NO! DO NOT ATTEMPT!, Baking soda is an abrasive, the lenses are extremely complex and are fragile. The surface of the lenses is NOT glass, (unlike eyeglasses) . You can make a scratch on them with a hard enough fingernail.
How did you get a scratch on your lenses?
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baking soda and thootpaste make great polish, but not at the level you expect for an optical lense. and this kind of DYI product will certainly have big and small grain mixed , so you would end up with more scratches. first it will make the lens hazy (you would need several pass of a lot finer polish to get it clear again) second, you could need a special tool to polish all the lense surface , because polishing only the sratch would make the lens flat on that part. and if you are at the point of dismantling the lens to polish it, you could as well replace it by a new one... Third , most of lenses are coated with layers to increase lens performance, then removing it (or worse, part of it) would probably ruin lens performance more the the scratch is.
