Kevin_A did you happen to test the Optolong L-Pro or the Svbony uvir cut filters as they are very popular?
Nope. I have zero interest in anything from SVBONY. Waste of time imaging with them.
But I did buy one from Amazon to measure, so it must be somewhere in the house. I think I had used the filter holder to hold some Baader glass because the Baader did not thread into a ZWO filter drawer. I'll see if I can find it. I usually throw cheap glass like Tiffens and SVBONYs away; keeping the holders for other uses. I'll look for it, but need to wait for night time to get the room dark enough -- perhaps not, if it leaks UV as strong as the Optolong IR-UV cut leaks UV.
After seeing the numbers on the Optolong UV-IR Cut filter, I will probably thrash its glass too, and use the holder to hold Baader glass instead. I had used it as a prefilter for the NBZ-II with that disastrous huge halo, but it looks like I need to make another pass on a prefilter, using the Chroma L glass. There is probably next to zero 21st century anti-reflection coating on that thing. If I no longer see a halo, and the SVBONY measures out to have similar UV suppression to it, I would highly recommend that you thrash the SVBONY.
With optics, good things are seldom cheap.
If I remember correctly, the SVBONY's glass did measure out with a thickness gauge to have identical glass thickness as the Optolong UV-IR cut. Notice the huge difference between the Optolong UV-IR cut's UV performance and their L-series filters -- they are not from the same universe. There is a big cost difference between the Optolong ($65) and the SVBONY ($25). There is always some fishy stuff in the astronomy world -- like the markup on the Radian Sharpstar re-badging (before OPT went belly up).
Hey... look what UPS just delivered.
Will see if I can drill some holes in an EAF to mount it (or use my 'big hole plate") so it does not stick below the plane of the Losmandy dovetail plate. The pictures I have see with the ZWO EAF mounting plates is that it will stick below the Pleiades' dovetail.
Chen
P.S., guess what, CloudBreak dropped the new WO spacers in two plastic bags, into the Pleiades 68 box. Presumably that would make it a 55mm back focus (with no filter glass). WO is pretty fast about upgrading customers.
The backfocus adjuster is 18mm +/- 2mm, the ZWO filter drawer is 20mm, the camera flange is about 17.5mm, placing the focal plane nominally at 55.5mm +/- 2mm without glass. With 2mm glass, the EAF ∆ zero crossing should be close to the center of the backfocus adjuster.
With the new adapter, I should be able to adjust for proper backfocus without adding any extra spacers/stop rings than the backfocus adjuste... we shall see . The optical path of the new 54mm adapter is 5.09mm (constant all around -- so may be OK with tilt without having to go to PreciseParts). The OTA end has a 60mm/1.0mm thread -- odd diameter. Here is WO adapter, Askar backfocus adjuster and ZWO 54mm filter drawer...
I haven't looked at the thickness of the original 54mm yet... haven't gotten that far. Probably between 2mm and 3mm.
Chen
