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Night Vision w/ 5nm and 12nm H-a Filters

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#51 shams42

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Posted 11 August 2016 - 06:10 AM

I'm thinking it must because the relatively tall filter housing is vignetting the off axis rays.



#52 cnoct

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Posted 11 August 2016 - 06:24 AM

Yea there's definite falloff, pretty significant actually. There's a bit of falloff with the Astronomik 12nm as well but certainly less noticeable. My old Schüler 9nm also has some pretty significant falloff, about what the 5nm Astrodon exhibits. 

 

Here's a set of images that show the zonal fall off a bit better than the previous ones.

 

Orion%20no%20H-a.jpg

 

Orion%2012nm%20H-a.jpg

 

Orion%205nm%20H-a.jpg


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#53 shams42

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Posted 11 August 2016 - 06:47 AM

From what I saw last night, the nebulas in those images would *completely* disappear as they approach the edge of the field.



#54 cnoct

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Posted 11 August 2016 - 07:03 AM

Exactly!

 

In the last photo, look how much of Barnard's Loop is cut off, all of zone 3 and nearly half of zone 2. 

 

Regardless of the falloff, the Astrodon is my go to H-a filter. Only wish I'd gone a bit narrower and picked up the 3nm. The 5nm is phenomenal though and I hadn't had a chance to compare it with a 3nm until some time after receiving it so I'm good with 5nm.



#55 JimP

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Posted 11 August 2016 - 02:58 PM

Would you say I should expect similar results in terms of views with 3 vs 5 vs 12nm  using a telescope? LOMO 80 F/6  and Tak TSA 120?

Except for imaging are folks not using telescopes?


Edited by JimP, 11 August 2016 - 02:59 PM.


#56 jdbastro

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Posted 11 August 2016 - 05:22 PM

Would you say I should expect similar results in terms of views with 3 vs 5 vs 12nm  using a telescope? LOMO 80 F/6  and Tak TSA 120?

Except for imaging are folks not using telescopes?

You're asking about visual, right?

 

In my experience, with a Tak TSA 120 at f7.5, I would stick with 12nm.  The others will light starve your intensifier too much.   With the f6 scope, you could probably get by with the 5nm, maybe.  3 nm with your scopes is WAY too narrow, in my opinion.



#57 GlennLeDrew

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Posted 11 August 2016 - 06:51 PM

The great diminution of nebulosity at increasing field angle is due to the bandpass shift that occurs over the considerably wide FOV. Even though the incoming light from any one image point arrives parallel, the net angular tilt of the incoming light bundle shifts the spectral window for transmission.

 

To see this in operation, hold a UHC or O-III filter near your eye right now, and see how the scene's tint shifts as the view angle becomes increasingly tilted from perpendicular. I got the same thing when using LP and UHC filters attached to wide angle camera lenses in my film imaging days.

 

Band pass shifting is not restricted to the too-steep light cones of fast optics when the filter is mounted behind the objective. It operates as well when a front-mounted filter is covering a large field angle.


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#58 shams42

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Posted 11 August 2016 - 07:22 PM

I had initially dismissed the bandpass shift idea due to the filter being in front of the objective, but given that the objective is seeing 40 degrees of sky, this makes a lot of sense.

I'm guessing the 3nm filter would do this even more severely.

#59 GlennLeDrew

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Posted 11 August 2016 - 07:43 PM

Yep!



#60 Eddgie

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Posted 12 August 2016 - 09:38 AM

I did a test last night.   Using ENVIS lens, I defocused a bright star and move it to the edge of the field.  As I did, I could clearly see that there was off axis vignetting because I saw the defocused pattern start to show an ever increasing arc occluding it.

 

I would estimate that at the edge of the field, illumination had fallen by about 60% bu the time a bright star hit the edge of the field.  

 

I would say that while much of the lost nebula may be band pass shift, at least some of the loss is due to the fact that most of these very fast lenses vignette badly off axis. 

 

I did not test the PVS-7 Objective but I should have. 

 

Not enough to account for the amount of nebula missing, but a combination of loosing brightness starting within about 5 degrees off axis and some band pass shift together seems to have a pretty meaningful impact. 



#61 shams42

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Posted 12 August 2016 - 12:02 PM

The effect is strange. It feels like you are holding an immensely powerful flashlight, and as you sweep around you light up various structures. It's a compelling illusion.

The 5nm filter cuts stars to the point that navigation becomes a bit difficult, especially with some magnification.

Still, it has a lot more contrast than the 12nm filter. It shows tons of huge faint gas clouds flowing between the brighter nebulae. I bet some of them have never been catalogued.

I'm glad I didn't go with a 3nm filter.

#62 Vondragonnoggin

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Posted 12 August 2016 - 01:23 PM

I rather like my 3nm. I do not find navigation difficult because the nebulae in my low power use are quite obvious. I imagine PN's would be more difficult.

 

There is definitely a contrast boost vs 7nm. I do not have a 5nm.



#63 GlennLeDrew

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Posted 12 August 2016 - 03:22 PM

Ed,

While vignetting will contribute to the fading of the nebulosity, for an estimated field edge illumination of 60% (or even 40%) this will not be so significant. Sky and nebula dim equally, and so for this aspect contrast is unchanged. To appreciate this, see how much of the aperture must be masked for the on-axis nebulosity to fade to near nothing. It will require rather more than 1/2 the area to be blocked.

