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Broadband Coatings

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18 replies to this topic

#1 Hosea100

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Posted 07 August 2019 - 10:26 AM

I'm interested in buying a used Questar but have 2 questions:

 

1. Can BBs be resurfaced?

 

2. There are scopes for sale that are 40+ years old, thus, how long to BB coatings last?

 

Thanks for any help.



#2 Gregory Gross

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Posted 07 August 2019 - 11:15 AM

Have a look at these two Cloudy Nights threads:

Are Broadband and Zerodur Worth It?

Would you get BB (Broadband) coatings?

You’ll find ample viewpoints on both sides of the question as to the value and longevity of broadband coatings.

#3 Gregory Gross

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Posted 07 August 2019 - 11:16 AM

And by the way, welcome to the Questar forum on Cloudy Nights! I see that the above is your first posting.
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#4 Terra Nova

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Posted 07 August 2019 - 02:20 PM

The broadband coatings on my 34 year old Q-Standard are holding up beautifully. They still look new.


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#5 Mike Allen

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Posted 07 August 2019 - 03:10 PM

The advice Questar gave me when buying a new instrument was not to purchase broadband coatings if I lived near the ocean.  If I were to purchase a used Q that spent all or most of its life near the ocean, I would exercise extra caution if it had broadband coatings.  On the other hand, broadband coatings can last a long time if properly cared for.  I can also testify from my own experience that broadband coatings do improve the visual experience.  As far as re-coating broadband, I would call Questar in New Hope to get accurate information.


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#6 Hosea100

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Posted 07 August 2019 - 10:40 PM

Mr. Gross,

Thanks for the info.



#7 ehallspqr

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Posted 13 August 2019 - 12:37 AM

I have both a standard coating and a BB Questar. I can definitely see a difference in brightness and contrast between the two. My BB Questar is from 1993 and spent most of it’s life in a dry climate. I echo the advice from Mike Allen about salt air and or improper storage degrading Broad band coatings much faster than the standard coatings. I’ve heard enough stories about badly degraded BB coatings on much newer scopes to know that there’s probably something to those stories. That said my last full service at Questar in 2018 they examined the coatings at my request and said they were still well within serviceable condition. That’s 26 years and still 90% intact. Unfortunately BB coatings are hard to recoat onto the optics so Questar merely replaces them at a steep price. There are people on this forum that have mentioned you can get recoating done by 3rd party companies for a much cheaper price.

 

Personally I would want BB on any Questar I would consider buying. At only 90mm the little Questar needs all the help it can receive from the advanced BB coatings. You just need to exercise more caution when evaluating a prospective example to make sure the optical coatings are up to snuff. Pay special attention to the outer edges on the primary mirror. Any degradation will usually manifest itself there first.


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#8 GR1973

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Posted 13 August 2019 - 05:51 AM

I was in your situation many years ago. I changed my order from standard to BB. C7 and many senior members recommended changing to BB

I did not regret. It was a good decision.

Do not buy BB if you live near the shore or in a place relative humidity above 85% most of the days in the year (Amazon, Hawaii...eg)

Other than these, BB is the best choice

With a desiccant canister in your Q case

your coating will be fine for many years


Regards
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#9 JonTeets

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Posted 13 August 2019 - 09:05 AM

I like the BB coatings.  They help a bit with dimmer objects.  

 

On nights with good seeing, though, I find that my scope standard coating throws up a sharper image.   There's a bit more detail on the moon and planets.


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#10 Pragmatist

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Posted 14 August 2019 - 01:52 PM

I’ve not had the chance to compare but I absolutely love my little BB Questar. I’m about 7 miles from the coast so have not really felt the need to worry. 



#11 BillHarris

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Posted 16 August 2019 - 11:38 PM

My '80's-vintage Questar has BB coatings in excellent condition, and to ensure that they last longer, I've started using a dessicant eyepiece cap. I don't know if it will do anything, but it can't hurt to keep the inside as dry as possible.
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#12 Hosea100

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Posted 17 August 2019 - 10:57 AM

You all have been very helpful. CN is definitely the place for advice.

