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Posted: 11/19/2012 7:55:18 PM EST
[Last Edit: 11/19/2012 8:49:06 PM EST by mgeh]
I asked for troubleshooting on another forum a long time back and was told to collimate my NVG's.

The problem was that unless if I have the lens cap on everything looked too blurry. I did adjust the focus rings but it does not sharpen the image. When I first got them they worked well and this problem came about a year later.

My question is how do I collimate? I googled it and was not sure what source to use.

Any help is appreciated. Thanks.

ETA: I just remembered that not only is it blurry but the image is washed out in light.
Link Posted: 11/19/2012 8:34:41 PM EST
What are you trying to collimate it with?
Link Posted: 11/19/2012 8:48:07 PM EST
I'm trying to fix them so I don't have to have the lens cap on to be able to ? Is that the wrong use of the word?
Link Posted: 11/19/2012 9:21:36 PM EST
No, you collimate two or more sights so they are aligned at a specific range. You can adjust focus of the 7b using the front twisty, the two rear lenses, bightness, and contrast knobs, if I rember right. Never used 7b, only ever used 14's hope that helps.
Link Posted: 11/19/2012 9:49:41 PM EST
Does anyone know what to do then? I messed with all the knobs several times and haven't been able to make them work.
Link Posted: 11/19/2012 11:07:42 PM EST
i could be wrong but i thought when out of collimation , you would see double instead of one image with both eyes - your problem sounds like the front lens out of adjustment somehow - can you adjust the eyepeices to get the ' grain' of the image ( or see any dust or spots clearly ) on the rear of the tube , to show the diopter adjustment is ok - if the rear parts seem ok i would look at the front lens and make sure the tube housing is tight , tube cant move etc.
Link Posted: 11/20/2012 1:41:43 AM EST
[Last Edit: 11/20/2012 1:59:15 AM EST by cj7hawk]
Yes, collimation is different. You probably have a lens that's adjusted out of focus. The PVS-7B has lock rings like the PVS-14.

Loosen the lock ring all the way back, then adjust until you can focus on stars ( may take a little playing with front and back lenses ) then when the stars are in focus, tighten the lock ring up, then loosen off about 1/8 of a turn.

That should do it.


Infinity Focus Lock Ring - P 3-19
Objective Lens Infinity Focus Adjustment - Section 3-13.

Regards
David
Link Posted: 11/20/2012 2:08:26 AM EST
[Last Edit: 11/20/2012 2:14:11 AM EST by XCQTR]
Originally Posted By cj7hawk:
Yes, collimation is different. You probably have a lens that's adjusted out of focus. The PVS-7B has lock rings like the PVS-14.

Loosen the lock ring all the way back, then adjust until you can focus on stars ( may take a little playing with front and back lenses ) then when the stars are in focus, tighten the lock ring up, then loosen off about 1/8 of a turn.

That should do it.


Infinity Focus Lock Ring - P 3-19
Objective Lens Infinity Focus Adjustment - Section 3-13.

Regards
David


Precisely that. Unless you have an out of whack dichroic splitter (prism) after the image tube, then that's a bit different, but you will notice right away that the image isn't right....kinda like binocs that's out of collimation (each side is looking at a different spot). I've built a PVS-7, don't recall the prism alignment was a big process....IIRC, it's a drop-in module.

To add, you can't use lens cap to collimate....that's like a pinhole camera. In factory, they use a collimator (fancy word for things that light ray in parallel - off-axis reflective parabolic mirror, or less often use for this purpose, a refractive convex lens). Think of your headlamp/flashlight reflector (but much better job at making the ray parallel). Theoretically, you'd want a point source at infinite distance so the light rays are perfectly parallel. But in practicality, a star is the furthest object you'd ever see....so who cares, it'll do. High precision lens maybe as good or not as good.
Link Posted: 11/20/2012 6:01:49 AM EST
Here are a couple of things I can think of off the top of my head. The PVS-7B is pretty simple, but everything must be lined up correctly. Luckily, there are tabs and grooves in the various parts the lign up with each other. Since they are easy to take apart, many do so and don't assembly them back together properly.

First, make sure the rear lens are moving in and out when you adjust them. When I got my first PVS-7B, the rear lens adjustment tabs were broken. So it was out of focus unless I pulled the rear lens out. I ended up buying a replacement assembly. Just turn the rear lens adjustment and verify they are going in/out. If they are not, pull or push on the rear lens to see if you can get it to move and focus.

Second, make sure the front lens is screwed on all the way. The PVS-7B housing has plastic threads that can strip if one is not careful as the front lens has aluminum threads. It can also cause peices of plastic from the threads to come off and clog up the threads, so it feels like it is on when it really isn't. There is also an O-ring in the front lens assembly that can break and bind up the lens. Remove the batteries (so the unit doesn't accidentally go on) and unscrew the front lens. It has the standard thread pattern (lefty loosy, righty tighty). Make sure the retaining ring on the inside of the front lens is screwed down all that way. If it isn't on properly, it can mess with the focus. Then reassembly, use a can of air dust remover to blow everything out to minimize dust. Make sure all the parts line up. The colimator has a tab to center it. The intensifier tube has a groove which matches up with the body. The front lens just screws back on. It isn't hard, just take your time and be sure not to cross thread it. It is a tad tricky as you have to keep everything lined up as you screw on the lens. It isn't hard, but be sure to pay attention to what you are doing and take your time.

