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The front of the front element of a lens (Tamron SP 35-210/3.5-4.2 BBAR MC, made 1983-1987) has streaks that are visible only when light is shone through them at some angles. They do not appear to be scratches. The element looks fine in normal lighting.

They look like cleaning or water marks, but I cannot remove them. I've tried peroxide, vinegar, 70% isopropyl alcohol, 90% isopropyl alcohol, detergent, water. I left each solution on the lens for about a minute each.

What are these streaks? Could they have been caused by improper cleaning by the lens' previous owner? How can they be removed?

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For those interested, I am unable to discern any effect that may be caused by the streaks. Sharpness, color, and contrast are good. There is no noticeable veiling glare when pointed toward large windows, which affects most other lenses.

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Upon close inspection of the provided images, it appears that someone has tried to wipe the lens element with the wrong tool. This left light streaks on the surface of the element. From that perspective, you now have several choices from safe to diy depending on the value of the lens (your affect/price).

Safest: leave it as is

Small streaks like these should not change the lens properties. If you don't mind the lens look and/or don't have the money, the safest solution is to keep it as-is. You probably won't notice it in your photos.

Safe: professional re-coating

If your lens is vintage and you want this lens to have a brand new look, you can ask an optic professional for re-coating the lens (under 100$ but can take a while). Vintage lenses are easier to re-coat than modern ones due to softer and more primitive coating techniques (as opposed to multi-coating, oil free treatment and hard metal based coating).

Safe alternative: get another copy

If this lens is not rare and rather inexpensive, you may consider buying another copy that looks good.

DIY: remove coating yourself

The flare-loving community has a few tutorials on how to remove the lens coating. This lens specialized shop has a good one. Beware, removing lens coating is an abrasive process, not chemical. It can make your element non-spherical, introducing additional optical aberrations to your lens. This educative page illustrates the process, the result and the risks associated to this kind of operation.

Other information may be found in this interesting thread on photrio.

  • What counts as vintage? The lens was made sometime during 1983-1987 and says "BBAR MC" on it. – xiota Jan 18 at 20:34
  • I'm going to leave it alone because the marks don't even show up during normal inspection. They're most visible when the element is separated from the rest of the lens, as in the pictures I've shown. – xiota Jan 18 at 20:36
  • I guess MC stands for Multi Coating, a more modern coating technique that adds multiple coatings on the same lens element surface. This technique is more difficult to reproduce than single coating. So this lens is not "vintage" as per coating technique. – jihems Jan 21 at 8:25
  • BBAR MC = Broad Band Anti-Reflective Multi-Coating – xiota Jan 21 at 8:40
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I think some damage has been dealt to the lens coating. Without much exception, camera lenses are coated with a thin deposit of minerals called coating or blooming. These super thin coats are applied by placing the lens in a vacuum chamber. The minerals are heated and they evaporate and then condense on the glass. The thickness of the coat is 1/4 the wavelength of light. Their may be multiple coats for controlling the action of different colors of light. Again the coats are super thin, there purpose is to reduce light reflection off the polished surface of the glass. In a multi lens system 50 to 60 percent of the image forming light rays are lost due to reflection. The outside coat is the least important coat. It is unlikely that you will see any performance loss due to this damage. In other words, this is more cosmetic. Don't worry abut it and stop trying to clean the lens surface. Your actions will only result in more coating damage.

  • Your description of lens coatings was applicable in the last quarter of the 20th century. Today, not so much. – Michael C Jan 18 at 16:34
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    Alan has a good eye. The element came from a lens manufactured 1983-1987. – xiota Jan 18 at 20:29
  • @ Michael C -- Now 80 1/2 years old. I went to school in the sixties with slide rule on belt. We learned to vacuum coat. Nowadays, an electron beam coating is the rage. But this new method is limited to substances with a low melting point. Silicon dioxide, and aluminum oxide do this trick and are very hard. Tip of the hat to Harold Taylor who in 1892 observed that old lenses passes more light because they were bloomed (aged) with a coat of fumes from coal fires (pollution) in London. Coat works by destructive interference. – Alan Marcus Jan 18 at 21:20
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The straight lines look like mechanical damage from wiping the lens with a cloth with abrasive grains embedded.

It could be a desperate cleaning attempt: some of the round spots (when viewed in detail) partly look like fern or developing tendrils. That could well be lens fungus or the damage it dealt out. Don't bring this near healthy lenses. Lens fungus secretes acid that can etch coatings and glass. Screwing this to a good lens can well wash spores into the fittings when you clean it at a later point of time.

  • Speculating that it could be anything and everything is not helpful. I doubt abrasion because of the absence of scratches and the evenness with which the element is covered with the marks. I doubt fungus because I doubt fungus grows in a linear pattern like that. – xiota Jan 21 at 8:43
  • It's not a filter that can be "screwed" onto another lens. It is the front element of a lens. – xiota Feb 12 at 17:09

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