 

Hope all your nights are good seeing.

 

Oscar


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#13 W9tr

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Posted 30 September 2019 - 11:11 AM

I bought a Questar 3.5" BB several  years ago from a lady in Miineapolis whose husband had died. I did a star test and  cursory inspection of the optics with a normal flashlight and everything looked good. Later I used a bright blue LED flashlight and could see the BB coating on the primary had deteriorated. Turns out from looking at some documentation that came with the scope that they llived in Florida for many years. So caveat emptor wrt BB coatings. If you can't inspect them in person and know how to do it correctly, I'd stay away from BB coatings. 

 

I subsequently dropped the scope and sent it back to Questar this Spring for refurbishment. I now have a like-new instrument with BB coatings.  It cost more to refurbish than the price I paid for it used. The sunk cost of the original purchase is a distant memory, and I intend to keep the scope, so I think the outcome is acceptable. I haven't had a chance to use the scope yet, so I'm really looking forward to that. 

Tom


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#14 hieronymus

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Posted 22 November 2019 - 08:34 PM

Tom, if you could please elaborate on the correct method of inspecting the BB coatings. Is it essential to use a blue LED?

Thanks,

Joe



#15 Optics Patent

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Posted 23 November 2019 - 01:55 PM

Every coating flaw I’ve ever seen is revealed by a bright LED flashlight. 
 

Which also tends to make good coatings and clean surfaces look bad. 


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#16 Darkskyaz

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Posted 23 November 2019 - 11:18 PM

I recently purchased a 50 year old Questar with BB coatings. Subsequently I sent it to Questar for refurbishing, which is the first time this telescope had been to the mother ship. I was told that the coatings were in good shape, and should last many more years. I was also told that unless you are literally right on the ocean, there would be no problem with BB coatings from living in Florida. 


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#17 eyekazoo

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Posted 25 November 2019 - 11:58 AM

I like the BB coatings.  They help a bit with dimmer objects.  

 

On nights with good seeing, though, I find that my scope standard coating throws up a sharper image.   There's a bit more detail on the moon and planets.

I find this very interesting. Elsewhere there are reports of more scatter with enhanced multilayer coatings (comparison of various star diagonals) https://www.cloudyni...omparison-r2877

 

Anyone else have have direct experience like Jon’s?



#18 Loren Gibson

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Posted 25 November 2019 - 01:07 PM

I can't give you any answers based on my own experience. That said, for coatings on lenses, Brandon is said to have tested multilayer coatings on their eyepieces and rejected changing production from magnesium fluoride coatings. I've seen it stated that "narrow angle scatter" is the trade-off when you move from magnesium fluoride to multilayer coatings (in exchange for the greater transmission). I'm reciting this from memory; I don't have a link handy at the moment.

 

For the quartz substrate primary mirrors, Questar is said (e.g., description on Astronomics web site for the Classic Titanium Seven with broadband coatings) to use magnesium fluoride on the corrector rather than the higher-transmission broadband, but the reason stated is that "mag fluoride coatings are optimally matched to the reflectivity response of the quartz/silver/thorium-coated mirrors." I'm not sure why that reason would not also apply to non-quartz substrates.

 

For whatever that is worth.

 

Loren


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#19 Darkskyaz

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Posted 13 December 2019 - 11:01 PM

I can't give you any answers based on my own experience. That said, for coatings on lenses, Brandon is said to have tested multilayer coatings on their eyepieces and rejected changing production from magnesium fluoride coatings. I've seen it stated that "narrow angle scatter" is the trade-off when you move from magnesium fluoride to multilayer coatings (in exchange for the greater transmission). I'm reciting this from memory; I don't have a link handy at the moment.

 

For whatever that is worth.

 

Loren

Interesting point on the potential extra scatter with BB coatings. That might explain why I don’t see as black of a background when I’m looking at the Moon or Sun with my Questar as I see with my 5” Orion Mak. 




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