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Dual OVNI-M <-> OVNI-B Advantages and Disadvantages - Thoughts

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#1 ArsMachina

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Posted 15 July 2021 - 08:10 AM

As told before I think about stepping into Night Vision.

Actually I do own an APM 150 SD big binocular and my first idea was to put two OVNI-M to the eyepieces.

But this is terribly expensive and the more I am thinking about I am no longer sure if this is the best way to go.

 

With just optical tubes and eyepieces the advantages of two tubes with one objective for each eye are clear, binocular addidion gives us the following:

 

- 1.4x gain for pinpoint targest (stars)

- Even higher gain for diffuse objects like galaxies and nebulae

- 1.2x "virtual" magnification

- "image faults" at one eye like seeing condition can be eliminated by brain calculation

 

I believe with night vision the situation might be different.

Light and gain should not be an issue, the tubes will produce enough photons, maybe even too many so we need to dim the tubes down.

So I do not see the urge to give one OVNI-M to each eye to make the images brighter.

 

Using a OVNI-B with just one tube should still deliver enough light to each eye even with the losses of the beamsplitter.

The 1.4x brightness gain of binocular addition will stell be there like the 1.2x magnification gain with an OVNI-B

 

One thing is the szintillation, here two OVNI-M wolr have the advantage to deliver different scintillation patterns to our two eyes so our brain will eliminate a bog part of it.

But actually this does seem to be the only real advantage of two OVNI-M over one OVNI-B

But perhaps I am missing something.

 

How about the quality of the beam splitter in an OVNI-B?

Probably it is not as high quality as in good binoviewers.

But does the quality of the beam splitter in an OVNI-B affect the images?

Are star less sharp or pinpoint in an OVNI-B than in an OVNI-M?

 

Apart from this I do only see advantages of the OVNI-B

Only a singe objective is needed and from a 60mm APO up to a C14 all is possible

 

Also in low mag handheld use I do see advantages, with two OVNI-M the size of the two objectives is limited to around 55mm by the IPD

With the OVNI-B there is no limit.

 

And for the special case of my APM 150 SD, would there be a big difference in the views by using one OVNI-B with just one tube compared to using two OVNI-M in both tubes?

My feeling is no.

 

I am really interested in your thoughts and experiences so I can make the right decision

 

Jochen



#2 AllStarez

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Posted 15 July 2021 - 08:37 AM

I do have an Ovni M and did use for a short time a second hand biocular. What i can say is that i prefer the Monocular for its size and versality, since i mainly use it with camera lenses (but also with a TV76 and a soon to come 12’ dosbon). I really liked the Biocular’s feeling using both eyes but im more happy to have a monocular now, it’s more like an EP’s feeling to my opinion.

 

 

And for the special case of my APM 150 SD, would there be a big difference in the views by using one OVNI-B with just one tube compared to using two OVNI-M in both tubes?

My feeling is no.

 

It looks it makes a Big difference if you read some threadS of members using NV with binoscope. Check for Gavin (Gavster) ‘s messages. Using 2 NV devices makes it more 3D


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#3 a__l

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Posted 15 July 2021 - 05:12 PM

ArsMachina, for bino-vision PVS-7 is mainly used.

It has no manual brightness control.
But this can be corrected by a user who has some experience with electronic devices.

 

Briefly.
The disadvantage is weight and size.
Advantage, can be used for photo and visual use at the same time.



#4 Joko

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Posted 16 July 2021 - 02:01 AM

ArsMachina, for bino-vision PVS-7 is mainly used.

It has no manual brightness control.

OVNI-B has manual gain control.


Edited by Joko, 16 July 2021 - 02:06 AM.

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#5 PEterW

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Posted 18 July 2021 - 02:33 PM

Not sure about 3D… using 2 tubes if you close one eye the amount of nebulosity drops, open both eyes and more faint nebulosity is visible as the brain filters the random noise out. It would be interesting to see a well constructed test of double tube NV vs NV bino-unit.
If you can reach focus with the 67mm-plossl NV system in the APM150 then you know what the best option is.

Peter
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#6 Fivemileshigh

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Posted 22 July 2021 - 09:14 AM

The 67mm Plossl does reach focus in the APM 150SD but you need a few 2” barrel extensions.
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#7 ArsMachina

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Posted 22 July 2021 - 11:03 AM

The 67mm Plossl does reach focus in the APM 150SD but you need a few 2” barrel extensions.

I am sure this will look very strange, do you have a picture?

 

The setup behind the focusers might be even longer than the objective tubes :-)

 

Jochen


Edited by ArsMachina, 22 July 2021 - 11:03 AM.


#8 Joko

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Posted 22 July 2021 - 11:59 AM

I am sure this will look very strange, do you have a picture?

