I have found a very large aspheric lens but it has some scratches on it. Is there any way to cheaply and effectively polish some of the scratches out of the lens?
A glass lens has a very smooth finish, essentially a mirror finish.
I think using even the highest grit sandpaper or polishing compound would make the lens hazy. Do you see any beam artifacts from the small scratches?
I don’t own it. I’m considering purchasing it. It is far from perfect. It has some scratches and is slightly discolored. I only want it to try to make something out of it. The price is reasonable for what it is, but still rather expensive, about $70
There are in fact ways to polish out scratches, but unless you have the right equipment (and we aren’t talking about thousands of dollars, we are talking about tens of thousands of dollars or more), you will degrade the performance of the lens far more by altering the shape around the scratches, than the scratches themselves cause. High quality lenses and telescope mirrors are in fact ground, and then polished using progressively finer materials until they are finally polished. It is a very slow process. IRRC the mirror on the Hubble space telescope took more than a year to grind and polish at the Optical Sciences Center at the University of Arizona (and they didn’t quite get it right).
My step mother is an astronomer, and quite a few years ago someone fired a gun at the large reflector telescope at Smith College (where she taught at the time) and chipped some fair sized pieces of glass out of the mirror. They couldn’t afford to replace the mirror, so they just painted over the chipped areas with flat black paint. There was some loss light gathering power, but the impact on resolution and image quality was imperceptible. The point is that you would be surprised as just how messed up a lens has to be before it makes a lot of difference. Consider the area of the scratch relative to the area of front surface of the lens. Unless you are using the lens for imaging (as opposed to focusing a beam of light), the improvement you can get from polishing out the scratches isn’t worth anywhere the cost and time required to do so.
You can try toothpaste and microfiber cloth to polish them slow and steady if your lens is a giant plastic piece
Toothpaste and moist newspaper for glass
Proceed if you don’t bother about perfect optics.
The original mirror on the Hubble was improperly ground to give blurred image. It was made/grounded by Corning. Don’t know if the fix was by mirror or lens and who made it.
You mentioned having an aspheric; is the lens glass or plastic?
It’s glass, and big
What about jewellers rouge?
Edit to add link with some info:
I would say dont buy a project. There is a reason it is “sort of” discounted.
If it was free, sure! if you want it perfect then buy one. if you can afford it and can live with less then perfect then dont bother with the effort/project and just go right to assembly and use. 
The loss in area must be very small, but the scratches will scatter some light. If you want a very clean beam, you could rub paint or something black in the scratches and take the spill off the good part, as mentioned above for the telescope. If you polish the scratches out, without very special methods, you will distort the shape. That might be better or worse than the scratches, depending on what you want. For imaging it would be worse. An other thing that helps very small scratches is wax, such as floor wax. It doesn’t eliminate the scratches, but it makes them shallower.
Amateur astronomers grind and polish lenses and mirrors all the time.
Here is a quote from the below site, which gives detailed directions:
“Polishing [a lens] is straightforward and proceeds just as in mirror making.”
http://bobmay.astronomy.net/refractor/Refrindex.htm
The directions given are pretty interesting. But it looks like a big project, for sure.
I’m pretty sure if I were doing it the lens would be unusable when I got done.
I had a room mate in college who kept an 8 inch. (20.32 cm.) telescope on a surveyor’s tripod in the center of our room. He and his father had ground the mirror.
I may just go ahead and purchase it. Just FYI it’s a 200mm aspheric lens. Can you say 1,000,000 kcd LED bazooka!
The Girl’s dorm was just across the quad? We just had a cheap pair of binoculars.
When I saw it pointed at the girls’ dorm, the whole field was taken up by part of the title of a Webster’s New World Dictionary.
Actually, Perkin-Elmer made the mirror. And they apparently knew or strongly suspected that it was made wrong, but shipped it anyway. Also, they would not let anybody into their hush-hush facility to verify or inspect the mirror while it was being made.
What were you doing? Checking the girls for STD’s from across the campus?
n10sivern wrote:
I may just go ahead and purchase it. Just FYI it’s a 200mm aspheric lens. Can you say 1,000,000 kcd LED bazooka!
Oh my! Hoping you get it. Wondering how far away you could burn things with a rig like that.
Just leave the scratches there, they will hardly affect the beam, but any unperfect polishing attempt will affect the beam bigtime!
Btw, from a good quality 200mm aspheric, expect 4000kcd :-) (a bad quality 360mm fresnel lens gave 5000kcd in an experiment, this should be better quality than a fresnel. How heavy is it 
)