Why do I get full disk with Binoviewers? I am not complaining by the way but when using my 100mm PST mod (with 5mm standard PST blocking filter) I cannot get full disk no matter what eyepiece I use. This is usually a 15mm plossl which provides 66x magnification and a true field of 0.75 degrees so it is the BF that is vignetting the field. However, when I use my BVs, with a 1.7x GPC, I can get full disk with my 32mm BCP (53x and 0.94 field), my 25mm TV Plossl (68x and 0.73 field) and ev