Celestron AVX + Meade DSI -- part 2

This blog is about the Meade DSI which I've had since 2011 using with both enjoyment and frustration. In recent years my frustration has been with stubborn CCD hot pixels that persist despite being subtracted by dark frames.

Based on a comment by another DSI user I have started only acquiring dark frames for the exposure time I will use for the next target deep sky object(DSO). This saves time and ensures fresh dark frames for each new image acquisition. DSI will complain if there is no 1s exposure dark frame for the current temperature. Thus I collect dark frames between 1s and 8s. 

All of my imaging to date has been unguided as I have not been willing to invest a second imager, scope, etc needed to automatically guide the mount. That said, the AVX mount tracks beautifully even without periodic error correction(PEC) training.

One of the really great features in the AVX is the "All Sky Polar Alignment". After doing a two star alignment and refining go-to accuracy with four calibration stars  you can refine the accuracy of the polar alignment by pointing to a star near the meridian and following the All Sky Polar Alignment procedure. The procedure saves a ton of time compared to the drift alignment method 

My most recent imaging has been in Maryland where clear nights have been few the last couple of weeks and seeing has sucked. In any case a few images will be shown in the next post(s).

Also, because of the small size of the Meade DSI CCD chip I use a fairly aggressive focal reduction strategy. I always keep an Atik 0.5X  focal reducer screwed into the DSI. This also serves to protect against dust. I also have a Celestron 0.67 field flattening focal reducer for more extended targets such as M42. As will be seen in part 3 

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. 

It's been a good two years since I posted here. I'm ashamed to  admit I forgot I created the blog. That's not to say I have abandoned the DSI-II. For some reason I no longer remember I stopped posting. Time to give it a renewed try. For the near future posts will catch up on past activities.

Meade no longer produces the DSI-II. There was a DSI-III which has been discontinued along with the full DSI line. In fact I was "lucky" to grab mine for a substantial discount as Meade was closing out the IIs. I put lucky in quotes because the DSI-II is a mixed blessing. It was cheap $290. It does work as you can see from the earlier images.

With its automatic dark frame subtraction it is easy to use. On the other hand the product is really poorly documented and the software interface is poorly designed. Meade left it to an enthusiast to create a video tutorial that is not done under the dark but none the less is more informative than the included documentation. The documentation does little to explain how to use the various settings or what many of them mean. This has been a recent pattern with Meade. The documentation for its Autostar

Whoever coded the software interface did not account for varying screen resolution. Thus the user must futz around with screen resolution settings on a high resolution laptop just to get a usable screen. The lack of temperature regulation is another source of frustration on nights when temperatures constantly change. One is forced to keep generating new sets of dark frames as the device cools along with the night air. A few users have modded their DSI-II with Peltier cooling. I'm not yet brave enough to try that.