Sunday, September 27, 2009

Astigmatism and Color Fringing, Sigma 50mm f/1.4

I went out to Chiricahua National Monument yesterday to try some sunset photography but got there too late and ended up taking some night images at Massai Point. The moon is at first quarter so I knew I wouldn't be able to get the sort of deep sky images that I enjoy taking but figured it would be a challenge to see what I could get with the moon up. I try to take exposures that are either short enough so the stars in the sky don't smear too much or long enough so they make long trails. Lately, I've enjoyed the short exposure (< 45 seconds) shots so I tried some of those. I wanted to get some of the Chiricahua rocks clearly exposed and found that in the light of the first quarter moon I needed to shoot at a fairly wide aperture to keep the exposure times short. Both of the images shown here have ~35 second exposures taken at an aperture of f/1.6.

I've been pleased with the results I've gotten with my Sigma 50mm f/1.4 lens on my Canon 5D mk II but I hadn't paid close attention to some of the lens distortions that show themselves when shooting star fields. This first image shows a couple of the rocks near Massai point illuminated by the moon and with stars in the background sky.

In this image, in addition to the rocks and bushes, you can see a lot of stars in the sky, a galaxy, and a couple of satellite trails. If you look closely, you will also notice some distortions in the stars in the upper left and lower right. (click on images to see larger versions.)  This is meriodional astigmatism and it gets worse the closer to the corners of the field you get. I found this effect easier to see in the following image which shows a distant view of Cochise Head from Massai Point.

Look at the top of the image, the stars are distorted so they look like little line segments oriented tangential to a circle centered on the image.

I also noticed that some of the stars looked more red than they should be and closer inspection shows that there are red/cyan fringes around the very brightest stars.  This happens all over the image, not just near the edges.  I'll show a couple of full resolution crops from the second image below.   The first full res crop shows the meriodional or tangential astigmatism and is taken from the top left of the Cochise Head image.  The second crop shows the color fringing and is taken from the center of the same image.

Apparently, night sky imaging at wide apertures requires extremely fine lenses!

Monday, September 21, 2009

Ghost Beads for a Bellagonna

I went up to the Navajo reservation over the weekend. This time of year I'm getting tired of the heat in Tucson and I want to go somewhere that I can find cool weather. I've always enjoyed staying at the Thunderbird Lodge in Chinle, AZ near Canyon de Chelly so I made my way there.

I've been to the Chinle area many times and have lots of photographs of the canyon at various times of year as well as photographs of nearby areas so I was looking to do something different. I enjoy photographing people but find it more difficult than landscapes or wildlife. My main problem is shyness I think, it is difficult to ask a stranger if I can take their portrait. Native Americans are even more difficult because some of them are very sensitive about photography. There are usually a number of venders selling jewelry along the rim of the canyon as well as at White House ruin on the canyon floor. I decided to try to photograph some of the venders in both places. I ended up photographing five Dineh (Navajo) people. I promised to send them the results either by e-mail or prints by ground so I got their names and addresses.

Pearl Joe's daughter had jewelry spread out on a blanket in front of her car at the Tunnel overlook. Pearl sat in the back seat of the car stringing juniper seeds and turquoise beads into necklaces and bracelets. Pearl told me juniper seeds are also called "Ghost Beads" and keep away bad dreams and evil spirits, hang them on your bed post at night and you'll never have a bad dream. I wonder if they work for a Bellagonna (non-Navajo person) like me? I bought a small string of seeds, we'll see. Pearl was a little shy about having her photograph made, she told me people try to make money from her photograph or make a painting from the photograph and sell that. I told her I wasn't doing that and that I was just trying to learn to take better people pictures. She let me make her portrait. (click on the photos for a better size image)

Don Charley is a flutist and not shy at all. At the age of 29, he is trying to make his career playing traditional Dineh flute music. Unlike Pearl Joe, who doesn't use a computer much, Don studied web design in college, has e-mail, a myspace page, and other modern social connections. He was trying to sell CD's of his music and not having too much luck in spite of his long and complex sales pitch. I didn't buy a CD but I did promise to send him a couple of photographs that he could use on his web site with my blessing and that was enough to peak his enthusiasm. In talking to Don and his girlfriend (didn't get her name) I learned that young Dineh have trouble staying in Chinle because there are no jobs around. In particular, the distance to the nearest Wal-Mart was mentioned. The Gallup Wal-Mart is pretty far away and if you can't get a job there, you might have to go all the way to the Wal-Mart in Flagstaff! I photographed Don playing his flute.

A while later I hiked down the trail to White House Ruin and talked to, and photographed, a few venders who were waiting for the tour jeeps to arrive. White House is one of the main stopping points and breaks for the passengers of the half day jeep tours that leave from the Thunderbird Lodge. Delores Sam lamented the fact that the tour goes up Canyon del Muerto first before it comes down Canyon de Chelly so the venders in the more northern canyon get the first crack at the tourists. I very much enjoyed sitting in the cool shade under the cottonwood trees having an interesting conversation in the beautiful canyon.

