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C8 Night Vision

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#1 GOLGO13

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Posted 13 October 2019 - 08:48 PM

Tried out my C8 tonight using the Afocal with my TV40 plossl and 9mm Nagler

 

It worked pretty well with the Plossl. It was OK with the Nagler, but maybe a bit high power for the unit. But still was fine.

 

How do I know what focal ratio I was running at?

 

I looked at M13, Cresent nebula, and the Veil. And also panned around the North American area. I felt it did pretty well on M13, and the nebulas looked pretty good considering the full moon was out. I'm thinking from memory the 10 inch dob probably does better, but I would have to check that again.

 

One thing I really appreciate is my grab and go alt/az 6 inch F4. Setting up an EQ mount and the C8 isn't horrible, but it's way more work than my alt/az. And I personally like using alt/az much more. I'd also say for night vision, it seems to be fine in most cases.

 

Yes, I do live on the side of a fairly steep hill. Click on the picture to see it in full screen.

 

C8 nightvision

 

Side note: Is night vision observing affected by using the scope on a deck? Maybe because of the low powers it would be fine. Or the way it works it wouldn't be as affected. I used it once on the deck with the 6 inch F4 and it seems quite good.



#2 TOMDEY

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Posted 13 October 2019 - 09:45 PM

If you're going afocal with the eyepiece feeding the (typically 1x ~26mm Night Vision objective) then Your Focal Ratio that is feeding the GaAs photocathode is:

 

F# = scope F# x (26 / feyep).

 

So, if your C8 operates at F10, then your TV 40mm eyepiece delivers F/6.5 to the photocathode, and the 9mm Nagler delivers a (pathetic) F/29.

 

Generally, Night Vision likes to see a very fast feed. Even F/3 or F/2 are not unreasonable.

 

Tom



#3 Jeff Morgan

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Posted 13 October 2019 - 11:02 PM

Tried out my C8 tonight using the Afocal with my TV40 plossl and 9mm Nagler

 

It worked pretty well with the Plossl. It was OK with the Nagler, but maybe a bit high power for the unit. But still was fine.

 

How do I know what focal ratio I was running at?

 

I looked at M13, Cresent nebula, and the Veil. And also panned around the North American area. I felt it did pretty well on M13, and the nebulas looked pretty good considering the full moon was out. I'm thinking from memory the 10 inch dob probably does better, but I would have to check that again.

 

One thing I really appreciate is my grab and go alt/az 6 inch F4. Setting up an EQ mount and the C8 isn't horrible, but it's way more work than my alt/az. And I personally like using alt/az much more. I'd also say for night vision, it seems to be fine in most cases.

 

Yes, I do live on the side of a fairly steep hill. Click on the picture to see it in full screen.

 

 

 

Side note: Is night vision observing affected by using the scope on a deck? Maybe because of the low powers it would be fine. Or the way it works it wouldn't be as affected. I used it once on the deck with the 6 inch F4 and it seems quite good.

 

I use a simple approximation for speed: NVD Focal Length / Host Eyepiece Focal Length.

 

The NVD focal length is a constant, 27mm. So, 40 Plossl looks like:

 

 

27 / 40 = 0.675 reduction.

 

For your f/10 scope that works out to f/6.75.

 

Not the best for nebula (although still fabulous compared to a standard eyepiece). Use a wider bandpass h-alpha.

 

The C8 should prove very nice on star clusters.

 

The 9 Nagler functions like a 3x barlow:

 

27 / 9 = 3

 

About f/30! But for point sources (stars) not as critical. Nice to get the image scale (222x) on the clusters.

 

The key on the high power side will be finding the point of diminishing returns.



#4 GOLGO13

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Posted 14 October 2019 - 07:26 AM

Wow...still pretty slow focal ratio. However I felt it still did ok. I was really just testing how it did on globular clusters. I have a dioptrix adapter coming for my 24 pan. So that should mostly cover the afocal range.

I don't plan to use the C8 too much for night vision, but it does seem to work ok.

#5 Mazerski

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Posted 14 October 2019 - 09:16 AM

I picked up an f10 8” ACF (Meade) for moon, planets and with night vision for globs, planetary Nebula, galaxies with PVS7 and Mod3. The Antares 0.7x FR works. Used it a few times and the Ring, Dumbbell, M82 (and a few others) and globs look very nice. 
 

