I am involved in a project to make mosaics. I have chosen DSLR lenses, such as Canon EF 200mm f/2 and Zeiss or Rokinon 135mm f/2 because they are both fast but also have good star image quality in the corners even wide open at f/2. Many people also like the Sigma ART series of lenses for this type of work.
In order to make a good mosaic of an arbitrary spot in the sky it is convenient to have to have a motorized rotator. Contrary to what you made hear, every panel in a mosaic requires a different orientation angle. Very small mosaics, with a very narrow field of view, that have targets with low declination can be done with setting one angle per mosaic, but that is just an approximation. If your mosaic is large (many panels) or spans a wide enough range in RA, or is high declination (which tends to force it to have a large range in RA, then the approximation fails.
A lot of the reason that people have trouble with mosaic overlap is due to this.
The reality is that every mosaic is better done with a rotation angle per panel.
Unfortunately there is a problem - the thinnest commercial rotators are models like the Pegasus Falcon, which is 18mm front to back.
The flange focal distance for a Canon EF mount is 44mm, and it expects to mount directly onto a camera. So you can't use a Canon DSLR - any distance at all between the lens mount and the camera body will act like an extension tube and the lens will not focus at infinity.
If you have a mirrorless camera - like the Canon R5, or the Sony Alpha series, they have flange focal distance of 19 - 20 mm.
The QHY 128c, which is what I use, has a very similar "flange" focal distance with a minimum of about 18mm.
So if you have mirrorless or QHY, and you want to use an 18mm thick rotator, you have 44 minus 18, minus the flange focal distance, and this leaves you 6 to 8mm to play with, depending on which camera you have.
Unfortunately, a conventional Canon adapter for QHY is 10mm thick, and the connector that would attach the QHY camera to the M54 thread in the rotator is 6mm thick. https://www.qhyccd.c...atid=193&id=115
So you have room for 6 to 8 mm but the minimum thickness is 16 mm - it won't work.
The adapters for mirrorless cameras like Canon R5 or Sony Alpha are similarly sized.
One approach we considered was to rotate the camera and lens together. However this approach has some issues - it would work with the Canon 200mm f/2 which has a tripod foot, but not with any of the 135mm or shorter lenses which don't have a foot. If you (in effect) replace the tripod foot collar with a bearing so you can turn it, the lens/camera combination is not held very well. Most field rotators for astrophotography are the "shoot through" kind and they would be hard to adapt - one would likely have to build a homemade rotator which is not as convenient as buying one.
This rotate camera-and-lens-together approach probably could be made to work, but we decided against it.
Rather than be daunted by this, my friends and I took a look and there is really no need for most of the adapter space.
We took a commercial Canon adapter from QHY, took it apart, and then in a machine shop we have access to, we sunk the Canon mount into the Pegasus Falcon rotator. In effect this is exactly what Canon does with the mount on a camera body - it is embedded into the body.
On the other side we remade the adapter that connects the QHY camera to the M54 mount. There was no need for 6mm of wasted space.
Here are some photos of the final unit from the
here it is from the camera side, with the QHY camera taken off. a baffle that hides the silver mount and lens contacts has been taken off for this picture.
In a perfect world Pegasus or other rotator manufacturers would do this - it would not be very hard. I know that there are machine shops that cater to astrophotographers; perhaps they could do something similar.