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DIY lens collimation

collimation optivaron Super8

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#1 Carl Looper

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Posted 15 January 2015 - 10:12 PM

I've never done this before but I completely understand the theory.

So I want to collimate a lens and in particular a C-mount Optivaron (6-66mm), originally collimated for the Beaulieu, but for repurposing on a standard C mount camera (the Logmar).

I can follow the theory of what's going on in the following guide - basically it's using a camera and lens already understood to be correctly collimated, and focused at infinity, to image the image plane on the other camera, with it's lens also set to infinity, but in an unknown collimated state:

http://elekm.net/zei...pair/collimate/

This I can manage quite well using a DSLR as the imaging camera - or rig up some alternative setup with diode lasers etc. Can do all the required levelling, making sure it's all parallel etc.

What I don't know, but would love to know, is what I need to do with the Optivaron lens in order to modify it's collimation setting. I understand it will need to be partly disassembled. I'm perfectly fine with that. Just don't know what rings/notches/or whatever, inside the lens, need to be rotated/moved in order to tweak it's collimation setting. I can certainly open it up and experiment (and will eventually work it out) but if someone knows how to do it already, that will certainly save me some anxiety.

Any advice much appreciated.

Carl


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#2 Dennis Couzin

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Posted 16 January 2015 - 12:08 AM

My old article on DIY optical adjustments describes completely different methods from Mr. Elek's, but there is one point of disagreement: there are reasons not to use maximum aperture.  


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#3 Carl Looper

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Posted 16 January 2015 - 01:45 AM

My old article on DIY optical adjustments describes completely different methods from Mr. Elek's, but there is one point of disagreement: there are reasons not to use maximum aperture.  

 

Thanks so much Dennis.

 

Carl


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#4 Dom Jaeger

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Posted 16 January 2015 - 02:48 AM

Hi Carl,

 

the proper way to adjust back-focus on the Schneider 6-66 Optiivaron is to undo the outer lock ring at the rear, lift out the rear optical group, and change the shims beneath. Without knowing exactly how many hundredths of a mm you need to add or remove, this would be something of a chore, particularly as you would need to cut your own shims and test them by trial and error.

 

The rear C-mount assembly screws on, so you could potentially undo the grub screw(s) locking it in place and unscrew it while checking collimation, to get a sense of where correct back-focus might be, but you can only do this adjustment in the one direction (adding distance), because the assembly is screwed down to a flat surface. 

 

To correctly adjust a zoom, you start by setting focus at the telephoto end, then go to the wide end to adjust back-focus for best sharpness. You generally need to go back to the long end to re-adjust focus again, then back to the wide end to tweak the back-focus.

 

If you like, you're welcome to drop in to my workshop and I can check/adjust both camera and lens for you, I'd be curious to see the Logmar if you have it already. But you'll need to do it in the next 2 weeks as I'm about to go on a year-long sabbatical.

 


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#5 Simon Wyss

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Posted 16 January 2015 - 03:25 AM

The terms again, let me please correct.

 

Collimation has nothing to do with the adjustment of focus. One cannot set a lens’ focus with a collimator. The (auto)collimator is an instrument for checking and adjusting deviating angles.

 

Dennis will most certainly protest and try to shoot this down.

 

Would everybody please express themselves as precisely as possible, always. Carl wants sharp pictures. A sharp mind is a prerequisite.

 

Else, Dom says it all.


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#6 Carl Looper

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Posted 16 January 2015 - 05:01 AM

Hi Carl,

 

the proper way to adjust back-focus on the Schneider 6-66 Optiivaron is to undo the outer lock ring at the rear, lift out the rear optical group, and change the shims beneath. Without knowing exactly how many hundredths of a mm you need to add or remove, this would be something of a chore, particularly as you would need to cut your own shims and test them by trial and error.

 

The rear C-mount assembly screws on, so you could potentially undo the grub screw(s) locking it in place and unscrew it while checking collimation, to get a sense of where correct back-focus might be, but you can only do this adjustment in the one direction (adding distance), because the assembly is screwed down to a flat surface. 

 

To correctly adjust a zoom, you start by setting focus at the telephoto end, then go to the wide end to adjust back-focus for best sharpness. You generally need to go back to the long end to re-adjust focus again, then back to the wide end to tweak the back-focus.

 

If you like, you're welcome to drop in to my workshop and I can check/adjust both camera and lens for you, I'd be curious to see the Logmar if you have it already. But you'll need to do it in the next 2 weeks as I'm about to go on a year-long sabbatical.

 

 

Thanks Dom - I don't think the camera will be here in the next two weeks. From what I understand they are testing the first batch as we speak, individually testing each one with a roll of film, before shipping them out. But if it does arrive in nthe next 2 weeks will certainly give you a call. However I may get the lens sooner, so perhaps I could come and see you and you could show me what sort of things I'll need to play with to adjust it. Pick your brains!

 

From what I understand the Optivaron was calibrated (if that is a better term) for the Beaulieu Super8 camera (which used a gelatin filter). So in theory, one could use Dennis' geurilla method for "negative shimming" and just re-insert a clear gelatin filter back into the path to get it behaving on the Logmar - assuming of course that the Beaulieu otherwise had a standard C-mount flange to film plane distance. But of course, if it has shims already in there (to accomodate for a gelatin filter) can just remove those instead (for a clearer optical path).

