An article appeared on Apartment Therapy that claimed that a scratched camera lens can be repaired using peanut butter and/or toothpaste. This strikes me as a horrible idea that could make a bad situation worse due to surface coatings or just adding new scratches.
Is this a correct assessment, or can you actually remove scratches from a lens with light abrasives in such a way that the optics are not impacted?
Most minor scratches on lens' have an infinitesimal impact on image quality. They look a lot worse than they are, especially in terms of the front element of a lens. This is because the light from a point source in the scene being photographed is spread over the entire area of the lens as it enters the front element before being focused (hopefully) to a point on the image plane behind the lens.
As they say, a picture is worth a thousand words. Look at the results, and then the lens they were shot with at this blog post from lensrentals.com.
By introducing an oily substance such as peanut butter to the surface of the lens you are just going to increase the amount of the lens' surface that is affected by less than optimum performance, and will probably cause more dirt and dust to "stick" to the lens. The toothpaste, especially if it is clear, would be less problematic than the peanut butter but would only serve to possibly make a scratch on the lens less noticeable when inspecting the lens at the cost of optical performance when actually taking pictures with the lens.
Toothpaste (and more professional polishers, like Brasso) is able to remove scratches from things like CDs and lenses because it has very small micro-abrasives that (when combined with force) smooth-out the area around the scratch.
This works well for CDs, but because lenses have such strict tolerences, making the lens even a little bit thinner by polishing it will cause the light that enters the camera through that area to hit the sensor slightly off-center. This will result in your images being slightly more blurry. A scratch, on the other hand, will scatter the light even more, but because it's scattered so much, it will probably actually be less visible in the final image because the intensity of the scattered light will be so much lower.
Thus, unless your scratch is extremely shallow, you are probably better off leaving the scratch in the lens than trying to polish it away, using any method.
(Though, note that the placement of the scratch is important - a scratch in the center of the lens may have a large effect when using small apertures, where only a small portion of the lens is actually used)
I would expect it would cause more harm than good. Minor scratches are insignificant, but it's going to be just about impossible to get the oils from the peanut butter off the lens without damaging the coating which does matter, particularly when using filters.
I am pretty sure that the article is wrong about why it supposedly works. I believe the oil in peanut butter or tooth paste tends to fill in the crack and refract light such that it is less of a distortion than the crack would normally cause, however, toothpaste particularly has slightly abrasive properties that may have a bigger impact on the optical properties than the scratch it "heals" by removing image coatings from the lens. Additionally, both peanut butter and toothpaste would leave an oily residue that is hard to remove and would cause a negative impact on performance.
