Riccardi 2.5" 0.75x vs Explore Scientific 3" 0.7x APO flattener-reducer?

[pipnina]

I have a 130mm f6.6 triplet and so far have struggled with the current Photoline ED 0.79x corrector i'm using, as regardless of the spacing I use some astigmatism and curvature seems to remain.

I have seen the riccardi m63 0.75x as one option as a flattener-reducer upgrade, but the explore scientific looks like it could be a good alternative at a similar price.

The ES can screw directly into my TS 3" R&P focuser I think, as it has an m68 "zeiss" (?) thread. It also has a slightly stronger reduction which could be good for my setup as my guiding isn't great, the backfocus is also a bit longer than the riccardi, so I might be able to fit in an OAG and a backfocus-adjuster.

Meanwhile, the riccardi looks good because it still has more backfocus than my current flattener, and also shows me the spot diagram and vignette I can expect (very tight stars even on full frame, and no vignette until the very corner of a full frame sensor, and even then it's only supposed to be 3%). If the ES is better, it sure doesn't, advertise it...

Does anyone know which one might be better? At the moment I am leaning toward the riccardi.

Cheers!

[tooth_dr]

I have the 0.75x Riccardi reducer M63.  It fits inside my drawtube (3.5" FT focuser).  I have no idea on the ES version, but the RIR seems to suffer from stray reflections with some brands of filters.  There is an M82 version of the Riccardi reducer, it has a slightly large spot diagram but illuminates a larger area.  I use my RIR with APS-C, and it delivers good small stars right to the corners.

[KP82]

I've got both the TS 0.79x reducer and the riccardi M63. With the TS the corners always show a bit of curvature on APS-C no matter what spacing I used until I replaced my DSLR with an QHY163 (smaller M4/3).

The riccardi is a lot better in terms of field correction, tight stars and flat across the entire field of APS-C. My sample is an older version I bought used here. The surface of its internal barrel is matte black. The later version seems to suffer from stray reflection due to its shiny barrel surface. I can't remember where I saw the thread (could be on CN) in which a member posted a comparison between the two versions. The shiny internal surface could be clearly seen in the pictures.

Edited December 3, 2022 by KP82