Birger Collimation Lessons Learned

[Bob Gruen]

It took a little analysis to figure it out so I thought I'd share what I learned.

First, the Birger is a three piece unit. The collimation ring is actually a screw (for lack of a better term) and it is what actually butts up against the face of the camera. The large outer piece is actually best visualized as a large clamp that presses the collimation screw into the face of the camera via the 4 4mm screws. The center piece is the Birger lens mount itself.

There are two things that will make your experience easier.

First is to loosen the collimation screw before you mount the unit. mine was tightened down to the point where applying pressure from the back was the only thing that would break it loose. (I suspect it was hand tight when shipped but it was pretty cold when I was working with it.) Once it was free is spun easily.

Second is the method: I used two different prime lenses to set the collimation, a 50mm and an 85mm. I set up a target 3 feet from the focal plane because both of the lenses had discreet markings for 3 feet. With the collimation lens at 0 I loosened the 4 4mm screws that hold the clamp to the screw and gently pulled on the mount while watching the monitor, keeping the clamp against the screw heads. I continued to loosen the 4 screws until the focus got close. Then I removed the lens and screwed the collimation ring into the camera face to tighten the assembly up. At this point it was close and just an iterative process of mounting the lens, popping it off, adjusting the 4 4mm screws and collimation ring in tandem and remounting the lens. In 4 or 5 attempts I was finished. Checked it with both lenses at 3 feet then both lenses at their respective minimum focal lengths. The only thing to watch out for is that the final tightening of the clamp should be slow and even, doing each screw in a criss cross pattern.

Did a little shooting and was very impressed. The only problem was the 85mm 1.8 lens needs to be internally driven as the clutch between the manual focus ring and the lens is just too loose. Maybe mine is defective...

Bob

 

[Clint Johnson]

I would think that a wider lens would make for a better collimation since the focal plane is shallow with them than with the longer lenses. With the longer lenses you can collimate them adequately while leaving the focal plane of wider lenses in front of or behind the sensor. If you get it zoned in with a lens like the 24mm f1.4L II then it should be more likely that most lenses will fall into focus.

 

[Karl Gustav H.]

I would think that a wider lens would make for a better collimation since the focal plane is shallow with them than with the longer lenses. With the longer lenses you can collimate them adequately while leaving the focal plane of wider lenses in front of or behind the sensor. If you get it zoned in with a lens like the 24mm f1.4L II then it should be more likely that most lenses will fall into focus.

Yep, always collimate with the widest, fastest lens possible to ensure that the focus plane is as shallow as possible. It's also a good idea to make sure that the lens is strait and true. Get a friendly lens tech or rental house to throw it up on a projector.

 

[Bob Gruen]

These were the only two primes that I had on hand. I plan on testing each lens in my set as they come in.

Also, these are still lenses and as such do not have the exacting markings that cine lenses do. To get any more exacting will require access to the internal counter of the lenses to find absolute lens zero. That's on the way as well...

Bob

 

[Ivan Cortazar]

If you get it zoned in with a lens like the 24mm f1.4L II then it should be more likely that most lenses will fall into focus.

I've been trying to get a hold on that one. But it has been back ordered since December. I am starting to think that that lens doesn't exist!