Rod base, bridge plate/dovetail solutions for ACLs

[Gregg MacPherson]

The ACL 1, 1.5, 2 all have a different vertical dimension between the lens axis and the bottom of the base. Hence, adapting generic accessories to these cameras can be problematic. ACL 1 could be given a spacer to raise the base,  but ACL 2 is too tall, unless the rod clamp can be packed up. The 1.5 may be close to OK on generic base plates/bridge plates. I'm hoping that Heikki will measure the vertical dimension on his 1.5. Here's a drawing of the ACL 2 with all rod positions shown, 15mm LWS, 15mm studio, 19mm studio...If you print the pdf below at 100% it will be 1:1 scale. There's a link to Arri's drawing with the rod position dimensions at the bottom of this post.

ACL rods and camera base w tie down.pdf

It would be useful to know the position of the ACL 1 and 1.5 base on that drawing. One could measure on the camera. An accurate mark for the lens axis on a lens cap (the centre), then measure vertically down to a flat bench. A builder's square helps. 

Ready made solutions for mounting 15mm LWS rods on ACL 1.5 and 2 (and maybe ACL 1) are available as rod mount brackets (plates) that screw to the camera base. Les Bosher's version for example. These designs are monofunctional. Multifunctional designs can obviously be more useful and from a design perspective they are very interesting.

The support (base plate/bridge plate) immediately under the camera might have multiple functions including some or all of...

- Rod mounts for 15mm LWS/15mm studio/19mm studio
- Dovetail interface for balance.
- Accepts a shoulder mount.
- Enables mounting batteries to the rear
- Rossetts for front handle sets

The Proaim bridge plate/dovetail CH-DTPQ-01 came up on the forum recently and was favourably reviewed. 

(the dimension in red, Proaim gives it as 14mm)

The Proaim page may change, but here it is...
https://www.proaim.com/products/proaim-19-15mm-camera-base-plate-with-dovetail-tripod-plate-arri-standard

Proaim, manufacturing in India I think, have a history of cloning/paraphrasing generic high end industry gear. Out of design curiosity I bought, a few years ago, cheap, used, a Proaim 4x5.65 swing away MB and a studio FF that looked like a Chrosziel. They both had some really good design engineering but were let down by (literally) one or two really small but sometimes fatal errors. So I've always been interested in ideas from Proaim.

The CH-DTPQ-01 would be an inexpensive way to enable 19mm support for big lenses. Does anyone know if 3/4" (19.05mm) tube will fit generic 19mm machined rod mounts. Thin walled chrome molly steel would be an easy way to get stiffness, but I've only seen it in Imperial sizes. (Edit: I just tried some imperial 4130 tube on the Proaim and it fitted well. I wonder if Arri 19mm hole sizes would also fit. 

If mounting the ACL 2 on this bridge plate the lens axis would be too high for the integral 19mm rod mounts, but some adaptions could be possible -  custom risers for the MB and lens support. I wonder how close to OK the ACL 1.5 lens axis is. If not using the 19mm rods for MB or FF then the 15mm rod mount can be packed up to height. 

This bridge plate adds some height and if a shoulder pad is mounted under it the result may shift the camera too high, considering the eyepiece position and the sense of balance and stability.

The dimension in red in the photo above , Proaim give it as 14mm.

If you want to measure the height of the lens axis on your ACL 1 or 1.5 that would be really useful. (thanks in advance) If you have any experiences adapting an ACL to generic bridge plates, rod mounts feel free to share here....

There is an Arri drawing showing the measured positions of the various rods relative to the lens axis here...

https://thecinelens.com/2014/01/27/iris-rods-a-simple-explanation/

 

Gregg.

 

 

Edited October 13, 2023 by Gregg MacPherson
more words.update dwg

[Gregg MacPherson]

The ACL 1.5 lens height (distance from the camera's lens axis to the bottom of the base) looks very close to lining up to the matte box axis  on the CH-DTPQ-01 bridge plate.  Heikki could check.?

[Gregg MacPherson]

The other thing we did not consider yet is the tie down screw offset.

Proaim give the position of the 3/8" tie down screws as being centred on the 19mm rods, but ACL 2 has the screw about 9mm offset to camera left. I'll update that drawing. Doesn't look like there is room to make a new hole or slot in the bridge plate. One needs to tap a new hole in the camera base.

Does anyone know if the 3/8' tie down taped hole is also offset in the ACL 1 and 1.5 base? To be clear, the offset referred to is  horizontally from the lens axis.

Edited October 2, 2023 by Gregg MacPherson
grammar