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UHTC Coating

Started by NYRose, 06/16/2005 09:13PM
Posted 06/16/2005 09:13PM Opening Post
Would anyone be able to elaborate on the significance of Meade's UHTC coating vs. the standard coating?
As far as I know, in photographic lenses coating help reduce flare and therefore achieve a sharper image in a light rich environment. As far as I can tell this should not be a major issue in sky watching?

Thank you,

MR
Posted 06/16/2005 09:46PM #1
Menahem,
I don't know all that much about coatings per se, but I believe when you are trying to observe light that has been traveling through space for millions of years, EVERYTHING between the front end of your scope and your eye is important.
Linton
Posted 06/16/2005 11:57PM #2
My understading is that you can actually "see" a difference when comparing versions of each type of coating side by side. In general, the smaller the aperture, the more important it is to maximize light transmission. In other words, a 10" SCT without UHTC would still be a great scope, whereas a ETX 105 can use any help it can get.

Rey Cordero
Berkeley, CA
Posted 06/17/2005 03:24AM #3
Would anyone be able to elaborate on the significance of Meade's UHTC coating vs. the standard coating?

Thank you,

MR
-

Hi:

The most common justification I see for buy the UHTC is that it increases resale value....

The coating on an SCT involve both the corrector and the 2 mirrors. Mirrors have the most to gain by improving the coatings, these are coatings that improve the reflectivity. A standard mirror will have something like 90% reflectivity. Two standard mirrors will transmit about 80% of the light (.89*.89). Improved coatings can improve this. 20% loss sounds like a lot but when one considers that an 8 inch scope gathers about 80% more light than a 6 inch scope, it is a small factor in the big picture.

>>>As far as I know, in photographic lenses coating help reduce flare and therefore achieve a sharper image in a light rich environment. As far as I can tell this should not be a major issue in sky watching?
---

Actually flare and internal reflections are a bigger issue in astronomy than in photography. The reason is simple, stars are extremely bright point sources of light surrounded by perfect black. Any flare, internal reflection, or other aberration is immediately apparent. In a photo, what would be relatively major aberrations in telescope are hidden by the surrounding area. Chromatic aberration is also apparent for the same reason. Nothing to hide behind.

Adding to this problem is the high magnifications used in astronomy. This is why there are so few lens in a telescope objective, either 2 or 3, but they are so expensive. Those 8 or 10 pieces of glass in a photo lens are designed to flatten the field and provide zoom functions but in a telescope they would be a serious problem.

In a telescope, the goal is to achieve the theoretical limit of the resolution in the center of the field of view. Good telescopes do this. In a camera lens, the goal is to achieve the best possible resolution across the entire field of view, quite a different problem resulting in different solutions.


Jon