Plastic lens polishing.. any advice ?

[bojan]

When astro-modifying my Canon cameras, I also removed the frosted focus lens.. resulting in much clearer and brighter image in the viewer, which proved to be helpful in aiming the scope.

However, the eye relief is now strange - i need to position the eye precisely and away from eyepiece (that was not a surprise..), which is not easy in the dark, so I thought to polish the frosted side of the focus screen lens and put it back in the camera.
Does anybody have experience with plastic lens polishing, what did you use, and how did you ensure the polished flat surface remained flat?

[Mosc_007 (Charles)]

Tamiya has a plastic polish designed for polishing plastic models. It might be worth a try. Can get it from a hobby shop.

[bojan]

Originally Posted by Mosc_007

Tamiya has a plastic polish designed for polishing plastic models. It might be worth a try. Can get it from a hobby shop.

Thanks! I will try that.

[Leo.G (Leo)]

I'm not sure about lenses but I used to make perspex display cases for shops (mostly cameras shops, and timber display cases) in my own time at home and the plastics expert who supplied and folded my stuff if necessary (accurately and easier than me with a bar heater) told me the best way to polish it was with brasso, a very fine grade of polish and minimal abrasion, same as Silvo I believe, I've used both in the past.
For more serious scratches I've used toothpaste but it is rather abrasive in comparison and I wouldn't use it on a lens
As I always do, try and find a similar material to test it on for an idea of the results you can expect. Something less critical.

[Saturnine (Jeff)]

Hi Bojan, there are polishing kits available from varioius outlets for reconditioning the polycarbonate lens of car headlights , that become "frosted" by UV and probably by being "sand blasted" after thousands of kilometres of driving. Have seen the kits for sale at Aldis', on Ebay, at Supercheap Auto etc and probably many more retail outlets.

https://www.supercheapauto.com.au/p/...it-17pc/385468
https://www.ebay.com.au/sch/i.html?_...570.l2632.html

May be worth a look to see if suitable for your needs. These kits may be too abrasive for optical gear but you could also try using a few grades of rouge for polishing.

[JA]

Hi Bojan,

The frosted surface looks very fine and probably produced by vapour honing during molding.

You could experiment with VERY FINE sandpaper, on ANOTHER piece of plastic to compare, but with grits in the 1200/1600 to 3000 range, with the sandpaper taped or glued on to a glass sheet to help maintain flatness. Then apply some fine automotive cutting compound, polish, brasso perhaps onto a sheet of glass and rub the flat lens over that.

TRY ALL OF THE ABOVE ON A TEST PIECE OF CLEAR PERSPEX OR POLYCARBONATE FIRST. The lens is probably made form polycarbonate so that might be best to try with.

If the frosted lens surface is already super smooth, you could also forget any of the sandpapers and simply apply the polish and polish the lens against a flat sheet of glass.

Best
JA

[RAJAH235]

Hi Bojan,

You can always use "Cerium Oxide" to polish glass or plastic.....Just be careful with the plastic items though.
It is much finer than rouge & windscreen replacement firms use it to polish any scratches out of any glass items they come across.


Cerium Oxide can be purchased off eBay at very reasonable cost.

Here's a link for you...
Reduced via tiny URL...(eBay link is way too large.)

> https://tinyurl.com/272tq7v9

Lots to choose from but this should suit your requirements.
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Just use a small clean glass container & mix a small amount (a dessert spoonful is more than enough) of cerium oxide with plain water to the consistency of Brasso or just a tad thinner.

Apply with a small piece of clean flannelette (shirt) material & carefully apply in a circular motion.

Do not concentrate in one area.

Wash off with clean water.

[toc (Tim)]

My advice is 'Dont'.

I wouldnt recommend messing around with the focusing screen. Any reason why you cant just use live view?

[bojan]

Originally Posted by toc

My advice is 'Dont'. I wouldnt recommend messing around with the focusing screen. Any reason why you cant just use live view?

I can, and am using live view of course.. but sometimes, especially with dimmer objects, this is not possible, so using the camera viewer as low power eyepiece is better (IMO) because it produces brighter image for the eye.
OK, Magic Lantern uses longer exposure time in Live View which could also be better approach.. but I have a surplus of those focusing screens (from faulty cameras I am using as source of spare parts, so why not try?
BTW, Bunnings stores polishing paste for plastic ($12), so I will try that soon.