IPB

Welcome Guest ( Log In | Register )

 
Reply to this topicStart new topic
> Advice on Coatings
ghonis
post Jan 2 2008, 08:54 PM
Post #1


Interstellar Medium
*

Group: Members
Posts: 2
Joined: 2-January 08
Member No.: 721



Paul,

I need to have my Starmaster's 20" mirror recoated and appreciate any advice. My mirror was made in November 1999 by Pegasus. I have used it almost continously since then for observing and imaging and it has traveled with me to star parties across the country. It has seen a lot of use in all types of conditions and has served me well for both visual use and astro-imaging. I'm pretty sure that Pegasus was sending mirrors out to Spectrum in 1999 for coating. I cleaned the mirror about once a year on average using only distilled water. I can now see through the coatings of the mirror but am pleased that the coatings lasted as long as they did, considering how much the scope has beeen used in the field.

Spectrum now has three options for coatings:

(PAL) Protected Aluminum w/quartz(SiO2)overcoat...91.6% reflectivity
(EAL) Regular Enhanced Aluminum overcoat............96.9% reflectivity
(MAX) - "REAL"..................................................98.8% reflectivity

The Starmaster web site now offering Zambuto mirrors says this:

"Primary mirror coatings utilize Ion-Assisted Deposition (IAD) and quartz overcoat. This provides higher reflectivity than the "standard" 89% sputtered coatings. Using a single IAD metallic layer also eliminates the tendency of multilayer "enhanced" metallic coatings to roughen the mirror surface thereby degrading the image. We believe that the fidelity of the optical images are better preserved with this process, with the additional assurance that the optical coatings will outlast "run of the mill" SiO-overcoated (monoxide, not the superior quartz) sputtered coatings. Downsized secondary mirror provides superb full aperture planetary views & high contrast deep sky images. 96-97% enhanced coatings are standard."

The Obsession telescope website offering OMI and Galaxy mirrors says this:

"Primary mirror coatings are 96% enhanced aluminum which are more durable and more reflective than standard 88% aluminum. Secondary mirrors are 1/10 wave or better and coated with super enhanced 98% Brilliant-Diamond. This premium multi-dielectric aluminum coating has 98% reflectivity at 550 nm. These highly reflective coatings are standard on both mirrors at no extra charge. No one else offers this level of performance. Compared to scopes with plain aluminum, it's ike getting an extra two inches of aperture for free! Faint galaxies and nebulae are brighter and easier to see. When it comes to deep sky observing, there is nothing better."

On the observing field I have observed through large Obsession scopes with the enhanced aluminum (96%) coatings and have not noticed "degraded images". My preference would be to have my primary re-coated for the highest reflectivity.

My questions:

Has Spectrum been coating large primaries with EAL and MAX coatings with good results?

Is the concern on Starmaster's web site about "the tendency of multilayer "enhanced" metallic coatings to roughen the mirror surface thereby degrading the image" valid?

If the primary is EAL or MAX coated, is the needed stripping process for eventual recoating harmful to the figure of the mirror?

Are EAL or MAX coatings expected to have a longer life than the standard PAL coatings?

The coatings on my secondary appear to be in good shape. Is sending the secondary off for recoating at the same time as the primary recommended?

Thanks for any help with these questions.

Gary Honis
http://ghonis2.ho8.com/
Go to the top of the page
 
+Quote Post
Spectrum
post Jan 4 2008, 03:28 PM
Post #2


Interstellar Medium
*

Group: Members
Posts: 4
Joined: 4-January 08
Member No.: 726



My Questions:
Thanks for any help with these questions.

Gary Honis
http://ghonis2.ho8.com/
[/quote]





Hello Gary,

I deleted most of your info relative to your question to save some space is this reply. I labeled your questions below for clarity concerning my answers.





Answers:

1. --- Has Spectrum been coating large primaries with EAL and MAX coatings with good results?


Answer Question 1. Yes, I have been coating large primary mirrors for Pegasus, Swayze, R.C. Optical Systems and other companies as well as countless individuals seeking to restore their optics. I have coated these mirrors with my regular enhance (EAL) and my MaxR coatings. I have received no negative feedback whatsoever. Only positive.

2. --- Is the concern on Starmaster's web site about "the tendency of multilayer "enhanced" metallic coatings to roughen the mirror surface thereby degrading the image" valid?


Answer Question 2. Starmaster's concerns could certainly be valid in some cases. However, with the advent of superior coating vapor deposition techniques, mainly Ion Assisted Deposition (IAD), which is the technique that I use, IAD greatly reduces any surface quality problems that may be associated with out dated processes. (See my Animated 3D video explaining my process at www.spectrum-coatings.com. Also, with re-designed layer thicknesses and layer sequences, these EAL films are optimized for reflection verses layer thickness, thereby reducing light scatter and surface "roughness" to a level that becomes a none issue. Incidentally, "sputtering" is a process that is not used for coating astronomical mirrors. It is another type of process entirely. Sputtering is use primarily in semi-conductors and micro-electronics, rarely if ever used in optical thim films. Someone has gotten their terms mixed up.

