Hi - I’m a newbie to SGPro so apologies if I am repeating a question or am missing something obvious. I was imaging Helix over the last weekend with 150 lights over 5 filters and the image slowly rotated across the page as the phd2 settling and dither caused delays. Can we add an option to re-centre after each event so that we could pull the image back into frame. Helix is quite big and hence a little movement moved it quite out of centre.
David
Yep, it came up just recently. It’s caused by flexure between your imaging and guiding scope/cameras. At the moment, it doesn’t appear to possible. Feature request has been requested for this, as well as every x number of shots, or perhaps every x mins. Workaround, which is a bit cludgy, is to set up different targets with same coords and you can set SGP to recentre between targets, just not events at the moment.
One way to do this would be to create multiple targets of the same object, and make sure that “Center on when target starts” is enabled in the target settings. But, I would suggest that if you are getting that much movement over the course of one night you should check your polar alignment. Unless you have a really sloppy mount it shouldn’t move that much.
If the image is rotating as well as moving then it’s definitely polar alignment and no amount of recentering will help with the rotation.
It sounds like you have both problems because polar alignment should just cause rotation if the guider can keep up with the real movement with rotation that comes from polar misalignment. I was skeptical about guide scope sag as the night progressed and have been suffering for a while with image drift. My guide scope is very tight and doesn’t seem to move much when I push and pull, so I always blamed guiding and alignment. My field of view is 30 arc minutes and the image drifts about 3 or 4 arc minutes each hour of imaging with no rotation. This isn’t bad for a bright object, but if I image all night the image comes close to falling off the edge of my main camera even with good guiding that is reporting everything is fine. In search of a solution I experimented. I cut a piece of 1/4" balsa sheet to the curve of the main scope at one end and to the curve of the dew shield on the guide-scope at the other end. I stuck on some weather seal foam and wedged the balsa between the two scopes at the dew shield end of the guide-scope. I then adjusted the rear guide-scope screws to re-align the guide image to the main camera and hold the balsa in tightly. A full night of imaging showed, for the first time, an image that only dithered. The lesson I learned here is that checking that the guide-scope is tight is not enough and proper support is needed - better than the manufacturers give you. Because my magnification is so high, if I can see movement when I push on it, there is much more movement than can be allowed. I would never have thought that a tight scope would have sagged enough to matter, but it does.
Hi. So you basically created a balsa clamp between the Guidescope and main scope? An interesting idea. As I’m driving a 2032mm FL anything to dampen this flexure is of interest. I wonder if a simple wire loop would do the same.
I’ve also recently purchased an 120 Sywatcher Esprit with FL840mm which should make things easier. Or an OAG?
Hi David, I also have 2032mm FL and tried this out with the expectation of having to hold it in place with a cable tie, but the door seal foam and adjustment screws did the job.
I have attempted to use an OAG, but found that with such a long FL the image is too dim and I have too few stars. When I did manage to get it to work I was mostly obtaining the same guiding accuracy, but every so often sub 0.8arc sec. With the balsa I get about 0.8 arc sec all the time and virtually no image drift. I suspect I have achieved the limit of the CGEM mount, so OAG isn’t going to get further improvement.Thank you Generator for the photo and the bit about the OAG. I’ll experiment with the balsa idea as I want to get the 2032 going as it gives me more framing options.
