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Equipment Discussions >> Equipment

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Tamiji Homma
Carpal Tunnel
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Reged: 02/24/07

Loc: California, USA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Starman1]
      #6318520 - 01/17/14 12:20 PM

Quote:

Tammy,
Who, currently, is selling silver-coated star diagonals and/or doing silver mirror coating?




Hi Don,

I don't know who is making EMS silver coated mirror for Matsumoto-san in Japan. I am sure it is custom made for him.

Here is one example of the mirror:
http://www.page.sannet.ne.jp/mazmoto/lfmrs.jpg

Tammy


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urassner
sage
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Reged: 07/08/12

Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Starman1]
      #6318569 - 01/17/14 12:44 PM

Vernonscope Quartz diagonal is silver coated.

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BillP
Postmaster
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Reged: 11/26/06

Loc: Vienna, VA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Starman1]
      #6318760 - 01/17/14 02:10 PM

Quote:

Who, currently, is selling silver-coated star diagonals and/or doing silver mirror coating?




Folks who market silver or enhanced silver diagonals are:

Vernonscope
APM
Antares
Denkmeier (with their powerswitch)

And of course to confuse folks GSO markets a "dielectric enhanced silver"


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Starman1
Vendor (EyepiecesEtc.com)
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Reged: 06/24/03

Loc: Los Angeles
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Tamiji Homma]
      #6318939 - 01/17/14 03:28 PM

Quote:

Quote:

Tammy,
Who, currently, is selling silver-coated star diagonals and/or doing silver mirror coating?




Hi Don,

I don't know who is making EMS silver coated mirror for Matsumoto-san in Japan. I am sure it is custom made for him.

Here is one example of the mirror:
http://www.page.sannet.ne.jp/mazmoto/lfmrs.jpg

Tammy



Seeing those mirrors makes me think that using a high-quality secondary mirror (like a 1/30 wave Antares Optical) in a star diagonal might be a very nice thing:
--no edge problems
--no issues with surface accuracy or smoothness
http://www.antaresoptics.com/SecEM.php
http://www.antaresoptics.com/SecAdvantages.html


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BillP
Postmaster
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Reged: 11/26/06

Loc: Vienna, VA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Starman1]
      #6318978 - 01/17/14 03:58 PM

Based on this site, "enhanced" Silver means that dielectric layers are put on top of the Silver. So increases the transmission of the Silver some. But is this now taking something good and ruining it by adding scatter!?

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: BillP]
      #6319000 - 01/17/14 04:07 PM

Quote:

Based on this site, "enhanced" Silver means that dielectric layers are put on top of the Silver. So increases the transmission of the Silver some. But is this now taking something good and ruining it by adding scatter!?



It's more of a protection for the silver than it is to enhance the already >97% reflectivity.
Theoretically, it could enhance scatter. But we all put overcoats on top of the aluminum on our mirrors, and besides, 1 or 2 layers means nothing compared to the 20-45 layers on a dielectric-coated diagonal mirror.


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SteveC
Post Laureate
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Reged: 06/15/06

Loc: Sunshine State & Ocean State
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: BillP]
      #6319744 - 01/18/14 12:57 AM

Bill,

Is there any benefit to owning 2" prism diagonal as opposed to a 1.25"? I'm considering buying prism a diagonal for use with the TEC140, and I'll probably be using Supermonos, XO 5mm, and ball eyepieces most of the time.


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Daniel Mounsey
Vendor (Woodland Hills)
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Reged: 06/12/02

Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Tamiji Homma]
      #6319849 - 01/18/14 04:28 AM Attachment (22 downloads)

Tammy,
I wonder how my Vernonscope Gold would do in the torture test.

Daniel


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StarDust1
super member


Reged: 08/21/12

Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: SteveC]
      #6319908 - 01/18/14 05:53 AM

That's a good question, I wonder the same thing. What would be the reason owning a 2" prism diagonal as opposed to a 1.25", except for the 2" eyepieces

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BillP
Postmaster
*****

Reged: 11/26/06

Loc: Vienna, VA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: SteveC]
      #6320029 - 01/18/14 09:08 AM

Quote:

Bill,

Is there any benefit to owning 2" prism diagonal as opposed to a 1.25"? I'm considering buying prism a diagonal for use with the TEC140, and I'll probably be using Supermonos, XO 5mm, and ball eyepieces most of the time.




