Tuesday, June 30, 2009

Flowers of Summer

Since I'm working this summer, my photo time is limited so I took a walk around my block the other day and shot some images of flowers growing in my neighbor's yards. Not my usual thing, but we photograph what we see, don't we? The third one down shows a yellow crab spider sitting inside a Lilly in my front yard. The crab spider hangs out inside flowers and waits for unsuspecting honey bees to come along.

Sunday, June 14, 2009

Diffraction limits for Wollensack 135mm Optar

With some leftover film, I decided to do some tests to determine the diffraction limits on my Wollensack 135mm Optar. Every lens has its "sweet spot" - the f-stop at which it provides the greatest depth of field with the least amount of diffraction. What is diffraction? Simply put, lens design is a process of finding compromises. Optics, such as they are, are always a trade-off. When a lens is opened up wide, the depth of field (DOF) is shallow and you get fuzziness around the edges, particularly in the corners since the lens projects a rounded cone against the rectangular film plane. When you stop the lens down to increase DOF, the edges of that cone get fuzzy because of diffraction - the light gets bent so radically that it loses sharpness. The more you stop down, the more diffraction you get. Thus, every lens has a "sweet spot" where you get the best overall DOF with the least amount of diffraction. Usually, this is somewhere in the middle of the f-stop range for that lens. But each specimen is different and the only way to know for certain what the best working aperture for a lens is, is to test it. To do this, simply set up the camera with something in extreme foreground that you want in focus, and something in the extreme background that you want in focus and take the same shot at every aperture, then compare each shot to see where you start losing clarity in the corners. For this test, I took this shot at f8 through f32:

The above shot was taken at f16. Below are sections of the bottom left corner of each image at each f-stop:






As you can see, in the first two shots, the DOF is too shallow provide clarity in the corner, while in the last two shots, the diffraction is so great that the DOF is useless. The sweet spot for this lens is F16. At the F16, I get sufficient DOF with as little diffraction as possible. Had I executed a little front, downward tilt on the lens plane, I'd have clear image with good definition in the corners and plenty of DOF.

Sunday, June 7, 2009

School is Out!

Now that the Spring session is over, I can take some time to post a few images taken over the past 10 weeks. This first one was taken at my father-in-law's place near Salem. The original was captured on Velvia 100F in landscape format and some of the highlights were completely blown out. So I cropped out the hot areas and converted it to black and white. It looks much better. Directly below it is the original image. All of these were taken with my 4x5.

Original image in color:

The dam above Dexter lake at sunset - Kodak T-Max 100:

Dexter Lake at sunset - Kodak T-Max 100:

One of my favorite railroad bridges located a couple of miles above Dexter Lake. This line is still used frequently. Kodak T-Max 100: