100 replies to this topic

[Vondragonnoggin]

Well, tonight was the first clear night out, and it was a bust, unfortunately. Somehow it seems like I don’t have enough in-focus travel. I would have thought that back-focus would have been the problem. I guess I’ll need to upgrade the focuser first, wah wah.

You tried without reducer? 

 

Back focus - inward drawtube travel - https://www.cloudyni...s-a-definition/

 

using a reducer requires extra back focus - extra inward travel of the drawtube.

 

this is why the shortened adapter plate for the 120ST allows room to use a reducer. The whole focuser sits closer to the back of the scope. 

Edited by Vondragonnoggin, 30 March 2019 - 01:43 AM.

[DMala]

Sorry to hear of the trouble, but you are not alone, I guess it happened to most of us to get stuck with focus problems. One small suggestion is during cloudy nights to try a new setup first on terrestrial targets.  Another possibility, if your setup allows it, is to temporarily switch to a 1.25" diagonal which has a shorter light path, while you work out the 2" problems.  With my own short refractor I have not yet found a way to use both the reducer and the NV device.

[Eddgie]

Well, tonight was the first clear night out, and it was a bust, unfortunately.

Since there is not instruction sheet with these, not everyone realizes that the Mod 3 eyepiece has to be focused independently of the telescope by using the diopter ring around the eyepiece.  Not sure if you knew this or not but if this is the first time you have used it and you never had an objective on it to try it, maybe this is the problem????

[Vondragonnoggin]

Just want to clear up optical train needed here too.

 

telescope - diagonal - (filter goes here if 2” filter) - reducer - nosepiece - (1.25” filter goes here if using ScopeStuff 2” nosepiece with inset 1.25” filter threads) - Mod 3

 

Scopestuff 2” nosepiece with 7nm 1.25” filter screwed on inset filter threads and 2” reducer screwed on outside of nosepiece :

 

Side view of Monocular with nosepiece and reducer that just goes into diagonal (ignore plastic cap):

 

 

Difference in focuser end with linear bearing being shorter is enough on my skywatcher to come to focus with a 2” .5x reducer on the end of the 2” nosepiece. If I put my Scopestuff GSO Crayford adapter on instead of the white adapter that came with the Skywatcher, I would gain yet another inch or so of back focus ability if I needed it. So far have not needed it. The ScopeStuff adapter would butt right up to the black end of the tube, replacing the white adapter and give me the extra back focus if needed:

 

[Vondragonnoggin]

When all is finished, I end up with just a couple mm left of back focus (with Skywatcher adapter, not ScopeStuff adapter) - this is a pvs 7 pictured, but the same for my M942 and for my NVD Micro

 

Edited by Vondragonnoggin, 30 March 2019 - 08:54 AM.

[DMala]

Thanks for the clear explanation, I did not realize that you guys were screwing the reducer directly on the nose piece. Well, in my case however, since I can use the reducer in afocal mode, I may choose to put the prime focus mode issue aside for now, as I do not really need to use both techniques.

[Vondragonnoggin]

Thanks for the clear explanation, I did not realize that you guys were screwing the reducer directly on the nose piece. Well, in my case however, since I can use the reducer in afocal mode, I may choose to put the prime focus mode issue aside for now, as I do not really need to use both techniques.

Afocal turned out completely the opposite of Prime Focus for me with my 56mm plossl. Had to rack the drawtube way out to get focus. Several inches out on my AT72ED. The same principle in placement works in afocal mode for me except the reducer screws on to the end of the 56mm plossl. Still did not have enough back focus to put the reducer before the diagonal. I did however have enough back focus left to possibly add a 25mm extension between the reducer and the end of the eyepiece which would give me more than .5x true reduction, but that stack is very high.

 

I tried in afocal the following optical trains that worked:

 

telescope - diagonal - 2” Ha filter - 56mm plossl - NVD Micro (with no reducer the drawtube was racked out almost 3”)

 

and 

 

telescope - diagonal - 2” Ha filter - reducer - 56mm plossl - NVD Micro (still had to rack the drawtube out about 2”) 

 

will try next:

 

telescope - diagonal - 2” Ha filter - reducer - 25mm extension - 56mm plossl - NVD Micro (should give me greater than .5x reduction)

 

I don’t know if this would be the same with a Televue 55mm plossl, but this is the configuration and result I had with a Meade 56mm plossl. I’m looking to experiment with this on my mak 150 next. Hoping for around F/4 on the mak which is F/12 natively.

