68 replies to this topic

[gatorengineer]

Well a 6 F4 imaging new, with the ASA reducer gives you roughly the same field at about 4.5x times as much "brightness" F1.4 to F2 is 2x, then the aperature factor, with a 55 plossl as the 67 with the FSQ.  The 1/3 the cost of the 106FSQ and the 1/10 the cost of the 130 also are in play

 

With the image "blurr" from the NV device, I dont see much difference between refractor and reflector.  Agreed without NV the refractor is a much more pleasing view.

[Gavster]

Well a 6 F4 imaging new, with the ASA reducer gives you roughly the same field at about 4.5x times as much "brightness" F1.4 to F2 is 2x, then the aperature factor, with a 55 plossl as the 67 with the FSQ.  The 1/3 the cost of the 106FSQ and the 1/10 the cost of the 130 also are in play

 

With the image "blurr" from the NV device, I dont see much difference between refractor and reflector.  Agreed without NV the refractor is a much more pleasing view.

My understanding is that it’s the f ratio (or exit pupil going into the intensifier) that solely determines the brightness. Allowing for the light transmission losses, the 6 inch f4 becomes more like f4.5. With the 55mm plossl and 0.73x reducer the effective f ratio is f1.6, compared to the f1.9 of the 106mm  f5 fsq, ie about 1.5x brighter, which won’t be that noticeable. My 130 fsq will give broadly the same brightness as the 6 inch newt at similar image scale.

 

Of course the imaging newt is far cheaper than the fsqs  and so I agree is a more appropriate scope for most nv users. But in terms of views given the brightness should be quite similar.

 

In terms of star sharpness a 55mm plossl is going to really struggle at the very fast f ratios of the reduced imaging newt, giving curved lines as you move towards the edge of the fov (that’s from my experience with my Tak 130mm f3.3 Epsilon, as per below).

 

https://www.cloudyni...on-scope/page-2

Also, I use thin filmed gen 3 tubes which I understand from comparisons posted on CN do give noticeably sharper stars than filmless gen 3 tubes (but the filmless have the advantage of greater sensitivity). Therefore I do notice the difference between a refractor and reflector when using night vision in terms of aesthetics and I do like nice sharp stars across the full fov when doing afocal observing. I understand that other people may well have different preferences (eg focusing on centre of fov etc) and hence the significant extra cost of a flatfield refractor for nv is not worthwhile. However, for my personal preferences, I really enjoy nv observing with my Fsqs.

[gatorengineer]

Gav you are forgetting the aperature difference  150 vs 106....  and that F ratio is not linear, 1.4 is 2x as fast as 2.... So over a factor of 4 difference between the two scopes...  that is very visible...

[Gavster]

Gav you are forgetting the aperature difference  150 vs 106....  and that F ratio is not linear, 1.4 is 2x as fast as 2.... So over a factor of 4 difference between the two scopes...  that is very visible...

The aperture difference doesn’t impact on brightness on nebulae and galaxies, it’s only the effective f ratio/exit pupil that is being used that has an impact. See this link for an explanation.

 

https://medium.com/@...ew-24507147d7fc

 

I also explained above that due to light transmission losses the effective f ratio of the reduced newt with a 55mm plossl is around f1.6 rather than f1.4 vs the f1.9 of the fsq (a refractor has minimal light transmission losses in comparison) so only 1.5x difference in effective brightness as f1.6 to f1.9 is half a f stop. 

I’ll leave this discussion there now.

Edited by Gavster, 20 March 2021 - 03:16 AM.

[gatorengineer]

"The aperture difference doesn’t impact on brightness on nebulae and galaxies, it’s only the effective f ratio/exit pupil that is being used that has an impact. See this link for an explanation."

 

The scientific community could sure save alot of money on things like the MMT, and Keck then, and just invest in a couple of astroscans......  My 80mm F3.5 finder and my 36 F3.6 certainly present VERY different views Even when dialed to a comparable exit pupils or magnifications.  Anyone who would like to do a side by side of an FSQ106 and a 6 f4 newt with a reducer are certainly welcome any time.  You have fantastic gear, but using your argument, there is no reason to own an FSQ130 when it wont be any better than an FSQ85, nor own an 18" when it wouldnt be any better than a 4.5" for NV.