3. ---If the primary is EAL or MAX coated, is the needed stripping process for eventual recoating harmful to the figure of the mirror?


Answer Question 3. No, no problem whatsoever. ALL of my coatings have the standard layer of aluminum UNDERNEATH ANY subsequent over coats (meaning the oxide layers that protect the aluminum as well as boost the reflection that are applied on top of the aluminum). I use no adhesion layers in my process. That being said, the mirrors are stripped in the exact, and I do mean exact way that any other aluminized mirror is stripped - no difference. The mirrors are submerged in the etch and the etch penetrates the overcoat until it reaches the metal (in this case aluminum) and form there, once the aluminum is attacked, the rest of the "system" (the oxide overcoats) just lift off and float away, nothing more for the oxides to adhere to.


4. ---Are EAL or MAX coatings expected to have a longer life than the standard PAL coatings?

Answer Question 4.
Maybe, only time will tell. What is sure is that the life is no shorter; none have failed as of today. Please note that occasionally there can be process anomalies that can occur that may cause a coating to fail. The possibility is equal in reference to any of my types coatings.

5. ---The coatings on my secondary appear to be in good shape. Is sending the secondary off for recoating at the same time as the primary recommended?

Answer Question 5.
Even though I do not charge for recoating the secondary mirror (3.1"ma and below), I always say, if isn't broke, why fit it? The way I look at it is every time you handle anything that is fragile, the probability of damage increases. If the mirror, primary or secondary, looks clean, uniform and shiny, with no coating degradations while sitting on your kitchen table in normal light, the chances are that the coating is still performing well.
Go to the top of the page
 
+Quote Post
ghonis
post Jan 4 2008, 05:17 PM
Post #3


Interstellar Medium
*

Group: Members
Posts: 2
Joined: 2-January 08
Member No.: 721



Hi Paul,

Thanks for your detailed answers to my questions.

I will be sending my 20" mirror to you for the MaxR coatings. I found the original box that you used to send the mirror to me (Ref# 20GH991114-90.2) when it was first coated. The box has cardboard spacers for on top and bottom of the mirror, along with cardboard strips around the edge of the mirror.

A few more questions:

1. Would it be okay to reuse the original box or would the foam boxed method as explained on your website be safer?

2. The original box also has the white felt material/masking tape cover that was over the mirror. Should I reuse that when sending it to you?

3. I'd like to have the secondary MaxR coated as well but I noticed on your web site that most of your secondaries are Regular EAL coated. Could my secondary be MaxR coated? I noticed in the original papers with my Starmaster telescope that the 3.5" secondary was "99% enhanced". Do you know if that means it has MaxR coatings? Maybe this is some other type of coating at the time (February 99) that would be hard to remove?

4. Should I clean the primary mirror before sending it to you?

Thanks again,

Gary Honis



Go to the top of the page
 
+Quote Post
Spectrum
post Jan 4 2008, 05:57 PM
Post #4


Interstellar Medium
*

Group: Members
Posts: 4
Joined: 4-January 08
Member No.: 726



Hello again, Gary. Please find the answers to your questions below found in blue. Thank you! Paul

QUOTE(ghonis @ Jan 4 2008, 06:17 PM) *
Hi Paul,

Thanks for your detailed answers to my questions.

I will be sending my 20" mirror to you for the MaxR coatings. I found the original box that you used to send the mirror to me (Ref# 20GH991114-90.2) when it was first coated. The box has cardboard spacers for on top and bottom of the mirror, along with cardboard strips around the edge of the mirror.

A few more questions:

1. Would it be okay to reuse the original box or would the foam boxed method as explained on your website be safer?

If the original box looks like it will hold up it should be fine.

2. The original box also has the white felt material/masking tape cover that was over the mirror. Should I reuse that when sending it to you?

Yes, you can reuse that wrap.

3. I'd like to have the secondary MaxR coated as well but I noticed on your web site that most of your secondaries are Regular EAL coated. Could my secondary be MaxR coated? I cannot coat the secondary mirror with the MaxR due to the way I hold the secondary mirrors. The process is somewhat longer and the possibility of falling is increased. I noticed in the original papers with my Starmaster telescope that the 3.5" secondary was "99% enhanced". Do you know if that means it has MaxR coatings? Maybe this is some other type of coating at the time (February 99) that would be hard to remove?

If it is a pure dielectric coating (having no metallic layer) than it cannot be removed. It must be polished off. It the flatness is good, it can be overcoated. Please not that what ever surface defects may be present in the old coating, they will still be there after the new coating is applied.

4. Should I clean the primary mirror before sending it to you?

No need to clean it, but be careful there is no sand or any abrasive that may cause the glass surface to be damaged during shipping.

Thanks again,

Gary Honis
Go to the top of the page
 
+Quote Post

Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



Lo-Fi Version Time is now: 21st September 2019 - 03:41 AM