Mirror Coatings and Contrast

Hello To Everyone:
Does the reflectivity of the mirror coating affect image contrast in addition to brightness, and how much? It would seem that a more reflective surface will scatter less light and reflect it with less noise. So, I would want the best coatings possible, but the advantage at the eyepiece could be minor or nil. From my experiences with planetary Newtonians, good baffling, good optics, and smaller (good quality) secondaries contribute to good contrast. Right now I have two mirrors at L and L Optical, and I am having both the 6" and the 8" given semi-enhanced coatings, about 93% reflectivity. Both mirrors are f/8's for planetary, and I am looking for ways to squeeze as much performance from them as I can. Some opinions/experiences or research on this question. Some of you have excellent experience building planetary-optimized newts.

You should read more about coatings and then you will be able to make the decision yourself.
There are many articles by the best in the business. One thing that you will discover is that the finest makers of mirrors will not use enhanced coatings on their primary mirrors. They have their reasons and I find them compelling.
The refective difference is not nearly as important as the quality of the surface finish in providing contrast or even brightness.

It's interesting that this topic pops to the top again. My loveley wife just updated our web site and linked a white paper on coatings that I wrote a month ago... I tried to separate the human/operations/policital aspects from what can be objectified and evaluate on those merits alone. I leave it to the reader to draw thier own conclusion.

Check the "information" section at our web site: http://www.wodenoptics.com


-Cary

I'm up at Mt. Hopkins every week testing the VERITAS mirrors. We check for focal length, spot size an reflectivity. I've literally tested more than 200 24"+ mirrors.

We check the reflectivity against a standard freshly coated mirror. The mirrors on the telescope are anodized and the standard mirror is not.

There is very little difference between the tested mirrors and between the standard and the tested mirrors. Even when some of the mirrors come out of the anodizing with a slight visible purplish large spot, there still is very little difference in the reflectivity. We check these mirrors from 260-700nm.

From this I can conclude that there is little difference between mirror coatings as long as the job is of quality nature and not done by some hack.

Darrell