Polishing a damaged lens – cerium-oxide

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.

WP_20170130_21_48_04_Pro WP_20170130_21_48_16_Pro

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.

WP_20170130_21_49_35_Pro WP_20170130_21_49_52_Pro WP_20170130_21_52_29_Pro

You can see in the section, that one surface is spherical, the second not.

WP_20170130_22_11_31_Pro WP_20170130_22_12_38_Pro WP_20170130_22_13_14_Pro

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.

WP_20170130_21_50_25_Pro WP_20170130_22_16_35_Pro WP_20170130_21_52_00_Pro 

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.

WP_20170130_21_55_59_Pro WP_20170130_21_57_35_Pro WP_20170130_21_58_02_Pro

I used an optical cloth for a polishing compound carrier, the green fabric.

WP_20170201_00_14_14_Pro WP_20170201_00_13_36_Pro 3M 60150 cerium glass polish

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 Mosolygó arc.

About canonrepair

Ruzsa János. Amatőr fotós, Canon DSLR váz. Amateur photographer. Canon DSLR user.
This entry was posted in dirty, dust, lens, tools. Bookmark the permalink.

3 Responses to Polishing a damaged lens – cerium-oxide

  1. jabcam says:

    Good job! In my teens I started grinding a mirror for a 12″ newton reflector. I was into astronomy at the time. The glass plate was circa 50 mm thick and the working tool perhaps half of that. MANY hours of hard labour and dust as you say (even though the carborundum was kept wet with water) ensued. My ankles still hurt by just thinking of it:) In the end I managed to get the mirror spherical but before the final polishing with jeweller’s rouge and parabolisation my interest ran out.

    Your way of making a mold was cool. Must remember that!

  2. Gonçalo Martins says:

    Can you show a picture of the final results? Best regards

    • canonrepair says:

      unfortunatelly not. I was too excited to assemble it, to see, if works or not, so forgotten to take a shoot. But there were NO scratches at all. But this was only plastic, like eyeglasses…. (The second problem was the question of positioning the lens in the condenser system -I have never done something like this before).

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