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New adapter for converting pvs-14 to prime

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#51 sixela

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Posted 14 March 2024 - 12:02 PM

Yes sir. I'm using the Skywatcher equivalent (reduced to f/3.45, it comes with a coma corrector/reducer) and it's my widefield nebula scope.

#52 RaulBloodworth

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Posted 14 March 2024 - 12:05 PM

Good stuff! I appreciate the guidance thank you!

#53 GirtAllerton

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Posted 18 April 2024 - 09:16 AM

Thanks to All for the contributions and specifically to Gavster for the work. 

 

I have a question regarding this modification and magnification during use of a PVS-14 in prime. 

Is this a 1x mag with use of your scope since your remove the objective lens from the PVS-14?

or Can you still calculate using 26mm? 

 

My confusion stems from: 

https://televue.com/...-demonstration/

 

1) Prime Focus Method – Removing the objective from a night vision unit and coupling the remaining “intensified” portion as the “eyepiece” to your telescope, allows placing the night vision’s 18mm sensor surface (acting as the field stop) at the telescope’s focal surface.  You, therefore, have a true field of 18mm/Telescope Focal Length X 57.2°.  For example, a 1,000mm focal length telescope then gives 18/1000 x 57.3° = 1.03° true field of view.  Since the night vision eyepiece = 26mm focal length, your telescope’s magnification = 1,000/26 = 38.5x.  Therefore, you effectively have a 40° apparent field viewing a 1.03° true field at 38.5x night vision enhanced telescope system.  To gain higher power, you can add Barlow or Powermate lenses to the telescope, for example, 2x would yield roughly 80x with a 0.5° TFoV or 4x yields about 160x with a 0.25° TFoV.

 

This would give my C-8 SCT a mag of 78x and .5 degree FOV in prime. Scope is  2032 FL.  That doesn't seem correct. 

 

Lastly, could you just leave the objective lens in place set at infinity and just screw a 2" EP adapter on "over it"? I presume that would give you the effect of a 26mm EP. 

 

Thanks



#54 GirtAllerton

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Posted 18 April 2024 - 09:46 AM

Hopefully, Bob won't mind my posting of his reply to the above question that I sent to him via pm. 

I think it helps us newbies understand.  

 

Bobhen: 

 

"It's my understanding that in Prime the intensifier is about 26mm. So that would be around 78x give or take. Remember why you want the C8. It's for image scale. In Prime one controls magnification increases or reductions with reducers or Barlows.

 

One night 2 years ago I used my C8 and intensifier to observe 47 galaxies at F10. I would not do that with my fast 4" F5 refractor because the details in the galaxies would be around 4x smaller. For the brighter globulars, I have even Barlowed the C8.

 

Just like with visual, the inherent brightness of the target object will determine how much magnification you can use. Globulars can take more than say the Horse Head nebula.

 

The "core" of M42, the Orion Nebula will just knock you out in a C8 at F10. The core is bright and the detail is 3-d like."

 

Bob


Edited by GirtAllerton, 18 April 2024 - 09:48 AM.


#55 sixela

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Posted 19 April 2024 - 05:55 AM

Can you still calculate using 26mm?

Yes. The eyepiece side is made to deliver 1x when coupled with a 26-27mm° objective, so if you remove the objective it really does function like a 26mm 40° eyepiece. See footnote for some calculations.
 

This would give my C-8 SCT a mag of 78x and roughly 0.5 degree FOV in prime. Scope is 2032 [mm] FL. That doesn't seem correct.

What doesn't seem correct? 2032/26 is indeed roughly 78x. And a 40° AFov eyepiece at that magnification does indeed have a roughly 0.5° field (40/78°).
 

Lastly, could you just leave the objective lens in place set at infinity and just screw a 2" EP adapter on "over it"? I presume that would give you the effect of a 26mm EP.

Nope, what functions as a 26mm EP is the NVD without an objective to get an image on the photocathode and then the NVD eyepiece to look at the output of the tube. The NVD objective set for infinity focus requires an afocal system (degenerate case: nothing at all; afocal setup: telescope plus eyepiece) in front of it to get a focused image on the photocathode, not a focal system like a telescope without an eyepiece. If you use the NVD objective as the "telescope eyepiece", you get an afocal system in front of the photocathode and you get a perfectly unfocused image on the photocathode°°
--
°The objective is actually paraxially a 27mm objective, but with some distortion that means that using 26mm for FoV computations will work better. The FoV does not depend on the eyepiece of the NVD: you have an 18 mm diameter field on the focal plane, and the TFoV in degrees is thus 18/FL_telescope*57.3. That TFoV is then converted to an AFoV of 40°. In a distortionless 40° eyepiece M*TFoV=40° and M=FL_telescope/FL_eff_eyepiece. Solve for FL_eff and you get 25.785mm.

