What are some eco-friendly, nontoxic lens cleaning recipes?

My camera cleaning kit came with an empty spray bottle.    Not sure what to put in it.

Any suggestions for a safe camera lens cleaner?

The two things you're trying to get off are likely grease and dust. Do you consider rubbing alcohol to be safe? That on a soft, lint-free cloth, followed up by those computer screen cleaning cloths that specialize in picking up the dust would be my first approach. Hopefully some other people will chime in.

Rubbing alcohol releases VOCs (volatile organic compounds), which aren't good to breath and are air pollutants. BUT, vodka does not! Vodka should work well as a glass cleaner, perhaps combined with a bit of vinegar and water (I once saw a blogger compare a bunch of different recipes).

So, if there's no alcoholics or other objections to storing drinking alcohol in the house for cleaning purposes, then a vodka recipe might work well for you!

Perhaps-related side note: This week I learned that eye contact cleaner has borax in it. My kids made "Slime" in thier science class as a way to learn about polymers. When borax and school glue combine, it makes a funky/fun substance called Slime. Kids love it--it makes fart noises when you push into it, and it turns solid when you push on it too hard, and liquid when there's no force on it. It stretches and so on. ANYWAY, a lot of parents got concerned about making Slime, because it has borax in it. So they started making it with contact cleaner...which has (you guessed it) borax in it! The scientist came to the conclusion that, if the borax was safe for eyes, it's safe in small doses in Slime. Meanwhile, I'm thinking, "I'm glad I don't use contacts, and hope there's better contact cleaning solutions out there!"

My biggest concern is not hurting the lens.  Lenses are really expensive and I don't want to damage it by trying to clean it.

Dust and grime should be removed prior to cleaning with a cloth.  So the cleaner doesn't need to do this.  

The goal of the lens cleaner is to remove fingerprints and smudges without leaving any streaks.  That last part, not leaving any streaks is vital.  

Another possible problem is older lenses have coatings on the outside of the glass and using the wrong cleaner can dissolve these.  

I'm thinking something like denatured alcohol might be good... maybe.  I remember reading that rubbing alcohol contains oil so it doesn't dry out the skin.  We don't want to add oil to the lens

One trick for decreasing the risk of streaks is to have a clean, dry cloth ready to 'polish' the lens while the wetting agent is still there. On our glasses, we've got some hemmed sections of *very* old fabric from the rolled toweling dispensers you find in public washrooms. I inherited this from my mother in law, who got it from a friend who worked in a factory that sewed them to fit their brand of dispensers and had "end of rolls" left that weren't long enough for business, but would easily make up a lifetime's worth of glasses cleaning cloths. Don't know how you'd find a good equivalent nowadays, although I know at least two restaurants that still use those cloth towels, and I personally like them much better than paper!

I've been using a lens pen for the past 12 years. I'm not sure exactly how it works, but I've been using the same one without any problems for all that time, so although it's made from plastic, it might be a 'buy it for life' solution.

I emailed an acquaintance who's an artist and professional photographer. His reply, "Might need to see the lens??  How bad is it?

I would use a blower to clear any loose dust, then very carefully apply lens cleaner using a soft photo paper or cloth.

Have a picture??"

So clearly there is something out there specifically called, "lens cleaner", but I have *no* idea what it might contain. My acquaintance may have interpreted my question as relating to a really badly treated lens, rather than a mostly cared for lens that just needs some regular maintenance. The problem with professional training sometimes is that the trainees may "follow the standard procedure" without questioning it. That's what I like about permaculture - it's all about asking the tough questions that many people simply accept as "the way it's always been" (even if in reality, it's only "been" that way for the last "insert a number" years.)

I've been using this stuff called Cat Crap. It's a lens cleaner and antifogger. Though I don't have the list of ingredients off the package, it's something like "water, Glycerol, Coconut tallow soaps", essentially an emulsifier keeping saponified coconut oil smooth and uniform in application. The coating, properly applied, is imperceptible.

It's a great antifogger, which is indispensable out here. At nightfall the air is so full of microdroplets, it's hard to take a picture. Condensation on the lens combines with ambient moisture to blur out all visibility. You can also get it in the optical department at cough, Walmart, cough.