C8 primary coating resilience

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michael
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C8 primary coating resilience

Post by michael »

hi,
i just wondering how many years can last for C8 primary mirror coating?

any one can answer it?
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rlow
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Post by rlow »

It all depends on how well you take care and maintain the optics. I have a friend with the orange C8 that is probably about 20 years old and it is still in a very good condition (I help him to maintain the optics occasionally). It still gives a sharp and clear images despite some small permanent spots on the primary mirror as these spots do not noticeably affect the final image viewed.
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Airconvent
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Post by Airconvent »

Some guy did some study previously and discovered the reflectivity increases with time. Standard coatings degrade much more slowly than exotic ones. So while the Starbright and UHTC coatings offer better performance when new, they also degrade faster. He did emphasise that inspite of this, the difference is obvious by measurements but doubt you can see real life difference unless you are looking at a very faint object and trying to resolve it above the threshold.

rich
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rlow
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Post by rlow »

Some guy did some study previously and discovered the reflectivity increases with time.
:roll: Pardon me, but where is your reference source?
Last edited by rlow on Sat Aug 11, 2007 12:07 pm, edited 1 time in total.
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Tachyon
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Post by Tachyon »

Some guy did some study previously and discovered the reflectivity increases with time.
I don't understand. Can explain more?
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weixing
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Post by weixing »

Hi,
Base on the sentence behind:
Standard coatings degrade much more slowly than exotic ones. So while the Starbright and UHTC coatings offer better performance when new, they also degrade faster.
Some guy did some study previously and discovered the reflectivity increases with time.
I think it's quite obvious that this is a typo error... it's should be "decrease" instead of "increase".

Have a nice day.
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ariefm71
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Post by ariefm71 »

I don't think it's a typo, because everybody knows as a fact that reflectivity decreases with time, no need to be discovered. Only this "few guys" discovered that it actually increases over time.

I think this whole thing is a hoax, same as the comments about modern coatings degrade faster. Wait, degrade? i thought coating performance should increase over time?

I'm confused
Last edited by ariefm71 on Sat Aug 11, 2007 1:15 pm, edited 1 time in total.
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Airconvent
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Post by Airconvent »

weixing wrote:Hi,
Base on the sentence behind:
Standard coatings degrade much more slowly than exotic ones. So while the Starbright and UHTC coatings offer better performance when new, they also degrade faster.
Some guy did some study previously and discovered the reflectivity increases with time.
I think it's quite obvious that this is a typo error... it's should be "decrease" instead of "increase".

Have a nice day.
haha weixing..you are right and wrong depending on whether we are talking about the mirror or the corrector plate. I had actually changed the word from "decrease" to "increase" because of this but now realise he is asking about mirrors and not corrector plates..heh
In this respect, it should decrease with time...

:D
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Airconvent
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Post by Airconvent »

rlow wrote:
Some guy did some study previously and discovered the reflectivity increases with time.
:roll: Pardon me, but where is your reference source?
Hi richII

I can't seem to find the link now and my bookmarks do not have it. I think I lost it when my pc surrendered on my some years back.
Else will link it here. This old guy has tens of scopes bought since the late 60s. From what I gathered, his house is a scope museum. He is (or was) in the optics industry so he has equipment for testing his scope's transmission and reflection properties. He took detailed readings of selected SCTs and refractors with standard and new coatings and then redo the measurements 6-10 years later. His conclusion is for exotic coatings (on corrector plates) when new , they far exceed standard coatings but then the degradation is faster, so at the end of 10 years, its performance is similar to standard ones.
By year 12, the standard coatings out performed the exotic ones, only because the degraded slower. But he did indicate at some point the degradation will stop because glass is transparent to a point after all.

Clay sherrod also did some tests on Meade coatings but stopped short of measuring them over a period of time.

richI
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weixing
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Post by weixing »

Hi,
I think this whole thing is a hoax, same as the comments about modern coatings degrade faster. Wait, degrade? i thought coating performance should increase over time?
Why coating performance should increase over time?? Coating will degrade over time, so the coating performance should also decrease over time.
haha weixing..you are right and wrong depending on whether we are talking about the mirror or the corrector plate. I had actually changed the word from "decrease" to "increase" because of this but now realise he is asking about mirrors and not corrector plates..heh
In this respect, it should decrease with time...
You mean corrector plate performance will increase over time?? Hmm... Logic tell me that this should not be true: The coating on lens and corrector plate is basically use to reduce reflectivity and scattering. Therefore increase the transmission (uncoated lens(2 surface) loss about 8%, single layer coating lens(2 surface) loss about 4% and multilayers coating lens(2 surface) loss about 1%). Over the time as the coating degrade, the transmission will decrease.

Anyway, if this is true, why put the coating in the first place... this doesn't make sense.

Have a nice day.
Yang Weixing
:mrgreen: "The universe is composed mainly of hydrogen and ignorance." :mrgreen:
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