Faster, larger imaging circle and OK performance.
Sunday, 16 August 2020 | C
I have a FLT132, fitted with a Feathertouch focuser and previously owned the FFIV reducer and the FF68 flattener. I sold the FFIV for this one, to obtain a slightly wider FOV and imaging circle. This is an expensive item and is built well, as you would expect. Used on an APS-C sensor, I found the amount of field curvature to be relatively insensitive to adjustment, a few mm either way made little difference (visually and using CCDInspector). I struggled to get a truly flat field however. Something that I could achieve with the FFIV. It is a heavy beast and the Feathertouch focuser is pretty robust. With an aligned camera, I still had some tilt and curvature. Stars in some corners were clearly slightly elongated.
Changing the spacing also rotates the camera, something to watch out for. It is a pain during the process to find the right spacing. (The FFIV did not rotate the camera and had a rotation device too).