 

The setup behind the focusers might be even longer than the objective tubes :-)

 

Jochen

This is explained by TV on their website : https://www.televue...._page.asp?id=36

"the 55mm Plössl already requires more drawtube out travel than most eyepieces and 67mm Converter Lens moves it out by an additional 1" (25mm)"

 

For this reason TV sell a package including the 55mm Plössl with 67mm Converter & 2" Extension Tube.


Edited by Joko, 22 July 2021 - 12:04 PM.


#9 longbond

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Posted 22 July 2021 - 02:34 PM

I am sure this will look very strange, do you have a picture?

 

The setup behind the focusers might be even longer than the objective tubes :-)

 

Jochen

This might give you an idea how crazy it can get. Here is my 6-inch f/4 astrograph set-up for afocal with TeleVue 67mm and Mod-3. I call it "The Boomerang". It works okay and the TV 67mm is impressive, but I'd like this setup a lot more if the main telescope tube were 6 inches longer to shorten the stack.

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#10 Kstevens

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Posted 22 July 2021 - 03:03 PM

This might give you an idea how crazy it can get. Here is my 6-inch f/4 astrograph set-up for afocal with TeleVue 67mm and Mod-3. I call it "The Boomerang". It works okay and the TV 67mm is impressive, but I'd like this setup a lot more if the main telescope tube were 6 inches longer to shorten the stack.

 

Would a 2" diagonal, folding the train back along the tube 90 degrees and greatly reducing the moment arm of this arrangement give you some more back focus, work?



#11 ArsMachina

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Posted 22 July 2021 - 03:19 PM

Thank you for this picture, Eric.

 

With a mono telescope this might work ok but I do not want to imagine me two of these "towers" with a 150mm binoscope.

Merging the two images will be tricky then...

 

My feeling is that I would stay with focal mode or really go with an OVNI-B and just one tube.

 

Jochen


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#12 longbond

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Posted 22 July 2021 - 03:24 PM

Yes, you can get about 4-inches off the stack by using a 2" diagonal. Make sure that the orientation doesn't result in too much torsion on the diagonal. The eyepiece is very heavy and the NVD/camera at the end adds a lot of torque.


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#13 Fivemileshigh

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Posted 22 July 2021 - 05:03 PM

I am sure this will look very strange, do you have a picture?

 

The setup behind the focusers might be even longer than the objective tubes :-)

 

Jochen

Unfortunately I don't and i'm away at the moment so I can't get you one. From memory, the TV67 is only somewhat taller than the 17 Ethos. Of course, you then have to add the OVNI on top but i don't think it will be a problem. One issue you will have to figure out is how to connect the OVNI to the TV 67 in binocular mode, because the OVNI afocal adapter is 80mm wide, so you can't have 2 side by side. You will likely have to make a little aluminum tube threaded at one end to use the Televue PVS-14 afocal adapter, and bored to fit the OVNI objective at the other end. That's what I will do.

 

This is explained by TV on their website : https://www.televue...._page.asp?id=36

"the 55mm Plössl already requires more drawtube out travel than most eyepieces and 67mm Converter Lens moves it out by an additional 1" (25mm)"

 

For this reason TV sell a package including the 55mm Plössl with 67mm Converter & 2" Extension Tube.

I hesitate to argue with Televue, but I don't think the eyepiece focal plane moves by 25mm, it's closer to 15mm or so. I haven't tried measuring it in a focuser but it's not that bad. Most fast newtonians have the focal plane ridiculously far out though, so, yes, it can add up. Giving up on afocal and doing only prime focus would severely restrict the field of view compared to the TV67. 


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#14 longbond

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Posted 22 July 2021 - 05:46 PM

I hesitate to argue with Televue, but I don't think the eyepiece focal plane moves by 25mm, it's closer to 15mm or so. I haven't tried measuring it in a focuser but it's not that bad. Most fast newtonians have the focal plane ridiculously far out though, so, yes, it can add up. Giving up on afocal and doing only prime focus would severely restrict the field of view compared to the TV67. 

TeleVue can make mistakes, but this time they appear to be pretty much on the money. I routinely measure the focus points of my eyepieces relative to the focal plane. Here are the numbers for my big Plossls:

 

47.6mm for 85mm Russell

26.5mm for 56mm Meade

35.5mm for 55mm TeleVue

58.6mm for 67mm TeleVue

 

I show a 23.1mm increase for the TV67 relative to the TV55. I'll grant you, when I first measured the 67, I was  a bit surprised.



#15 a__l

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Posted 22 July 2021 - 11:01 PM

35.5mm for 55mm TeleVue

 

https://www.televue....page.asp?id=214

 

It is not very clear to me what distance are talking about.
If this is F from the table on the link, then for TV55 it will be 1.16" (29.5 mm). This F distance is critical for use with paracorr or parfocal lines. Therefore, I doubt that Televue arbitrarily made these distances over a large range (with mistakes).

