About secondary mirrors

About two weeks ago I ordered and replaced my current large secondary "27 percent obstruction". I replaced it with a high quality secondary with a 13 percent obstruction. What a difference !! :-) I could tell the moment I looked at Jupiter. Alot more contrast and a primary that seemed funky is now worth keeping. Why are we using such huge secondarys in scopes that don't need them ? Every name brand scope I have has a secondary that is to large. Most are 22 percent all the way up to 30 percent. Some I know require a larger secondary "ie: Short focal length" but even these can be trimmed down to smaller sizes. Standard sizes are the culprit and I really wonder about the quality of these mass produced secondarys. I'm waiting for a half inch secondary to replace the 1.3 inch secondary "factory" in my 6 inch f/10 reflector. I'm betting it will be a real difference.

I hear ya, but don't carry things too far. In general I think they're oversized for 'full field illumination' for photography and visually to have maximum image consistency across the whole of the apparent field. Also I think once you get down to about 15% you reach a point of diminishing returns in terms of the gains you make.

And if you squeeze it too tight, i.e. start vignetting the light cone, it has the same optical effect as an aperture mask covering the outer edge of the mirror -- which can mask a turned edge, or over/under-correction, which can make even a 'lousy' mirror suddenly perform 'great'!