 

A refractor looses at every air to glass surface, a Petzval has many of them think (0.95 to 0.97)^8, a newt looses roughly 10-15 percent at its two surfaces (0.85-0.90^2), not a huge difference, when you do the math, certainly nowhere near approaching 150^2/106^2

[Deadlake]

For refractors the absorption is usually less then 1%, here someone has run the numbers and has got around 0.8% for a Petzval. See:

https://www.cloudyni...s/#entry8186946

However for how much the APO cost you could certainly make up the difference with a larger aperture for point objects.

Edited by Deadlake, 20 March 2021 - 10:14 AM.

[Gavster]

To clarify, I use my larger scopes eg my 16 inch dob to observe smaller objects like galaxies, globulars and smaller nebulae. I can get 30x mag at effective f2 giving nice bright views due to the fast effective speed (and sometimes 60x at f4 to give even more image scale but with dimmer views).

For large objects like big nebulae (eg North American, California) I use my smaller refractors to give 7x to 10x magnification and 4-6 degrees field of views still at a fast effective speed of f2 giving similar brightness of views but very different fov.
 

It’s the ability to get varying image scale but with similar fast f ratios that is the reason I have both big and small aperture scopes. My big scopes give very different views to my smaller scopes due to the very different magnifications used (ie different image scales). Using my smaller scopes at higher magnifications eg 30x to 60x with night vision isn’t satisfactory to me as then the effective f ratios are too slow and the views too dim for my liking.

[Deadlake]

Does your 16” give you a lot more scale then then the C11? I would have room at the moment for a C11, so another option, but what would you get a 16” DOB as the next size up?

Edited by Deadlake, 27 March 2021 - 03:27 AM.

[Supernova74]

Admittedly I would love to own a night vision monocular for Amateur Astronomy!? However as the technology is not necessarily a new one I just cannot justify the price tags these devices are perhaps a few years down the line the price will drop hopefully and make it easier accessible to the more working mans pockets!? Just like plasma screen,LCD,LED the market was demanding enough it was the next best thing from sliced bread so obviously more units are manufactured and produced so the prices drop so let’s hope NV follows the trend.as for now the next best thing would be a highly sensitive imaging rig which not every one wants to do.

[Gavster]

Does your 16” give you a lot more scale then then the C11? I would have room at the moment for a C11, so another option, but what would you get a 16” DOB as the next size up?

My c11 edge with 0.7x edge reducer, and 67mm eyepiece afocally I get 30x (so very similar to dob) but at slower effective speed of f2.7 (which is probably more like f3ish due to light transmission losses). This gives similar views to my dob but a bit dimmer, still very nice. When I travel to my astro club meetings it’s usually my c11edge with panther TTS mount that I take. Showing people m42 in this setup blows their socks off In my dob I also like using my 41mm panoptic afocally which gives bigger image scale at 45x but at an effective f3.

[a__l]

Admittedly I would love to own a night vision monocular for Amateur Astronomy!? However as the technology is not necessarily a new one I just cannot justify the price tags these devices are perhaps a few years down the line the price will drop hopefully and make it easier accessible to the more working mans pockets!? Just like plasma screen,LCD,LED the market was demanding enough it was the next best thing from sliced bread so obviously more units are manufactured and produced so the prices drop so let’s hope NV follows the trend.as for now the next best thing would be a highly sensitive imaging rig which not every one wants to do.

Most likely no. The market is limited for civilian products.

[Joko]

Admittedly I would love to own a night vision monocular for Amateur Astronomy!? However as the technology is not necessarily a new one I just cannot justify the price tags these devices are perhaps a few years down the line the price will drop hopefully and make it easier accessible to the more working mans pockets!? Just like plasma screen,LCD,LED the market was demanding enough it was the next best thing from sliced bread so obviously more units are manufactured and produced so the prices drop so let’s hope NV follows the trend.as for now the next best thing would be a highly sensitive imaging rig which not every one wants to do.

