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Red Birger Lens Mount unofficial mini-FAQ and thread compilation.

The following is a compilation of REDUSER posts made by Birger’s own Erik Widding. Alot of this info is scattered among different threads so I decided to organize them for easy reference. Some of this information is subject to change until the first units are released. REDModz is not affiliated with the Birger company but we do have an early reservation and will be conducting a review as soon as it lands.

Update by Erik posted on REDUSER 1/15/07.
“This poll was started because of a conversation I had with Stuart last week. I expressed that it seemed as if the camera was designed to make it easy to change the mounts occasionally but not often. He asked if my customers really had a need to swap mounts often. Rather than assume I knew, I asked. Thanks to all for the feedback. What I need to do is obvious now.

PL has a focal distance of 52mm and Canon is 44mm. So it is not possible to adapt the second to the first. The P+S route won’t work either, if they can mate to a c-mount(17.526mm back focus) there is no way to get this onto a camera with a 17+mm front face.

I have attached a photograph of the front of the camera, with the /i cable hanging out of the front. This cable is not designed for repeated plugging and unplugging.

There are three different connectors that we can attach to on the camera, we need to connect to two of them to get everything we need. The /i connector has a data connection, but not enough power. The auxillary (lens) connector has a data connection but not enough power, and uses a freaking expensive LEMO connector. The auxillary power, has enough power, but no data connection, and uses a much cheaper LEMO. So connecting to the /i inside the mount really makes a lot of sense.

The adjustable feature on the mount from RED is not really a reasonable choice for the mount system from Birger. The mounts can be manufactured to a tolerance of +0 -0.02mm, so if the camera has a reference surface any mount can be attached to any camera.


The solution to these problems is to use shims to get the front of the camera zeroed out, and to use a plate to retain these shims on the camera so this zeroing only has to be done once. This plate will also have a small connector board on it to allow the four /i contacts to be picked up by the mount with spring loaded pins. Any Birger lens mount will simply attach with four or eight M4 screw, and a LEMO cable to the auxillary power on the back of the camera. No additional collimation (beyond the first time) will be required.

Now for the PL mount need. If it is being done occasionally, one can remove the shims and plate from the front of the camera, and reattach the RED PL mount. Or if one is going to be swapping mounts all of the time, he can use a Birger PL mount, which we will announce in a week or two. We may offer other mounts in the future.

Collimation (shimming) of the mounts is quite straightforward. It can be done in about an hour, by an inexperienced person, with an allen wrench, a good zoom lens, and something to look at. We will also offer an inexpensive collimator, and will look at ways to make these available to area RED user groups.

There will be no additional cost for the changes. The shim kit plus an auxilllary power cable (LEMO 4pin + 4pin) will be the same cost as the old camera cable (LEMO 10 pin + 4pin). The mount concept is finished. THe final details (like shim thicknesses and such) will take a few more days. We need the rest of the week to work out final details.

If it weren’t for Stuart’s support at RED, this product wouldn’t be on track.”

Update by Erik posted on REDUSER 1/04/07.

“We can’t finalize the design and tooling until I get aqua’s camera (a real production 100+ serial number camera). Aqua will get his camera back with a pre-beta unit. Which will make three units in circulation. The other two are with the DP of a popular national TV program and a production company that shoots mostly commercials. Both have agreed to post, and or allow me to post, some frames next week. Beta units will be available one to two weeks after that date, and production will start up another week after that. I will post next when I have something new to communicate.”

Erik also added “I have kept the “free remote” offer open.” So it looks like you can still jump into the action (until Erik says otherwise) by downloading their order form:

Left pic: is a pre-beta lens mount, which also happens to be a production lens mount that has been adapted to the camera, rather than one custom designed for it.
Right pic: is a pre-production board in the pick and place machine. The board takes about 90 seconds to populate. (The truly observant will note that I placed the board back in the machine, after it had been through the oven)

Will it have autofocus?

No autofocus. Not yet at least. We have a future module planned that will communicate with the lens mount and watch the video tap on the camera to effect auto-focus, and more importantly for cinema applications, an auto-interactive focus, which will overcome some of the problems with a traditional auto-focus. The system will not simply be based on the two dimensional image from the camera sensor. It will also be based on a three dimensional understanding of the dynamic scene. This is based on something we are working on for a homeland security application. I will not be releasing any more details about this until we are ready to demonstrate the technology. This will probably be 2Q08.