I have the Boren-Simon 8” f/2.8 for wide field views. 



#6 bobhen

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Posted 14 October 2019 - 09:29 AM

Don’t give up on the C8. I use a Mewlon 210 at F11.5 and F8 at around 2,500 and 1,700mm FL.

I use the Mewlon for image scale for observing the small stuff: planetary nebulas, globular clusters, etc.

 

The best visual view of M27 (the Dumbell Nebula) I’ve seen in any of my scopes was with my Mewlon/Micro/ 6nm Ha filter working at around F8. This was like a 5 to 10-second video exposure.

 

The best visual view I’ve had of the “core” of the Orion Nebula was with my Mewlon/Micro/6 nm Ha filter working at 1,700 and 2,500 mm FL. The view was better than any other telescope I owned including the unassisted views in my old 15” reflector: folded clouds of nebula easy to see superimposed dark nebula and all very 3-D-like. Better than most photos. Really engaging.

 

There are also some people here that love using their C11s with Night Vision.

 

Bob



#7 GOLGO13

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Posted 14 October 2019 - 09:33 AM

Yes. I'm glad I kept the C8 for these purposes. Plus it's a cool old scope.

#8 Eddgie

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Posted 14 October 2019 - 04:02 PM

Yeah, for unfiltered work (or light red pass like 610nm or 650nm, f/10 is more than fine for almost all types of clusters and doubles, many galaxies, and it is even 'ok-ish" for very bright nebula. Now I don't have an f/10 scope, but I use a Barlow on my 12" f/4.9 frequently for the kinds of targets I mentioned, and the image is more than just "Acceptable".  I can resolve many globulars that were barely detectable in my C14 using conventional eyepieces and the extra magnification helps pull them apart.

 

Nebula generally do better with faster scopes, but even here, sometimes a slower scope with a bigger image scale is better.

 

For example, in my 6" f/2.8, the Eagle Nebula is huge and bright, and with the nebula around it, it almost covers the field.  Ah, but the scale is so small that I cannot resolve the pillars of creation.  In the 12" at f/4.9 though the pillars have enough angular size that I can see them.  Sure, there is more noise, but it is the first time in my 35 years of observing that I ever saw the Pillars of Creation.   

 

At a star party under Bortle 4-5 skies, we used a C8 to look at M82. With no filter under moderately dark skies, even at f/10, M82 showed more detail than I had ever seen in it before I started using NV.  It is better in the 12" (not as noisy) but because it is still pretty bright, the extra scale provides a little nicer level of detail. 

 

The only reason I don't have a C8 for NV use is that mine was a total dew magnet and I am into simplicity these days.  If I had to carry out an extension cord or heavy battery to run a dew strip, I would not use it that much.  


Edited by Eddgie, 14 October 2019 - 04:07 PM.


#9 Gavster

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Posted 14 October 2019 - 04:16 PM

Below is a comment I made a few months ago about how much I like my c11 for night vision - it remains my favourite setup for viewing smaller dsos.

A Celestron C11. This is where afocal NV use can be really beneficial imo over prime. With my C11 I use an AP 0.75 astro physics photo visual reducer to get the scope down to f7.5 and then use a 55mm plossl to get the speed of the overall system down to a very respectable f3.5 (resulting in a fov of 1 degree and a mag of 40x). At f7.5, the 55mm plossl works well. The setup won't deliver the brightness of my f2 epsilon set up, but it gives much more image scale which is critical imo for smaller nebulae such as the Crescent or Wizard and also most galaxies such as M51 (love seeing the spirals in this one) and Leo Triplet (great to see the dark lane in the fainter third galaxy). It is also a great setup for visually spotting supernova (got my first one earlier this year with this exact setup). It mounts nicely on my Panther TTS-160 and I find the whole setup pretty compact for the aperture size and straightforward to setup and use.

#10 slavicek

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Posted 14 October 2019 - 06:09 PM

On your side note:

I do my "grab and go" observing on my deck, with good results, especially if I am the only person on the deck. NV is no different then anything else. I usually mix eyepiece observing (for planets) and NV (for nebulas) at the same night.




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