Lastly, do as stated above and loosen the focus lock ring on the front lens. Some are glued into place, so you may have to get the proper tool for it. You can usually see the glue if it is glued in place. But try it by hand to see if you can get it. I bought a tool specifically for that, it was $45 or so. I had one lens that turned effortlessly by hand, but I also have one that is absolutely frozen in place as it has been heavily glued in place. Of the 6 or so I have played with, most are in the middle and take a little effort to move them. If you got some surplus parts, there can be a ton of dirt, grease, etc in the threads under the ring where you can't see it.
Link Posted: 11/20/2012 2:45:39 PM EST
I just went through all the suggestions and found it was the front focus lock ring. Now it is working again.

Thanks for the help guys. Now I don't have a couple grand of gear sitting in my closet anymore.
Link Posted: 11/21/2012 8:34:29 AM EST
[Last Edit: 11/21/2012 8:52:25 AM EST by Mk13]
[snipped]
Originally Posted By ihon:

Make sure the retaining ring on the inside of the front lens is screwed down all that way. If it isn't on properly, it can mess with the focus.


[/snipped]

This is a good discussion. I'm sure plenty of people have wondered if there's a way to fine tune the focus on either 7's or 14's.

I don't see what you are describing though in what I quoted. I can remove my 14's whole objective assembly when it unscrews from the housing as it apparently does not have close focus stop ring installed. I don't have the tool to remove the image tube but I have the replacement ring if I ever do take her down that far apart. With that said, I'm not sure my 14 is as crisp as it can be. I can remove the obj. assembly as stated and I don't see a ring inside of the obj. lens assembly. Most folks wouldn't be able to unscrew the obj. assembly off I would think anyway so are you referring to the exterior but maybe an inner ring where it's recessed a bit. I have an LIF on my exterior lens in case that matters.

If anybody wants to comment on getting the close focus stop installed I'd like to learn about that too. I've gotten pretty adapt to breaking her down, cleaning off the lens and intensifier, and then DIY purging it. My unit did not have a purge screw or o-ring for some of it's life before coming to me. Corrected that and in the process found out that a modestly sized dark spot on the tube turned out to be dust or something because I cleaned it so well it was gone after that. Nice surprise and these are the challenges faced when going the used route when buying NVD's. Gotta learn all you can.

BTW, what size is that set screw for the infinity lock ring? I have tens of allen keys and nothing that small.
Link Posted: 11/21/2012 9:30:16 AM EST
[Last Edit: 11/21/2012 9:36:05 AM EST by ihon]
On the PVS-7 & -14 there is a retaining ring the keeps the lens from unscrewing when you adjust the focus. It is on the lens closest to the image tube and is inside the front lens assembly. It is what keeps the front lens attached to the part that screws into the actual body housing on the PVS-14. There is a separate ring that retains the entire front lens assembly to the PVS-14 tube housing. It's job is merely to retain the front lens, not to set the focus.

But, I had a PVS-7 front lens (part of a batch of parts that I bought used), where the ring needed to be tighten by a quarter turn to allow it to focus 100%. It need to be turned because the infinity stop ring was glued in place (with JB Weld). Not to mention, when I removed it to inspect, there was a tone of dust mixed in with grease that caused it to bind up a bit at the end of it's rotation. I should have made that a little clearer and explained that is was only really an issue if the infinity stop ring was glued in place. But if you have an infinity stop ring that is too tight, a front lens that isn't screwed all the way in (or has something binding it) and the front lens retaining ring is too tight/loose, that tolerances stack up. If all are at the upper end of the tolerance spectrum, it can affect focus.

The PVS-7 was a little too easy to take apart, which isn't a good think with bored people. If you notice, the PVS-14 requires more tools to take apart. On the PVS-7, many ended up taking it apart and not paying attention when they reassembled it. Also, many of the retaining rings required specialized tools which the end user didn't have on hand. So many of the rings (including the infinity stop ring) weren't set correctly or are only hand tight.

If you notice, the PVS-14 infinity stop gin has a small set screw in it to set it in place. Out of the 6 or 7 PVS-7 front lens assemblies I have bought (all used), none had a set screw in it. So the set screw either wasn't installed originally, or more likely, it got lost. To fix them in place, many glued them. Some used silicone caulking which could be removed, but some have JB Weld which really freezes it in place.

I should also state that I am only familiar with these issues because I have assembled a couple of PVS-7 from used parts from different batches. I was frustrated on a few when the parts didn't work well together. I also used a Russian tube on one which caused even more variance between the parts. So I noticed different housings fit the tube and front lens differently. I also noticed that the rear lens assembly were built differently on different models. I am assuming the differences were by one being built by ITT and the other by Litton. Moving different tubes from housing to housing required me to reset the focus adjustments to focus properly.
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