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Live videos of night vision observing


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Posted (edited)

On YouTube there are several videos of observing with night vision monoculars. They are fun to watch and give a “feel” of what night vision astronomy is about. However, generally I feel the videos do not show how nice the actual live views are and have a lot of scintillation in them. I have posted quite a few still phone images of the view through my night vision monoculars but have so far struggled to get my phone to produce decent videos of the live views.

However, after watching a few more night vision videos this week, I decided to have another attempt using the nightcap camera app. This app enabled me to adjust the frame rate and iso used for the video recording. By reducing the frame rate to 1 per second and reducing the iso to a relatively low 650, I’ve managed to produce some videos that, although not as good as the live views, do give a reasonable feel of the live nv experience. These were done using my 92mm refractor, 67mm eyepiece and pvs-14 nv monoculars giving around 10x magnification. The first video is a mini tour through Cygnus ie North America, gamma cygni, crescent and nebula containing the elephant’s trunk. The second is a tour through Sagittarius Witt the lagoon, Trifid, swan and eagle nebulae.

I want to stick just with my phone rather than get a specialist astro camera, but hopefully I will be able to gradually improve the results. It was a lot of fun producing these!

 

 

 

Edited by GavStar
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Agreed, very interesting to get a feel for the experience. The mount sound adds a lot to the 'live-ness'. Given you've set the exposure to 1s, it made me wonder what the kind of non-NV based EEVA stuff I do would look like at 1s exposures for these objects. There is a qualitative difference between the kind of image produced in this way and those from an astro camera without NV -- different kind of noise for one thing, and a different nebula vs star balance, the latter much tighter in NV it seems. Please do post more of these when you can.

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53 minutes ago, Martin Meredith said:

Agreed, very interesting to get a feel for the experience. The mount sound adds a lot to the 'live-ness'. Given you've set the exposure to 1s, it made me wonder what the kind of non-NV based EEVA stuff I do would look like at 1s exposures for these objects. There is a qualitative difference between the kind of image produced in this way and those from an astro camera without NV -- different kind of noise for one thing, and a different nebula vs star balance, the latter much tighter in NV it seems. Please do post more of these when you can.

Thanks Martin. Please could you expand a bit more on nv having a much tighter nebula vs star balance?

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Sorry, I meant two related but different things but didn't express it too well:

(1) The nebulae seem to stand out more than the stars compared to "non-NV with a camera" ie better nebula contrast

(2) The stars themselves seem tighter than "non-NV with a camera"

Both of these could be down to seeing conditions, equipment/tracking etc, but those are my first impressions comparing to what I typically get with EEVA. I haven't got any 1s shots of these objects handy for a proper comparison but I'm inspired to collect some.

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Fascinating. Thank you for taking the trouble to find a way to at least give a feel for the night vision experience. I look forward to seeing other examples, please.

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The nebulae standout as @GavStar is using a very narrow hydrogen alpha filter that nukes the stars (and light pollution) and only shows the nebulosity. If you add a longpass filter you end up with a sky full of stars and no nebulae. bright star will “bloom” slightly and the resolution is limited by the microchannel plate, but like camera pixels… so depends on what camera you are using as to how the stars look.
Gavs mount is actually quite quiet, not like the old Meade “coffee grinders” of old. Getting good footage that gives a faithful view of what you can see with your eye is a challenge. The view is real-time with no integration, just that phone camera need a little longer to give a representative view.

Peter

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Posted (edited)

As Peter says I was using a very narrow 3nm ha filter to maximise the contrast of the nebulae and make it bright through the eyepiece. Nebulae are much trickier to capture as a video than globs/galaxies etc since the narrow ha filter results in more scintillation and light starvation which is a challenging situation for the iPhone camera. I have done 30fps videos of globs and brighter galaxies with night vision reasonably easily from very light polluted sites, as per below (the phone camera exaggerates the scintillation- in practice the gain can be adjusted on the nv monocular to effectively remove the scintillation visible)

 

Edited by GavStar
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Nice demonstration. NV is clearly a great way to observe. The last nebula of the first video was very confusing as it looked looked like the Owl Nebula with its two eyes, but was clearly way too big! I get it now though. 

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Excellent pictures as usual @GavStar. Buried in EEVA I didn’t see them till today. Obviously some discussion before I joined but why not post in DSO section where more accessible? The intensifier is just like an eye piece in use, i.e. it walks talks and quacks like one. Putting NV in EEVA is a classification similar to making all pics taken with an OIII filter in a separate section, it’s just another tool for visual observation. NV is different to EEVA as not stacking taking place.

Rant over.

@GavStar Where did you observe, London?

How so you feel the viewing would be using your FSQ-85 versus the AP stowaway I guess you used here?

Do you feel the slower speed of the AP was lead to more frequency shift in the image?

