STL 4020 and SC -2

Hi

I am having problems and not sure what the exact problem is but suspect it is related to the backfocus distance.
My setup is simple
STL 4020 (mechanical backfocus is 39.59mm)
SBIG 2 inch starchaser (backfocus 20.3mm to the main imager and a focus range on the starchaser chip of 43.9 to 75.2mm)
SBIG starchaser face plate (backfocus 3.175mm)
SFFX Flattener for SVX 152 (backfocus adapter (measures 19mm as diagrammed below but not sure exactly what it is as some of this may be on a threaded portion of the SFFX). Back Focus requirements 79mm for this to provide flat field effectively

Main camera comes into focus but cannot bring the starchaser with the 43.9 to 75.2 mm backfocus range into focus without oblong stars (like light rods rather than stars). I would expect that I should come into focus on this chip even if the SFFX adapter was conservatively half the distance I listed as 19mm). What I am seeing are oblong stars and that suggests to me that the backspace is off on this camera. The mirror on the starchaser is fully extended so I can dial in with the starchaser focuser. I tried this with the mirror all the way in and all the way out. I only can see stars when it is all the way out. Don't get anything like a star when the mirror is all the way in. The max on starchaser is 75.2 mm and with the added supposed 19mm SFFX adapter should be in range somewhere along the way.

Do you agree with the math here? What are your thoughts?

Thanks for the time.

Bob

 

Absolutely, I just need a clear night....in MI...so it might be a while. The flattener is noted to have a flat field of 90. 5mm so didn't think this was going to be a problem with a 2 inch opening. But yes, I will upload once the opportunity shows up. Thanks

 

Greatly appreciate your time here. Bottom line is that this is resolved. First is that the spacing was still off. I discussed with Stellarvue and they explained that the back focus is 79 for the flattener but with the spacer they put in place it is 70mm from the rear that would flush with the SC-2. Without the FW8 I was too far in. With the new set up the numbers line up, (STL -38mm, FW8-9mm, SC2-20.3mm, SC2 face plate -3.175mm), So with the FW8 it is nearly perfectly spaced to 70.475 mm. Second was that there was a piece of plastic over the mirror. I saw a little bubble on the surface of the mirror and tried to gently eliminate it but it moved! That is when I noticed that this was the issue just like Mr. Croman noticed. This thin cover is very hard to see indeed.

So this is resolved! but ran into other problems that I need to sort out.

One is that the STL/FW8 does not allow the SC-2 to fit on the surface without rotating the entire device 45 or 90 degrees. I suppose that does not matter on STL 4020 because it is a square processor but on STL11000 will likely cause some vignette at 45 degrees so will need to flip to 90 probably. I will hook that one up later and see.

Second is that the #4-40 1 inch screws that go into the SC 2 to mount it to the FW8 shows just a small amount of the heads above the face plate adapter. The Stellarvue adapter abuts these and will not sit flush on the plate so I replaced the screws with #4-40 1 inch button head screws that are fully recessed and so that it is flush.

I haven't actually had the time to run the camera in full operation yet so looking forward to that soon. Just had enough time to do the above last night. Maybe some of these notes will help others. Once again thanks for listening and your support!