 

Not as anxious to try with the mak now though because I picked up a Skywatcher Startravel 150R F/5 refractor used last week. Going to replace the focuser and adapter plate on that one soon. Need to try it with stock focuser and Prime Focus first though. I wanted to try on my mak because the mak is 14lbs and my F/5.9 AT152 is 25lbs, but the used Startravel 150 is about 14 lbs also, so will use the new 150 and probably sell off the 25lb AT152. Too heavy for me and can get a faster F ratio with the Skywatcher.

[DMala]

Thinking about it, one big difference of the above setup for the PVS-7 is that its c-adapter already has a 2" step. But, how to avoid adding a second 2" adapter in order to be able to connect the focal reducer?

[Vondragonnoggin]

Thinking about it, one big difference of the above setup for the PVS-7 is that its c-adapter already has a 2" step. But, how to avoid adding a second 2" adapter in order to be able to connect the focal reducer?

PVS-7B/D maybe

 

I have a pvs-7 A/C body and use a 2” diagonal the same way I do on a Monocular. It’s the easiest way to use my 2” filters and 2” reducer also. I can take the c-mount nosepiece with reducer and filter on it and unscrew from the pvs-7 and screw right on my NVD Micro or M942 and use it the same way with approximately the same back focus requirements.

[DMala]

I have a 2", 35mm extender that may substitute for the 2" nosepiece to c. I will check this out and report back:

Attached Thumbnails

• 

[bobhen]

Here is my 102 mm F5 achromat set up for Night Vision. I had to swap-out the original focuser for a GSO when I bought the reducer.

 

From left to right…

 

1. The 102mm F5 optical tube
2. The GSO focuser
3. An Astro-physics 2” diagonal (these have a short light path)
4. An Antares 2” .7 reducer (the reducer screws onto the bottom of the 2” to 1.25” adapter that comes with most diagonals or can be bought separately)
5. The 2” to 1.25 adapter
6. The NVD Micro (the Micro has a c-mount adapter screwed onto its nose and a 1.25” filter screwed onto the end of that adapter)

 

All comes to focus at a native F5 or with the .7 reducer at F3.5.

 

I use the same basic setup with my Tak 120 and Mewlon 210 and they both come to focus.

 

Hope this helps. Oh, and killer views as well. 

 

Bob

Attached Thumbnails

• 

[DMala]

I have a 2", 35mm extender that may substitute for the 2" nosepiece to c. I will check this out and report back:

Nope, no luck, it doesn't work with my Televue Pronto.

[careysub]

Looking at the diagonals on this thread, I got to thinking. GaAs sensors (which I presume are what the Gen III tubes are using) are useful down to about 850nm, and people are using 685nm long pass filters so that they are viewing light in the band 685-850nm. Many fancy diagonals are dielectrics which are tuned to the visual band or enhanced aluminum with spectral reflectivity different from regular aluminum (the Televue site says of theirs "Enhanced Aluminum mirror coating provides a 96% reflective surface across all but the extreme ends of the visual spectrum").

 

Are there are gotchas here? Fancy high reflectivity mirrors that perform poorly or not at all in the near IR?

 

 

Attached Thumbnails

• 

[Vondragonnoggin]

Looking at the diagonals on this thread, I got to thinking. GaAs sensors (which I presume are what the Gen III tubes are using) are useful down to about 850nm, and people are using 685nm long pass filters so that they are viewing light in the band 685-850nm. Many fancy diagonals are dielectrics which are tuned to the visual band or enhanced aluminum with spectral reflectivity different from regular aluminum (the Televue site says of theirs "Enhanced Aluminum mirror coating provides a 96% reflective surface across all but the extreme ends of the visual spectrum").

 

Are there are gotchas here? Fancy high reflectivity mirrors that perform poorly or not at all in the near IR?

I have a couple 1/10th wave mirror star diagonals for IR response. Dielectrics are ok for narrowband though.

 

Dielectrics have extreme falloff at 700nm

Edited by Vondragonnoggin, 20 April 2019 - 10:11 AM.

[Vondragonnoggin]

Best Of NV thread has a lot of links for response, best filtering, afocal use, IR response of diagonals, etc

 

It was just organized by GeezerGazer and had a lot of contributors collecting the best info threads. Really useful now.

