bumpkin with the possible need for an extension tube to allow for back focus
The FRA600 is a Petzval instrument, accurate back-focus distance is not needed.
With the drawtube fully racked in,you can add up to 160mm of extensions, filter wheel, image rotator, off axis guider, image rotator, etc, to the FRA600.
With Petzval designs, once you can achieve focus, the back focus distance is automatically correct.
If you are only attaching the ASI071 to the FRA600, you will need to adapt the M90 interface (drawtube interface) to an M42 interface (ASI071 interface). Or you can use all of the adapters that came with it to adapt to M48 and then use your own M48 to M42 adapter.
An M48 to M42 adapter may have come with your camera. If not, places like Agena should have them right off the shelf.
Again, the length of the adapters is not important (as long as you don't add enough instrumentation so the camera sensor is more than 160mm from the M90 interface.
When you add a reducer to this scope, the backfocus between the reducer and the camera needs to be precise.
Chen
