Last Friday night I imaged for the first time from my backyard with the SBIG camera and did so on my 8" Celestron SCT, another first. Fall weather is definitely setting in. I could feel the moisture in the air and the temperature was much lower earlier in the evening than on other nights I've observed. I put together my setup with the idea that I would finish by around midnight to avoid any risk of dew affecting my optics or my camera.
Doing the setup for the first time with new equipment took awhile longer than usual of course and there was some learning involved. I had to use all three of my eleven pound counter-weights to balance the telescopes and accessories (C8 with the Orion 80mm guide scope attached, ST-402ME, flip-mirror, 30mm eyepiece) properly. I did the polar alignment with just two stars and it seemed to be adequate. What made it difficult was that I hadn't taken time to align my guide scope and C8, which made centering the alignment stars difficult. Using the APO I typically use a reflex sight, but do not yet I have it mounted on the C8 (something I need to do but it isn't trivial). As expected, with the C8's longer focal length I don't have the wider field of view that I have with the 80mm refractor, making finding the stars more difficult. It took longer than it should have, but I got it done.
My targets were to be Jupiter and the Dumbell nebula (which I've imaged with the 80mm refractor). Unfortunately, Jupiter passed behind the trees before I could get my scope set up, leaving me only a narrow window later in the night to capture it as it passed through a narrow gap between two other trees. I moved on to the Dumbell nebula and my alignment was good enough to put it in the scope on the first try, though some centering was necessary. I took a quick 30" monochrome image of it and was struck immediately by the higher level of background noise which I believe is associated with the light pollution in the city. I set up the auto-guiding and took a 120" image and found it to be decent enough to go ahead with an RGB image. Again I limited it to 120" and a version of it is shown above. Focus was good based upon the use of the Bahtinov mask, but this image has the appearance of being a bit out of focus; I believe (hope) that this is just a function of the poor seeing conditions. I am pleased with the fact that I fairly easily found and imaged this object with the 2000mm focal length C8 after being told by more experienced people of how difficult it is. It definitely makes me want to use the C8 more often in the future on the smaller objects. You can go to my earlier posting with the Dumbell through the 80mm refractor to appreciate the difference in the size of the object in the picture.
I did capture Jupiter in the narrow window available to me later that evening. However, as I half expected, it was way too bright for my camera even at the shortest exposure time. When I processed the image later and reduced the brightness I could barely make out the bands in the atmosphere. To try to address this in the future I've ordered a polarizing filter that should allow me to reduce the brightness up to 40%. I can also try to stop-down my aperture. Unfortunately, I apparently have no ability to adjust the gain on the ST-402. I'd like to hear other recommendations if anyone cares to comment.
Unfortunately clouds and rain are moving in and I will not be able to image again for the foreseeable future. I'm still hoping for an opportunity in October on the east side of the mountains.
No comments:
Post a Comment