Helical focusing mount for enlarging lenses

[David Brown]

How hard would it be for a decent machinist to make a simple helical focusing mount for standard 39mm enlarger lenses? Seems like it wouldn’t be much more than a short macro extension tube with the helical. Would not need that much play, since rough focusing could still be done with bellows, and then fine focusing with the helical.

Could it be adapted from an existing helical by a lens person (Flutot, Grimes, that ilk?)

Or, does such a thing already exist?

(Inspired by the thread on enlarger focus problems and tin foil …)

 

[ic-racer]

I didn't see the specific enlarger problem, but depending on the enlarger in question, something as simple as a larger focus wheel can help:

 

[tedr1]

Rodenstock made a helical mount for some of their enlarging lenses, one might turn up used perhaps?

How much travel do you need?
How many turns do you want?

The helical mount familiar from camera lenses usually has a small amount of travel, enough to focus the lens of a 35mm camera from infinity to close-up. However the travel that is usual for an enlarger lens to focus is much greater, many times greater, in part because the negative stays still and the lens has to move. There are long travel helical mounts, some are found on projectors for example, but the fabrication of the thread needed to do this is not a simple machining job unfortunately. It might become an expensive project.

 

[faberryman]

You need very little travel, just enough for fine focusing. My Beseler 45MXT bellows is a little rough.

 

[David Brown]

... depending on the enlarger in question, something as simple as a larger focus wheel can help:

I used to have an Omega D5 with a "Dual Range" attachment. It was essentially a geared device to do the same thing.



I found just what I was trying to describe on amazon, but not in a 39mm to 39mm configuration. Many m42 (42mm) models (I suspect the same thing marketed under many labels) and this one with an adapter for a 39mm mount screw lens. Usable with one of two options: 1) another adapter at the lens board, or 2) a lens board drilled for 42mm.

I think this would at least be a consideration for folks who have older enlargers that have play in the bellows.

https://www.amazon.com/Pixco-Adjust...910814&sr=1-3&keywords=39mm+focusing+helicoid

EDIT: and see below ...

 

[gorbas]

There are plenty of M42 helicoid ficusing rings on Ebay. Unfortunately they are not super smooth (at least one I bought from China was at best so-so). Also I have one made by Asahi Pentax and it’s superb. I have one made by Durst and its more focusing screw than helicoid. Its for sale if you are interested?

 

[Jim Jones]

Some enlargers don't have enough room to insert a helicoid between lens and lens board and still permit focusing for large prints.

 

[gorbas]

Jim, you are right. Durst lens board i mention before is deeply recessed and thats on other hand limits external diameter of the used lens. Im away from the home but will post picture of it when Im back

 

[ic-racer]

I don't think a focusing helicoid is not a good idea for an enlarger, unless the enlarger is so poorly designed or broken. I know all my 35mm, 6x6mm and 4x5in enlargers can focus a 25mm lens, one just needs a gentle touch on the focus knob. Alternately one can fine focus by moving the enlarger head up and down, if there is a knob for that. The only enlarger I know of with these focusing helicoids are some autofocus enlargers, in which case it is mandatory as the autofocus is not always perfect.

 

[gorbas]

There is Durst focusing recessed lens board:

 

[M Carter]

You need very little travel, just enough for fine focusing. My Beseler 45MXT bellows is a little rough.

There was a post some time ago here about opening up the MXT to get at the focusing teeth (pretty simple) and cleaning them, then adding a very light coating of lubriplate. The focus should be smooth, perhaps restoring it is a better solution than adding more parts?