Thinking of changing FF/FR. Thoughts on the SW 0.85x Flattener for 72ED?

[Ovi]

Hello! I've been using my SW 72ED with a StellaMira 0.8x FF for the past year and I can't say I'm too happy with its performance on an APS-C sensor. The stars in the corners are all around double the FWHM of those in the centre (pic below) and no amount of fiddling with the backfocus seems to fix it. Therefore, I've been thinking of buying another FF/FR, namely the one made specifically for this scope by SkyWatcher. Any experiences with it? If yes, does it fully correct and APS-C sized area? Suggestions for other field flatteners that you might use are welcome as well. Thanks!

[Clarkey]

Looking at the image above suggests it is more than just distance from the sensor - possibly some tilt as well. The star shapes are certainly not consistent with purely a back-focus issue. If it is was purely distance  all of the stars would be pointing away from centre or around the centre - but this is a mixture.

[AstroNebulee]

Before you get the dedicated FF reducer for your 72ed, make sure your scope is the newer shorter tube version and not the older slightly longer one. 

I tried one once (to replace my ovl FF) with my slightly longer 72ed and couldn't achieve focus as not enough inward travel. 

I think the newer 72ed has a sticker on the white collar saying it can be used with a 360° rotator I believe and were shipped after December 2019. The new version is 10mm shorter to compensate for the focus issue. Ask whom you bought the scope from to clarify which version you have. 

As Clarkey says theres not just a backfocus issue. Check that the focuser is properly tensioned, I had the issue of a bit of focuser sag which caused some problems and had to adjust my focuser. Here is my thread on it. (I also had some sensor tilt on my zwo 294mc pro at the time but fixed that with a tilt adjuster)

 

Lee 

Edited July 20, 2022 by AstroNebulee
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[Skyline]

Another reducer which will work with this scope is a TS Optics : TS279RED.