Celestron AVX + Meade DSI -- part 1

This will be the first of a series of posts on activities since the Summer! In June I mothballed my aging Meade 127ED and mount and procured a new Celestron 8 SCT with AVX mount.

Man do I love this mount. It's lighter, quieter when, more precise when tracking. The two star plus up to four calibration star polar alignment gives pointing accuracy that allows me to "go to" most targets without help from the finder. Yet, despite its lighter weight it is so much more stable than my 24 year old Meade LXD650. 

Cooler is the "All-Star Polar Alignment" feature.  With this feature after the initial two star  alignment and optional four star calibration you can point the scope to a second star and follow a procedure where you center that star with altitude and azimuth adjustments to correctly point the polar axis to the true north pole. This makes for truly excellent pointing and tracking.

If I miss one feature from the Meade mount it is the ability to store locations as I use the scope in Harvard, MA, Myles Standish Forest in Carver MA, and Maryland. There is a optional GPS accessory that can feed the scope its lat / lon location on start-up but I'll live with index cards for now.

Then there is the new scope. SCT with their center convex mirrors lose a little in contrast and sharpness to refractors. However, the extra 3 inches in aperture of the SCT gives me almost 2.4 times more light over the 5" refractor.

Compared to the rack and pinion focuser on the 127ED, I never upgraded it, the SCT focuser is so, so smooth and precise. And, there is no mirror shift when focusing which greatly helps with CCD imaging. Then there is the tiny move per turn of the knob which allows you to get a really precisely focused stars.

Sucky weather

Well here it is July 26 and I have yet to image through the new Celestron Advanced VX 8 Schmidt Cass with the DSI. Thank moonlit nights with sucky New England weather. Even relatively clear nights have been plagued with poor transparency. For the next couple of weeks I'm in Maryland. Mid Atlantic weather with its mediocre transparency and frequent cloudiness also tends to suck.  Some amateur astronomers will observe that my buying a new scope is at fault for the sucky weather. I agree with them. Okay, enough whining.

New Scope

New Telescope: In my last posting I wrote of my frustration with hot pixels and combined with drift. I had been thinking about upgrading my 24 year old Meade LXD650 drive. Then I noticed the Celestron Advanced VX combined with an 8 inch Schmidt Cassegrain would be a super upgrade for $1600. Combined that with free shipping and no sales tax, sorry Massachusetts, and I pounced.

I've had the scope for two weeks now. New England weather mostly sucks combined with a need to familiarize myself with the drive functionality and I have not had a chance to use the DSI. Also, after receiving the scope I ordered a 2 inch mirror diagonal and 0.63 focal reducer field flattener. 

I love this scope and drive combination. The tripod drive combination is so much lighter and less cumbersome to carry around than the Meade 127ED/LXD650 it replaces. Portability promotes more use. The drive is smoother when slewing and quieter. The drive certainly tracks better. Once nice feature is the ability of the scope to remember its last alignment, a feature I find useful when deploying the scope on my third floor patio. The straight through 30 mm finder is a neck pain but by using my 40mm ortho eyepiece the scope can be its own finder.

As of this writing the moon is full  delaying any chance of trying the DSI with the new scope.  I'll be heading to Maryland for a couple of weeks as the moon wanes and will try the scope/imaging combination then.

More frustration

In reference to last night's session, turning off auto-contrast and setting contrasts to the extremes did not work. The bright/hot pixels still leak through. I was not that careful aligning the polar axis thus the bright/hot pixel trails are still present. One different thing I did try was checking the sharp instead of soft setting in the color dialog. This substantially sharpened the star images but also increases noise and probably lowers sensitivity. See M13 below.

M13

I'm in Maryland but will return to Massachusetts tomorrow. Weather forecast suggests I won't have another opportunity until Wednesday earliest. I'll try to do a much better alignment and image then.

Some frustration

In the United States Northeast I don't get a lot of clear nights out. And, for the few I get transparency ain't that great. Since my early successes with the DSI things have not gone well. I get the camera temperature stabilized, collect dark frames and start imaging. Here's the problem. Dark frame subtraction seems never to get rid of the big permanent pixels. This manifests itself as colored streaks such as those in the image of M-13 below.

This had not been a problem with the DSI when I first started using it. I wondered if scope alignment was the big issue. I don't have a permanent location. When in Massachusetts I take the scope to a local park, set up and align, set up the camera and shoot. In Maryland, I use the back yard but have to do an alignment each time. I don't think my aligning is so much better than earlier times to make a difference.

Recently I found this this webpage where the author mentions the contrast control. I hooked up the DSI and it dawned on me that instead of leaving it with auto-contrast checked I should try setting the contrast to 0 and its maximum 65536. With this setting the bright pixels vanish. On my next night out I'll try this setting to see if the problems clear. Fingers crossed.