Night vision monoculars

[25585]

Russell-optics.com/two_inch.html do 60 & 80mm eps. 

[Scooot]

2 hours ago, YKSE said:

Yes, the long eyepiece is used to speed up the scope, i.e. to let the NVD to get larger exit pupil for more lights, therefore brighter image. It's not for increasing TFOV, because the NVD ifself can't get larger TFOV than its less than 1" field stop.

AMaybe we can consider a practical example? a comercial 10"f4.7 and 8"f6, both have fl 1200mm, you'll get 44x with a NVD, so the same image size. If you add 54mm eyepiece to 10", and 81mm to 8", which one will get brighter image?

My understanding is (can be wrong of course) that the 8" will show brighter image, because the exit pupil is 13.5mm in 8", and 11.5mm in 10", that's about 38% more area= 38% brighter image.

Besides, f6 scope is more tolerant to off-axis aberration, and more less coma from the scope will be seen than f4.7 scope, and 8" is much less bulky and costly than 10" too.

What  do you guys think?

BTW, there're some small eyepiece manufactures do these long eyepieces, and it doesn't cost a fortune.

Just trying to get my head around this .

an 11.5mm exit pupil from an eyepiece in a 10” is brighter than 11.5mm in an 8”, so is the extra 2mm of exit pupil from the eyepiece in the 8” enough to overcome the remaining 11.5mm of extra brightness from the larger aperture of the 10”? If that makes sense  

ignore me, I think this is probably rubbish ?

[YKSE]

ust trying to get my head around this .

an 11.5mm exit pupil from an eyepiece in a 10” is brighter than 11.5mm in an 8”, so is the extra 2mm of exit pupil from the eyepiece in the 8” enough to overcome the remaining 11.5mm of extra brightness from the larger aperture of the 10”? If that makes sense  

11.5mm exit pupil is exactly the same brightness in any scopes sizes.

If we look at visual without NVD, larger scopes will always give higher magnifications (i.e. larger image scale) over the smaller ones, as exit pupil is defined as

exit pupil=telescope Aperture/magnification (Check the followed link if you want the details).

As to visual without NVD, a large scopes delivers larger image at the same brighteness as a small one(We're talking about extended objects only, i.e. nebulas, galaxies and faint GC, not the points sources like stars, bright OC and GCs), it is similar to looking at a small picture on a well-litted wall, at 10m distance(like a small scope), you mayhardly see any detail, but moving in to 5m distance (= a scope of twice aperture of the small one), you'll be able to see more details, and there's no brightness change in these two cases, only the image scale.

[GavStar]

So further gear has arrived from Luxembourg and Russia, namely the 3x afocal magnifier and adapters to enable 1.25 filters to be fitted to the front objective lens of the monocular. Here is the monocular 3x mode with filter fitted. I had a quick look from my back garden (lots of LP). It showed m42 very well but not much other nebulosity was shown around Orion with the Ha alpha filter fitter. With the baader 685 filter fitted lots of stars and lovely star field sweeping. However key test is when tnvc televue adapter arrives on Monday and I can connect the monocular up to my scopes and reduce their f ratio to 3.5 by using the tv 55mm eyepiece.

 

[seiko]

this looks fantastic and from an earlier round of questions asking about a larger refractor for some deep sky I'm looking at getting one of these primarily for my FSQ 130. I've got the dedicated 645 reducer and a 1.6 extender allowing the scope to go from F3.5, F5 to F8 with focal lengths of (455mm, 650, 1040mm). Is this scope suited to the NV above?

Also, any chance of some simple pictures of the views that can be derived from a refractor and NV combo?

 

Thanks in advance

[PeterW]

We were using the NV on an adapter to a 55mm Televue plossl, which essentially divides the focal length in two. The advantage is that this doesn’t affect the focus position of the scope as focal rlength divers do. You want to be working <f4 for nebulae. For globs and planetary nebulae you might be able to run with a longer focal ratio (native or Barlow). For big nebulae you might want to go smaller still.

Peter

[GavStar]

Here’s some threads where I discuss observing with the night vision monoculars.

 

[AllanDystrup]

On 02/12/2017 at 09:24, GavStar said:

I only got one aa battery with mine - obviously shortchanged ?

Ahh well, I got ZERO batteries, so it seems they have run out of power now...