°°With glass eyepieces we get an afocal system at the exit pupil, and we need our eye's lens to focus on the retina...and yes, you can actually use the NVD objective sans NVD as an eyepiece if you put your eye behind it. Eye relief's pretty short though ;-) and aberrations are not minimised for that use case.

Edited by sixela, 19 April 2024 - 10:13 AM.

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#56 GirtAllerton

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Posted 22 April 2024 - 07:16 PM

Sixela. Thank you very much for the clarification it is appreciated and understood. 

 

Note to all, My objective lens lock ring had a very tiny set screw that I failed to identify and remove prior to disassembly. It started turning before it grabbed and I cracked the threaded end of that side of the housing. The set screw was embeddeded so look carefully for it. A 120$ mistake and I'm currently awaiting a new housing from Steele Industries. Just glad its salvageable. 



#57 GirtAllerton

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Posted 25 April 2024 - 06:44 PM

I just got my replacement housing from Steele Ind and unfortunately after all that I have the same issues as Dewbeard. The RAF adapter makes contact with the battery housing and the 10mm extension definitely doesn't clear. Threads are smooth and easy install without the battery cap. 



#58 GirtAllerton

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Posted 25 April 2024 - 06:55 PM

Any suggestions here?

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#59 GirtAllerton

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Posted 25 April 2024 - 07:22 PM

Before I throw any more dollars at this. Do you think the other RAF adapter is my only way forward? 

 

 

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#60 sixela

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Posted 25 April 2024 - 08:02 PM

Ask Raf. The newer adapters of the kind you have are no longer knurled but smooth and just a hair less wide as a result.

For clearing the battery cap along the tube axis just slap on any smooth 5-10mm T2 extension.

Edited by sixela, 25 April 2024 - 08:04 PM.


#61 GirtAllerton

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Posted 25 April 2024 - 08:41 PM

Sixela, The adapter was purchased this week from Raf and the smooth extensions also did not fit w/o contacting the battery cap. 

 

Trying to determine if the other adapter Gavster showed in post #46 would work here. And whether it had any effect on fov or vignetting. 

 

Thx


Edited by GirtAllerton, 25 April 2024 - 08:48 PM.


#62 sixela

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Posted 26 April 2024 - 01:33 AM

Mine is smooth all around and (on a Carson PVS-14) does not interfere with the cap. But it came from another warehouse, I think.

Of course if even a smooth T2 extension interferes with the battery cap you’re out of luck.

The other adapter also just works (I have both) and there is no danger of interference with the battery cap (you leave the existing infinity focus stop ring in place if you want to.)

The drawback is having to constantly screw and unscrew it when going from afocal to prime setups or vice-versa, so double the wear and possible cross-threading of the threads for the objective.

It also costs you just a bit more focuser in-travel because with the short adapter you can tweak your T2 extensions to just clear the cap more precisely. That also means I can’t mount the TMB barlow element as closely (so I end up with a slightly higher barlow factor).

This spacing (the TMB barlow is recessed into the T2 to M28.5 adapter ring here) is impossible with the other adapter:
IMG_5589.jpeg

But both adapters work to hook up a PVS-14 and a Paracorr Tyoe 2 (without the tunable top).

Edited by sixela, 26 April 2024 - 01:44 AM.


#63 GirtAllerton

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Posted 26 April 2024 - 07:52 AM

Sixela, 

 

Thank you once again. Very helpful and I appreciated your reply and photo. 

Looks like I'm just going to be too restricted on the clearances so will have to go with the R-T2F to PVS 14. 

I reached out to Gavster and he concurred. He noted no vignetting with his. 

Will report back on how it all works out and will definitely be careful with threading - replacing one housing is enough. 

 

Thanks again for all the help. 



#64 GirtAllerton

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Posted 14 May 2024 - 07:59 AM

All, 

I hate when you follow a thread and never find out what the final conclusion was. So, here is an update on this project. 

