I mainly wanted to test the FA 20 f2.8 against the DA 16-45 f4 at 20 mm. Various people don't like the FA 20 (or its predecessor, the A 20) because of corner weakness at wider apertures. So I wanted to see how it compares to my main alternative for that focal length. Partly just for fun and partly for serious results, I also tested the DA 14 f2.8, Zenitar 16 mm. f2.8 fisheye, and the FA 16-45 at 16 mm. Finally I tested the FA 20-35 f4 at 20 mm. to compare it to the DA 16-45 at 20 mm. Sit back. Some of the results are interesting.
1. FA 20 vs. DA 16-45 at 20 mm.:
Both lenses wide open (FA 20 at f2.8; DA 16-45 at f4): The FA 20 is sharper in the center, at the edges, and in the corners. With both lenses at f4 and f5.6 the results are the same (the FA 20 is sharper). At f8, center and edge sharpness of the two lenses are very close. The DA may be very slightly better. The FA is better in the corners.
Yes, I know that some of you are thinking that it is nuts to compare a prime to a zoom. Of course the prime is better. Right? Well, read on.
2. FA 20-35 at 20 mm. vs. DA 16-45 at 20 mm. (just for curiousity; both are well regarded zooms):
At f4 the FA lens is better all over. At f5.6 the FA is better in the center, but the DA is better at the edges and in the corners. F8 gives the same result, except that the center difference is quite slight.
3. DA 14 vs. DA 16-45 at 16 mm.
Prime lenses are always sharper than zooms, right? With both lenses wide open (f4 on the zoom, f2.8 on the DA 14), the DA 16-45 is sharper in the center and at the edges. The corners are close. At f4 (wide open for the zoom, closed down for the prime) the DA 16-45 is sharper in the center, at the edges, and in the corners (although the edges and corners are close). At f5.6 and f8, the zoom is sharper than the prime all across the field of view.
So sometimes it pays to compare apples and oranges.
4. Now the fun part. Zenitar 16 mm. f2.8 fisheye vs. DA 14 f2.8. Guess what? The Zenitar is sharper across the field of view, at all apertures from f2.8 to f8.
5. Zenitar vs. DA 16-45 at 16 mm:
F4 (DA) vs. f2.8 (Zenitar): The Zenitar is better across the viewing area. F 4, 5.6, and 8 (both lenses): The Zenitar is sharper across the board.
6. So now a contest between the day's two champions: the FA 20 f2.8 vs. the Zenitar 16 f2.8. This test was hard to evaluate because the edges and corners of the FA 20 were quite difficult to compare to the edges and corners rendered by the Zenitar. At all apertures from f2.8 to f8, the Zenitar was slightly sharper in the center, while the FA 20 may have bettered it at the edges and in the corners.
The inexpensive little Russian lens wins the day for sharpness. What a pity it has such distortion. What a pity they never developed a rectilinear version of it.
Other curious findings. If you set your D or DS to mtf program line, it will tell you that the DA 16-45 is sharpest at f4 from 16-28 mm., and at f4.5 from 28 to 45 mm. Well, in my tests at 16 and 20 mm. today, sharpness increases from f4 to f5.6 to f8 at both focal lengths. I cannot confirm Pentax's belief that this lens is sharpest at f4 below 28 mm.
The DA 14 came out worst in these tests. This doesn't mean that it is a bad lens. The evaluation was done at actual pixels, and in actual use you would have to go to an enormous enlargement to see the differences I was looking at. I haven't given this lens enough real-world use yet to know if I am disappointed in it for the price.
It was the corner performance of the FA 20 f2.8 that prompted me to do these tests. The FA 20 gave the best corner results of any of these lenses. Could it be better in the corners? Perhaps. But I see no reason to slight it if we don't also slight the DA 16-45 and the DA 14 for their corners.
Joe
