Learning Curve

DSLR Sky Photography

On a clear windy March 15th evening I fled glaring neighborhood lights for a serious first attempt at wide angle DSLR sky photography. I carried my tripod-mounted sky tracker with Nikon D40 camera to a darker nearby field, about a quarter mile from home, where I could actually see Polaris in the polar alignment scope instead of reflected lights. Once the mount was polar aligned I patiently took systematic exposures to gain practical experience with the camera and mount. Eventually, after two hours, I quit when the temperature dropped near 40 degrees, wind gusted stronger, and my fingers got too numb to operate the equipment.

I learned some valuable lessons during my time in the field. First, exposures longer than two minutes captured too much sky brightness from light pollution. In the future I'll use shorter exposures. Second, the camera mount and tripod were shaky. Every time I adjusted or moved the camera the mount was nudged and polar alignment was destroyed. I need to check and adjust polar alignment after every camera adjustment. Third, I should try setting ISO to 800 instead of 1600. Maybe that will reduce noise a bit. Fourth, I need to take more than three images for stacking in order to increase effective exposure time. Maybe I'll try for 9 images in the future.

Capturing images is only the first step towards producing a good picture. The camera's raw images need to be processed to remove flaws and bring out all the details. I downloaded three new image processing programs and spent hours learning to use them, mostly by trial and error. One of these programs, Star Tools, does a great job removing brightness gradients and vignetting which plague all my sky photos.

The first decent image obtained with my new equipment is the following picture of Jupiter and nearby star cluster M44, the Beehive Cluster, in the constellation Cancer. This is a single 120-second exposure through a 55-200 mm telephoto lens set at about 150 mm. I subtracted a dark frame, but did not apply a flat field. Stars are nice and round indicating good tracking, but colors are not vivid, and bright Jupiter at lower left is very overexposed. Color management is still a mystery to me.

The following picture of the Pleiades star cluster in the constellation Taurus reveals stars down to magnitude 11.8 as well as hints of blue reflection nebulosity present in the cluster. But the bright stars are overexposed, and the blue color seems too light. This is also a single 120 second exposure through a 150m lens with dark subtraction but no flat field.

I'll try stacking some images in my next post.

Solitary Sunspot

Sunspot Action

A long period of bitter cold, clouds, and snow followed my last solar observing session in February. Hardly any sunspots formed during this time, so I didn't miss much. Lousy weather finally ended on March 7th. Snow had melted and temperature was in the low 50's. One modest sunspot had rotated into view on the Sun's east side with some nice filaments nearby. Unfortunately, seeing was not good.

The following 6-image mosaic shows solitary sunspot 2297 near the eastern limb on the left with two distinctive filaments near the frame's bottom.

I noticed a faint thin stream of gas connected to a bright spot below the sunspot. The gas seemed to be arching up into space as you can see in the next image.

The sunspot had been erupting recently, so, I thought, with luck, I might record some action in a time lapse movie. I began recording movie frames at 1:54 pm EST, recording one image every 60 seconds. When seeing deteriorated drastically, I stopped recording at 2:26 pm EST after accumulating 32 frames. So the following movie captures 32 minutes of solar action. Hot gas seems to rain down from a magnetic arch into a thin stream hitting the bright spot below the sunspot.

There were also some nice prominences on the Sun's western limb shown in this 5-image mosaic.

I quit when bad seeing smeared detail into a blurry mess.

Sky Tracker

New Camera Mount

Over the years I've used my Nikon D40 DSLR camera to take pictures of constellations, conjunctions, and comets. Time exposures were limited to a maximum of 30 seconds for two reasons. First, 30 seconds is the longest available automatically timed exposure that can be done without unavoidable vibration caused by a finger physically depressing the shutter button. Second, 30 seconds is the maximum time before star images elongate due to Earth's rotation. I'm happy to say the 30 second barrier has been removed!

My new Ioptron Sky Tracker can follow Earth's rotation, so star images will remain round in long exposures. I also purchased a remote shutter control so I can manually control exposure time on the "bulb" setting without physically touching the shutter button. Check out my new sky photography setup below. The small cylindrical telescope tube to the right of the camera is the polar alignment scope. While gazing up through the polar alignment scope I adjust the black rectangular box in altitude and azimuth to bring the North Star, Polaris, to the proper position on an illuminated reticle. Once the mount is polar aligned, a battery powered motor inside the black rectangular box turns the camera at just the right speed to keep up with Earth's rotation.

The ball head camera attachment seen below allows variable camera pointing.

The whole camera mount is attached to a tripod.

I waited several weeks to try the new equipment. Weather was miserable - either too cold, too cloudy, or snowing. Finally, on March 7th the sky was clear and temperature was in the 40's. I carried the tripod into my back yard where I immediately cursed the many neighboring spotlights glaring at me from every direction. These lights made it hard to see Polaris through the alignment scope. I also learned alignment could easily be lost by the slightest nudge to the tripod. Camera position had to be changed very slowly and gently in order to maintain alignment.

With my lens set at 18mm I took 60- second and 120-second exposures of Orion, Taurus, and the Pleiades. The 120-second exposure is shown below. Tracking was excellent! Star images are round, though not in perfect focus. The winter Milky Way is visible to the left of Orion. The Hyades and Pleiades are to the upper right of Orion. Hints of pink hydrogen gas are present. This is a single image recorded in JPEG format with no fancy processing. I'm really pleased with the result and anxious to try again with better focus, image stacking, and dark subtraction.

Achieving exact focus continues to be a problem. All my attempts at magnified images were out of focus even though I thought they were in focus when I activated the shutter. It's so hard to judge focus on the camera's display screen. I make test exposures, magnify the results on the camera's image display, make small adjustments to the focus ring, and repeat until star images look sharp. But it's hard to see the display with so any blasted glaring lights all around, and it's hard to remain patient when my hands are freezing. I need to pay more attention to this in the future. I also need to get away from neighborhood lights.

The next image shows the effect of light pollution. This is a 120-second exposure of the constellation Cancer. The brightest object near center is Jupiter. Just above and to the right of Jupiter is the Beehive star cluster. I tried a more magnified image of Jupiter and the star cluster, but the result was out of focus. Notice how the sky is brighter in the lower left than in the upper right. The lower left was closer to the horizon and lit by neighborhood lights.

The zenith sky from my back yard was reasonably dark in 120-second exposures. When I tried 180-second exposures the background sky became light gray instead of black.

These first attempts are promising. I hope to try again soon.