Optivaron collimation

[carllooper]

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/zeiss-ikon/repair/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

[carllooper]

I posed the same question over at cinematography.com.

While not providing anything specific to the Optivaron, Dennis Couzin did provide a fabulous article on various methods for testing and determining requisite adjustments, including some material regarding the difficulties with a Bolex prism. There's enough information there to provide a good context for performing surgery on the lens:

http://www.cinematography.com/index.php ... 6&p=422712

Interestingly a guerilla method he suggested for any "negative shim" requirement on any back focus lens adjustment, was to insert a gelatin filter between lens and camera. This would insert a 0.03 mm difference to the adjustment. It's interesting because the reason a Beaulieu lens isn't optimal on a standard C mount camera (as I've discovered) is that the Beaulieu (like other Super8 cameras) used a gelatin filter. The lenses were collimated to account for this gelatin filter, making them non-standard on a standard C mount camera!

So a guerilla approach to using a Beaulieu specific lens on a standard C mount camera (such as the Logmar) is to just put a gelatin filter back in again (assuming the flange distance on the Beaulieu camera was otherwise a standard distance for C mount lenses). Of course this will introduce some additional material through which the image must pass, so not entirely optimal.

In any case I've got enough information to bite the bullet and perform tests and any requisite surgery on the Optivaron. Found these pics for lens dissassembly on the M-mount version of the lens:

http://www.mondofoto.com/tips/leicina-s ... on-repair/

I'll post some follow ups on how I went and what I did - once the lens (and camera!) arrives, and I've summoned the necessary courage.

C

[carllooper]

Update.

It turns out that the C mount Optivaron lens, made for the Beaulieu, was made to the C mount standard!

With the Beaulieu, it was the camera body flange depth that was adjusted a tad (to a non-standard depth) to compensate for the filter - not the lens. In other words the filter + non standard flange depth of the Beaulieu restored the effective flange depth of the Beaulieu as a standard C mount flange depth! Which would have been a very wise thing to do because it meant that any C mount lens (if it also conformed to the standard) would also work on the Beaulieu.

So that means if the Optivaron lens hasn't been altered since it was made (ie. it still conforms to the C mount standard), and the Logmar conforms to the C mount standard (as one would hope), then there's no need to re-collimate the Optivaron lens, at least not in terms of any reason to do with that lens having been made specifically for the Beaulieu. It should work, as is, on the Logmar.

Many thanks to Dom Jageur for clearing this up on cinematography.com. He has two C mount Optivarons and has confirmed they both conform to the C mount standard.

http://www.cinematography.com/index.php ... 6&p=422724

Yay.

Carl

[milesandjules]

Cool to know the beaulieu lens are standard. Cant wait to see what you do with your logmar to.

[carllooper]

Cool to know the beaulieu lens are standard. Cant wait to see what you do with your logmar to.

Me too!

I feel like a 14 year old again - eager to open a belated christmas present!

Speaking of which, there was a christmas I missed 40 years ago. On christmas eve we went to bed. On christmas day we climbed out of the complete rubble that was our home that summer, into the devastation that was Darwin on that particular day. A vista not unlike old black and white photos I'd seen of bombed cities. And out of that experience a kind of unshakeable respect for (and fear of) the forces of nature.

Waxing lyrical again ... ha ha.



C

[milesandjules]

Wow Cyclone Tracey survivor…well apart from that, i know the feeling of anticipation…it was bit like that waiting for our retro 8... how long till ya cam arrives?

[carllooper]

They're getting the film test back next week, and FedExing after that. Not sure how long it will take to get here.

C

[nikonr10]

Cool to know the beaulieu lens are standard. Cant wait to see what you do with your logmar to.

Me too!

I feel like a 14 year old again - eager to open a belated christmas present!

Speaking of which, there was a christmas I missed 40 years ago. On christmas eve we went to bed. On christmas day we climbed out of the complete rubble that was our home that summer, into the devastation that was Darwin on that particular day. A vista not unlike old black and white photos I'd seen of bombed cities. And out of that experience a kind of unshakeable respect for (and fear of) the forces of nature.

Waxing lyrical again ... ha ha.



C

Wow Carl look's like the higher power's ,were looking out for you ! Know that feeling off looking so much too that belate christmas present , hope you get it soon !

[carllooper]

So the Optivaron arrived yesterday.

I removed the "reglomatic" (or whatever it's called) and threaded the lens into a Bolex 16mm - just for the fun of it. According to what I understand, the lens should work on a Bolex 16mm, if used at the telephoto end, and one ignores the fact that is doesn't cover the entire 16mm frame. And indeed, the lens behaved in just such a way. At the telephoto end the image was perfectly sharp. On wide-angle it should be sub-optimal on the Bolex, but one would probably have to expose some film and blow it up large to tell, as I couldn't tell looking through the viewfinder.

