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Using a Gen 2+ Monocular as an eyepiece?

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#1 cloud_cover

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Posted 24 January 2014 - 11:51 AM

Hello!
I'm wondering if using a Gen 2+ Monocular such as the Armasight Sirius Gen2 as an eyepiece would be worth the effort?
I know there are dedicated Gen 3 eyepieces out there but as I'm non-US these are not legal for me to obtain. However, the above monocular eyepiece is legal for me
I've read on most web postings that if its not Gen 3 then don't bother but I'm wondering does anyone here have experience? :)
I'm also wondering how to mount it to my scope without dis-assembling the monocular since I'd want to use it... as a monocular as well. Right now I'm thinking afocally using one of those camera adapters to mate it to an eyepiece but of course but again I'm not sure if practically this is even a good idea.
Will appreciate any advice on this subject! :)
Thanks!

#2 cnoct

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Posted 24 January 2014 - 12:50 PM

Gen 2 tubes are quite capable for astronomy purposes, especially those of modern design but even some older tech Gen 2 do fairly well. The Dutch Gen 2 and the Russian Gen 2 and 3 are quite good. I strongly disagree with those statements discouraging the use of anything but Gen 3. If you can see it with Gen 3 then you will see it with Gen 2 and if you can't see it with Gen 2 you won't see it with Gen 3.

The Sirius Gen 2 uses a fairly good glass to glass non-inverting tube but the optical relay inverter and eye piece severely degrades the image produced by the tube. This is one of the few monoculars in which tube performance is determined by the optics. To bad as the tubes (Russian Gen 2) in those units are fairly nice.

Afocal imaging with image intensified eyepieces (monoculars etc...) will significantly reduce image quality and this is regardless of the device or tube technology used. You really want to aim for a "prime" setup i.e. the telescope becoming your primary lens. Plan on having to buy or have an adapter made that will allow you to mate the monocular to the telescope without any optical elements between the input of the image intensifier (photocathode) and telescope.

I use late manufactured Photonis XD-4 Gen 2 tubes, early DEP Gen 2, Late manufacture Harder Gen 2 tubes, early Varo Gen 2 tubes, ITT and L-3 Gen 3 tubes of various vintage. They all work for astronomy purposes, some better than others but they all work better than Gen 1 an nothing.

#3 cloud_cover

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Posted 24 January 2014 - 12:57 PM

Thanks for your reply!
I'm actually thinking of getting the Sirius QSi version (white phosphor)since the difference in price is about $100 and its SNR is a touch higher than "stock" green phosphor tubes.
I figure with the front lens mounted there's no way I can go prime focus unless I want to disassemble it and the waterproofing does seem to be a desirable trait, particularly as its other use will be hiking in the tropical rainforest (yep, you guessed, its rather wet and humid *grin*)
As I have absolutely no experience with NVDs, in this case what do you mean that the Sirius's inverter degrades the picture severely? Would using the same tube in a different body then provide a much better result? :)
Oh, just to clarify: I wasn't thinking about imaging with an IIT - I do have CCDs for that and anyway with young kids I can no longer commit to all-nighters aligning, setting up, focusing, hours of image acquisition, running out of batteries :p so the purpose of my question is solely for visual, to be able to see things I otherwise can't see in my light polluted zone with a 14" as my maximum aperture scope
Thanks!

#4 cnoct

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Posted 27 January 2014 - 09:28 AM

Using any night vision device in an afocal configuration is a recipe for disappointment and poor imaging/viewing, usually very poor when compared with a prime configuration!

The objective assembly on the Sirius can be easily unthreaded/removed so that a telescope barrel adapter can be fitted. The adapter will need to be custom made or you can simply fashion one that gets the job done. The objective end of the Sirius is sealed with an o-ring so that when the objective is installed the unit is water proof.

The Sirius I had was from 2012. It was a Sirius SD (standard definition) with a non-inverting Russian image intensifier w/out manual gain (MG).

From what I understand, the Sirius monoculars were built to accept various type and format image intensifiers (inverting and non-inverting etc...) as well as intensifiers equipped with external gain adjustment circuits (EGAC i.e. manual gain).

Armasight designed the Sirius to accept a wide variety of image intensifiers to better adapt to changes in suppliers, tube formats and tube types.

In general, night vision housings that use inverting tubes have better optical characteristics than those which use non-inverting tubes. Optical inversion, through the use of post tube optics, tends to induce optical noise i.e. distortion. With my particular unit, the tube was fairly good, a bit noisy but pretty good. It was the inverting optical assembly that ruined the image.

Using the tube with better inverting optics (PVS-7 and similar) would have made all the difference, so yes, a different housing would have yielded better views i.e. minimal distortion.

Armasight may no longer be using non-inverting tubes in the Sirius line so the inversion induced distortion may now be a non issue. Inquire with Armasight to find out wether the tubes themselves are inverting.

May I suggest you look at the PVS-7 or a monocular that has a c-mount interface. The PVS-7's perform exceptionally well for astronomy use and there are c-mount adapters available for them or can be custom made for fairly easily. You could place an inquiry on some of the night vision forums asking for suggestions where you could source an ITAR compliant housing suitable for your applications, remember that a housing with a c-mount is optimal for astronomy.

Here's a look inside the unit I had. The inverting optics take up more than half the monoculars length.

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#5 cloud_cover

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Posted 27 January 2014 - 09:52 AM

Thanks for a very detailed reply! :)
I just "spoke" to the rep who said that the Sirius will perform poorly for astronomy applications (sigh!)
Then again, looking at what the other IIT thread is doing with Gen 1 tubes, I'd say its great already, and that's with Gen 1 equipment.
I'll check in if the Sirius is still using an inverting tube
Might end up simply ordering a camera step-up/step down ring to thread to a 1.25" or a 2" adapter. I'm a TOTAL klutz when it comes to making things...






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