I'm very slowly learning a few Navajo words and know a handful. I discovered, on this trip, that even the few I've learned, some I've learned wrong! I learned to say "Hello" as "ya-tah-HAY" somewhere, but it is "ya-eh-Teeh" instead. I'm not good with languages.

Sunday, September 13, 2009

Chasing storms and galaxies

I looked at the weather map Saturday afternoon and decided there might be some thunderstorms in south-east Arizona that evening so I loaded my camera stuff and "sleeping in the car" stuff into the outback and headed east. It looked like the storms would be near Sierra Vista, but when I turned on the Sierra Vista turn-off just west of Benson, AZ, it didn't look promising. The storms looked better further east so I headed for Willcox. I had read on the web about a little visited BLM picnic area called "Indian Bread Rocks" south of Bowie, AZ on the east side of the Dos Cabezas Mountains and I figured I could sleep there.

When I got near Willcox, it was clear that there were storms north of the city so I followed N. Fort Grant Road as the sun set and it grew dark. When I got, probably, 15 miles north of Willcox, I found a dirt road I could turn off on, and it wasn't raining there, and I had a good view of some of the storms so I figured I'd photograph some lightning. Well, lightning photography is tricky, you have to make sure you get your focus set right, etc., autofocus won't work on a black sky! Here is one of the photos of lightning, I need more practice doing this, too bad the monsoon has fizzled this year.

After the storms started winding down, I headed for Willcox for a bite to eat and then out to "Indian Bread Rocks". To get there, you go south from downtown Bowie, under I-10, drive through a few miles of pistachio groves, turn right on a nice graded dirt road, and then drive a couple more miles to the picnic area.

As expected, there was nobody there and everything was quiet and very dark. I appreciated the outhouse and garbage container and, while walking around, noticed that the sky was very clear and that I could see the Milky Way quite clearly. The brightest part of the galaxy in the sky was to the south so I set up the tripod again and took a few time exposures. I had read that if your exposure is longer than 30 seconds, the stars will streak too much to make a nice image. Of course, you might WANT star trails. I tried a few different exposures and tried to get the camera focused properly. Thank goodness for "live view" on the 5D MK II and the zoom, you can set the focus quite accurately. The best image was a 20 second exposure taken at f/1.6 with my 50mm f/1.4 Sigma lens. In hindsight, I should have done some wide angle shots too with the 17-40mm lens. Here is the image:

I had a somewhat restless night in the car wondering if anyone would show up and chase me away, wondering if any large animals lived in the area, and what kinds of insects live there. But my fears were unfounded and the night was cool, quiet and peaceful. The next morning I tried to take some sunrise photos but there were clouds veiling the sun in the east.

Friday, September 4, 2009

Mixing work and play (photography)

This last week I attended a meeting in the Denver area and gave a presentation about some new software we are developing for planning observations with the VIMS instrument (Visual and Infrared Mapping Spectrometer) aboard the Cassini spacecraft. Since one of the people on the science team is a photographer friend of mine, I decided to take a few extra days so I could photograph on the way to Denver, while in Denver, and on the way home.

My path took me first to Moab, and the slick-rock country of south-east Utah. I visited Moab 15 years ago and went to see some of the sites while I was in the area but didn't bring back many pleasing photographs from that trip. This time I visited new places I hadn't been to before in Arches National Park, Canyonlands National Park (Island in the Sky), and Dead Horse Point state park. Here is a sunrise photograph I took at Dead Horse Point looking toward the La Sal mountains. I used a wide angle lens (17mm on a full frame DSLR, f/11, 1/13 sec) to emphasize the broad expanse of the landscape. The color on the upper clouds only lasted about a minute.

Next, I drove to Denver and gave myself a couple of days to explore the mountains nearby. The most interesting place I went was to the top of Mount Evans (14,250 feet above sea level). Amazingly, there is a road to the top and my friend Roger picked me up at 5 AM and we got up there before sunrise. It is a beautiful place to be and there is a surprising amount of wildlife. We saw mountain goats, yellow-bellied marmots, pica, and ptarmigan. Here are two photographs, one showing the landscape (looking south-east from near the top just after sunrise, 28mm, f/16, 1/50 sec) and one showing a mom goat and her kid (300mm, f/11, 1/250 sec).

The next day I visited Brainard Lake recreation area west of Boulder and did a hike around Long Lake. On the way in I stopped at a small lake covered with water lilies named Red Rock Lake and photographed the sunrise over the lake (40mm, f/11, 1/320 sec).

After the meeting, on the way home I drove late into the night to get to Almogordo, NM so I could get up early and photograph at White Sands National Monument. They don't open the gate there until 7 AM which is a little late for the sunrise but fortunately there were quite a few clouds in the east which helped with the light a bit. I plan to revisit the area later this fall when it is a bit cooler and camp in the park so I can get some images earlier in the day. This photo features some of the insect tracks I saw in the sand. They had had some rain on previous days which changes the texture of the sand a bit.

When I get a chance to go though my photos and process more of them I'll post them on my website at