 

cheers

 

Carl


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#7 Carl Looper

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Posted 16 January 2015 - 05:15 AM

The terms again, let me please correct.

 

Collimation has nothing to do with the adjustment of focus. One cannot set a lens’ focus with a collimator. The (auto)collimator is an instrument for checking and adjusting deviating angles.

 

Dennis will most certainly protest and try to shoot this down.

 

Would everybody please express themselves as precisely as possible, always. Carl wants sharp pictures. A sharp mind is a prerequisite.

 

Else, Dom says it all.

 

Yes, that's very true - but I understand the origin of the short hand. A lens, if focused at infinity, is effectively creating a focused image from parallel (collimated) light rays (so to speak). This is the reference state for the lens, ie. the state in which you want it to be when establishing the distance it needs to be from the film plane. One speaks of "collimating" the lens, but really one is collimating the light (or the image) - not the lens - but a byproduct of which then allows the lens focus plane to be found.

 

C


Edited by Carl Looper, 16 January 2015 - 05:15 AM.

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#8 Carl Looper

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Posted 16 January 2015 - 05:32 AM

I should have said "focal plane" in that last sentence.

 

C


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#9 Dom Jaeger

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Posted 16 January 2015 - 05:43 AM

Both of the Optivarons I own are perfectly collimated to the C- mount standard of 17.52mm, I believe the Beaulieu camera flange depth is what was (very slightly) adjusted to compensate for the gelatin filter rather than the back-focus of the stock zoom. This makes sense as the camera can then accept other C-mount lenses.

So chances are the zoom will work fine on the Logmar, as long as the Logmar flange depth is good.

I recently had someone bring in a Digital Bolex that had a very badly set flange depth, not only off but not even flat to the sensor! Hopefully the Logmar guys are more diligent.
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#10 Carl Looper

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Posted 16 January 2015 - 06:13 AM

Both of the Optivarons I own are perfectly collimated to the C- mount standard of 17.52mm, I believe the Beaulieu camera flange depth is what was (very slightly) adjusted to compensate for the gelatin filter rather than the back-focus of the stock zoom. This makes sense as the camera can then accept other C-mount lenses.

So chances are the zoom will work fine on the Logmar, as long as the Logmar flange depth is good.

I recently had someone bring in a Digital Bolex that had a very badly set flange depth, not only off but not even flat to the sensor! Hopefully the Logmar guys are more diligent.

 

Ah okay. So the Optivaron was made to the C mount standard and it was the Beaulieu flange depth that was adjusted to accomodate the filter - not the lens. So if the logmar flange depth is standard (and correct), and the lens is good, then nothing required.

 

I went back over my research and found my error - it's in a misreading of the following:

 

http://www.cinematog...=30721&p=229845

 

While Jean-Louis does say it was the camera flange depth that differed, I completely glossed over that. Indeed re-reading it now, I'm not sure I understand his reply at all. If it was the Beaulieu flange depth that was non-standard - to accomodate the filter, then the lens wouldn't have been "collimated" to this particular camera at all - since the non-standard flange depth + filter would have recorrected everything, ie. before the lens was brought into the picture..

 

Anyway, so all that's left to consider is how precise the Logmar is in terms of it conforming to the C mount spec. And if the lens is still good.

 

cheers

 

C


Edited by Carl Looper, 16 January 2015 - 06:13 AM.

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#11 Dom Jaeger

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Posted 16 January 2015 - 06:45 AM

Well maybe I've been lucky that both my 4008 Optivarons were correctly set, from that thread it seems other people didn't have the same experience. Perhaps Beaulieu's quality control wasn't always the best and so lenses were adjusted to the camera without particular regard to the standard. But it would certainly have made sense for them to at least try and make the camera flange depth be adjusted for the permanent filters so it would work for other C-mount lenses.
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#12 Carl Looper

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Posted 16 January 2015 - 07:51 AM

Well maybe I've been lucky that both my 4008 Optivarons were correctly set, from that thread it seems other people didn't have the same experience. Perhaps Beaulieu's quality control wasn't always the best and so lenses were adjusted to the camera without particular regard to the standard. But it would certainly have made sense for them to at least try and make the camera flange depth be adjusted for the permanent filters so it would work for other C-mount lenses.

 

Yeah for sure. It makes complete sense that the body + filter would be intended as a complete correction. As you say, in that way a range of lenses could be used on the Beaulieu - not just the Optivaron.

 

And considerig that you have two Optivarons, both of which just happen to conform to the C-mount standard, I reckon that makes it a pretty safe bet that such was the idea.

 

Anyway, will see what happens. Just got word from Logmar that they are getting their test back next week, after which they'll be FedExing the camera.

 

cheers

C


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#13 Dennis Couzin

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Posted 16 January 2015 - 03:18 PM

...

 

Collimation has nothing to do with the adjustment of focus. ...

 

Dennis will most certainly protest and try to shoot this down.

 

...  A sharp mind is a prerequisite.

 

No protest on that.  If you'd read my 1991 article on DIY optical adjustment, you'd find no words "collimate" or "collimator" in that. Optical knowledge is to the point, and doesn't hide behind fancy words.

 

I thank Carl Looper for correctly dubbing a method in the old article as guerrilla.


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