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Gold coated Mirror diagonal for NV?

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#1 M44

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Posted 16 January 2022 - 11:20 PM

Vernonscope Gold

 

I am not really looking for purchase these but wondering if anyone uses the gold coated diagonals for NV? Any advantages over Aluminum/Silver coated diagonals?

 

 



#2 chemisted

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Posted 17 January 2022 - 05:31 AM

Vernonscope Gold

 

Any advantages over Aluminum/Silver coated diagonals?

There are none that I can think of.  If they are currently available then that is certainly an advantage over the others that are not.



#3 astrokeith

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Posted 17 January 2022 - 06:08 AM

The gold version will be better in infra-red. So how much infra-red does your NV device use?



#4 chemisted

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Posted 17 January 2022 - 06:21 AM

The gold version will be better in infra-red. So how much infra-red does your NV device use?

Gold is not better than silver in IR wavelengths that our intensifier tubes detect - out to about 900 nm.
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#5 astrokeith

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Posted 17 January 2022 - 07:20 AM

Gold is not better than silver in IR wavelengths that our intensifier tubes detect - out to about 900 nm.

Ah true.

I used to work in the infra-red but it was 3- 14 microns! So I'm biassed!

 

Gold is way better than Aluminium though I think even at 900nm



#6 chemisted

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Posted 17 January 2022 - 07:36 AM

 

Gold is way better than Aluminium though I think even at 900nm

I demonstrated a visible difference between aluminum and silver in the following thread so I suspect gold would show the same advantage.

 

https://www.cloudyni...bular-clusters/

 

The somewhat humorous conclusion of that thread was that a simple prism diagonal was the match to the silver!


Edited by chemisted, 17 January 2022 - 07:37 AM.

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#7 M44

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Posted 17 January 2022 - 11:20 AM

Currently I use Takahashi enhanced Aluminum 2" diagonal for visual and NV. I remember reading the thread about Silver diagonals (nv) but never delved into it.

I do have T2 Zeiss Prism that I use with binoviewer, never tried with NV. 

 

I also hear that Gold will suppress blue wavelengths. Then will that be a disadvantage for NV? 


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#8 Mort H

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Posted 17 January 2022 - 12:08 PM

I use the Baader T2 non-BBHS prism diagonal #2456005 for NV with excellent results.

 

I've had the BBHS (a.k.a. Zeiss) version on order for a long time now, it's been unobtainium for a while.  So in the meantime I went with the non-BBHS version and having used it I'm frankly at a loss to see how the BBHS version could possibly improve the view, it's already that good.  I guess when my BBHS version finally arrives, I'll see for sure.

 

Good news for any reader looking to get a T2 diagonal for NV is I can assure you a mirror diagonal (aluminum, silver, gold, whatever) is not necessary, neither is the BBHS prism, the non-BBHS prism works awesomely well for NV.

 

Prism diagonal will also give you the shortest optical path, which can also be helpful/critical to some.

 

Added:  Stay away from dielectric diagonals, they are not optimal for NV.  They will "sort of" work "OK", but are known to under-perform for globulars especially (which have a lot of red giant stars).


Edited by Mort H, 17 January 2022 - 12:14 PM.

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#9 chemisted

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Posted 17 January 2022 - 12:53 PM

 

I also hear that Gold will suppress blue wavelengths. Then will that be a disadvantage for NV? 

I suppose it depends on how you look at it.  Generation 3 tubes have sensitivity that falls rapidly at wavelengths shorter than 500nm.  You might think that is OK since gold is also weak at those wavelengths.  OTOH, it might be a 'double whammy' for blue stars and I could envision losing some of them with gold that might be retained with other coatings.


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#10 PEterW

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Posted 17 January 2022 - 01:54 PM

Aluminium has a dip in reflectance around 700nm, so pulls it below gold (85-90%) about 80%. (*data from Thorlabs).
You certainly don’t want to use gold if you care about anything<600nm or so. Silver is in the high 90s%. Of course if people are using dielectric layers on top of a metal coating they can pull the reflectance up, so it depends on the specific supplier.

