Maksutov-Cassegrain conundrum.

[hal9550]

12 hours ago, Louis D said:

I haven't tried 2" eyepieces all that much in my recently acquired JOC (ES/Bresser) 127mm Mak, but my Synta (Orion/Celestron) 127mm Mak just vignettes somewhat all the way to a 46mm field stop.  It's hard to perceive visually.  There is not hard cutoff point.

Here's my well work comparison image in the Synta 127mm Mak:

As you can see, there is light falloff in the 40mm SWA which has a 46mm field stop.  I think I measured it to be about 35% falloff, IIRC.

Thanks for getting back to me - yes i get what you mean. I guess i am just going to have to wait and see! Im really curious as to when there is a fall off - and when the fall off begins - 

Its difficult to estimate that without actually having the scope, to trial - I will have several 2" EPs whos field stops are very close to 1.25 (im thinking of my 2" Omegon Redline which is less than a single mm above the cut off for 1.25) - 

For me, a slight drop off is nothing to worry about, but i am looking forward to seeing when it kicks in, relative to fieldstop

[Louis D]

Visually, the vignetting is difficult to see.  What you can see are odd oval reflections as bright stars are moved past the 27mm clear aperture edge.  They start to reflect off the inside of the poorly blackened baffles creating larger and larger ovals as they near the eyepiece field stop.  I keep meaning to slide some flocking up inside the rear baffle to see if it helps to eliminate the reflections.  I've read of folks actually sticking the flocking to the inside using a pencil or similar to help guide it into place.