.
Your test gives an answer based on typical Australian conditions, comparing one of the better TCs with a stellar prime alone. Can't ask for more than that.
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Forum: Pentax SLR Lens Discussion
12-24-2015, 04:21 AM
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Forum: Pentax SLR Lens Discussion
12-12-2015, 04:56 PM
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Thanks for sharing Mark. Very good comparison and well tested.
My take-home message is that on a sharp prime there isn't a huge difference between the third-placed Kenko and the Sigma, even at f5/f5.6 and certainly at f8. On the zoom, where there is more risk of CA, the differences are wider.
The tougher question in the field is the age-old one: in a particular situation should I use my TC or just crop? Depends on the lens and body combination of course, and on the conditions, particularly the available light. My limited experience with the Sigma 400 f5.6 on the K-30 is that if the subject is a wading bird 80m away in good light, maybe the TC at f8; but at some point between, the advantage is in just cropping. Now I have a K-3 the field-distance where the TC is worthwhile might have increased.
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