Shim for 39mm enlarger lens (illuminated aperture scale alignment)

I am setting up my darkroom again. My darkroom equipment has been gathering (a lot of) dust for many years. I have cleaned up my LPL 6600 B&W enlarger and all seems well. I basically stripped it down as far as practical and got rid of all the dust. I found that the holder for the 2 large condenser lenses comes apart to enable the lenses to be cleaned. I don't think I ever realised that the first time around....wish I had done, would have avoided a lot of dust marked prints.

My enlarging lenses were stored in their cases so they are fine. However, I now find that when I screw a lens in, the illuminated aperture scale is 180 degrees out. That is to say it is at the back where I can't see it. I presume it must have been like this last time but it isn't very convenient. I know I could just learn how many clicks etc but it does rather defeat the object of the illumination. The mount thread is part of the casting of the lens board so there is no adjustment there (I had the bellows out for cleaning so I sure the lens mount cannot be adjusted). Could I use a shim on the lens to bring the alignment to what it should be? I could make one out of card but as I will be swapping between 50mm and 80mm for different formats I'd like a more durable solution than card/paper really. Any ideas?

rotate the lens board?... does it only mount one way?

It only goes one way. I have found some O-rings that are 39mm inside diameter. Might work as a shim I suppose but they are probably too thick (2mm). A thin fibre washer or gasket material would be quite good I think. I'm not sure what thickness I need so I can experiment with paper. Gasket sheet comes in different thicknesses and might be durable enough. It's a little annoying because one of my lenses aligns fairly well but the others don't. Exactly 180 degrees out is odd. It also occurred to me that there might be more than one start to the thread but that doesn't seem to be the case.

Some enlarger lenses can rotate the aperture ring once mounted, I have an 80mm Nikkor that has this feature.
Once mounted I can rotate the aperture ring to the smallest aperture then keep turning until the aperture scale is where I need it as the whole ring turns on the mount.
What lens do you have?

Can you turn the lens board over?

Is there enough thread on the lens to also use a nut ring?
You can use it like a lock nut to hold the lens in the position you like.

try spining the lens base, i have used lenses that allow this. if not just count the aperture clicks. or just leave it at the working aperture always.

I have Schneider Companon-S 50mm and 80mm and a Rodagon 50mm (incidentally no Rodenstock written on it). They don't seem to allow rotation of the aperture scale.

Get yourself another lensboard. Mount both lenses with shims if needed for the aperture scale to show and then you'll have two permanent set-ups. Change the whole lensboard/lens assembly when you change lenses.

Best,

Doremus

As I recall, the LPL C6600 enlarger does not have a removable lens board. Certainly, none are listed under accessories in the user manual, nor is any mention made in said document.

Assuming that your lens has 39mm x 26 thread-per-inch Leica thread and that the aperture index is about 180° from the front, you need a shim that is 1/2 of the thread pitch in thickness so that when you tighten the lens the aperture index will face forward.

The required shim thickness is (1/2)*(1/26)” = (1/52)” = 0.019” = 0.49 mm.

When the lens is tightened the shim might compress slightly if made of paper, so the adjustment might be imperfect (you can compensate by using a slightly thicker shim). The result will generally be close enough to position the aperture index facing approximately forward for easy viewing.

The LPL 6600 has a fixed 39 mm Leica-thread lens board, so your options are limited.

The relationship between the thread and flange surface of any two lenses will almost never be the same. All you need do is leave the custom-made shim on the lens that needs it. You might even have a different shim on each lens. For example, if the second lens required about 250° of rotation, then the required shim thickness for that lens is

(250°/360°)*(1/26)” = 0.027” = 0.68 mm.

The general formula is

Thickness = (θ°/360°)*p

θ = required rotation angle (0° < θ° < 360°)

p = thread pitch

a drop nail polish or crazy glue n leave it cure at the right rotation.

Thank you for all your replies and thank you especially to Ian C. I did not know how to calculate the required shim thickness. This is exactly the information I needed. It is not important for the aperture scale to align perfectly, just to be near the front and visible. I have ordered a mixed packet of gasket material of different thicknesses for £2 and I will use that to make shims that will stay on the various lenses. Problem solved! Thanks again.

PS: I fixed something else on the enlarger just now. The upper column stop had sheared off. Probably banged on something whilst in my junk room. The column stop is a brass threaded post with a rubber cap over it. I found the part on KHB and had it shipped. Today I managed to get the broken piece out of the thread. It was very straingforwand. The column cap comes off and there was enough thread sticking through inside to continue screwing the broken thread all the way through by gripping the exposed thread inside with pliers. Pleased with that too.

Just need to wait for my dark proofing stuff to arrive, put that up and I am up and running again.

paul_c5x4 said:

As I recall, the LPL C6600 enlarger does not have a removable lens board. Certainly, none are listed under accessories in the user manual, nor is any mention made in said document.

Click to expand...

My mistake! I was not aware of this. Ian has the answer.

Doremus