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Can you use an Amici Diagonal with Night Vision? Does it need to be Baader BBHS coated?

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#1 ABQJeff

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Posted 18 October 2020 - 04:17 PM

Greetings,

 

I am putting a 120ST with 2" diagonal and manual mount on my Christmas wish list.  This will be for 3 Degree+ wide field viewing/skywalking of big nebula, M31, the Milky Way.    I currently do this in my ED80/SSIV and I use an Amici prism diagonal, which is great because it helps when seeing big star fields and big objects for it to align with my RACI finder and star charts.

 

With the 120ST, I want to go to 2", but still get those big correct image fields with an Amici. This narrows me to Baader choices: one with a 38mm clear aperture ($300) and the other with a 44mm clear aperture with BBHS coating on the reflective edge for $720 (shocked.gif!). The $720 astro grade one, though, would then let me use pretty much all 2" EPs, even TV 55mm (yes may get some very slight vignetting with 46 mm field stop EPs.

 

My question is: my plan is eventually to use NV with my 120ST (especially for when I can't get to a dark sky spot).   Before I drop $720 on an Amici prism diagonal, I want to know if Amici prism diagonals can be used for NV.  Namely, does the Amici prism absorb the deeper IR part of the spectrum (like dielectric coated diagonals don't reflect the deep IR)?  Would the BBHS coated one be truly better at this (like the BBHS coated mirror diagonals do very well for NV), or would a non-BBHS amici work just fine for NV? 

 

I welcome input from anyone using any Amici with NV, because that would answer the core question on the interaction of the prism and >700nm wavelength light.

 

(And related to all this, feel free to comment, since the TV PVS-14 NV system is limited to 40 degrees FOV, does it really make sense to use 2" with NV, or should I just scan around the Veil, NA/Pelican, etc. with 1.25" EPs and NV (still with amici is the plan, so need to know the answer to the main question).  I do this now with my ED80 and 1.25" 40mmx43 deg Plossl and /24x68 deg ES Eps, and it is fun (ie not horrbile).  I just see one side of the Veil or other, or see the Pelican or NA, just not both their entireties at once....and that just forgoes all this expense for 2" EPs, 2" filters, etc. and would gets me $$s for an NV set-up that much sooner).

 

Thank you and CS!

 

ABQJeff


Edited by ABQJeff, 18 October 2020 - 04:19 PM.


#2 jay.i

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Posted 18 October 2020 - 05:04 PM

I can't speak to limitations of various wavelengths based on diagonal coatings, BUT I can say that you'll want to go 2" so you can use 2" eyepieces for afocal observing to get really big exit pupils for narrowband observing. That's certainly a spendy diagonal you're looking at. My Baader BBHS mirror diagonal was $500 which was already tough to swallow, but it's been fantastic. If you buy quality, you almost certainly won't regret it. Hopefully someone can help answer your questions about IR and coatings.


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#3 ABQJeff

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Posted 18 October 2020 - 05:43 PM

I can't speak to limitations of various wavelengths based on diagonal coatings, BUT I can say that you'll want to go 2" so you can use 2" eyepieces for afocal observing to get really big exit pupils for narrowband observing. That's certainly a spendy diagonal you're looking at. My Baader BBHS mirror diagonal was $500 which was already tough to swallow, but it's been fantastic. If you buy quality, you almost certainly won't regret it. Hopefully someone can help answer your questions about IR and coatings.

Thanks Jay, I definitely find taking iphone pics easier with my 20mm+ EPs vs my 6mm EP (harder to line up EP exactly right) probably same effect (ie larger exit pupil that goes into afocal lens system).



#4 ABQJeff

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Posted 18 October 2020 - 08:52 PM

All,

 

Doing research on the Baader site, their BBHS coated prism diagonals state "Prism made of BaK4 with sealed BBHS® coating".  Looking up the Schott specs:  Attached File  SCHOTT-datasheet-N-BAK4.pdf   425.99KB   2 downloads

 

You will see it is 90%+ transmittive from 370nm to 2000nm, so the prism material in the BBHS version is good, also the BBHS coating as has been noted in CN is good from 390 to 2000nm.  So the BBHS Amici Prism is good (better be for $720).