Keith, are you one of those people who thinks in wave numbers ;-)!

Peter
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#11 careysub

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Posted 17 January 2022 - 02:20 PM


I also hear that Gold will suppress blue wavelengths. Then will that be a disadvantage for NV? 

Based on these two charts (below) I would say "a bit". but not very much. Gold reflectivity drops sharply around 550 nm, while Gen III GaAs sensitivity is still going strong. If we adopt the FHW standard as the effective performance limit the IT tube quits at 450 (and at 875) and gold's limit is 500. The Hbeta line is at 486.2, and takes a big hit with gold, but which the IT tube can easily detect. So you do lose something. Blue stars will take a hit too. It is a bad combination to take a sensitivity hit and a reflectivity hit at the same time. You would much rather the reflector perform excellently out to the limit of the sensor.

 

Protected silver is better, you lose very little. It out performs aluminum until 500, and is still strong at 400. It falls off a cliff at 350, but here the IT tube is already done. Gold has only a slight advantage over silver at any point in the IT tube range of operation.

Attached Thumbnails

  • GaAsSpectral.png
  • Image-Metal-reflectance.png

Edited by careysub, 17 January 2022 - 02:26 PM.

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#12 slavicek

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Posted 17 January 2022 - 05:00 PM

Maybe you should call and ask Veronscope about it. The info they provide on their web is identical for both diagonals.



#13 ButterFly

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Posted 17 January 2022 - 05:02 PM

Gold doesn't oxidize.  That's its advantage over silver.  Both gold and silver do better than aluminum in near-IR.  Aluminum has a natural dip around 850.  For what it's worth, the IR observatories around here tend to use aluminum primaries with silvered secondaries.


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#14 M44

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Posted 17 January 2022 - 05:06 PM

Gold doesn't oxidize.  That's its advantage over silver. 

Doesn't matter. Both Silver and Gold diagonals are  coated with protective quartz overcoat. 


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#15 M44

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Posted 17 January 2022 - 05:08 PM

Maybe you should call and ask Veronscope about it. The info they provide on their web is identical for both diagonals.

Vernonscope did not advertise the Gold diagonal for Night Vision. As I said, I am not looking to purchase, wanted to hear other's opinions other than my limited understanding. 



#16 chemisted

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Posted 17 January 2022 - 06:11 PM

Keith, are you one of those people who thinks in wave numbers ;-)!

Peter

Wavenumbers Rule!!  I was raised on wavenumbers.  Who can forget  the C=O stretching frequency of acetone is 1716 cm-1?  And that it is by far the strongest band in the spectrum?  And when acetone is reduced to isopropanol that huge band disappears completely?  Exciting stuff . . .



#17 careysub

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Posted 17 January 2022 - 07:28 PM

Gold doesn't oxidize.  That's its advantage over silver.

That is why I specified "protected silver".

 

Baader Broadband Hardened Silver... overcomes the tarnishing issue through the use of a dielectric overcoat to create a durable protective layer for the silvered mirror.  With this dielectric overcoat the BBHS silver diagonal is purported to have the same life expectancy as high quality protected aluminum when cleaning is performed with the same care and attention recommended for all precision optical surfaces.

 

 

https://www.cloudyni...-diagonal-r3038

 

But the BBHS product is in no way unique. Back in the day of silvered telescope mirrors, before vacuum coating technology, mirrors were re-silvered regularly due to silver tarnish. This would not fly in any commercial optical product today.

All silver mirrors produced today have protecting coatings of some kind.

 

BTW - I notice that Edmund Optics enhanced aluminum coating on its 1/20 wave first surface mirror line takes a reflectivity dive at 700 nm, reaching 60% at 850 nm. It might be a good idea when getting any enhanced aluminum product to confirm its IR curve.

 

https://www.edmundop...-mirrors/15043/


Edited by careysub, 18 January 2022 - 07:02 AM.

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#18 Deadlake

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Posted 20 January 2022 - 12:52 PM

That is why I specified "protected silver".