It's going to be interesting testing this on the Logmar. If there is going to be any problems we won't know where to put the problem. The lens, the Logmar, or both? We can always guess of course, but that only provides a starting position for any test - it doesn't give us an actual answer.

The Logmar is a brand new camera and we don't know how exacting it might have been made in terms of flange depth. However we do know that the Logmar is manufactured with the intention that it have the precise flange depth required by the C-mount standard, ie. 17.526mm. And we know (both evidently and by good reason) that the Beaulieu Optivaron lens is likewise manufactured with the intention that it work with such a flange depth (on the Beaulieu camera we'd call it an 'effective flange depth' rather than physical one, but it means the same thing).

In reality one, or both could be out. How do we find out - short of a lab setup? Or indeed, with a lab setup? Because one of the things about the Logmar (or two things) is that backlighting the gate could be quite difficult, due to the position of the unit just behind the gate, and that the viewfinder isn't optical (otherwise one could shine a light through the viewfinder).

From what I've learned recently, RX lenses would also work on the Logmar, if sufficiently stopped down. The only difference between RX and otherwise regular C-mount lenses, is that the prism-correcting optics of the RX (which becomes a problem in this case since no Bolex prism on the Logmar) only becomes apparent when the aperture is wider open (and the problem they were designed to correct isn't as apparent when an otherwise ordinary lens is stopped down).

And machine vision lenses could also work just fine. But they may require stopping down as well, because like RX lenses, some may have some correctional optics involved, because digital sensors in machine vision cameras, while they don't have prisms, they do have something called a "sensor stack", which refers to protective glass and various filters (eg. IR) in front of the sensor. And some lenses may arguably correct for this. The sensor stack, however, won't be as thick as a Bolex prism, so if there is any correctional optics in a lens to accomodate a sensor stack, one may not have to stop down as far (compared to an RX) to bypass such corrections. But I'm unsure how many machine vision lenses could actually intend any such corrections. Many seem quite (and quietly) promiscuous in terms of what sensor/cameras they are happy to propose themselves as compatible. As if the term "C-mount", and a sensor size spec, was all that was required to decide compatibility. Perhaps there is some average stack depth that most assume. But in any case, like an RX lens, bright sunlight and an aperture ring would become a friend here.

In any case, looking forward to devising some ingenious DIY way of trapping the optical parameters into giving up their particular identity, and devising any particular corrections, if any, that may be required.

And of course, just shooting some film whatever the outcome.

C

[S8 Booster]

if you can get holt of some old Canon collimation tool stuff - they were designed for the 1014 & 814 XLS used for lens collimation - using the projection method - this was hi res films with tight route cross pattern all over the plane with a resolution of a minimum of 115 or 125 lpm to be projected through the lens (should be easy with your new cam) adjusting the collimation at two different distances. The cross hairs becoming in line all over the plane - something which may be difficult to achieve with the Optivaron but it may give you a sweet spot anyway.

if you know of some former Canon work shops in AUS the may by miracle still have some of these films/tools or possibly you can get hold of it elsewhere.

shoot......

[carllooper]

if you can get holt of some old Canon collimation tool stuff - they were designed for the 1014 & 814 XLS used for lens collimation - using the projection method - this was hi res films with tight route cross pattern all over the plane with a resolution of a minimum of 115 or 125 lpm to be projected through the lens (should be easy with your new cam) adjusting the collimation at two different distances. The cross hairs becoming in line all over the plane - something which may be difficult to achieve with the Optivaron but it may give you a sweet spot anyway.

if you know of some former Canon work shops in AUS the may by miracle still have some of these films/tools or possibly you can get hold of it elsewhere.

shoot......

Thanks for that info. I've worked out one way to check the Logmar camera flange depth using a motor driven postitioning platform I picked up off ebay, and a macro lens I use in transfers. I put a film loop in the Logmar, with markings on it. If it can't be backlit, it can be front lit, since no lens on the Logmar will play a role here. I then image the film plane, on a digital camera with the macro lens, ensuring the image is in precise focus. And then using the positioning platform I rack the Logmar camera away from the digital camera, counting off the number of steps (which have a resolution of about 2 microns) until the flange comes into focus (or some marker for such). I then have the flange to film plane distance in the number of steps taken.

I don't expect there to be any problem in the Logmar flange depth. Tommy at Logmar was quite specific about the flange depth being exactly 17.526mm.

But always good to do a sanity test on such.

The lens. With a lens on the Logmar it becomes difficult to illuminate the film plane. A better bet might be to test the lens independantly. I can work out a collimation based test to determine it's flange depth, but the real problem is in what to do if the lens proves incorrect. How to adjust the lens? I don't yet have any idea how to do this with the Optivaron.

If I'm lucky the lens remains, as it was originally designed, and I won't have anything to do at all.

Just shoot some film.

C