I checked my line of Ethos and N31, they all parfocal in P2 (with a difference in a small range), hence there are no mistakes there.


Edited by a__l, 23 July 2021 - 12:03 AM.


#16 Joko

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Posted 23 July 2021 - 02:34 AM

Thank you for this picture, Eric.

 

With a mono telescope this might work ok but I do not want to imagine me two of these "towers" with a 150mm binoscope.

Merging the two images will be tricky then...

 

My feeling is that I would stay with focal mode or really go with an OVNI-B and just one tube.

 

Jochen

Afocal and prime are must have. I would not suggest you only use focal mode (prime).

It will be interesting to have a pic from Fivemileshigh, the stack might not be that long on the APM150.

 

And there is an other solution, that doesn't not require any stack...use a focal reducer on the prime mode. There are 0.5x focal reducer that could go up to 0.3x. I'm not very familiar with this method but the 26mm OVNI-M would become a 52mm with 0.5x and 85mm at the lowest position (0.3x) with a focal reducer.

 

So using a focal reducer is way shorter and lighter than afocal.


Edited by Joko, 23 July 2021 - 02:39 AM.


#17 ArsMachina

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Posted 23 July 2021 - 04:22 AM

Hi Jonathan,

 

yes, I thought about focal reducers but with them you will run into the opposite problem, you will not have enough focus intravel.

The 0,7x may still work but I expect the 0,5 to be already too tough.

 

Maybe Fivemileshigh will also play with reducers, so we will know for sure what is possible and what not.

 

Jochen



#18 Fivemileshigh

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Posted 23 July 2021 - 05:01 AM

Hi Jonathan,

 

yes, I thought about focal reducers but with them you will run into the opposite problem, you will not have enough focus intravel.

The 0,7x may still work but I expect the 0,5 to be already too tough.

 

Maybe Fivemileshigh will also play with reducers, so we will know for sure what is possible and what not.

 

Jochen

Sadly, the APM 150 and the OVNI's are in different countries and will not meet each other anytime soon, however I am working on a pair of afocal adaptors for the APM 100 with Baader 32mm Plossls, plus I have my other scopes to play with. 

 

On the subject of focal reducers, the combination of the NV device objective lens (26mm f/1.2) and various eyepieces effectively act as focal reducers. Yes, a dedicated focal reducer would likely be better optically and would be shorter, but as you know, it would have to be custom designed and custom made due to the very short in-focus available. You would also need a different FR for every magnification, and Jochen will need 2 of each!!! shocked.gif lol.gif

 

By comparison, to reduce the 47mm field of the TV67 to the 18mm NV sensor diameter would require a 0.38x reducer !!! It's just not going to happen, we will have to find a way to deal with the long stack. There's also the advantage of being able to change the magnification by changing eyepieces.

 

Cheers,

 

Dumitru


Edited by Fivemileshigh, 23 July 2021 - 05:02 AM.

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#19 PEterW

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Posted 25 July 2021 - 09:09 AM

Given the view you’ll get with the APM150 operating at F2.2 I would accept the “long stack”. Being able to work at prime does make for more convenience, but tends to limit the speed you can reach. I note that Gav has just mentioned that the WO Pegasus will not be made anymore, so true binocular NV looks like it’ll rely on the APM150, or an EMS made homebrew….

Peter
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#20 Fivemileshigh

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Posted 25 July 2021 - 11:03 PM

I've done a lot of testing by now and there's a lot to talk about, enough that most of it would be off topic, but to answer the question posted by the OP I will limit this post to the testing I've done with my 2 identical OVNI-M's in binocular mode. The main test configurations were with a pair of 75mm f/1.4 Pentax CCTV lenses bridged together with a custom 3D printed bridge, and afocal with 32mm Plossl eyepieces in my APM 100 ED-APO binocular. I did the tests on faint extended objects with 2x Ha filters (North America, the Sadr region and the Veils). I did not have the ability to do tests on other targets, but for purposes of this discussion, this is sufficient for now.

 

In short the improvement in what I can see with one eye versus two is at least as great as it is with strictly visual, unaided equipment. Despite being very good optically and having their own strengths, there is inherently more "noise" in the resulting image at the eyepiece of the intensifiers compared to unaided eyepieces, and having 2 sources of information definitely helps the brain sort out the signal from the noise. Keep in mind I don't have a PVS-7 or OVNI-B to compare with.

 

Your Mileage May Definitely Vary.

 

Cheers,

 

Dumitru

 

PS: the OVNI with the factory supplied prime focus adapter does not reach focus in the APM 100's, but it's very close. I believe a custom machined adapter with no shoulder will, as I can reach focus if I simply rest the housing of the OVNI on the focusers. This is on a binocular already modified for a little more in-focus, so depending on production tolerance, you may or may not reach focus on yours.


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