Using Filters with Convertible Large Format Lenses (Rear Group Only)

[blee1996]

For convertible large format lenses, typically you use rear lens group only for longer focal length. But without front lens group, how do you use filters? I guess people already figured this out one way or another?

 

[AZD]

I have not done this specifically with a convertible lens, but behind-the-lens filters are fine. Like all topics, subject to debate and such, but it’ll work.

My 12 inch f/4.5 Ektar has a 77mm thread up front and 72mm on the rear, so you can see the possibilities. I have also placed very thin gel filters against the rear cell, like a light cyan filter to knock down some of Foma 400’s extra red sensitivity. I have considered building/adapting a magnetic holder specifically for this.

The down side is you have to remove the back for any filter changes, and will likely (and probably should) end up focusing through the filter. This will of course result in dimmer image on the ground glass.

You could also devise a way to put a filter and shade on the shutter’s front side. That’ll work too, and may be more practical.

Over the years I have made many specialty photographic bits and bobs from cardboard, electrical tape, tin cans, metal scraps, balsa wood, discarded furniture, salvaged junk, and other treasures. Ugly but functional. There’s always a way.

 

[xkaes]

As mentioned, filters on the rear are possible, but a PITA.

All you need to add filters to the front is an appropriate step-up ring. Regular step-up rings won't work because the threads are usually not deep enough for most shutters, but some are made to do this. Check out RAF (at the bottom of the URL page.). That's where I got mine. Once you get an adapter ring, you can get a regular step-up ring(s) to whatever size you need. (And lens shades are just as important when only the REAR group is used).

https://www.subclub.org/fujinon/

 

[AZD]

That seems like the best option.

 

[blee1996]

The lens I have in mind is a Wollensak Raptar Series Ia triple-convertible mounted on Alphax #4 shutter. Ideally there will be a thread adapter for the front thread of the shutter.

Thanks for the pointer to RAF, from which I have bought several adapters in the past. Unfortunately they don't have anything for Alphax #4. Maybe I will send them the specs if they can make one. SKGrimes might be able to as well.

 

[blee1996]

I found a reasonable solution:

- Found an adapter ring for the Alphax #4 from another shutter
- Lee filter system holder with rubber band

The original lens front group and the adapter ring has a weird filter thread size: I measured about 60mm. I don't know if 60mm threaded filters and adapters exist or not.

 

[xkaes]

Since it says US ARMY on the shutter, it's probably not mm anyway.

 

[AnselMortensen]

The front threads on an Alphax #4 shutter are 2.422 in x 40 tpi.

 

[Focomatter]

I found a reasonable solution:


The original lens front group and the adapter ring has a weird filter thread size: I measured about 60mm. I don't know if 60mm threaded filters and adapters exist or not.

Leica has produced lenses with a 60mm filter thread. 60 to 62mm step-up rings can be used for more common 62mm filters.