Re: How feasible is tandem imaging with AP1100 with or without AE and 2 1000mm refractors with ~0.8"/px image scale?

Ray Gralak

Hi Nathan,

I have done tandem imaging with 600mm f/4 camera lenses - essentially 150mm refractors, This is with QHY
cameras with 5.94 micron pixels. The pixel scale is 2 arc/sec per pixel. This was on a 10micron GM 1000 shot
unguided, with a model made on one of the two OTA.

It worked for me. There are people on CloudyNights who use longer focal lengths in tandem rigs.
It's not the mount but the rigidity of the mounting and the similarity of the scopes. As in your case, two of the same type of scope will have by far the best chance of working with a common model. And, auto-guided or not, the differential flexure between the scopes will limit the maximum exposure duration.

BTW, if this is your post on CN, there are a couple of things I would like to mention:

With plate solving and recentering in many apps, pointing correction is not as crucial as the tracking-rate correction.

APCC has two tracking rate algorithms: All-Sky, and Dec-Arc. The All-sky and Dec-Arc tracking models use the same data points collected by APPM. They coexist independently and simultaneously within APCC. APCC can use the All-Sky model for pointing correction and the All-sky *or* Dec-Arc model for tracking-rate correction. You can switch between them while tracking using a checkbox in APCC.

And, given the posts on CN, people posting there may not realize that APCC's Dec-Arc Tracking is not just an All-Sky model created from points near the same declination as other mounts might do. Dec-Arc Tracking is a new, optimized tracking algorithm independent of the All-Sky algorithm. Dec-Arc tracking does not use the standard pointing terms used in an All-Sky model because those pointing terms cannot cover all of the idiosyncrasies of every telescope.

Another attribute of APCC's pointing model is that it supports unlimited sky data points, while some mounts only support a limited count. Pointing/tracking-rate accuracy goes up roughly as the square root of the number of sky data points. An APCC user can thus create a dense All-sky model with unprecedented all-sky tracking accuracy using Dec-Arc Tracking, or a similarly dense model for one declination patch using the NINA plugin by Dale Ghent.

-Ray Gralak
(Author of APCC)

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