Kevin, remember that I was going to move the ZWO filter drawer (EFW has same thickness, so if drawer works, so will 2" EFW) so that is is on the OTA side of the Takahashi 1.01x flattener?
Well, here is the result without adjusting a thing (I have the backfocus adjuster in there just in case, but had set the backfocus to match the 18mm of the backfocus adjuster). I am using standard spacers and a PreciseParts that is already on hand to get the 56.2mm backfocus of the flattener
The above is 0 dB gain and 180 seconds, to bring out the dimmer stars with Alioth at center. Plate solved focal length is 458mm.
Alioth registers an ADU of 44K with 0.01 sec exposure, and this is 180 seconds, so equivalent to Alioth with an ADU of about 8 million :-).
With 0.1 second, and Alioth moved to right next to a short edge of the image frame, it looks like this. No aperture vignetting (the two notches) in sight.
An IDAS HEUIB is in the filter drawer.
What this means is that filter drawer location (with some M72 adapters) works fine. And when I change filters, I can now simply refocus when I change filter without having to adjust backfocus, since there is no glass change between the flattener and the sensor.
Because the field is flat enough, I had no problem with ASIAIR's "autofocus."
By the way, this is the same ASI2600 that I used on the Sigma 40 earlier. So, the tilt earlier was not caused by the camera but by the Sigma 40 train.
This is f/4,5, by the way (only a little slower than my Pleiades 68, which measured an f/4.0, instead of the f/3.8 lie.)
Chen
Psst: with all the government agencies (even local government) requiring smart phones to do business with, I finally broke down and switched to the cheapest and smallest iPhone (SE).
