cleaning barrel lenses (elements)

[tenderobject]

hi guys,

i tried to search the forum but i'm not that lucky enough..

well, i have a few barrel lenses (petzval, dialyte, russian lens).. the glass elements needs cleaning. since these are old lenses i'm hesitant to clean them.. do you guys have proper way on cleaning old barrel lenses especially the glass elements? what kind of liquid solution / tools are you using for these kind of lenses?

thank you very much!

[steven_e007]

Hi,

I often clean optics as part of my day job. There are lots of different methods that work, here are my thoughts:

The biggest problem with cleaning a lens is scratching it in the process. For this reason you should always do two things:

First, remove as much dust etc. as possible with a blower brush / compressed air, then with a very soft paintbrush (if it has a metal ferule, wrap it it tape so you don't accidentally scratch the glass).

Second, clean it WET. Wash it. Most damage is done by rubbing with a dry lens cloth. That would be fine if the lens was already quite clean, but if it is old then it will surely have containments stuck to the glass and they may well be have gritty particles stuck to them.

There are lots of different ways of actually cleaning the glass - some swear by lens tissue (I never use the stuff) and there are various cleaning mixtures you can use. Modern Health and Safety rules often mean the best solvents are no longer available to most of us.

If a lens is really mucky, unscrew the element mounts from the barrel (if you can). NEVER attempt to remove the glass from the mounts you would need special equipment to re-collimate the elements if you did this - just unscrew the threaded mounts. You can't go far wrong by blowing off as much lose matter as possible, soaking a cotton bud in some simple detergent (liquid soap) - and holding the lens under luke warm running water whilst very gently making small circles from the centre outwards. Use your common sense about not giving the water too much chance to soak under the edges of the lens. Dry the element quickly in warm air (hairdryer, maybe, but not too hot). After this you can clean it with more cotton on a stick and a solvent to remove the drying marks, such as ethanol or propanol. Better is petroleum napther or petroleum benzine or petroleum ether (same group of solvents - but with different names in different countries. It is basically cigarette lighter fluid - but you need some that is pure and oil free...)

I make my own cotton buds using a small wooden stick (you can buy wooden cotton buds and reuse the stick - Thai bamboo skewers also work!). By a big back of pure cotton wool from a pharmacist/drug store. Dip the end of the stick in water and use this to pick up a little pure cotton wool. Pull a tuft off and roll it against the inside of the plastic bag. Don't touch the cotton with your fingers. Use just once, pull off and throw away. You can roll dozens in a few minutes once you get the knack... Much safer than using a lens cloth which gets contaminated really quickly.
Moisten in your solvent of choice (don't get it too wet, it will just run and streak) and clean in a spiral working from the inside to the edge, then discard and roll a new one. Never go over the surface a second time with the same bud - it may have picked up grit...

Before you re-assemble - make sure the elements are completely dry. If the space between the elements is sealed - the increase in pressure will make any moisture condense - fogging the inside. No harm done - just separate and dry with warm air - but not good to screw / unscrew more than you need to. Make sure the threads are clean - and be very careful not to cross thread!

And never use acetone on a lens!
(It won't hurt glass, but it is a great solvent for balsam, lacquer and paint :eek: )

Final tip: the coloured LED torches, the ones with a single coloured light emitting diode - are excellent for showing up the dirt in a lens. In subdued light, shine the light through the lens from behind the whilst you look through the front. For some reason, blue works best ;)

HTH

[tenderobject]

thanks steven!