I attempted to install a ZWO OAG+Helical focuser in my imaging train. (Esprit 100ED, ZWO Filter drawer, ASI2600MC-P).
Two issues occured which resulted in my returning the OAG/Helical focuser and going back to my external guide camera.
1) I had the prism stem set to clear the OSC sensor. However I found that I could not reach focus on the guide camera.
After some experimentation, I found resolved the issue by adjusting the stem further outward, much further that I really felt should have been necessary. This allowed me to 'fix' my daylight focus at about 30% from being bottomed out. Still short of midpoint initial setting I was after, but at least there was some 'slack' for adjustment.
2) After achieving focus with both primary/guide camera, there was noticeable off center vignetting of the guide camera image, probably only 70-80% of the image was 'clear'. Other users had reported that the prism is only held i place by friction, allowing a misalignment which caused similar results and precluded guiding due to poor star shapes.
After returning the OAG/Focuser, I have considered that the vignetting MIGHT have been the result of the stem placement required to reach focus with the 290MM Mini and the helical focuser. The stem seem to need at least another 5mm length to provide sufficient room for reasonable prism placement and still achieve focus.
If this is true, then it would seem that the Helical focuser is not completely compatible with the ZWO OAG, but I haven't seen anything to indicate that in documentation (what little there is). Is this a known issue, or is prism alignment more likely the culprit in the vignetting?
