I have for sale an original Spectra Sure Sharp SCT focuser.
This is a Spectra custom made product.
It is specific to SCT's.It sold for about $200. new
It is the neatest, easiest way to get critical focus on an sct and then be absolutely par focal for your 35mm camera.
If you are doing astrophotos on 35mm film, there is nothing that can get you to critical focus as well, as quick or as easy as the Sure Sharp
This is the deluxe version with a right angle viewer.
The camera adapter fits OLYMPUS cameras. (I don't know where you could source adapters for other camera models because Spectra went out of business a year ago,)
It has its original instruction sheets.
$150 plus shipping