Is this possible with Skywatcher F5 Newtonians?

In the standard ZWO 55mm backfocus config (+1mm for filters) you squeeze an OAG and a camera and a filter wheel. The OAG has 16.5 mm optical length, and you have 13mm between OAG and filter wheel (20mm). Does that fit with the back focus requirements of your scope/corrector? Manual rotators have about 13mm optical length, so in principle it should work if you replace the 13mm m42 tube (usually a 2 male m42 adapter (2mm) and a 2 female m42 spacer (11 mm), so net 13m male/female) with a manual rotator with two m42 threads. If it gets too tight, there are OAGs from TS Optics at 11mm net, give you some extra space. For an motorized rotator (like a Pegasus Falcon) you need to find more like 22mm, which probably gets too tight.

Matthias

I feel with you, I try to find a combination that fits a external focuser, an ONAG, a rotator, and a FW into to 146.5mm of my Edge11 - all „affordable“ ones (whatever that means) miss, often just by a few mm. There is a solution, but it costs more than my scope …

Matthias

Get a filterwheel with built-OAG. They exist as far as I know and should create enough additional backspace room for all the parts you want.

CS Sean

Andy Wray:
I have all but the field rotator and all is well, however I can't see that my Skywatcher 200PDS has enough back focus to accomodate it as well.

It's not the Skywatcher 200PDS that determines your back focus.
It's the coma corrector that determines the back focus and how much space you have in between the coma corrector and the camera.


I did find this coma corrector - it has a far larger back focus of 91.5mm (most others have 55mm). I have 0 experience with that coma corrector so I have no idea how it performs.  - But in theory, that should give you enough space in between the coma corrector and the camera to put in a rotator.


Before that though; what do you need a rotator for?

I'm no expert. And others that have experience with rotators might be able to give better information.
But I see it as just another element that can fail/move/vibrate/cause flex/backlash, etc into your imaging train.

And here is the tricky one. Technically you would need flats for every single angle that you use, as dust particles and stuff on the mirrors won't rotate together with your imaging train, and you would need new flats for that. - same goes for collimation, that one needs to be absolutely spot on, errors there are less noticeable if you stick to one angle.. but rotating the imaging train in a Newtonian will be affected by imperfect collimation. Which might also affect vignetting slightly..  And again, would require flats for every angle that you use.

Depending on your use, it might just be a lot easier to stay clear of it and stick to the rotation/crop tool in photoshop.
Good uses are Alt/Az mounts, remote rigs, or big mosaic use.. but for single target use in the back yard.. I might stay clear.

andrea tasselli:
Image train rotators (to distinguish them from field rotators as used in Alt-Az configs) aren't really worth their money for what they do and much less worth the additional hassle of having to re-calibrate flats and everything that goes with it, including obviously PE curves. So much so that none of the remote service providers that I know of offer this as a add-on extra.

OK, that's given me food for thought.  I guess with the right camera and OTA combination I could just take care of image composition in post and with mosaics it would just be some careful planning.

Good point and one less mechanical thing to worry about.