Is the Birger Mount Upgradeable?
It is a system based concept. All modules are software upgradeable for the life of the system. The auto-interactive-focus module, will simply be a plug in accessory.

Will it have image stabilization support for EFS?
All mounts support IS, VR, etc…

Will it have breathing compensation?
It is one of many features on a list for later. Once we either release our own zoom motor, or have integrated with the RED motor, we will look at implementing this. The real issue is the production of the calibration data. We have ways to do this automagically… but that will require our auto-interactive focus module that we will not be announcing for some time…The other request that comes quite often is aperture comensation on variable aperture zooms. Because of the quarter stop steps of the Canon iris mechanism, this feature may not be that interesting without some intervention in post. THis also requires a zoom motor

Will you always have the same full control range on the slider/ff knob?
Range of motion is the same across lenses. But the resolution of that motion may be different. The knob will always have the same 4000 steps. But the lenses vary from a few hundred steps, to many thousand.

Is there any time delay or lag in the focus knob?
Minimal. The knob poisiton is measured, and then the result is communicated to mount, which then commands the lens to update its position. This measurement happens at a fixed interval, which has in testing been on the order of 25 to more than 60 times per second. We will probably want to synchronize this to the frame rate of the camera. The lag is on the order of one time interval, plus the motor response time. If the knob is moved faster than the lens is capable of moving, the lens will eventually catch up. If memory serves, an iris move takes about 50mS.

On power off then on, does your focus and fstop return to previous values?
No, but we certainly could make this a software feature. The iris stays in the same phsical position when powered up, but its absolute position is not known (unless of course we store it in the mount). The focus position can be measured on power up and moved back to the same location. Regardless of operating mode, when powering up, a homing operation is required on both axes.zz

How is the iris set?
The iris is set through a second knob, a bluetooth enabled PDA or computer, our wireless remote control, some third party bluetooth device… or a menu in the RED camera or using the RED superGrip… if and when this makes RED’s priority list.

Erik, how many steps for the Canon 24-70 f2.8L and Canon 70-200 f2.8L IS?
Only have the data readily available for a few lenses:
CANON LENS EF 50mm 1:1.4 USM: 660
CANON ZOOM LENS EF-S 10-22mm 1:3.5-4.5 USM: 1185
CANON LENS EF 14mm 1:2.8L USM: 1398
CANON ZOOM LENS 16-35mm 1:2.8L USM: 1566
CANON LENS EF 100mm 1:2 USM: 1687
CANON LENS EF 28mm 1:1.8 USM: 1800
CANON ZOOM LENS EF 28-105mm 1:3.5-4.5 USM: 1900
CANON LENS EF 200mm 1:2.8L USM: 2098
CANON ZOOM LENS EF 28-135mm 1:3.5-5.6 IS USM: 2276
CANON ZOOM LENS EF 70-200mm 1:2.8L IS USM: 2512
CANON LENS EF 35mm 1:1.4L USM: 2517
CANON LENS EF 24mm 1:1.4L USM: 2521
CANON MACRO LENS EF 100mm 1:2.8 USM: 2535
CANON MACRO LENS EF-S 60mm 1:2.8 USM: 3298
CANON LENS EF 200mm 1:1.8L USM: 3706
CANON LENS EF 85mm 1:1.2L USM: 4212

Posted by Erik on 07/03/07

Attached are pictures of the rail-mount follow focus knob and Canon EF lens mount prototypes. These were printed on a Dimension 3D printer using ABS plastic. The main housings of both will be made from aluminum, and the knob from injection molded polycarbonate. The bayonets will be made from stainless steel.

The follow-focus knob contains a 4096 count magnetic encoder; is selectable between single turn with hard stops, and multi-turn; has a friction adjustment; and has snap-off markable rings (white part). The lens mount has a built in bluetooth antenna. Each module has two LEMO 0B connectors for daisy-chaining power and RS232 from the camera to these (and yet to be announced) modules.

In addition to the open Birger protocol, the lens mount also speaks Fuji and Cooke-like lens protocols so it can be used with existing lens control, data-logging and data-display equipment. The protocol used on each of the three ports (bluetooth, 2 x RS232) is configurable on a port by port basis.

Changing lens mounts requires disconnecting one (or two) LEMO 0B connectors from the bottom of the mount, and removing and replacing the four screws (visible from the front of the mount in the images) with an allen key.

Pics posted By Ketch Rossi -preliminary Tests on Manny’s camera:


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