Is my field flattener working?

[Darkest_Element]

Hi everyone!

I just used my new telescope for the first time and with that I also used a field flattener for the first time. My new telescope is the Altair 72EDF FPL53 and I have a Sharpstar 2 inch field flattener. As I myself don't know much about these things since I am relatively new I let the nice person that owns the shop choose a flattener for me. I let him know that I am using a DSLR camera with an APS-C sensor, he said that this flattener can be used with my camera without any spacers.
I just took my first photo but still noticed some field curvature in the edges. This photo is also cropped in slightly.
Is this just normal since it can never be perfect (which in that case I am totaly fine with) or am I doing something wrong?
I would love to hear from you all!

~DE

[Star Dad]

To me that looks about right. I get some minor elongation on the far corners of my photos. I finally stopped using my flattener for ordinary images. I now only use it when I use my Barlow as the barlow really accentuates the elongation. Of course, I no longer use my DSLR so maybe that's why I stopped using the flattener. Maybe make some comparison images without the flattener to confirm the flattener is doing what it is supposed to do?

[AstroBee]

As Star Dad says, some comparison shots with and without the flattener will help. Also, don't crop. The extreme edges is what you want to be looking at.

You are correct though, it will never be perfect.