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Repairing rear lens element scratches/gouges
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PostPosted: Wed Jun 21, 2017 11:24 am    Post subject: Repairing rear lens element scratches/gouges Reply with quote

Damage to rear lens element is always a concern. Here is how one chap dealt with this dilemma:

http://www.instructables.com/id/Fixing-the-Dreaded-Scratch-on-Rear-Element-of-a-Le/


PostPosted: Sat Sep 02, 2017 2:47 pm    Post subject: Reply with quote

windscreen repair kit -- of course! Best of all it seems to have repaired severe rear element scratches...


PostPosted: Sat Sep 09, 2017 4:08 pm    Post subject: Reply with quote

Hard to say how it will perform with colour pictures, I wonder if optical UV cure glue would perform better?


PostPosted: Sun Sep 10, 2017 12:25 am    Post subject: Reply with quote

As long as the scratches remain visible but no more detectable with the finger there are no improvements in IQ or in the overall aspect of the lens. The IQ and coatings could degradate because of the new layer applied.
My conclusion - DON'T DO THIS AT HOME! Smile


PostPosted: Sun Sep 10, 2017 1:38 am    Post subject: Reply with quote

dan_ wrote:
As long as the scratches remain visible but no more detectable with the finger there are no improvements in IQ or in the overall aspect of the lens. The IQ and coatings could degradate because of the new layer applied.
My conclusion - DON'T DO THIS AT HOME! Smile


+1

This is Great Advice for example those lenses with rear elements showing many cleaning scratches... Fingernail is surprising sensitive! Everybody knows the best lens grinders outperformed machinery for many many years, due to finger sensitivity. Smile


PostPosted: Sun Sep 17, 2017 2:38 pm    Post subject: Reply with quote

LOL! WOW! Epoxy on optical glass_!_ Even idiot like me would not do such a barbarian thing... There are parameters like lines per milimeter for the resolution, I read there are polishing services here and there, but what you get, polishing epoxy?!? And polishing only from outside. The main problem I suppose is teh IOR, index of refraction, or whatever it is called, the optical angle of the passing light I mean. I would buy a broken copy of the lens on ebay and change an element, if available of course. Maybe a similar element can be put too - then make photos and share on flickr as DIY bokeh monster, not a bad idea.

Cheerz!


PostPosted: Mon Sep 18, 2017 8:51 am    Post subject: Reply with quote

baychlen wrote:
LOL! WOW! Epoxy on optical glass_!_ Even idiot like me would not do such a barbarian thing... There are parameters like lines per milimeter for the resolution, I read there are polishing services here and there, but what you get, polishing epoxy?!? And polishing only from outside. The main problem I suppose is teh IOR, index of refraction, or whatever it is called, the optical angle of the passing light I mean. I would buy a broken copy of the lens on ebay and change an element, if available of course. Maybe a similar element can be put too - then make photos and share on flickr as DIY bokeh monster, not a bad idea.

Cheerz!


Refractive index varies with wavelength, and the way it varies depends on the glass (a property called dispersion). Any quality lens will use at least 2 different types of glass ('crown' & 'flint' being the early favorites though 'low dispersion', 'extra low dispersion' etc. have become common more recently). The epoxy can't automatically match it's properties to the glass it's applied too.
The epoxy is probably designed to closely match the typical refractive index of windscreen glass, the change in dispersion unlikely to be an issue for windscreens, but will often be for lenses. It will be closer to optical glass than air is, so might show some improvement over the untreated lens, but with more critical subjects I'm sure the errors will show clearly.

Adding dispersion into the equation makes this approach even worse than you make out. The age old approach of simply filling the scratches with matt black paint to remove their contribution to the image is far preferable IMO.


PostPosted: Mon Sep 18, 2017 9:00 am    Post subject: Reply with quote

DConvert wrote:
The age old approach of simply filling the scratches with matt black paint to remove their contribution to the image is far preferable IMO.

I fully agree.