 

First, The RAF Camera T2F-PVS-14 is nicely made and fit my PVS 14 with no difficulties.

However, I excitedly dropped it into the Vixen ED103S on the first clear night and it did not have enough back focus to make it work with a 2" diagonal. Crap.... 

I tried my 2" Televue Everbrite & ES 2" Mirror diagonals - both fails. 

Next, I adapted a Celestron 1.25" mirror diagonal from my C-8 - Just on the edge of focus. 

Finally, A 1.25" Tak prism - Success with a 67mm light path + Adapter. This gave me the focal range I needed. Determined I need a light path shorter than 90mm total to make this work.  

So, I ordered a Baader T2 Zeiss prism with 2" nose and 1.25 Click Lock and got time to try it last night. Worked perfectly. Interesting thing happened while trying a 2x TV Powermate, it gave me a lot more focal range.

I was surprised as I thought they were parfocal? I did have a small O-ring on the tube just to ensure it didn't bottom out in my new diagonal but the increase in out travel was significant..  

 

I have to say my initial impressions are positive. It really simplifies the use and ease of the pvs-14. The reduction of the stack size alone is worth it in my mind. 

I like the ability to swap directly back & forth with visual Eps.  The "stack" just  made that too complicated. 

Next to try my C-8 with the Tak dia to see if it has the focal range to work. Plan is to primarily hunt galaxies & work through the Messier catalog. 

I just have experiment with magnification using powermates and barlows. Any suggestions? 

 

Next step for me will be a Rowan Az100 to make things a little easier to find. 

 

Thanks to all.

G

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Edited by GirtAllerton, 14 May 2024 - 08:09 AM.


#65 GirtAllerton

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Posted 14 May 2024 - 08:02 AM

Additional photos, sorry about rotation... 

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#66 vicuna

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Posted 14 May 2024 - 12:46 PM

looks like you got it sorted out but if it helps you, can you use something like this quick connector to go directly into the diagonal? to shorten the light path even more?

 

https://www.baader-p...6a-and-07).html

 

then have another quick connect with that focusing eyepiece for when you wanna switch to regular eyepieces. one extra step but maybe that'll be useful on another scope that doesn't focus.

 

 

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#67 GirtAllerton

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Posted 14 May 2024 - 01:04 PM

Vicuna, 

 

Gavster actually sent me the same suggestion except it was direct with the T2 threads. . 

 

Sharing my reply:

 

Well ****, didn't even think about that but yes it could be done. But with that diagonal and the click lock I have plenty of focal room now.

In fact I was probably going to add small 5mm or 10mm spacer just to ensure I have enough clearance for a powermate or barlow so they don't contact the prism.

Also, I like the flexibility to just pull the NV and drop in a visual EP. I wouldn't be night adapted but I would get a chance to see the colors and build a stronger mental image of what I'm looking at.

That's the plan anyway until I can dual mount the scopes.

 

Thanks!

 

Vicuna, I agree its is a good idea. Thanks for suggestion. 


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#68 vineyard

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Posted 14 May 2024 - 01:57 PM

@GirtAllerton yes I use a Tak prism for precisely those reasons w my PVS14 modded to prime focus mode using that same adapter that Gav got RAF camera to develop.  And v nice to put them on a SBS on an AZ100.  I mount a Mak on one side and a fast refractor on the other, and can switch EPs/NV from one to the other depending on what sort of view I want.  You will enjoy globulars through a long focal length scope and NV!



#69 vicuna

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Posted 14 May 2024 - 04:02 PM

 

In fact I was probably going to add small 5mm or 10mm spacer just to ensure I have enough clearance for a powermate or barlow so they don't contact the prism.

Also, I like the flexibility to just pull the NV and drop in a visual EP. I wouldn't be night adapted but I would get a chance to see the colors and build a stronger mental image of what I'm looking at.

 

yea actually it'll be easier too if you use a barlow or filters on the pvs-14

 

I ordered my RAF adapter last week...so thank you for posting your process. hoping to be up and running in prime soonish. i think i'll enjoy just plugging it in without eyepieces for quick sessions. i'm so lazy sometimes I know i'll do that more often. 



#70 GirtAllerton

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Posted 14 May 2024 - 04:15 PM

Vicuna, I think I'm the same. Simpler is aways a benefit. Just make sure to locate and remove that little locking allen head screw before disassembly!


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