Setting the back focus on a Birger EF mount

[Nick_Brown]

I'm going to make a note here because it took me a while to figure out. Most of the tutorials and instructional videos have long since been taken down so maybe it can help someone else. Eric Birger was very responsive when I reached out but I couldn't quite visualize what he was saying.

When mounted the Birger EF adapter to my camera, and found that I could turn the innermost ring by hand. However, I noticed that I could only turn it a little bit, not all the way around like the numbers suggested. I realized that what you have to do is to take the WHOLE Birger mount off (leave the Canon lens adapter attached), and then you can freely turn the collimation ring from the back side of the adapter. It turns easily without the camera body pushing up against it.



To collimate, I mounted a lens (at fastest f-stop) to the detached mount, measured out the minimum focus distance marked on the lens and placed the camera accordingly, powered the camera on, and then just held the Birger mount up to the camera to see if my target was in focus. Did this a few times until I got a tack sharp image.

 

[180Legacy]

Thanks for the info! Any chance you know where I could get one of these mounts?

 

[Michael Hastings]

Nick: IIRC you can just loosen the screws and turn it from the front by putting your fingers internally and rotate it without actually fully removing it. Should be a little quicker to rotate then tighten to test if it is right or loosen again for more adjustment without having to take it all the way off and on again. (I had the very first Birger mounts)

 

[Matt Minott]

If anyone can answer this would be most helpful. I just purchased a kit with the birger mount. I'm likely returning it because the fan is no good. But how would I go about adjusting Iris with this mount? It came with the wireless controller by Viewfactor but that too doesn't work. So with a new non-manual canon/sigma lens, how do I adjust iris?

I suppose if I can find a way to fix the fan i'll consider keeping it!

 

[Nick_Brown]

@Michael I was able turn the collimating ring from the front, but not enough to make the adjustment I needed to make. The only way I was able to achieve that was by removing the mount and adjusting as mentioned above. I don't know, maybe once that's been done it can be adjusted from the front for fine tuning.

@Matt Mine doesn't have the wireless controller but I'm pretty sure that you can control the aperture with the silver buttons on the sides of the adapter. However, the mount needs to be powered to do this. I have a 4pin lemo but I haven't been able to power mine from the aux ports. That might be the result of needing to regulate power from the aux port, dead aux ports (I tried them both), or possibly a limitation of the mount firmware. Erik Birger told me "do not update the software on the unit. Newer versions do not support the lens data to the camera, or the push buttons." At this point, I'm treating it like a dumb, passive adapter. But if you figure it out, please let us know.

 

[Michael Hastings]

@Michael I was able turn the collimating ring from the front, but not enough to make the adjustment I needed to make. The only way I was able to achieve that was by removing the mount and adjusting as mentioned above. I don't know, maybe once that's been done it can be adjusted from the front for fine tuning.

@Matt Mine doesn't have the wireless controller but I'm pretty sure that you can control the aperture with the silver buttons on the sides of the adapter. However, the mount needs to be powered to do this. I have a 4pin lemo but I haven't been able to power mine from the aux ports. That might be the result of needing to regulate power from the aux port, dead aux ports (I tried them both), or possibly a limitation of the mount firmware. Erik Birger told me "do not update the software on the unit. Newer versions do not support the lens data to the camera, or the push buttons." At this point, I'm treating it like a dumb, passive adapter. But if you figure it out, please let us know.

Nick: yes, if the sensor on your Red is too far off to do the adjustment with the screws just loosened you would have to take it off. RedOne sensors were notoriously all over the place which is why they had to come up with the adjustable PL mount (first 100 cameras had a fixed pl that required shims to adjust and were recalled).

BTW you will void the warranty on your RedOne if you weren't one of the original 200 or so Birger people. :wink5: might be out of warranty after 12 years anyway.

seriously however, be very careful not to get the data wire from the pl mount jammed improperly under the Birger, if it gets cut and shorted there isn't any protection and you may fry some circuit boards.