Timeline for Can a lens's MgF2 anti-reflective coating be damaged by salt water?
Current License: CC BY-SA 3.0
24 events
| when toggle format | what | by | license | comment | |
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| Aug 24, 2017 at 12:23 | vote | accept | xbuster | ||
| Jul 30, 2017 at 16:50 | comment | added | paracetamol | @xbuster sigh: If you're using the coated lens (i.e- lens with an ARC), then if the coating degrades over time (as a result of the "cleaning regime") you'd have patches of the ARC over your lens (which would possibly screw up the photograph, but not the lens as such...). If you're using the un-coated lens, regular and frequent cleaning would result in minor scratches over time (won't screw up photograph that much). { I still find your last question...odd...though, sorry} | |
| Jul 30, 2017 at 11:34 | comment | added | xbuster | @paracetamol What I meant to ask that: theoretically speaking, under the same exposure to the seawater and the same cleaning regime what lens will be in better condition over time coated or uncoated? | |
| Jul 30, 2017 at 8:43 | comment | added | paracetamol | @xbuster What concerns you more: A damaged ARC or a damaged lens? (Honestly, even I'm lost now :P) | |
| Jul 30, 2017 at 8:03 | comment | added | xbuster | @paracetamol The only question that remained (for me) is if I've both MgF2 coated and Uncoated does the coated one will be damaged much sooner then uncoated one? Thank you for your help! | |
| Jul 26, 2017 at 8:59 | comment | added | paracetamol | @xbuster You can use it in sea water, but that'll have to be immediately followed up by some meticulous care: I'd recommend rinsing the lens with distilled water to eliminate as much salt(s) that has deposited over the lens, lightly dabbing it with a piece of soft cloth and leaving it to dry. My experience in photography is altogether, very limited...so I'm not sure how bad the picture would turn out when using an uncoated lens than a coated one; so you'll have to make that call. | |
| Jul 26, 2017 at 8:42 | comment | added | Digital Lightcraft | -1 as you managed to write a 15-line answer that in no way answers the direct question. | |
| Jul 26, 2017 at 8:36 | comment | added | xbuster | @paracetamol Just to make sure that I understand correct. For a frequent usage sea/salt water environment significant better choice to use Uncoated lens vs. MgF2 coated one. Is it correct? | |
| Jul 26, 2017 at 8:22 | comment | added | paracetamol | @xbuster I was talking about MgF2 coats this whole time ;) | |
| Jul 26, 2017 at 8:05 | comment | added | xbuster | @paracetamol Will this process be the same for MgF2 coated or Uncoated lens? | |
| Jul 26, 2017 at 7:53 | comment | added | paracetamol | In conclusion (to my arguments): Sea/salt-water doesn't really damage the coating per se. However, as Stephen points out, traces of the water will remain on the lens, which would quickly evaporate to leave a fine layer of solid salts "...waiting to be rubbed by someone and this will erode the coatings." | |
| Jul 26, 2017 at 7:48 | comment | added | paracetamol | @xbuster In addition to what I've already said...if the coating has already be damaged (by physical means) before it's immersed in sea-water...it might be a different story (i.e- The coating may break down). I ran a few more cursory Google searches a while back, and apparently the binder used to "stick" the MgF2 on the lens is some sort of fluoropolymer. The exact nature of the substance may vary, but I can vouch for the remarkable resilience of fluorpolymer coatings (they're commonplace in laboratories as they're inert to most chemical reagents). | |
| Jul 26, 2017 at 7:36 | comment | added | paracetamol | @Doktor By all means, of course! But the onus on citing reliable sources (Wikipedia and Google scholar might be of some help) to that info would be on him. {Not sure if "citations" are a biggie on Photo.SE... but they are on the Chem. and Phys. SEs} | |
| Jul 26, 2017 at 5:06 | comment | added | xbuster | Just a clarification. What I meant to ask relates ONLY to lens itself. No electronics, no seals or plastic of any kind just bare glass lens with MgF2 coating. | |
| Jul 26, 2017 at 1:13 | comment | added | Doktor J | @paracetamol maybe Stephen can add your info to his answer here? | |
| Jul 25, 2017 at 21:24 | comment | added | paracetamol | Meh, I'll just stick to haunting the comments-section ;) My conclusion doesn't deviate from yours, so there's really no point. | |
| Jul 25, 2017 at 20:07 | comment | added | StephenG - Help Ukraine | @paracetamol That info is very directly on the point, so maybe you could convert that to an answer, as comments can be deleted by the system's automatic housecleaning functions. | |
| Jul 25, 2017 at 18:44 | comment | added | paracetamol | {Continuation...} It's been a while since I've studied anti-reflective coatings (ARCs) and how they're employed in optical instruments... but I'm fairly confident that the polymeric binder used here is effectively "shielded" from the external medium by the MgF2 layer over it. So yes, sea-water contains all sorts of ions...but if they can't get past the MgF2 (they can't, because the MgF2 isn't going to come off easily for the reasons I've mentioned), they won't be able to get to the binder, and the coating stays intact. | |
| Jul 25, 2017 at 18:44 | comment | added | paracetamol | Herr @Doktor good point. Bringing up what I said in a previous comment: The MgF2 is bound to the surface of the lens by a polymeric binder, the latter, being something that's inert to polar solvents, ensures that the coating won't simply be "washed away". Then again, MgF2 is sparingly soluble in polar solvents (like water) anyways (as can be concluded by a cursory analysis using Fajan's Rules). Second to sodium, magnesium is the most abundant cation in sea-water, and this further serves to reduce the solubility of MgF2 in sea-water (See: Le Chatelier's Principle). {Continued...} | |
| Jul 25, 2017 at 17:57 | comment | added | Doktor J | Well seawater is a lot more than just salt and water... lots of other things floating around in there. Isn't it feasible that there may be some trace stuff that will happily react with the coating (especially in the presence of said salt water)? | |
| Jul 25, 2017 at 17:45 | comment | added | paracetamol | Salt water accelerates rate of corrosion (most notably, in metals), it is not "corrosive" per se. However, I speak of "corrosion" with regard to the lens...not of the metal bits that constitute a camera (I'm assuming it's sealed pretty well, so salt water doesn't seep into the device). If you want to talk about "corrosion" and its usage more, drop by at the Chemistry.SE ;) I'm not into photography; just thought I'd point out that the "corrosion" bit isn't correct (from a chemist's perspective)... I can't vouch for the rest of the answer, but it seems reasonable to me O:) | |
| Jul 25, 2017 at 17:35 | comment | added | StephenG - Help Ukraine | I think most engineers would regard salt water as corrosive. Try googling those terms and see what ya get. But perhaps not the major issue in relation to a camera. | |
| Jul 25, 2017 at 17:23 | comment | added | paracetamol | "Corrosive" isn't really a word I'd use to describe salt-water (brine). The highlight here seems to be traces of brine drying out on the lens leaving behind solid salt...something rubbing against the lens at this point would damage the coating. Also, magnesium fluoride isn't simply powdered onto the lens (as you would know), but is instead fixed in place by a polymeric binder... so even if magnesium fluoride is highly soluble in salt water (reality: it is not), it would not be appreciably dissolved/washed away by immersion in salt water. | |
| Jul 25, 2017 at 12:33 | history | answered | StephenG - Help Ukraine | CC BY-SA 3.0 |