The OVL flattener didn't work on my EVO72 APO

Equipment Flattener Help Needed
3 replies•260 views
André Moleiro avatar
André Moleiro avatar
I'm wondering if I'm doing anything wrong. I recently acquired this field flattener: https://www.firstlightoptics.com/reducersflatteners/ovl-field-flattener.html

It's supposed to work well with my Skywatcher EvoStar ED 72 APO. After imaging it two nights ago though, I can still see that the stars from the border are really affected by the curvature of the lenses: https://www.astrobin.com/v586ll/

This is how I assembled the rig:

1 - the OTA
2 - the 2" filter
3 - an extension bar (for backfocus)
4 - the field flattenet
5 - the camera

Am I doing anything wrong here?
Thanks!
andrea tasselli avatar
andrea tasselli avatar
You should have heeded my (as well as others) advice and get something else. It's all in there, in the review page.

Beside that you should keep a 55mm +/- 0.5 mm back-focus inclusive of camera's flange to sensor back-space. If filter is used between flattener and sensor add 0.6 mm to that number. If this doesn't work return it to FLO.
Tommy Blomqvist avatar
Tommy Blomqvist avatar
André Moleiro:
I'm wondering if I'm doing anything wrong. I recently acquired this field flattener: https://www.firstlightoptics.com/reducersflatteners/ovl-field-flattener.html

It's supposed to work well with my Skywatcher EvoStar ED 72 APO. After imaging it two nights ago though, I can still see that the stars from the border are really affected by the curvature of the lenses: https://www.astrobin.com/v586ll/

This is how I assembled the rig:

1 - the OTA
2 - the 2" filter
3 - an extension bar (for backfocus)
4 - the field flattenet
5 - the camera

Am I doing anything wrong here?
Thanks!


Shouldn't the "extension bar" be between the flattnerer and the camera?
Andy Wray avatar
Andy Wray avatar
I'm assuming it has the standard backfocus distance of 55mm.  Your camera has it's sensor 6.5mm in from it's body, so that would mean you need extension tubes that combined give you 48.5mm between the back element of the field flattener and the camera body (without the 11mm extension that comes attached to it).  So, I agree wiith the previous post that the backfocus extension tubes are between the OVL FF and the camera.  See ZWO image below:

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