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Posted: 8/6/2014 10:49:03 AM EDT
[Last Edit: 8/6/2014 10:49:39 AM EDT by murtis]
I'm having a slight collimation issue with my MUM which I would like to resolve somehow to make head mounted use comfortable. The issue is that when I look trough the MUM with one eye and keep the other naked, objects don't align unless the MUM is in one certain position. If I rotate the whole device the image makes a full circle, at one point being fully collimated, 180 degrees from that being the furthest from good. Unfortunately, with a standard J-arm the position is wrong for both eyes, especially so for my right eye, then it's full 180 deg from the optimal. I would estimate the collimation is off by a few degrees.

Turning the objective lens or the eyepiece doesn't have any effect, only by turning the whole device I can get my vision to align. Would this suggest that the tube is sitting slightly misaligned?

Anyone have ideas how to fix this or somehow change it so that I could comfortably wear it over one of my eyes?
Link Posted: 8/6/2014 11:26:14 AM EDT
Originally Posted By murtis:
I'm having a slight collimation issue with my MUM which I would like to resolve somehow to make head mounted use comfortable. The issue is that when I look trough the MUM with one eye and keep the other naked, objects don't align unless the MUM is in one certain position. If I rotate the whole device the image makes a full circle, at one point being fully collimated, 180 degrees from that being the furthest from good. Unfortunately, with a standard J-arm the position is wrong for both eyes, especially so for my right eye, then it's full 180 deg from the optimal. I would estimate the collimation is off by a few degrees.

Turning the objective lens or the eyepiece doesn't have any effect, only by turning the whole device I can get my vision to align. Would this suggest that the tube is sitting slightly misaligned?

Anyone have ideas how to fix this or somehow change it so that I could comfortably wear it over one of my eyes?
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Either that or one of the objective lenses is out of alignment. Can you disassemble it? Shouldn't be difficult to determine which of the three is the culprit.
Link Posted: 8/6/2014 11:35:42 AM EDT
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Originally Posted By TheHorta:

Either that or one of the objective lenses is out of alignment. Can you disassemble it? Shouldn't be difficult to determine which of the three is the culprit.
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I did already, but didn't notice anything out of ordinary. Such a small error might be hard to spot I guess. What do you mean that one of the objective lenses is out of alignment, the whole package comes out as one, how can I determine if one of the lenses is misaligned?
Link Posted: 8/6/2014 11:43:06 AM EDT
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Originally Posted By murtis:


I did already, but didn't notice anything out of ordinary. Such a small error might be hard to spot I guess. What do you mean that one of the objective lenses is out of alignment, the whole package comes out as one, how can I determine if one of the lenses is misaligned?
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Originally Posted By murtis:
Originally Posted By TheHorta:

Either that or one of the objective lenses is out of alignment. Can you disassemble it? Shouldn't be difficult to determine which of the three is the culprit.


I did already, but didn't notice anything out of ordinary. Such a small error might be hard to spot I guess. What do you mean that one of the objective lenses is out of alignment, the whole package comes out as one, how can I determine if one of the lenses is misaligned?


Not the tube only but the front and rear objective lenses themselves on the housing. With the tube out you should be able to discern any axial distortion in either of them, unless it's too slight, in which case I doubt it would appear so pronounced when looking through the MUM.
Link Posted: 8/6/2014 12:01:23 PM EDT
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Originally Posted By TheHorta:

Not the tube only but the front and rear objective lenses themselves on the housing. With the tube out you should be able to discern any axial distortion in either of them, unless it's too slight, in which case I doubt it would appear so pronounced when looking through the MUM.
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Okay thanks for the tips, I will take a better look at it.
Link Posted: 8/7/2014 10:43:41 AM EDT
[Last Edit: 8/7/2014 10:49:32 AM EDT by murtis]
Alright, took it apart but could not really see anything wrong with it. One thing I noticed is if I leave the eyepiece a little loose the optical path (if it's called that) changes (pretty much identically to turning the whole device), so that way I could tune it to suit one or the other of my eyes. Does it need to be turned all the way in until it's tight, or can I leave it say a half a turn loose?

