I found out something last night about aperture masks: I setup with the 12.5 reflector, just waiting for mars, but the wind come up cancelling out the nights viewing. But anyhow, while I was out there stuffing about, I decided to muck around with my 3 round holed aperture mask, by blocking up 2 of the 3 holes, knocking back the aperture from 12.5" to 5"
I hopped straight to a medium bright star, & had a bit of a gander. I decided to de-focus for some reason, & low & behold the diffraction rings & airy disc were SOOO much easier to see than usual.
I'll be collimating the scope this way from now on I think?