Originally posted by Medium FormatPro But based upon design specs, optics and all - that there are three existing Sigma PK lens which clearly outperform the 560... The 300 is clearly better as is the 500. And that's sad given what Pentax is expecting consumers to pay for the 560
How do you know that? Counting the elements, comparing a telephoto with a long lens design? Looking at the brand name, and deciding Pentax can't do a good lens, even if they did that, countless times? Because you simply "know" Sigma "is" better?
Originally posted by ElJamoquio Actually, I based it on my previous lens testing of actual performance vs. theoretical lens ideals, and my experience choosing/using lenses in the lab, etc. Feel free to discount it of course, I'm not a lens designer by a LONG stretch, but I have a bit more experience with actual performance of lenses than the average person (or photographer) off the street.
If you'd like to do some back-of-the-envelope-research yourself - take a look at the BEST 500mm stuff out there - and figure out how much degradation from best the 800mm would have to be for the 560mm to be better than 800mm. We're talking an increase of 43% of length, which in my experience is far more than the difference between a perfect lens and a mediocre lens.
That looks like using thin air to justify evaluating an unknown lens' performance. Sorry, I don't buy that; I still believe it's not over until the fat lady things (i.e. we have samples).
And next paragraph, do I spot a strawman? I never said the 560mm on an APS-C camera is better than an 800mm on a D600. It's
you who claimed the latter is
a lot better, it's
you who claimed you don't expect the former to be "fantastic", without having a clue about how the Pentax lens performs.
By the way, that 43%, while mathematically correct, it's just the most inflated figure you could think of (pushing the discussion on the theoretical domain, to compensate for the D600 low-ish resolution?). The difference in focal length is more than taken care of by the crop factor, and, if the 560mm will manage to outresolve the sensor (likely IMO), we should see no image degradation.
I would not be surprised if the K-5 IIs + 560mm would be a very sharp combination. It's not like all the odds are against it; the lack of an AA filter, the simpler, non-telephoto design, prime vs. zoom... we'll see if the "a lot better IQ" claim stands, when the samples are out.