I read that ANVIS 6 has one lens slightly offset so you can collimate it by rotating that. Would be nice if all monoculars had this option too. Not a huge deal with one eye use, but I would assume guys turning monos into binos having nasty problems with collimation. I wonder if one way to solve this was an additional lens that is screwed before the objective lens or after the ocular, which then would allow collimation by rotating it. No idea if that is even possible with only one lens, guess it needs more than one to change the path but not change magnification, focal lenght or anything else.
Link Posted: 8/7/2014 11:52:41 AM EDT
on the mum its the eyepiece that holds the tube tight so i would not loosen that - also if you tighten it back up dont overtighten it as the lite pipe can be broken if its overtightened,
i did hear of a mum that was dropped on the front lens and it was mis-alighned - have you dismantled the front lens unit to make sure none are cross threaded ? allthough it sounds like you say its the rear lens at fault - are the actual lens elements tight and fitted properly?
Link Posted: 8/7/2014 12:16:20 PM EDT
[Last Edit: 8/7/2014 12:24:39 PM EDT by murtis]
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Originally Posted By johnelot:
on the mum its the eyepiece that holds the tube tight so i would not loosen that - also if you tighten it back up dont overtighten it as the lite pipe can be broken if its overtightened,
i did hear of a mum that was dropped on the front lens and it was mis-alighned - have you dismantled the front lens unit to make sure none are cross threaded ? allthough it sounds like you say its the rear lens at fault - are the actual lens elements tight and fitted properly?
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No I haven't taken it apart, I'm not an expert so I'm a little cautious when doing these operations on my precious equipment. I could take a look at this too though. There might be small misalignments everywhere, what you see trough the tube is all of them combined of course. Thanks for the tip on the light pipe and overtightening.

I have spent a good deal now reading about monocular collimation problems and have found that generally none of them are collimated, they usually have a slight misalignment somewhere. Some PVS14 models seem to have a way to collimate them, and there was a patent for that method which described the process. Very similar to that of ANVIS. This was to allow binocular use. They can't be collimated in the sense that it's dead straight regardless of orientation, but they can be collimated relative to each other so when mounted on a bino mount, they show the image fully overlapped. It's just to make the optical path offsets align, not to remove the offset alltogether.

All the monoculars I have previously owned had the same problem in varying degrees, but I never used them head mounted that much that it bothered me. When it's dark enough the problem obviously goes away, but if the sky is even bit lit the brightness showing trough trees is annoyingly separated between my eyes. When it comes to urban environments streetlights far away show as double which again is not nice. Not a big deal in other words, but would love to fix the issue.

If someone here has a MUM and is willing to do a quick test I would greatly appreciate. Just to know whether my unit is actually far from what it should or if this is just how they are. How I see the issue the clearest is by looking at a street light or some bright pinpoint object far away, keeping my both eyes open, and then turning the MUM with my other hand. Then try not to align your stereo vision, just stare as a drugged person to infinity, and if you see the pinpoint object doing a full circle relative to where you see the object with your naked eye, then it's not collimated. If you could describe how bad the effect was I'm interested. For example, can you align your stereo vision regardless of the MUM rotation angle, or can you do it only in certain orientations?

Edit: To add to the testing methods, stars in the sky is probably the easiest way. Look up and see how the images differ between your naked eye and the one behind the NV.
Link Posted: 8/13/2014 7:32:31 AM EDT
Took it apart and did some tests again and can't tell anything wrong with the lenses. But I did notice the tube might not be sitting dead straight in there. I can push it from one corner and it tilts to another position, for about 0.2-0.3mm I would guess. The amount could be pretty close to what I'm seeing trough the system so I might see if I can add some padding on one side of the tube to get it permanently to that other position. I think it's the leads connecting to the tube that are pushing it. Could be it is supposed to be that way, or maybe they are pushing a bit too much.
Link Posted: 8/13/2014 8:27:43 AM EDT
[Last Edit: 8/13/2014 8:28:40 AM EDT by TheHorta]
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Originally Posted By murtis:
Took it apart and did some tests again and can't tell anything wrong with the lenses. But I did notice the tube might not be sitting dead straight in there. I can push it from one corner and it tilts to another position, for about 0.2-0.3mm I would guess. The amount could be pretty close to what I'm seeing trough the system so I might see if I can add some padding on one side of the tube to get it permanently to that other position. I think it's the leads connecting to the tube that are pushing it. Could be it is supposed to be that way, or maybe they are pushing a bit too much.
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The tube is "keyed" and should align properly with that key. If it's even slightly out of alignment the tube will not seat properly and may be what's causing your problem.
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