I've done quite a bit of investigation on this subject, and it appears that the QE 0.73x reducer is not a very good choice. I have one, and can verify this by experience. Anything over a 1" sensor (ASI183) is a waste. Terrible star elongation in all corners, as well as the bright star vignetting. I've tried +/- up to 4mm of the manufacturer's metal back spec. (72.2mm) in 0.2mm increments. It improves some at closer spacing (even though pattern suggests it is already too close at 72.2). On larger format sensors (ASI294, 2600) there is obvious tilt, also. I have tried loosening the grub screws in collar, aligning and re-tightening carefully. Tilt changes a bit, but never goes away. I am ready to give up on it. I have none of these issues on APS-C and full frame with the 1.01x flattener. Clear nights are sparse here, can't afford to waste them experimenting with this.
My question concerns the other Tak reducer that is supposedly usable on the Baby Q, the CR 0.73 reducer. Has anyone used this with the Baby Q with good results?
I have looked at a few images on Astrobin that were done with the CR, but they are mostly highly cropped. Those that are not, seem to show some star distortion in corners and the bright star vignetting (light-house beam effect).
These Tak reducers are expensive, and I don't want to shell out more big bucks for the CR if it is not foolproof. I can live without wide field, no problem with mosaics, but the theoretic reduced imaging time would be nice.
I'm guessing the problem is with the configuration of the Petzval Baby Q. I have a TSA-120 triplet which I use with the Tak TOA 35 0.7x reducer (also expensive) with none of these issues, round stars in corners out to APS-C (have not tried full frame). I also read that some people use the QE on the FSQ-106, but no plans to get one of these.