Monthly Archives: April 2010

SCT testing and adjustment continues

M97-2010-04-12A clear night tonight, if a bit cold after recent warm days. SCT adjustment and alignment continues. Mount balance is pretty good now. However, I still haven’t solved the problem of getting autoguide light and being able to reach focus so I’m temporarily playing without autoguiding. After a couple of hours of tests and adjustments, I took one image of M97 for fun. Unguided, 24 minutes total (6 each of LRGB) all in 60 second subs, unguided.

SCT progress: collimation, visual, reducer

After a discouraging evening the other night, trying to do too many things at the same time, last night was more organized and more successful.

I took the SCT back to pure visual configuration and did a careful collimation using an out-of-focus star. More tuning later, using software help, but for now the collimation is pretty good.

Next, I tried a more methodical set of experiments with focal reducers. I couldn’t get the OpTec 0.5x reducer to work in any configuration that occured to me – only in a couple could I bring it to focus, and quality wasn’t good. I’ll try it more later but, for last night, I switched to the Celestron 0.63x reducer. It needs about 100mm distance to CCD so I had to mount the reducer outside the Crayford focuser, which meant a couple of threaded adaptors. That worked, and I was able to take test images and achieve focus. The unusual placement of the reducer means I’m not getting 0.63x reduction or f/6 results, but I haven’t done the math yet to figure out what reduction is happening. (Update: doing a plate solve on an image, this setup is yielding an effective reduction of 0.68x, for a resolution of 0.83 arc seconds per pixel.)

M51 Unguided

M51 Unguided

I took an unguided test image of M51 to get a sense of what this resolution will do. It’s quite a pleasing image scale – once guiding is working it should be good. I was surprised at the rather steep image vignetting that was happening in this setup – substantial flat correction was needed.

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