I am once again upgrading my 18" f4.3 EAA dob. I had a great deal on a 4" used secondary mirror. My current secondary is a 3.5" with dialectric coating. But after calculations and visual inspection, it is clear that I am not capturing the full image field of the primary with my 3.5". The great deal on the 4" was due to the fact that there is a small chip on the edge about 1/8" wide. I am wondering if that will cause any significant problems imaging? Could I somehow mask it? Anyone know how to make an elliptical mask?
As an unrelated side-note- I also just purchased the Starizona Nexus .73x coma corrector/reducer to make my setup an f3.1. Also got a Pegasus falcon rotator that I haven't put through its paces yet but should allow me to use it as a "de-rotator" to allow me to go much much longer on my live stacking in Sharpcap Pro. I can't wait but don't worry the forecast was already supposed to be cloudy this weekend even before I purchased the secondary so don't blame me for the sky conditions.