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My wife gave me a used Pentax 50mm f/1.7 SMC-M for my birthday. (I know some people get Leica 50mm f/0.95 Noctiluxes for their birthdays, but, y'know, kids to take care of and so on. And it's a very nice little lens!)

The glass is in good shape, but there's a small amount of rust around the lens mount. I don't think this is really a problem, but I'd like to clean it. What's the best approach?

Most rust-removal advice I've found online is geared towards much larger amounts of rust (cars!), and I'm concerned about affecting the plastic with an acid-based product.

Or should I just not worry about it? I'm a software guy, so all this physical-world-stuff is all confusing to me. Is there any concern of it spreading or causing other damage?

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Congrats on the lens, I have the same one and it's a fun lens to use. I don't have specific advice for DIY on this, but you can also probably take it to a photography store for cleaning. You may want to anyways, just to have the aperture blades and glass checked as well. –  John Cavan Jan 1 '11 at 15:13
    
Ever get the rust off, and how? –  rfusca Mar 21 '11 at 0:43
    
@rfusca — I tried the baking soda thing, and had trouble getting it all cleaned away so as to not get dried baking soda into my camera body, which seems like a bad thing. In the meantime, I've just been using it on my K1000 as-is. But white vinegar is next up. –  mattdm Mar 21 '11 at 13:08

2 Answers 2

up vote 2 down vote accepted

A few different things to try (in my order of preference):

  1. Baking Soda: Make a paste of baking soda and water. Spread it onto the metal and let it sit for 10 - 15 minutes (your mileage may vary depending on how deep the rust is. Reapply and let it sit longer if necessary). Wipe the baking soda away with a damp rag and gently scrub any remaining loose rust with toothbrush.

  2. White vinegar: Use a Q-Tip to apply white vinegar to the rusted area. Wipe away with a damp rag. You may need to apply more than once.

  3. Sandpaper/steel wool: My least favorite option in this case because you're working around optic elements and your lens isn't going to be too keen on small gritty dust getting into the cracks and moving parts, but sanding will work- especially if the rust isn't too deep, you go slow, and are careful with cleanup.

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Jay, have you used all these things on lenses? –  mattdm Jan 9 '11 at 14:38
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I have. #1 is the least messy option because you're working with a 'paste' as opposed to a free-flowing liquid, or dust. Unfortunately the least messy one also takes the longest to work... Sooo... If you're in a hurry, sandpaper works more quickly than the baking soda. I've used sandpaper twice... The first time I used painters tape and taped up every square inch of the lens to keep it protected. The second time I just taped off the immediate vicinity of the rust and used compressed air to keep the whole thing clean. If I had to do it again, I'd just use compressed air. Taping is a pain. :-) –  Jay Lance Photography Jan 9 '11 at 17:27
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Won't any of those approaches damage the chromed finish and expose the inside metal to "invite" more rust? This is probably a nice follow up: How to protect the recently cleaned surface? anti-rust paint? i've only seen it used in fences and gates xD –  JoséNunoFerreira Jan 29 '11 at 2:24
    
Perhaps it would if you were using these methods on a chromed finish, but if you read the question the OP is talking about rust on the lens mount, which is not a chromed surface simply because the metal-to-metal contact of attaching and detaching a lens would rub away a chrome finish in short order. –  Jay Lance Photography Jan 29 '11 at 7:06

I've had great experiences with a product called Evapo-Rust. I haven't used it on lenses, but I have used it on a lot of other things that had wood, glass, rubber and plastic parts, and haven't noticed any weakening of glues or anything (well, except for wheat-starch paste, but that's water-soluble and an unspeakably stupid mistake on my part -- I almost lost a very valuable antique label). Unfortunately, the smallest container I know of is 32 fl. oz. (one US quart, though we don't consider that a quart where I come from), and all you need is a saucer full.

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