Normally I repair only Canon DSLR-s – but sometimes I cant resist to other optical devices either.
I had to clean a DLP (!) video-projector for my sons school – it was terrible, a half kg of dust in a small box, lenses, the rotating colour filter – EVERYTHING full of dust. After compressed air i used some alcohol, to clean the optical elements. In normal cases I use pure methanol, its cheaper than ethylic alcohol, and much better properties. And I always check at first the surface, if tolerates the solvent. I have done exactly so – excepting the LAST lens – a very funny lens, which is part of the condenser lens system.
I shouldn’t. It is a plastic lens – and immediately after wiping with the cotton swab has got a matt surface. And I observed this only on the second surface.
Hrrrrrrr. The lens has a special form, no chance to purchase a used one.
So, there was only one possibility remaining: to polish the damaged surface. Unfortunately one surface was non-spherical.
You can see the scratches on the surface – and some waveforms too – so it was absolutely unusable.
One thing was to get back the shiny surface – the second to get out the waves. I needed a negative form for polishing, plus a polishing material. The ordered cerium-oxide didn’t arrived at time – but i have found a 3M material, which I have got months ago, without any technical specification. Worst could not be – let’s try it.
To make the negative, I covered the lens with a thin polyethylene bag, and as a form material I used Poxipol, a cheap but very good 2K epoxy-glue.
You can see in the section, that one surface is spherical, the second not.
The foil has protected the surface. I wanted to make the polishing with rotation – so I used a small grinding stone on a shaft as a support.
The glue hardened in a short time (10 min + 10 min for security), and after separating them, and peeling off the foil, I have a PERFECT negative of the lens. As You can see, the lens is not completely symmetrical – but this will not count, as I will rotate it, so the lens will be polished on the whole surface.
I used an optical cloth for a polishing compound carrier, the green fabric.
The small tool has 130 W power (230V), and is not the best quality, but for that price it’s perfect. after the rotating polishing, I had to make it manually too, on certain points of the lens. And yes, after doing this, I was like a pig on a farm. Just white.
The polishing compound is: 3M 60150, used in the car industry, for window repairs.
And the lens is PERFECT, the projector works, and I am happy .