Lens Resolution (long)
For the past few years I have been using exclusively prime lenses--not because they are necessarily sharper than zooms, but because they keep me from becoming lazy. Too often in the past I found myself using the zoom to avoid having to move myself. Rather than determining the perspective I wanted and then moving myself (and the camera) to where I had the right composition, I would ignore perspective entirely and just "zoom in" till I had framed the composition I wanted. Sometimes this is unavoidable, but not always. Using prime lenses has always forced me to think a little more.
Then my daughters were born. Suddenly, action photography took on a whole new meaning for me, and my primary subject matter didn't give me the time to fumble in my bag for the right lens. Last month I broke down and bought a 24-85 AF-S G to address this problem.
Over the years, I have learned which of my lenses I like the best based on both image quality and how my eye sees the world, but I have never performed any tests to determine what lenses are really sharp and at what aperatures. All my experience was anecdotal. Now that I suddenly had a choice of lenses for many focal lengths, I decided to finally do some testing.
I chose a rock pathway as a my test subject since it met some key criteria: it didn't move, it was flat (removing depth of field issues), it had fine detail, and it had a range of colors and brightnesses. I took photographs using my D1x on a stable tripod. All images were taken using the same magnification--or at least as close as I could arrange. The subject distance was pretty short, which could be a disadvantage to lenses that don't have CRC. All my images were taken in RAW and post processed in Photoshop. The only photoshop adjustments were to levels (maximizing contrast without clipping the highlights or shadow detail) and a moderate amount of sharpening. For those of you who are interested, here are my results:
Nikkor 20mm f/2.8D AF
At f/2.8 this lens is noticeably soft in the corners, but still useable. By f/4, things have improved pretty dramatically and are very good by f/5.6. Maximum sharpness is reached by f/8. Diffraction does not seem to affect image quality until f/l6, and even there the effects are pretty subtle. The lens has good contrast and has a neutral color cast.
Nikkor 24mm f/2.8D AF
Like the 20, this lens is moderately soft especially in the corners at f/2.8. By f/4 it has sharpened up considerably and is genuinely good by f/5.6. Image sharpness reaches a peak at f/8, and diffraction starts to have a small effect at f/11 and f/16. By f/22 the corners are starting to get a little soft. The color cast is a little cool, and contrast is very good.
Nikkor 35mm f/2D AF
At f/2, this lens is very soft, especially in the comers. Things are a little better at f/2.8, but don’t really get good until f/4. Image sharpness peaks at f/8, and there is only slight degradation at f/16. Deffraction really starts to affect quality at f/22. Images have moderate contrast and are neutral.
Nikkor 50mm f/1.8D AF
This lens has superb sharpness from f/4 to f/11, with diffraction just noticeable at f/16. By f/22 is it fairly soft. Even at f/2.8 images are crisp to the corners. F/1.8 is barely usable. Contrast is absolutely superb at all focal rations, and the color balance is neutral.
Nikkor 85mm f/1.8D AF
This lens is quite soft at maximum aperture, but is genuinely superb by f/4. Image sharpness reaches its maximum by f/5.6. Diffraction effects only start to become visible at f/11, and are mild even at f/16. Contrast is superb at all apertures except f/1.8, and the color cast is neutral.
Nikkor 24-85 f/3.5-4.5 AF-S G This general purpose zoom is surprisingly good for snapshots. At 24mm, it is fairly soft in the corners from f/3.5 to f/4. By f/5.6 image sharpness has improved dramatically. It still is not up to the level of the primes, but good for all but the most critical applications. Maximum image sharpness is reached at f/8 or f/11 (depending on focal length). The effects of diffraction are not noticeable except at f/22. The lens has a slight warm cast, and contrast is moderately good across all focal ranges. All in all, a creditable performance for an inexpensive, light weight, general purpose lens.
I will post the images in a follow-on message.