For long, I have been using a small Takahashi scope (FS-60C) as a luxury guide scope for a larger 100mm refractor. The small Tak was mounted on top of the refractor and has served its purpose very well, providing pinpoint stars to the guide camera.
Recently, I decided to switch to an off-axis guider instead, connected directly to the filter wheel and thus handy for use also for other setups, i.e for my Celestron SCT scope. This seemed to be a neat and working solution, so I put the old Takahashi back away to collect dust. It felt a bit awkward to send the telescope into retirement, as the Tak is an excellent scope with flourite optics, and have only done the "dirty work" of guiding for the last few years, a job that any cheap refractor could have done.
So, I got the idea of perhaps using the Takahashi for piggy-back imaging instead of putting it back on he shelf? The scope was already fixed in position and everything related was in place, so it was simply just to connect an imaging camera with a filter where the guide cam used to be. The setup has the two scopes obviously poiniting in parallell, roughly at the same target. The Tak provides a wide field of view with a one-shot color camera, and the main, larger telescope collects narrowband data.
On the software side, I am using two instances of Sequence Generator Pro, where all equipment is controlled by the main "master" scope, as before. The second instance of SGPro, for the piggy-back imaging only has the imaging camera and the focuser connected. Thus, it becomes a "slave" of the master and has no influence on the control of the mount, guiding, etc.
This setup works up two the point when the master scope is about to dither, and ruins the sub frame of the slave telescope. Even with a small dither, the noise is clearly seen on the piggy-back image. It is not practically possible to sync the two imaging sessions such that they both can finish their subframes simultaneously, as there are differences in sub lengths and time of download. In addition comes guider settling time, focus adjustment at irregular intervals, etc. In this situation, it would have been handy to have a setting where the master instance somehow gets a signal to wait until the slave is in a state where dither is harmless.
I have an imaging example from this setup here, where it is clearly seen that the slave image is more noisy than it had to be:
Master image: https://www.astrobin.com/ad3068/?nc=user
Slave image: https://www.astrobin.com/d1ufwa/?nc=user
If anyone has a come up with a working solution for piggy-back imaging, I would love to hear from you.
-Martin
Recently, I decided to switch to an off-axis guider instead, connected directly to the filter wheel and thus handy for use also for other setups, i.e for my Celestron SCT scope. This seemed to be a neat and working solution, so I put the old Takahashi back away to collect dust. It felt a bit awkward to send the telescope into retirement, as the Tak is an excellent scope with flourite optics, and have only done the "dirty work" of guiding for the last few years, a job that any cheap refractor could have done.
So, I got the idea of perhaps using the Takahashi for piggy-back imaging instead of putting it back on he shelf? The scope was already fixed in position and everything related was in place, so it was simply just to connect an imaging camera with a filter where the guide cam used to be. The setup has the two scopes obviously poiniting in parallell, roughly at the same target. The Tak provides a wide field of view with a one-shot color camera, and the main, larger telescope collects narrowband data.
On the software side, I am using two instances of Sequence Generator Pro, where all equipment is controlled by the main "master" scope, as before. The second instance of SGPro, for the piggy-back imaging only has the imaging camera and the focuser connected. Thus, it becomes a "slave" of the master and has no influence on the control of the mount, guiding, etc.
This setup works up two the point when the master scope is about to dither, and ruins the sub frame of the slave telescope. Even with a small dither, the noise is clearly seen on the piggy-back image. It is not practically possible to sync the two imaging sessions such that they both can finish their subframes simultaneously, as there are differences in sub lengths and time of download. In addition comes guider settling time, focus adjustment at irregular intervals, etc. In this situation, it would have been handy to have a setting where the master instance somehow gets a signal to wait until the slave is in a state where dither is harmless.
I have an imaging example from this setup here, where it is clearly seen that the slave image is more noisy than it had to be:
Master image: https://www.astrobin.com/ad3068/?nc=user
Slave image: https://www.astrobin.com/d1ufwa/?nc=user
If anyone has a come up with a working solution for piggy-back imaging, I would love to hear from you.
-Martin
