Thanks for the clear explanation, I did not realize that you guys were screwing the reducer directly on the nose piece. Well, in my case however, since I can use the reducer in afocal mode, I may choose to put the prime focus mode issue aside for now, as I do not really need to use both techniques.
Afocal turned out completely the opposite of Prime Focus for me with my 56mm plossl. Had to rack the drawtube way out to get focus. Several inches out on my AT72ED. The same principle in placement works in afocal mode for me except the reducer screws on to the end of the 56mm plossl. Still did not have enough back focus to put the reducer before the diagonal. I did however have enough back focus left to possibly add a 25mm extension between the reducer and the end of the eyepiece which would give me more than .5x true reduction, but that stack is very high.
I tried in afocal the following optical trains that worked:
telescope - diagonal - 2” Ha filter - 56mm plossl - NVD Micro (with no reducer the drawtube was racked out almost 3”)
telescope - diagonal - 2” Ha filter - reducer - 56mm plossl - NVD Micro (still had to rack the drawtube out about 2”)
will try next:
telescope - diagonal - 2” Ha filter - reducer - 25mm extension - 56mm plossl - NVD Micro (should give me greater than .5x reduction)
I don’t know if this would be the same with a Televue 55mm plossl, but this is the configuration and result I had with a Meade 56mm plossl. I’m looking to experiment with this on my mak 150 next. Hoping for around F/4 on the mak which is F/12 natively.
Not as anxious to try with the mak now though because I picked up a Skywatcher Startravel 150R F/5 refractor used last week. Going to replace the focuser and adapter plate on that one soon. Need to try it with stock focuser and Prime Focus first though. I wanted to try on my mak because the mak is 14lbs and my F/5.9 AT152 is 25lbs, but the used Startravel 150 is about 14 lbs also, so will use the new 150 and probably sell off the 25lb AT152. Too heavy for me and can get a faster F ratio with the Skywatcher.