cleaning inside arista 50mm enlarger lens

[kingoriole]

working in a darkroom at school

many old enlarger lenses (arista 50 mm) have some fuzz (mildew maybe) on the inside


how do I get these things apart?

 

[Jon Shiu]

In order to get the lenses out you have to unscrew the trim ring (larger ring around the ring where it says Arista). You can use something like a rubber jar opener to get some friction on it.

Jon

 

[kingoriole]

aha!
thanks! rubber gloves worked fine.

for future reference (for dummies like me), the trim ring is between between the 'aperture-changing grip-ring' and the inner ring that says Arista on it.

For a while I was just trying to unscrew the aperture changer ring with all of my might.

 

[Ian C]

If you have the 50mm f/3.5 model it is a Marumi triplet. These are, or have been sold under at least 20 different brand names. Apparently Marumi specializes in marking whatever brands onto its lenses that customers desire.

Both the front and rear retaining bezels (the round black aluminum discs surrounding the glass are simply threaded into the barrel.

You need a rubber friction driver of outside diameter somewhat smaller than the surrounding metal to provide necessary clearance. It must also have a clearance hole in the center large enough to guarantee that no part of the friction driver can contact the lens and mar the coating.

These tools are specifically made for the job:

Dead Link Removed

You choose the tool that fits the best, press it very firmly in contact with the bezel and turn counterclockwise. Marumi and all of the lenses I’ve worked on use strictly right-hand thread (but there might be exceptions that I’ve not seen).

You must be careful to note the curvature of the lens surface facing you BEFORE removing it from its metal seat. The rear element, for example, has a much more bellied-out shape on the rear surface than the front surface. Reassemble it wrong and it the image will be terrible.

Since the seat and the gripping surface of the retaining bezel are precisely machined to match the curvature of a specific surface, assembling the element the wrong way can ruin the lens when the retaining bezel is tightened.

The Marumi triplets are about the easiest lenses to work on.

Caution: The front bezel supplies the clamping force to keep the aperture ring in place. When you remove the bezel, the tiny coil spring of the aperture detent mechanism can lift the aperture ring and the stainless steel ball bearing detent can fall out (about 1.0mm in diameter and easily lost).

For this reason you should place the lens into something like a white (to make the small parts easy to see) plastic dishwashing pan as you work on it so that the ball bearing detent and its spring don’t get lost if they inadvertently fall out.