Yes it's an old technology, but it keeps improving. GEN3 thinfilm tubes FOM2600 are available since september 2020.

99% of the intensifier tubes are made for the military market. So even if all astronomers in the world use NV, prices won't dropped. Demand is already very high and in the US you often have to wait 3 to 6 months to get a good tube.

Unfortunately, in the coming years, militaries will tend to use less intensifier tubes, and more digital devices (not good for visual observation in astronomy).

As a comparison let's consider cars technology using fuel, it's an old technology, there are more and more cars, but i don't think cars are much less expensive now than 20 or 50 years ago.

 

Last but not least, it's really not expensive if you compare between buying NVD + 12" (for example) or buying a 40" telescope.

Edited by Joko, 27 March 2021 - 05:31 AM.

[Deadlake]

My c11 edge with 0.7x edge reducer, and 67mm eyepiece afocally I get 30x (so very similar to dob) but at slower effective speed of f2.7 (which is probably more like f3ish due to light transmission losses). This gives similar views to my dob but a bit dimmer, still very nice. When I travel to my astro club meetings it’s usually my c11edge with panther TTS mount that I take. Showing people m42 in this setup blows their socks off In my dob I also like using my 41mm panoptic afocally which gives bigger image scale at 45x but at an effective f3.

What would be the difference between the 16” DOB and the C11 under darker skies (like where I live, closer to the Isle of Wight in SQM).

I’d imagine the cost of the C11 and NV is less then a 20” SV and would perform better, exclude the mount for the C11 or adding GoTo to the DOB?

Edited by Deadlake, 27 March 2021 - 05:46 AM.

[Gavster]

What would be the difference between the 16” DOB and the C11 under darker skies (like where I live, closer to the Isle of Wight in SQM).

I’d imagine the cost of the C11 and NV is less then a 20” SV and would perform better, exclude the mount for the C11 or adding GoTo to the DOB?

I only use the dob in the dark skies of the Isle of Wight. So my comments about the relative differences apply - ie views with the dob are noticeably brighter and better but c11 is still very nice.

[a__l]

I liked that I saw Barnard's loop in a Fujinon CF75HA-1 (48mm diameter) in a dark site. I never thought that it could be seen in such a small aperture.

[Gavster]

Yes, very low magnification views of Barnard’s Loop from a dark site with night vision are awesome (as per the attached phone pic)

 

This is a nice article giving three different perspectives of using night vision for astronomy ranging from 1x, through small scopes to large dobs.

 

https://www.cloudyni...spectives-r3028

Attached Thumbnails

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Edited by Gavster, 28 March 2021 - 08:16 AM.

[gatorengineer]

For those here who say aperture doesn't matte rspeed doesn't matter all I can say is watch the video bow from the 10:15 mark and see the comment from AL Naglers whose NV gear was used with the scope in my sig line.. 

 

Planning on being with the scope and my NV gear next weekend in Bedford PA if anyone wants to see first hand if aperture and speed matter.  This scope will be running around f1. 3. With my Russell's. 

[ButterFly]

Aperture works the same way visually and with NV: at the same f/ratio, things are more resolved and bigger with larger aperture, with surface brightness about the same.  Changing the f/ratio with a constant aperture makes things dimmer and bigger with higher f/ratio, with resolution the same.  Changing the f/ratio at constant aperture is exactly what a zoom eyepiece does afocally.

 

As with Gavster, the 80mm refractor is my 15" dob's little buddy.  Each does well what the other can't, both visually and with the NV device afocally.  It's comparing f/4.78 with f/6, so the brightness is about the same.  Things are bigger and more resolved in one, but I can fit a lot more in the other.  Which scope does better depends on what I'm looking for out of the session.

[gatorengineer]

I guess we cant link youtube videos oh well its I drove 4 hours to photograph the milkway, somewhere around 500k views.....  its googleable.

 

ButterFly - what I was trying to say Same focal length Eg. 150/450FL Newt or a 200/600 Newt will give alot brighter view than a 106/530 refractor, and ""roughly"" comparable fields.