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Half fogged rear element group Nikor AF20mm F2.8D...
#1
Hi guys,

             (Sorry for the preamble)  I grabbed my old AF20mm F2.8 lens with the D750 and went over the other side of the river to take a few shots of the cutting down of more dying"platanes" trees, which unfortunately are infected by a disease called "le chancre coloré" a sort of mushroom infection. Unfortunately this will kill  42,000  platanes which were planted 200 years ago both for reinforcing the canal du midi's canal banks as well as providing some shade for the horses which pulled the barges before the motorization of canal traffic, this is not counting the millions of other platanes which are everywhere in France.

  Briefly, by the end of next week there will practically no trees left near me and in the next two years all will be denuded along the canal du midi from the med to Bordeaux.....very sad indeed!

   Strangely the infection was brought into Europe in 1944 when invading Italy, from the US wooden munition cases and slowly the disease has worked it's way across Europe and has taken this long to get here 73 years no less, there is talk of a treatment for the disease but it's too late for the canals platanes.

 

  Excuse me guys, I digressed!  Huh Anyway I took a couple of shots and was immediately surprised at the lack of contrast, on arriving home I shone a torch through the lens to find haze, last time I shot things looked OK.

 I jumped in and removed the rear element group to find the haze within, the rest of the lens looks reasonably alright. I had to make a tool to open the rear element assembly hoping to give the group of four a quick clean up, but it was the lens cement that was the culprit.

  Now I need to separate the couplet with a view to re-cementing, have any of you guys ever done such a thing, what method is used, is it done by warming or some sort of solvent? The rear group is only maybe 14mm in diameter so we are not talking about a large surface, some lens cement will also have to be found.

 I know many will say that it's a job for a professional, but I have little to lose as although the lens still functions in it's current state I don't envisage myself shooting with it, other than that I would have to find some a replacement rear group, not easy to find no doubt.

 

Tips from you guys would be welcome, BC, Klaus, Markus or any other experienced or knowledgeable folk! 

 

 Thanks in advance!

Dave's clichés
#2
I would be one of the "leave that to professionals"-advisors, but nonetheless, thank you for bringing these platanes to our attention. I don't know, but platanes to me are the most french trees. I see them in Alsace, in Midi, they belong to public places and canals. It's really sad if they are so sick they have to be cut.

#3
Since the lens is still current (I think???) or discontinued very recently - certainly not before the advent of the 20/1.8G - it's probably still serviced, and parts can be found. I would've left the entire job to the service workers, but since you've already gotten to it, I'd say things are more complicated now...

#4
Quote:I would be one of the "leave that to professionals"-advisors, but nonetheless, thank you for bringing these platanes to our attention. I don't know, but platanes to me are the most french trees. I see them in Alsace, in Midi, they belong to public places and canals. It's really sad if they are so sick they have to be cut.
  Yes a huge catastrophe about platanes JoJu, however there is talk of a insecticide, but apparently they have to treat the roots, last time I heard they were talking about about 100 liters per tree so it will cost zillions to treat. it is passed by water contamination, hence the rapidity  along the canal du midi. It is also a zone inondable here so every ten years or so when it floods a huge area is contaminated. 

 The last couple of years the hire boats have been ordered to carry an insecticide dip for the mooring ropes, all to no avail of course.

  The trees are being replanted with some form of oak trees said to be very resistant, all this is being funded by the EU.

 

 The couplet is currently bathing in acetone following research on the net from various "experts" who do this on a regular basis, another way is to heat the lenses in an oven at 300° F, for obvious reasons I didn't fancy that method.

 The lens was bought cheaply for 150 euros because of slight marks on the rear element, it's IQ was fine then and I thought I had a bargain, I'm sure it wasn't a problem of lens storage here as I keep my lenses in lightly heated "safes", two halogen bulbs just raise the temperature so as not to risk condensation as well as reusable silica gel packs, you know belt and braces method, so it came as quite a surprise, all my other lenses are fine, so this lens had "history". 

  I will ring Nikon but my guess is they will not sell me the spares and will insist on me sending the lens in, that will no doubt cost more than the lens is worth on the S/H market, a better idea is to sell the lens on ebay declaring the fault. I've been looking and lenses for spares or whatever still make reasonable money, I'll see how I get on!

Dave's clichés
#5
Alright, if you already dissolving the Canadian Balm, you can as well polish the rear element (tooth paste should do, but no whiteners...) and but the multicoating back by heating some crystals in a frying pan and put the lens in that steam. Vacuum is overrated anyway

 

Just kidding..
.
  Huh

 

Big Grin

#6
Quote:Since the lens is still current (I think???) or discontinued very recently - certainly not before the advent of the 20/1.8G - it's probably still serviced, and parts can be found. I would've left the entire job to the service workers, but since you've already gotten to it, I'd say things are more complicated now...
 Whether the lens is still being produced I doubt, but it's certainly available new and is listed. Nikon have a nasty habit of charging 300 euros for anything that needs anything... plus postage, there's plenty on the bon coin for €200 and mine is not the prettiest example on the planet. €300 was the quote I got for a replacement VR on my AF-S 70-300 VR with postage around €340, they are available new at that price.
Dave's clichés
#7
Quote:Alright, if you already dissolving the Canadian Balm, you can as well polish the rear element (tooth paste should do, but no whiteners...) and but the multicoating back by heating some crystals in a frying pan and put the lens in that steam. Vacuum is overrated anyway

 

Just kidding..
.
  Huh

 

Big Grin
Actually steam is not a bad idea, I'll have a cup of tea and a couplet for breakfast with a bit of ketchup for the coatings!!  Tongue
Dave's clichés
#8
 Well that's over a day and a half that the couplet sits in acetone and really it doesn't look as if the lens cement is affected by this solvent, although it does look a little less hazy. Other internet advice suggests xylene which is a more volatile solvent to more resistant glues/paints etc.It looks as if this is not Canadian balm, but the epoxy based Vitrelite. In theory pure epoxy has no known solvent!

  If I get nowhere there maybe the next step will be boiling it in water to soften the glue, we are in a softly softly situation here.

Dave's clichés
#9
I'd try the oven (not pre-heated and not fast heating up). If it is expoxy based, heat does nothing though.

If all fails, you can try order this group of elements?

 

 

http://jimshomeplanet.com/lensglue.html

#10
Even if you can part the couplet into lenses: How do you clean the lens? And more important, how do you glue them together perfectly centered and with no dust in between? Sure, it is a good strategy doing one step after another and don't pay too much attention to upcoming problems. If there's no alternative to that and no time to do complex research of get some help out of the internet, why not?

 

This is the way French nuclear power stations are realised  ^_^ no? We talk about the waste when we have it, we talk about disposal of the building when we need to wreck the first one (GoodyBye Fessenheim), maybe we can shoot it to Mercury until then. Hey, I was a young person demonstrating against the stupid stuff and now I actually read in the news "due to too much disasters, we close it down". It might be a strange sample but sometimes thinking it to the end doesn't cover all eventualities but can indicate a possible waste of resources.

 

Get another lens like that with a scratched front element and exchange the rear one with yours. It's no shame to step back from a project or find another solution.

  


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