 

Nope, for such narrow filters at such off-axis angles bandpass detuning is the biggest culprit. Which is supported by the more rapid diminution of the nebulosity than occurs for the sky.

 

Shams,

If you think these NV devices are probing deeply into the H-alpha, check out results from the WHAM (northern) and SHASSA (southern) H-alpha surveys.

 

WHAM:.   http://www.astro.wis...urvey/wham-nss/

 

Scroll down to a list of downloadable image fields (in galactic coordinates.)

 

 

SHASSA:.  http://amundsen.swarthmore.edu/#Images



#64 shams42

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Posted 13 August 2016 - 10:37 AM

Wow, Glen, that's amazing.

 

In the theme of comparing the 5nm to the 12nm filter, I can say this. The 5nm kicks the dog poo out of the 12nm filter at 1x, though the shifting bandpass issue is something that I find very distracting. The 5nm also produces more contrast in my telescope (f/4.5 with a reducer). For example, I can see the Elephant Trunk pretty clearly under a 1st quarter moon with the 5nm filter but cannot detect it with the 12nm filter. Same for the pillars in M16. I haven't tried running the 5nm in the big scope without the reducer yet.

 

In my 50mm f/4 finderscope setup, I find the 5nm filter to be significantly inferior to the 12nm. At 1x, IC 1396 is a huge and very easily visible round patch of nebula. However, the nebula is rather hard to detect in the 50mm finder with the 5nm filter in place. It is there, and can be seen with a little effort, but nowhere near as bright, and certainly no details are visible.

 

(The 50mm finder really rips with an IR pass filter, though. It's mind-boggling.)

 

Of course, this is under a typical suburban sky and significant moonglow. I'm sure it would work better under darker skies / no moon.

 

I'm tempted to conclude that somewhere around f/4 is a sort of switchover point where the 12nm filter becomes more satisfying.

 

I really need to get either a fast camera lens or an afocal magnifier.



#65 PEterW

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Posted 13 August 2016 - 11:41 AM

Elephants trunk.... Is a dark nebula that pokes into a big round bright nebula IC1396 in Cepheus, near the Garnet Star. 1396 is normally a bit harder to see than the North America, but the elephants truck i have "just" found.... Got a mate to have a look and then we compared what/where we thought we had seen it... Agreement.

Cheers

Peter

#66 cnoct

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Posted 13 May 2017 - 06:53 AM


As summer dawns.

Pairing of a 5nm Astrodon H-a filter and a Photonis XP6 (INTENS) image intensifier.


Photonis%20XP6.jpg
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#67 Luis Serrano

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Posted 13 May 2017 - 07:53 AM

Very nice pic!

 

Are "Photonis XP6", "Photonis G4" and "Photonis Intens" the same thing with different name? I'm a little bit confused with their nomenclature.



#68 pwang99

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Posted 13 May 2017 - 08:15 AM

That... doesn't suck.  :-)

 

The dark lane near Sadr is one of my favorite little areas of the summer sky.



#69 shams42

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Posted 13 May 2017 - 09:21 AM

Incredible!

 

And I must amend my previous report. After receiving the 5nm filter, I never reached for the 12nm any more. The 5nm is just... better, and in every way. 

 

In fact, I no longer have the 12nm filter. But the 5nm is not going anywhere. 



#70 cnoct

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Posted 28 December 2018 - 02:15 AM

Unfiltered view followed by AstroDon 5nm H-a filtered view.

 

The striking inversion cloud over the Ka'iwi channel is the reason I initially took the unfiltered photo. The uniqueness of the scene presented a perfect opportunity to capture Eta Carina in H-a and unfiltered. The scene was also captured through a Photonis P45(W) 4G tube, I'll have to dig that one up. The pics should show when logged in, otherwise just visit the CN gallery link.

 

gallery_139776_8407_3167438.jpg

 

gallery_139776_8407_2789725.jpg

 

The H-a capture is a bit saturated for my taste but the dynamic nature of clouds didn't allow for getting the shot just I'd have liked.


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#71 GeezerGazer

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Posted 28 December 2018 - 06:44 AM

cnoct, the unfiltered image is really beautiful, especially with the cloud formation above the water.  Nice work! 

 

This whole thread should be part of the NV pinned intro that is supposedly under construction.  Lots of great information.  



#72 Eddgie

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Posted 28 December 2018 - 09:37 AM

Beautiful pictures both filtered and unfiltered.  Is the P45 bluer than in the L3 tubes, or is that just the way the camera sees it?  

 

Nice to see some posts from you!



#73 cnoct

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Posted 23 February 2019 - 01:42 AM

The Photonis P45(W) tends greater to the blue end than L3's P45(W), really tube dependent as I've had a Photonis P45 that was much closer to B&W than any other P45 tube, including L3.



#74 cnoct

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Posted 23 February 2019 - 01:42 AM

Here's the same scene with a Photonis XP-6 4G tube and astrodon 5nm H-a

 

gallery_139776_8407_1021975.jpg

 

and one of the same region at a different time and without a filter

 

gallery_139776_8407_617129.jpg


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#75 Ptarmigan

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Posted 23 February 2019 - 04:29 PM

I always thought night vision is good for starwatching as it is used in total darkness. It is spectacular. The filters really enhance it greatly. cool.gif waytogo.gif




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