Scope Diagram Astrocamera.Net - Astrophotography by Dave Kodama

SBIG STV Autoguider/Imager

Here are my impressions of the new (as of April 2000) SBIG STV. Jumping the gun, I want to say that the firmware is very nice and easy to use, but during initial setup of the STV, I had some frustrating moments. The following is a basically chronological step-through of my experience, so it might seem a bit negative at first...

First, turn it on...

I almost didn't get past this point. When I first turned it on, the unit was completely dead! To say I was dismayed would be a big understatement.

So after checking the power supply, I proceeded to take the control box apart to get to the fuse. This checked out.

Unable to get any farther without documentation, I called SBIG's technical support. I'm sure they were as dismayed as I was to hear that the unit was dead! But in the end, all turned out fine. As I was probing points at their direction, I noticed that some pins in the connector between the power switch and the main board had backed out of the shell. Forcing the pin back into the connector shell fixed the problem! I want to thank the SBIG people for taking the time to try and get the problem solved while on the phone. In most cases, the immediate response of tech support is to have you send the unit back and after waiting 3+ months to get the unit, that would *really* have made me upset.

At any rate, that's why my first picture was the inside of the STV. Besides indicating the problem connector, I've pointed out some of the landmarks on the motherboard for interested engineers. While we're inside the STV, second photo shows the underside of the control panel -- circuitry to the LCD, keys, and alphanumeric display. When opening the cover, you have to be careful not to disconnect or damage the cable connections to the main board which sits in the bottom of the box.

Intro to the STV

The primary parts of the STV are the control box shown at right:

and the CCD camera head. The built-in display is an LCD display which surprisingly is a color display, though I don't know why since color doesn't seem to be used in the interface.

You can set a "night-vision" mode which turns the display all red, but the intensity is too high, which is probably why there is an additional flip up red filter. I just know that I'll eventually hit that filter when it's flipped up as shown, so one of the first mods will be to take it off the hinge and just velcro it in place.

The CCD camera head has T-threads cut into it and a nose-piece which threads into this to allow you to insert it into a standard 1-1/4" eyepiece tube (shown covered in the photo). This seems straightforward enough, but guess what? The nosepiece is just a little too large to fit straight into my Celestron 60mm f/7 guidescope! Subsequently, a friend measured the nosepiece OD at 1.253 inches, and SBIG acknowledged a problem. They are sending me a replacement.

Fortunately, the guidescope allows you to remove the eyepiece tube and put on a T-thread coupler. But this uncovered another awkwardness of the camera head. In the situation I had, I had to thread the CCD head onto the telescope. Because the cable can't be disconnected from the head, it naturally twists up. You can either have the cable disconnected from the controller and twist it as you screw the head onto the scope (assuming you haven't nicely arranged the cable up and down your mount already), or pre-twist the head so when you screw it down, it ends up with no net twists in the cable. It's not a fatal problem, but a definite annoyance which could be avoided by putting a connector on the head end of the cable.

Guiding with the STV

Ease of use of this second generation guider is really one of the reasons why I hand guided up to now instead of getting an ST-4, and the STV certainly seems to deliver on that. The main things of interest as an autoguider are:

  • Focusing is easy since you can see the guidestar.
  • Calibration has an "auto" mode.
  • Tracking has an "auto" mode.
Using my 60mm f/7 guidescope and a G11 mount, the firmware seemed to work very well. In auto mode, you just press "calibrate" twice and it automatically selects the brightest star, moves the scope in each direction, and calculates the distance and angle moved in each direction. There's no need to orient the CCD head to the scope axes.

Calibration Tip: Don't calibrate in a field full of stars. Even if the STV selects the central star for calibration, if too many stars fall off the edge of the field during its cal sequence, it will stop with an error. Calibration is best if there is a single bright (but not too bright) star in the center of the field.

To start tracking, you just press "track" twice, and away it goes, showing you the guidestar in a little box (though no reference crosshairs, which would be nice), and the correction magnitudes are graphed for each axis.

Of course at this point I haven't had a chance to really test the guiding on the comatic images of a dim guidestar in an off-axis guider, but certainly for guiding using a reasonably bright star in a guidescope, it's virtually point and shoot.

Imaging with the STV

Imaging is not the reason why I purchased the STV, but it's a nice plus. Here's a couple of my first shots from a reasonably dark site, taken with my 60mm f/7 guidescope in between film shots. The M65/M66 shot is a 60 second exposure, while the Omega Centauri shot is a 10 second exposure.

Again it was very easy to use. Just select the exposure time and whether or not to apply a dark frame, then fire away. When viewing the result, the brightness and contrast can be adjusted. And if you like it, you can save the image in nonvolatile internal storage for later downloading into your PC.

Though I haven't had a chance to use them yet, there are some intriguing imaging modes besides the basic ones. The "Best Sharp" mode continuously takes images and saves the sharpest one (said to be good on planets), and "Best Peak" does the same thing but uses the peak value as the save criterion (said to be good on double stars).

PC Software

The STV Remote software for Windows 95/98 comes on two floppy disks, a nice break from "heavy" Windows applications. In addition, it doesn't crash my computer -- always a big plus. The basic look of the program tries to emulate the front panel of the real instrument:

This emulation of the front panel isn't complete, though, because you can't turn knobs on your PC (you press the two pairs of unlabeled small buttons) and the remote screen doesn't automatically update due to the speed of the serial link and maybe the load on the processor in the box. You have to manually go up to the download pulldown menu to get the current screen image to the PC. So remote users will have to do as suggested in the manual and hook a video monitor up to the STV's video output in addition to running the RS-232 cable.

Given this incomplete emulation, I question the need to look like the box which is an interface designed around hardware components. A different Windows look optimized for a computer window would probably be better.

For the most part the software works fine, but here are some rough edges:

  • Cancelling a File/Save after putting in a duplicate file name inappropriately warns you about the duplicate file.
  • Cancelling a Process/Flat Field gives a file I/O error that shuts down the whole program.
  • Manually adjusting the brightness and contrast of the screen image requires typing in numbers rather than pushing a slider.

As I said, at least it doesn't crash my machine, so I can live with it until an update is available...