View Full Version : The King of Iris lens clamps?

Steven Tribe
27-Mar-2018, 05:06
I have realised that there was an alternative design for the most common German iris lens clamps used when the flange is is missing - or to speed up the selection of different lenses in the field. For every dozen or so German clamps there is perhaps a single Italian clamp. 3 or 4 of these have appeared in the "for sale" section here - although not currently.

A recent European auction landed me with one of these. The jumbo size, with a maximum opening of 120mm. This was stamped R.B.M Brevett 234175 - which must be an Italian patent number. The system must have considered reliable by the first user as it was still holding a 1850's large Voigtlander Petzval.

I think I can be considered to be able to compare this with the German variety, as I have owned six of these and overhauled a couple. The Italian is far superior in neatness of design and is far more robust in the turning mechanism and quality of the blades. Eddie, who sold one years ago, was equally impressed. There are plenty of good photos which appear using a search (titles only) here for iris clamps, but I have attached some of my own and a externally sold one which shows the missing turn screw on my example.

Does any know who R.B.M is? I think it is a quite late maker and may be the company name initials, like
F.I.A.T? They certainly deserve recognition in my view.

27-Mar-2018, 06:08
I have three of those Italian clamps (small, medium, xl). I would agree with you - they are a more robust design than the typical German models. The only downside is that they have a bit of a wider footprint to take into consideration when mounting.

27-Mar-2018, 22:15
How do these actually hold a lens? They seem thin to do so.

Steven Tribe
28-Mar-2018, 02:28
There are 24 quality steel blades that grip between the threads. To work properly, the edges must not be distorted or some of the blades will "hang" on the tops of the thread.

This is the same system as the common German variety. The total thickness is about the same but the mechanics are different:

- the Italian design avoids the 4 lugg design built into the casing by using a solid backplate which remains stationary in adjustment. The ends of the 24 pins are thus concealed.

- the front makes up the turning part of the iris. This is approximately 3 times thicker than in the German model. The gear and rack are similarly thicker - with finer and larger diameter gears.

I think it looks a lot cleaner in design than the German model. When I was looking at this mount on a photo showing a complete camera and lens, it took me some time to realise what it was.

Some photos of both types, the back of the R.B.M mount and with a lens mounted.

I have searched quite a few Scandinavian, German and French catalogues without being able to find the model. It would be nice to know whether there was a price differential compared with the more usual model.