I apologize if this has been asked before but I can't find it. Does the STX Guider have a shutter of any kind? I see what looks like a pic of a small motor in the product pic. Thanks! Jeff
Doug, Then, does it also follow that the shutter is ONLY used for Darks, but is NOT involved with control of the guider's exposure times? Perhaps exposure time is controlled by electronically removing DC power from the sensor at the end of a shot? So, there may be two different exposure controls, in that camera - one mechanical for Darks, and an electronic one for normal Light frames. I also assume that there is no TEM cooling of the chip ... ? Joe
It is an interline CCD sensor so it inherently has electronic shuttering for light frames. A substrate pulse is used to clear charge from the pixels. There is no TEC. It is not required for the short exposures used for guiding. The shutter allows for convenient removal of any hot pixels.
Doug - very Interesting ... I assume you mean "Guiding time" no longer than about 20 seconds. That 20 seconds, an interline CCD ... non-cooled Dark frame ... must show a significant amount of thermal noise. For your information, and as an example - back in 2007, I tested and graphed the room temperature Dark current images produced by my "lens-capped", Kodak DCS PRO SLRN/n ... CCD camera - which uses EXACTLY the same CCD chip as in the STL-11000. See ATTACHED ( uploaded ) two graph images which show the on-camera histograms, at a WIDE range of exposure times, and ISO settings - all taken at 16.8 degrees-C (exact exposure-times, ISO, & temperatures noted on graphs). The test results also have a small rectangle crop of the " dark frame image" at each exposure setting and duration - (but only for minimum and maximum ISO testing lines, in the graph arrays). Note how PINK the Dark frame gets ... even as short as 8 seconds exposure at room temperature, at its maximum ISO 1600 ... which I assume would be how an STL-11K exposure is normally operating - i.e. "maximum sensitivity" . So, I wonder what dark frame noise looks like on an STX Guider CCD, at an equivalent range of DARK's ( that is, "capped nosepiece"), exposure times - since both the STL and STX are "INTER-LINE" type CCD's. Joe Z.
Most people use exposures of 0.1 to 2 seconds for guiding. 20 seconds will result in only ~ 3 corrections per minute. That's nowhere near fast enough for most telescope mounts. You can't compare a KAI-11002 sensor in a DSLR with a KAI-0340 sensor in a CCD camera. The dark frame subtraction will eliminate any hot pixels, and you will get a clean image that is more than suitable for guiding. All of our guiders currently use the same sensor, and we have no problems with dark current whatsoever.
Thanks Doug - good to hear. But, I wonder whether just "2 seconds" exposure is far too short. perhaps that is at a very dark site. I use the often recommended minimum 5 seconds, even upto 10 seconds exposures, on my old SBIG "external RGH guide CCD camera". Joe Z
Depends on the instrument and the target. Some people use 5 seconds but I’ve personally never gone above 2 seconds.
I personaly use 6s normally at my dark site/observatory. But for this application since I have the AO-X, I'll be using quick exposures. At the moment I have a grand total of 35 testing minutes on the new rig (ao-x/stx guider/7-slot wheel/stx-16803) since the weather is horrid. Doug - my next question - in Maxim DL, say using .2s for the AO-X exposures, I assume it's still worth it to setup a dark/bias library? Any issues doing that? Jeff
The AO-X works a bit differently. It doesn't use the main calibration tools because of speed requirements. Instead when dark frames are enabled it automatically takes a bunch of dark frames and averages them.
