Starlight Xpress STAR 2000 Self Guiding System

John A. Blackwell
johnb@regulusastro.com

Introduction:

CCD imaging and the need for exact guiding go hand in hand. In fact, one really needs either an autoguider or one of the imagers on the market with a built in guide chip (ST-7/8). There is a new solution available, the STAR2000 system from Starlight Xpress. This is a hardware and software device that allows one to use the Starlight Xpress cameras to "self guide". Yes, you read that correctly.

The way it works is the software reads interlaced lines on the chip during the exposure: every other one for guiding, and the rest for imaging. Half way through the process, the image is downloaded to memory and the other half of the chip's pixel rows is used for imaging. The results are added together to form a final image.

The STAR system itself is a cable that runs to an opticoupler box (acts as relays to your scope's mount electronics), a cable from the box to the mount's drive, and control software for imaging and guiding. Any scope with an LX-200 or ST-4 capable drive system should work. You should contact Starlight Xpress if you are unsure.

Results

The preliminary results of the STAR2000 setup with the MX5c show great results. I decided to try the whole thing out using my newer C-8 in FASTAR mode (f/1.95) to make the night go "faster"...it didn't. In fact I spent the better part of the evening trying to train the software to the mount and vice-a-versa. No matter what I did, as soon as I started guiding, the software would send the guidestar sailing off the screen into the void!

I must have taken thirty or more images before I realized that I thought I had read someplace that the base of the camera (tripod mount plate) should be aligned with the East-West axis of the mount. In fact, that information was in the manual! That will teach me! Sure enough, my MX5c was aligned north-south. SO, I twisted it 90 degrees in the holder and started over (2 hours later). That did the trick, and I was able to train the guide software and guide flawlessly for exposures up to 30 minutes. It could have easily gone longer, but it was 1:00am local time, and I was getting tired.

The process I came up with for FASTAR mode C8's and the MX5c STAR2000 is as follows:

Insert MX5c such that its base runs east-west!
Find and focus the object to image.
Take a short 1 second integration.
Do not convert it to color.
Pick a guidestar (File menu).
Set the Losmandy G-11 guide correction speed to 2x.
Train the tracking software.
STAR200 software should report back values.
Take another short 1 second integration.
Pick a guidestar (brighter the better).
Take the long integration using the following method:
1. Check the "self guide next exposure" box.
2. It should auto fill in values of 1 second.
3. Do not bother with dark frames yet.
4. In the exposure range box, select Minutes, and enter the number of minutes for the longer exposure.
5. Click the "Take Exposure" button and watch the fun begin!
Save the image in the deafault format (file, save).
Convert the image to color without any filters but anti-alias.*
Save the color image to TIF.*
Import the image to MaxImDL for processing: DDP and stretch.

*Applies only to MX5c color imagers.

An oddity with the software: It gets the guide exposure data from the "Exposure Range" section of the dialog. If that is set to minutes, then you can not check the "self guide next exposure" box. Selecting 1 second in the "Exposure Range" box will again re-allow you to check the self guide box.

In the remaining time that I had before falling asleep, I tried a prime exposure shot. The rules are the same. Keep the base plate of the MX5c aligned east-west! Reset the drive correction rate on the G-11 to 0.5x, and all should be well. I was operating at f/6.3 on the C-8 for this.

Also noted, if when you are in the guiding process and the star seems to fly out of the field with increasing rapidity, you may have to check the appropriate reverse direction checkbox in the program defaults screen (swap e-w, swa n-s). This is easily seen though and is unlike the lost tracking first seen when the camera is aligned incorrectly in the focusser.

Exposure times for good color have to be long. Be aware that good saturations come with exposures in the 20 to 30 minute range or more. This is due to the fact that one is really losing 50% of the time of each integration to guiding the image.

I also found that the image processing ability of the STAR2000 software to be minimal. I followed the route of saving the image, then converting it to color and saving it as a TIF. I then took the TIF into MaxImDL and performed a color rebalance followed by a Digital Development Process to extract the best colors and contrast levels.

I have posted a couple of the images online for people to see:

The first is a 20 minute integration. The second is a 30 minute integration. The third is a mosaic of the two. You will note a lighter greenish glow in the upper left corner of the images. This is from the CCD's amp circuit and can be removed by using dark frames. I was just too tired (call me lazy ;-)

Conclusion:

The system works very well, In fact, so well that I have discovered new uses for it: autoguiding film exposures. It will be replacing my ST-4 imager/autoguider as the MX5c with STAR2000 is more versatile and compact. For FASTAR imaging it remains my choice as well. The ST-7 with filter wheel will not sit well at a FASTAR focus. The main drawbacks are that the system requires double the normal integration times to build up an image (no big issue if it guides itself), and that dark frames must be built up using a unique process to counteract the downloading of amplifier "noise".

Contents	What's Up	Feature	Papers	Photos
	Links	Observations	Spectra	Sketches