Curtis Bros Brass Lens

[AuditorOne]

I have an old brass lens that I know next to nothing about. I've done a couples internet searches but haven't come up with much info.

Curtis Bros and Dublin is engraved on the barrel. It has aperture setting starting at f8 and ending with f44. The sequence is f8, f11, f16, f22, f32 and f44.

It appears to have a lens or group of lens on either end with the aperture in the middle so I'm thinking it is a Rapid Rectilinear but I don't know. The aperture does move but it is very stiff and moves slowly.

Each lens, or lens group on either end is convex to the outside and is concave to the inside. The front part with the hood does unscrew so I could get to the aperture leaves in the middle to clean or oil them.

I see no other markings but the lens barrel is very scratched up. Any varnish coating that may have been on it is long gone.

The diameter of the barrel is 2.5 inches and it is a little over 4.5 inches long including what appears to be the built in hood at the one end. It has no retaining ring but the threads for one are on the end of the barrel.

Is there anyone who may have any information that may help me identify it. I guess I could send it to SK Grimes and have them make me a new retaining ring.

[BrianShaw]

It sounds like a RR and very well could have screwed into something like a Thornton Pickard shutter… the flange probably still on that shutter, wherever it ended up.

[arri]

It is an aplanatic lens and I guess that it is a rebranded one. A lot of sellers ordered lenses by the makers with their own names. I have a lens engraved with "Thomson Brothers" and I think it were made by Dallmeyer or Ross in UK.
There are not so much differents between the Aplanat lenses. Standard aperture were f/8 or f/9.
Portrait aplanat lenses were available with f/5 or f/3.5 (Voigtlander)

When the aperture is stiff please check if it is only the driver ring. The old grease is hardened and the rings are running in the thread with a very small pitch. This old grease hold the ring tight.
To check it: open the aperture to the max. value than remove the little screw with is the connection between the driver ring and the moving ring of the aperture inside the lens.
When this screw is removed you can unscrew the driver ring. Maybe you realise now that it turn very heavy, this is an indication of hardened grease.
Remove the ring complete, clean the thread of the driver ring and the barrel, mayby you need a glass fiber oder brass brush for it. A cleaning solvent helps also. No WD40 or other oils.
When the treads are cleaned you assemble the driver ring again and set the little screw, take care that the screw fits into the little bore inside the moving aperture ring.
Now the aperture should run smooth again.

When you clean anything please remove the lens cells first! The Canada balm is sensitive to a lot of cleaning agents, specially ethanol and acetone.

[AuditorOne]

That is great information. Thanks.

[Steven Tribe]

Neither Ross or Dallmeyer have been identified as supplying unengraved lenses to Magic Lantern makers or camera products retailers. But there were a host of smaller, recently started, UK lens makers that did. A lot of French makers did so as well.

[AuditorOne]

The lens barrel itself is scuffed up enough it may be impossible to see them but manufacturers leave marks of some type on the lenses, inside or outside. If so, is there a reference of those marks anywhere?

[Steven Tribe]

I doubt there are any maker’s Marks anywhere!
In the earlier era - pre 1870 - with lots more brass surfaces, there were often good areas to stamp initials, serial Numbers etc. and even the details of lathe work could reveal maker. But by the rapid rectilinear period, things had got pretty standardised.