Also let's say the astrophotographer on astrobin was doing something wrong. What could that possibly be given the image that you see? His guiding and focus must be good since the stars in the center are sharp.
Could he have gotten his spacing wrong? I find that also really hard to believe. For one thing the reducer used comes ready for a 55mm backfocus which is perfect for the Nikon camera used and a T-ring. So I don't think its easy to get the back focus wrong unless he added something to the optical train.
To be frank, I really don't think you should be making negative comments on one persons ability to produce,or not produce an image with a perfectly flat field, one that meets your criteria of how flat you think it should be. I would suggest that until you try and accomplish this very difficult, and possibly very expensive aspect of astro-imaging first, that you keep your comments in the realm of your own very limited to non-existent experience. Most of us here are not interested in what you think is the way that things should be, but more interested in learning how they actually are, and how to best deal with the shortcomings of non-professional astrophotography processes and it's equipment.
If you feel that the equipment (equipment that you never have used) is below your own lower limit of acceptability, then I suggest that you fork out the cash for the higher quality options as many of us have already done. No need to bash a company who has a lot of dedicated customers who appearently are very happy with their particular purchases. Maybe you should use your lack of knowledge and experience to design and build your own line up of telescopes, one with unparalleled quality, so that the rest of us can enjoy perfect optical quality at a very reasonable price.
Finally, get in the game or stop the negativity. We don't need a sideline "know it all" telling us how it should be. We are working and producing actual images in a world of reality.
Edited by PirateMike, 12 July 2019 - 12:15 PM.