Other than convenience of having just one diagonal for all purposes I can't imagine. But when the Moon goes away I will try and see if a wide field low power view has any different characteristics between the mirrors and prisms. Nothing like "looking" to tell


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Sarkikos
Postmaster
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: BillP]
      #6320095 - 01/18/14 09:52 AM

Bill,

I have heard that a 2" diagonal tends to be a better risk because in a 1.25" diagonal there is more of a chance that the image will be degraded by edge errors in the smaller mirror. Of course, this will depend on the quality of the diagonals.

Mike


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Cotts
Just Wondering
*****

Reged: 10/10/05

Loc: Toronto, Ontario
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Sarkikos]
      #6320140 - 01/18/14 10:25 AM

Great thread and kudos for all the 'experimenters' for their hard work!

I take it from reading all this that I should get a prism diagonal for my TEC 8" f/15.5 to replace the Astro-physics Maxbright which I have been using. I assume the new prism diagonal will reduce scatter and not add any false colour thanks to my loooong focal ratio of f/15.5

My primary viewing is double stars, the closer, the better and planets, in season...

Is there a recommended brand of 2" prism diagonal I should get?

Thanks

Dave


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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Daniel Mounsey]
      #6320157 - 01/18/14 10:38 AM Attachment (9 downloads)

Quote:

Tammy,
I wonder how my Vernonscope Gold would do in the torture test.

Daniel



Daniel,
Gold has a very flat transmission in the infrared, where it is the preferred material for high transmission (no overcoating necessary, no corrosion!),
but it chops off most of the blue/violet end of the spectrum, so it really isn't a visual coating. It could have some specialty uses, like H-alpha photography, or searching for red giants in globulars, etc.
But for a normal visual coating, it's the wrong material.

Edited by Starman1 (01/18/14 10:43 AM)


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BillP
Postmaster
*****

Reged: 11/26/06

Loc: Vienna, VA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Sarkikos]
      #6320331 - 01/18/14 11:56 AM

Quote:

Bill,

I have heard that a 2" diagonal tends to be a better risk because in a 1.25" diagonal there is more of a chance that the image will be degraded by edge errors in the smaller mirror. Of course, this will depend on the quality of the diagonals.

Mike




Hi Mike. I have heard this too, and I personally do not understand this logic. I have heard it lots of course...but I feel it is more a marketing thing rather than based in anything discrete. Seems it should matter little on the size of the mirror and find it hard to believe that manufacturers cannot produce smaller mirrors with quality to the edge. And if there is a general problem in the industry with the edge, then seems the solution is to use an oversized mirror, regardless if 1.25" or 2" format. At any rate, at present I take that popularism with a grain of salt.


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Sarkikos
Postmaster
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Reged: 12/18/07

Loc: Suburban Maryland, USA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: BillP]
      #6320429 - 01/18/14 12:41 PM

Well, a 2" format diagonal would by definition be oversized compared to any 1.25".

The preference for a 2" diagonal to avoid possible edge errors in a 1.25" diagonal is similar to the idea that a Newt should have a somewhat over-sized diagonal to avoid image degradation from edge errors. I don't know how valid this idea is, either. Seems that the best way to avoid both problems is to acquire an optically decent product.

Mike


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Full Sun
super member
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Reged: 11/19/06

Loc: Ontario
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Cotts]
      #6320530 - 01/18/14 01:26 PM

I take it from reading all this that I should get a prism diagonal for my TEC 8" f/15.5 to replace the Astro-physics Maxbright which I have been using. I assume the new prism diagonal will reduce scatter and not add any false colour thanks to my loooong focal ratio of f/15.5

My primary viewing is double stars, the closer, the better and planets, in season...

Is there a recommended brand of 2" prism diagonal I should get?

Dave
------------------------------------
__----_----

Yes, get the Zeiss Baader 2in Prism.
You can try mine but then again you would have to bring your baby over to my backyard.
It is superb on my C-14 but I have yet to test it on my refractors.
(I do think the Maxbright has less scatter then some other 'el-premo'mirror diagonals that I have laser tested).
Clears
Jerry

Edited by Full Sun (01/18/14 01:38 PM)


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mayidunk
Don't Ask...
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Reged: 02/17/10

Loc: Betwixt & Between...
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: Full Sun]
      #6320694 - 01/18/14 02:59 PM

Quote:

Quote:

Great thread and kudos for all the 'experimenters' for their hard work!

