I bought old M42 Pentacon 50mm f1.8 lens from a car boot sale. It works but is pretty dirty and it has also dirt inside (no mould/fungus though).

Opening the lens is not a problem but I would like to know how to get rid of grease and other dirt on lens element. I don't have access to ultrasonic washing machine. Undiluted isopropyl alcohol (IPA)?

  • \$\begingroup\$ This may be better worded with the title in the form "How do I ... ?" rather than as a statement, that could be interpreted as subjective \$\endgroup\$ Commented Aug 4, 2010 at 11:48
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    \$\begingroup\$ I am curious as well to the answer to this question. \$\endgroup\$ Commented Aug 4, 2010 at 12:59

4 Answers 4


For what it's worth, dirt on the lens might not be as detrimental as you would think. Kurt Munger performed a few tests comparing a clean lens, a lens with dirt, dust, fingerprints and even bits of masking tape, and a lens with a completely busted front element. The results are surprising.


Based on my un-scientific testing, I'd say there isn't any noticeable reduction in image quality as a result of normal dirt, smudges and small scratches on the front element. My dirt, smudges and scratches presented here are clearly more numerous and larger than what I'd consider "normal," but as I've shown, they have little effect on image quality.


Regular dish washing fluid is great for removing grease, as it not only dissolves it but also binds it. However, it might not be practical to use if you can't remove the lens elements and wash them separately.

Pure alcohol has the advantage that it evaporates and leaves no residue. You might want to use this after any other cleaning agent, dish washing fluid for example has some other components that might leave some residure that you want to remove completely.

Be careful what you clean when cleaning the lens. Any moving parts (focusing, aperture) needs to stay greased.


I can highly recommend ROR as a good cleaner for extremely dirty lens elements. I use it as a general cleaner, but was absolutely convinced when I cleaned an old 24" process lens that had sat in the closet of a heavy smoker for a decade or more. It was actually tinted from the residue, but came out flawless.

It's a mixture of dilute ammonia, isopropyl alcohol, and a mild surfactant. When used correctly (i.e., very sparingly) it removes greasy films easily and evaporates with no residue.


Some good answers here, however not much from a procedural standpoint. There are some specific things to address when cleaning a lens to ensure you don't add any permanent marks or scratches, and really thoroughly clean the lens.

  1. Blow or lightly brush off loose particulate!
    • Lenses tend to collect dust and other particular in addition to greasy residue
    • Particulate can be solid, and wiping it off can cause more damage than good, leaving nicks or scratches on the lens
    • Blowing across the lens is often enough to remove any particulate.
    • A very soft brush, such as a camel hair brush or something like a lens pen, can be used to lightly brush off stubborn particulate
  2. Use a soft micro-fiber cloth to wipe up loose grimy residue
    • Residue is often not that difficult to remove, and a very soft, clean, dry micro-fiber cloth is usually all that is necessary to remove
  3. Use a cleaning solution with lens cleaning tissues for tough grime
    • Lens cleaning tissues are specially designed to pull up grime and leave no scratches
    • They are cheap and disposable, and tough enough to handle use with cleaning solution
    • Isopropyl alcohol is a good cleaning solution that evaporates without leaving behind its own residue
    • Alcohol is not always effective, so more powerful cleaners may be necessary

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