Yep that’s ngc6744. If you ever have an unknown fov / object you can upload it to nova.astronomy.com and it will auto platesolves it for you. I just did it with you image and the results are attached.
Regarding the mask- that looks like the refraction pattern you get from a tri-bahtinov mask. It’s used for focus AND collimation. I’ve never used one so can’t really give much advice on how to use it but I understand that it needs to be aligned with the collimation screws and everything is made symmetrical (both the groups of 3 spikes by adjusting focus and also the individual spikes by turning the collimation screws). I think…