 

I can't find what the standard amici prism (38 mm clear aperture) is made of, but even if less expensive Bak7, all the data I found online shows transmittance to 2000 nm, so that is good as well, but without BBHS coatings not as good as the $720 version (but $420 difference not as good?, for purely low mag use on diffuse objects?, hmmm).

 

I still welcome discussion, but currently I am leaning to the less expensive of the two), and inputs from others who have used amici.  

 

I find this statement curious from Baader on using prism diagonals: "For fast telescopes which are designed for use without a prism, a mirror diagonal is the better choice; the limit for such use is in somewhere around f/6 and f/7, I haven't yet run across this concern with Amici's on CN (it is always just about the clear aperture and roof line).

 

Also from another thread on Amici's: https://www.cloudyni...k-for-high-mag/   from Coopman  "I e-mailed Bob at Alpine Astro and he said that both the $299 and the $719 models are good enough to support at least 200X.  The $719 model is obviously higher quality and would have a higher mag. limit.  He said that he has never had a customer return either type of the amici diagonals for a refund."

 

CS!


Edited by ABQJeff, 19 October 2020 - 08:06 PM.

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#5 jay.i

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Posted 19 October 2020 - 09:37 AM

Prisms refract light and can sometimes/usually exacerbate color error exhibited by fast refractors. They can add color error to otherwise color-free systems like say a Dall-Kirkham Cassegrain (no corrector plate). I prefer my A-P MaxBright and Baader BBHS mirrors and have not noticed enough contrast or color saturation improvement from my Baader/Zeiss T2 prism to prefer the prism for anything. Now of course an Amici prism is another story with the correct image, but you add the roof line consideration at higher magnifications. For lower mags typically used with NV, it shouldn't be an issue, so if you really prefer the correct image, it sounds like you're probably not "losing light" with the aforementioned prisms.


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#6 Jeff Morgan

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Posted 19 October 2020 - 09:48 AM

I have the BBHS mirror diagonal, and those coatings give a nicer (brighter) image with my NV image - as compared to my A-P Maxbright. And I love the ClickLock collar!

 

As to a $700 Amici - well, it's your money. I used to own a 2" Amici used for star hopping. Nice convenience. The roofline was easy to see if you looked for it, easy to forget if you weren't looking for it.

 

For astronomy, mirror reversed is not a big deal. Once I switched from paper atlases to SkySafari (which can mirror-reverse the charts with a tap of the screen) the Amici's star-hopping role vanished entirely. I sold mine, and that was long before getting into NV, so I can not tell you how well the two play together.

 

Where I am going with this is not if it is "better", but rather demand. If you don't like that expensive Amici, it will take a long time (or large discount) to sell it on the used market.


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#7 hoof

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Posted 19 October 2020 - 10:43 AM

I got the $700 acami prism recently but haven’t tried it with NV yet. I do have another 2” acami prism I use for my 80mm F/3.75 finder and that (as well as the stock erect image prism) works great.

Internal reflection is internal reflection, thus should work for any wavelength of light for a NV device. The Baader prisms come with silver coatings to reflect any light that doesn’t get internally reflected (due to incidence angle), so I suspect my Baader prism would be just fine.

I can’t stand mirrored views which is why I own my prisms, and they have made refractors appealing again for me.

That said, for much less money you can get a 6” F/4 astrograph newt, which works awesome for NV and should present NV views superior or equal to most refractors. When I got mu NV device, that was the first thing I bought after filters, and it’s been a great choice for me.
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#8 ABQJeff

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Posted 19 October 2020 - 08:04 PM

All, in another thread I was pointed to this 2" Amici from APM: http://www.apm-teles...nd-coating.html

 

46mm clear aperture (it states), clicklock type EP holder, and only $295 from Stargaze Optics!  So I have my Amici solution in gneral, and since BaK4 or Bak7 is good to 2 microns, I have solved my Amici for NV question as well.

 

Thank you all for the inputs, I will continue to follow the discussion.

 

CS!

 

ABQJeff 


Edited by ABQJeff, 19 October 2020 - 08:05 PM.



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