[Jeff Morgan]

Looking at the diagonals on this thread, I got to thinking. GaAs sensors (which I presume are what the Gen III tubes are using) are useful down to about 850nm, and people are using 685nm long pass filters so that they are viewing light in the band 685-850nm. Many fancy diagonals are dielectrics which are tuned to the visual band or enhanced aluminum with spectral reflectivity different from regular aluminum (the Televue site says of theirs "Enhanced Aluminum mirror coating provides a 96% reflective surface across all but the extreme ends of the visual spectrum").

 

Are there are gotchas here? Fancy high reflectivity mirrors that perform poorly or not at all in the near IR?

 

Do a search for ChemistEd's posts on globular observing.

 

He is a big fan of silver/enhanced silver for this very reason. 

[stargazer434]

Hello All!

 

I have really had the chance to enjoy this setup for quite a few viewing sessions now.  NV really does provide an amazing view!  Unfortunately, for me, I am moving to part of my local area that gets fogged in all the time, and my schedule precludes me from tracking down clearer spots.  I'm just not going to get to use it enough to justify keeping it!  I'm going to post the setup on the CN classifieds sometime soon but if you all know of anyone interested in a complete turn key MOD3 NV rig for around the price of a new MOD3 by itself let me know. 

 

Thanks,

John

Edited by stargazer434, 19 May 2019 - 02:27 PM.

[stargazer434]

Here is the CN ad for the complete rig:

 

https://www.cloudyni...od-accessories/

 

Bit of a bummer to have to sell but unexpected moves happen sometimes.

[Vondragonnoggin]

That’s a great price for everything. You are right. Complete turnkey solution for someone interested. Good luck with the move. Sorry to hear about observing conditions.

[Vondragonnoggin]

Hopefully no one scared away by the green phosphor that particular Mod 3C has. When I first started looking into Night Vision for astronomy, I was thinking I would get white phosphor only, but was convinced after talking to others here that green phosphor was perfectly acceptable so I bought green phosphor devices. 

 

Turns out they were right. Only the very brightest nebula actually show the green much. Most of the time the view still appears grey/white rather than green/white and the rest of the view is so dark due to narrowband filtering that it appears as a black background. Longpass filtering does show the green, but I just don’t care about that anymore. The device shows so much more of my Sky than a regular eyepiece that it is a non-issue plus longpass filtering is cutting down the light pollution so much that other objects appear with higher contrast and the green appears very dark anyway. The 685nm longpass is almost back to completely black background.

 

Next tube I get might be a white phosphor tube just so I can add to the variety I already have. Probably upgrade the tube in my M942. It’s an older Omni IV mx10160 tube. A white phosphor tube that at least matches performance of the tube in my NVD Micro would be nice.

[BJS]

What are the specs for the mod3?

[stargazer434]

What are the specs for the mod3?

The tube is a Gen 3 ITT OMNI 7 thin filmed, autogated image intensifier with a minimum SNR of 28 min.

[jdbastro]

Looking at the diagonals on this thread, I got to thinking. GaAs sensors (which I presume are what the Gen III tubes are using) are useful down to about 850nm, and people are using 685nm long pass filters so that they are viewing light in the band 685-850nm. Many fancy diagonals are dielectrics which are tuned to the visual band or enhanced aluminum with spectral reflectivity different from regular aluminum (the Televue site says of theirs "Enhanced Aluminum mirror coating provides a 96% reflective surface across all but the extreme ends of the visual spectrum").

 

Are there are gotchas here? Fancy high reflectivity mirrors that perform poorly or not at all in the near IR?

Instead consider using a prism diagonal like this one:

 

Baader Prism Diagonal

 

although you'll have to look elsewhere to find one in stock....

 

 

 

Here we go.

Edited by jdbastro, 20 May 2019 - 05:29 PM.

[Jeff Morgan]

Instead consider using a prism diagonal like this one:

 

Baader Prism Diagonal

 

although you'll have to look elsewhere to find one in stock....

 

 

 

Here we go.

 

Question about that - vignetting.

 

The T2 prism is 32mm clear aperture, and some of us are using 2" focal reducers. But, since the intensifier sensor is only 18mm, would it matter?

 

I'd love to get the 2" Zeiss prism, but more money and more path length (although still better than a 2" dielectric).

[stargazer434]

Another random but interesting thought.  Wouldn't it be really cool if one of those roboscope rental companies offered a NV setup option for real-time observing over the net in addition to their conventional astrophotography?