 

https://www.cloudyni...-diagonal-r3038

 

But the BBHS product is in no way unique. Back in the day of silvered telescope mirrors, before vacuum coating technology, mirrors were re-silvered regularly due to silver tarnish. This would not fly in any commercial optical product today.

All silver mirrors produced today have protecting coatings of some kind.

 

BTW - I notice that Edmund Optics enhanced aluminum coating on its 1/20 wave first surface mirror line takes a reflectivity dive at 700 nm, reaching 60% at 850 nm. It might be a good idea when getting any enhanced aluminum product to confirm its IR curve.

 

https://www.edmundop...-mirrors/15043/

The difference is the BBHS does not attenuated the infra-red spectrum which NV is sensitive too.

I've have a MaxBright Baader mirror and a BBHS mirror and you can see the difference.

With visual makes a difference when observing Jupiter, better reds and surface detail IMHO.



#19 careysub

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Posted 20 January 2022 - 03:19 PM

The difference is the BBHS does not attenuated the infra-red spectrum which NV is sensitive too.

I've have a MaxBright Baader mirror and a BBHS mirror and you can see the difference.

With visual makes a difference when observing Jupiter, better reds and surface detail IMHO.

There is no dispute or confusion about coatings sold as dielectrics (with 99% visual reflectivity) causing IR attenuation.

 

Similarly there is no confusion about protect silver coatings.

 

But there are a variety of enhanced aluminum coatings on offer, not described as dielectrics (though they do use dielectric layers on top of the aluminum), and have lower levels of reflection enhancement (OWL offers 92% and 96% enhanced). Some of these give you a significant  IR reflectivity hit and some don't.

 

My point is that if you get a coating described as "enhanced aluminum" you should confirm the IR spectrum.



#20 Deadlake

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Posted 20 January 2022 - 03:37 PM

There is no dispute or confusion about coatings sold as dielectrics (with 99% visual reflectivity) causing IR attenuation.

 

Similarly there is no confusion about protect silver coatings.

 

But there are a variety of enhanced aluminum coatings on offer, not described as dielectrics (though they do use dielectric layers on top of the aluminum), and have lower levels of reflection enhancement (OWL offers 92% and 96% enhanced). Some of these give you a significant  IR reflectivity hit and some don't.

 

My point is that if you get a coating described as "enhanced aluminum" you should confirm the IR spectrum.

I did ask about APM mirrored diagonal’s and there are no better then the Baader MaxBright as far as IR 

performance. 

The Baader BBHS diagonals have superior performance.

 

Note it’s hard to tell. For example a mirrored scope which has a dielectric coating and made by GSO may or may not have acceptable IR spectrum performance due to the difference processes GSO use. Hard to tell.
 



#21 Joko

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Posted 21 January 2022 - 04:38 AM

I don't have any BBHS for the simple reason that i don't have a refractor telescope yet.

But is there any difference between prism and mirror BBHS ? Which one would be the best for NV ?


Edited by Joko, 21 January 2022 - 04:38 AM.


#22 chemisted

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Posted 21 January 2022 - 05:51 AM

I don't have any BBHS for the simple reason that i don't have a refractor telescope yet.

But is there any difference between prism and mirror BBHS ? Which one would be the best for NV ?

I answered this in post#6 above.


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#23 Deadlake

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Posted 21 January 2022 - 09:02 AM

I don't have any BBHS for the simple reason that i don't have a refractor telescope yet.

But is there any difference between prism and mirror BBHS ? Which one would be the best for NV ?

As far as NV there is no difference between BBHS prism or mirror diagonals, both work well in the IR spectrum. 

The choice is really based on the refractor you have. Baader's guidance is go with a mirror diagonal unless you scope shows some red on a bright star.

In that case the prism might help correct it, i.e. the red shift.

I'd search the refractor forums where this is discussed in length, e.g.:

https://www.cloudyni...e/#entry7334377


Edited by Deadlake, 21 January 2022 - 09:03 AM.

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