I take it from reading all this that I should get a prism diagonal for my TEC 8" f/15.5 to replace the Astro-physics Maxbright which I have been using. I assume the new prism diagonal will reduce scatter and not add any false colour thanks to my loooong focal ratio of f/15.5

My primary viewing is double stars, the closer, the better and planets, in season...

Is there a recommended brand of 2" prism diagonal I should get?

Thanks

Dave



Yes, get the Zeiss Baader 2in Prism.
You can try mine but then again you would have to bring your baby over to my backyard.
It is superb on my C-14 but I have yet to test it on my refractors.
(I do think the Maxbright has less scatter then some other 'el-premo'mirror diagonals that I have laser tested).
Clears
Jerry



I've been thinking about getting that 2" Zeiss Baader prism as well, but I just can't wrap my head around the $425 it would cost!

I currently have a Lumicon LumiBrite 2" diagonal. It has a dielectric mirror, and appears to not have issues with scatter, though it may be that it does, and I just don't perceive it. I recently got a Kunming United Optics 102mm f/11 achro that Stellarvue was selling, and thought that it might benefit from having a good, prism diagonal. However, the views through the Lumicon diagonal aren't bad at all. Because of that, I keep thinking that might be wasting my money getting that Baader Zeiss prism diagonal; sort of like trying to make "more gooder" what's already "good enough!"

Would the 2" Baader be better than the 2" Lumicon?

BTW, I'd also like to thank everyone involved with doing this comparo, especially Bill for dong all the dirty work. Your efforts are greatly appreciated! Thanks.

Edited by mayidunk (01/18/14 03:03 PM)


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BillP
Postmaster
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Reged: 11/26/06

Loc: Vienna, VA
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: mayidunk]
      #6320724 - 01/18/14 03:16 PM

Remember everyone that I've just scratched the surface here with the initial report. Have a lot more tests to conduct and of course will be submitting it as an article here. So much more to come. Probably not any more interim results will be posted as time for me to get serious and ferret things out and ensure repeatability of results.

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Starman1
Vendor (EyepiecesEtc.com)
*****

Reged: 06/24/03

Loc: Los Angeles
Re: Mirror, Dielectric, & Prism Performance Comparison new [Re: BillP]
      #6321022 - 01/18/14 06:10 PM

Quote:

Quote:

Bill,

I have heard that a 2" diagonal tends to be a better risk because in a 1.25" diagonal there is more of a chance that the image will be degraded by edge errors in the smaller mirror. Of course, this will depend on the quality of the diagonals.

Mike




Hi Mike. I have heard this too, and I personally do not understand this logic. I have heard it lots of course...but I feel it is more a marketing thing rather than based in anything discrete. Seems it should matter little on the size of the mirror and find it hard to believe that manufacturers cannot produce smaller mirrors with quality to the edge. And if there is a general problem in the industry with the edge, then seems the solution is to use an oversized mirror, regardless if 1.25" or 2" format. At any rate, at present I take that popularism with a grain of salt.



I almost hate to throw this in, but this is from Roland Christen, concerning the edges of the AP MaxBright star diagonal:
http://geogdata.csun.edu/~voltaire/roland/dielectric.html
Also, if you exclude the outer 1mm of the edge of my secondary mirror (it came with an interferogram), the peak-to-valley measurement reduces by over 50%!. The edge is always the issue with secondary mirrors, but it isn't the only problem after mounting. Too much pressure from material behind it, and it can become convex. And, improperly-glued, it can become astigmatic. Both of those issues are worse than the edge of the mirror problem.


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SteveC
Post Laureate
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Reged: 06/15/06

Loc: Sunshine State & Ocean State
Re: Mirror, Dielectric, & Prism Performance Comparison [Re: Starman1]
      #6321131 - 01/18/14 07:19 PM

Can anyone explain how reflectivity and scatter relate?

According to AP, my dielectric Maxbright diagonal has 99% reflectivity, yet it has been implied in this thread that its dielectric coating may cause scatter.

According to TEC, my TEC enhanced aluminum mirrored turret has 97% reflectivity, yet it has been implied in this thread that it may have less scatter.

Edited by SteveC (01/18/14 07:22 PM)


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