All the best

Martin


 

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Posted (edited)
1 hour ago, Deadlake said:

Excellent pictures as usual @GavStar. Buried in EEVA I didn’t see them till today. Obviously some discussion before I joined but why not post in DSO section where more accessible? The intensifier is just like an eye piece in use, i.e. it walks talks and quacks like one. Putting NV in EEVA is a classification similar to making all pics taken with an OIII filter in a separate section, it’s just another tool for visual observation. NV is different to EEVA as not stacking taking place.

Rant over.

@GavStar Where did you observe, London?

How so you feel the viewing would be using your FSQ-85 versus the AP stowaway I guess you used here?

Do you feel the slower speed of the AP was lead to more frequency shift in the image?

All the best

Martin


 

Martin, 

I guess you haven’t read this (pretty long!) thread? I think it answers your question about why I posted these nv videos in this section 😀. Basically sgl does not allow nv posts in the observing section even if it is properly signposted. Any nv posts in the observing sections are moved to eeva by the mods.

The first videos were from pretty dark skies in Isle of Wight, and the second set in the subsequent post were from London.

With the 67mm eyepiece the stowaway is operating at f2.6 so pretty fast and it does give very nice views with pretty minimal fc. My Baader 95mm didn’t work with nv as well for reasons I’m not sure about hence I decided to sell it and keep the stowaway. However for normal visual the Baader was great, with no discernible difference in quality of views to the Stowaway.

My Fsq85 operates at f2 with the 67mm so gives nearly twice as bright a view as the stowaway with nv. This means I can turn the gain down a bit more to reduce noise/scintillation even further, so maybe get a bit better live views and hence video recordings. The iPhone is pretty poor at recording the live views even with a 1 second exposure time and the actual live views in the eyepiece are more detailed, completely stable and very natural.

Edited by GavStar
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1 hour ago, Deadlake said:

Do you feel the slower speed of the AP was lead to more frequency shift in the image?

Out of interest, what is frequency shift?

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5 hours ago, GavStar said:

I guess you haven’t read this (pretty long!) thread? I think it answers your question about why I posted these nv videos in this section 😀. Basically sgl does not allow nv posts in the observing section even if it is properly signposted. Any nv posts in the observing sections are moved to eeva by the mods.

 

I did read this thread a couple of months ago. I did get the impression that the word electronic precludes NV picture being published in the DSO section. I suspect that the people in question might have push to or go to electronic mounts but of course this is over looked in this case. If I'd spent my budget on a 24" dob and then NV came along then I would be pretty miffed as for the same cost I could see a lot more using new technology and a more lightweight scope like a C9.25 as commonly used in the USA. I also get the impression that this was imposed by non NV users on the small NV community here and I do see more UK NV users posting on cloudy nights then SGL, so if that was the purpose it has been a great success.

5 hours ago, GavStar said:

My Fsq85 operates at f2 with the 67mm so gives nearly twice as bright a view as the stowaway with nv. This means I can turn the gain down a bit more to reduce noise/scintillation even further, so maybe get a bit better live views and hence video recordings. The iPhone is pretty poor at recording the live views even with a 1 second exposure time and the actual live views in the eyepiece are more detailed, completely stable and very natural.

This is interesting so for the smaller number of objects that are served by the image scale of the fsq-85 (really its focal length?) is a better option. Noise I presume is more of an issue with your London 18.5 SQM you need the faster scope to rude the intensifiers gain. At the same F5 APO scopes are rare, if you where in SQM 20 skies whats the lower speed for a scope before noise becomes an issue, F6 which are more common? 

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Just get the fastest you can, “67mm plossl” afocal being the easiest method. Faster means brighter and you can then filter harder which helps under light pollution. Play with extra reducers, see what works for the kit you have.

I think some people are offended by NV and so we were banished to mix with the EEA community.

@Stu frequency shift aka band shift is when the band pass of the filter varies cross the image due to putting in a light cone that is too fast. Filters ideally like parallel light due to the multilayer etalon design they use. Manufacturers devise how fast their filters can operate so you just need to be aware… if the nebulae begin to fade around the edges on the field then you know what’s happening.

 

Peter

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Posted (edited)
6 hours ago, Stu said:

Out of interest, what is frequency shift?

Also known as band shift in narrowband filters. 



The narrow band filters consist of dozens  to hundreds of 1/4 wave thick medium of different refractive indexes.
When light passes normally (90º) through the filter each refractive layer is seen by the passing light as a 1/4 wave.
When the light is non normal (less than 90º) each layer appears to be thicker and this added thickness changes the spectral band admitted by the filter. This thickening  red shifts the admitted spectrum.

At any given focal ratio, sine(theta) = (D/2F) = 1/2f#, where theta is the maximum ray angle, D is the entrance pupil diameter and F is the system effective focal length.  The lower the focal ratio, the steeper the rim ray angle and the greater the wavelength.  Low f/# lenses are not compatible with narrow bandpass filters.

@PeterW Thanks you pressed enter while I was formatting...

 

Edited by Deadlake
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