Meade DSI

This is a collection of notes regarding my own experience with a Meade DSI. It was purchased in in UK, October 2005.

Installation.

• You must have USB 2 support on the computer in order to connect the camera. I could not get the system to connect to my DSI without USB2.
• You must download and install the latest software update from Meade. The software in the box would install apparently OK but the system would try and re-install the DSI driver every time I plugged it in.
• The camera is fussy about the type of USB cable used to connect it. A modest length of additional USB cable works OK but a powered USB extension does not. (I have seen some special powered extension cables for the DSI advertised but not tried them).
• The camera may not work with exposure times less than 1 second. Sometimes an exposure time of less than 1 second causes the camera window to go fuzzy. I have to unplug the camera, reboot the computer, reconnect the camera. This is less of a problem with the latest version of Envisage.

Dark Frames

• It really is necessary to use dark frames. Unlike cooled cameras the DSI is quite noisy at short exposures. There is a big patch of brightness in the top left of the image caused by internal heat. This is unacceptable for anything over a 1 or 2 second exposure, especially if you intend to enhance (stretch) the contrast. This patch is removed if dark frames are taken and used. They must be of the correct exposure (same as the images) and taken immediately before/after the images (to get the right temperature).
   
• Remember you only need the dark frames for the exposure length(s) you are actually going to use. The software will tend to waste time gathering dark frames for a wide range of exposure times unless you tell it otherwise.

Hot Pixels and Cosmic Rays

• I have several bright white pixels regardless of exposure. These are mostly removed by using dark frames.
• I seem to get CR hits quite often. They appear like 'temporary'  hot pixels and can be very bright. That is one good reason for saving all your uncombined or raw images so that you can (re)combine them later excluding the bad images.

Procedure for Deep Sky

Having used a Starlight Express MX5-C with very basic software the Autostar/Image software makes me feel rather out-of-control. For deep sky objects the auto-combine feature is OK for an initial look-see, but I prefer to capture the un-combined or raw images and process them later. That way I can try several different approaches.

Also, the contrast control is rather crude and I much prefer to take the image into some other software (like Maxim DL or PaintShop Pro) for contrast or histogram adjustments.

The procedure I use is:

• Scope set up with reasonably good N/S alignment.
• Focus on a moderately bright star in 'live' mode and get best possible focus.
• Align to the chosen object and use 'long exposure preview' to find the best exposure that is a reasonable compromise between brightness and tracking drift. Try different settings of sharp/soft colour and high gain. Decide on optimum exposure.
• Take dark frames (minimum 5 but 10 is better) at the chosen exposure. Switch on dark-frame subtract.
• Adjust contrast setting so that the image being displayed (and saved) is not too stretched. (i.e. set the low end to an image that makes the background a bit grey and the top end well above the brightest star). This will give plenty of scope for contrast/histogram adjustments later.
• Set 'colour auto' and 'save proc - save all uncombined images (jpeg).
• Select a star to track in the deep sky field (for the auto-combine).
• Start taking pictures. Collect as many as possible, (minimum 10 but I like to get 30-50 if time allows).

Autotracking and Drizzle

• If you have a telescope with appropriate connection protocol( e.g. LX200) then its worth trying autotracking with Drizzle. Exposures need to be quite short to get the autotracker to 'lock on' but you can leave the camera running for long periods and collect lots of images for stacking later.

Dont Fiddle with the 'live' image contrast.

The software will save each individual image while building up a combined image on the screen. Its best NOT to fiddle with the contrast settings while capturing images. Certainly do not fiddle with the 'live' image contrast as this will effect your un-combined images and make them unsuitable for stacking later.

Processing

There are various pieces of software that can be used to combine the raw images. I use:

• Registax or Maxim DL to align and stack the images. Registax is free and gives you the option of automatic or manual alignment, 'drizzle', colour control, 'wavelet' filters etc. However, Maxim  sometimes produces better images.
• The images may be quite noisy, especially after contrast stretch. I use Neat Image to reduce noise. PSP's Edge Preserving Smooth is also quite good.
• Sometimes maximum entropy deconvolution (e.g. Astroart or Maxim DL) can improve the stars, but more often than not it just makes a mess of an image.
• I use PaintShop Pro (PSP) for gamma/histogram/colour (etc.) adjustments.