Polishing out dings in condenser lens. Any ideas?

[George Nova Scotia]

I've a couple condenser lenses with tiny dings in each one. They don't seem very deep but are visible when I stop the lens down all the way. Has anyone tried polishing these out? If so what did you use. I've got a couple cloth wheels with jewelers polish on them, I was thinking about giving them a try.

 

[Monito]

Hi George,

Perhaps give a try the same sort of techniques telescope lens and mirror makers use. Maybe cast a plaster of paris depression in the shape of the condenser, line it with felt or some suitable cloth and then put a bit of polish or paste at the bottom where the dings are and move the condenser around.

I'd probably just do it by hand, and put a bit of paste on a cloth and put that part of the cloth in the palm of my hand near the base of my thumb and polish.

Making a mold could work if one especially wanted to retain the identical (spherical?) shape of the condenser by polishing the whole surface down the same number of micrometers. I don't know how important that might be, but I'd guess it's not too important or necessary.

 

[Louis Nargi]

Try some Brasso or copper and metal polish it contains an abrasive that very fine and maybe you could polish the blemish out. I try it on my Omaga condensers with some success.

 

[ic-racer]

I'd try an automotive windshield glass polish kit.

 

[George Nova Scotia]

Thanks guys. Last night I tried some tripoli polish on a buffing wheel. I put some scratches in an old jam jar with the diamonds laying on my work bench. The polish quickly took off the sharp edges but didn't get very deep. Looks like I'll be needing something more aggressive to start but the polish should leave a good surface. Time to see what else is in the basement.

 

[vpwphoto]

You are likely to make things out of specification and ruin the focal point of the condenser... I'd just let it be or find a new lens. This is the same reason scratches can't be buffed out of eyeglasses.

 

[George Nova Scotia]

Likely true, but can't do much harm. Like you said I can always get new lenses (Omega D5) but it's worth a try. The ding on one lens is very shallow and just barely visible when I stop the lens all the way down. I suspect it might polish out. The other is a little deeper but I haven't looked too hard at it yet. Besides it's a spare enlarger for my spare enlarger

 

[Smudger]

Just curious - why would you want to "stop all the way down" - the diffraction would surely be horrible ?
In your case,I would be tempted to try filling the scratch with clear nail polish :if it's not successful it is easily removed.

 

[George Nova Scotia]

I might give nail polish a try, not something I keep around but cheap and easy to get and easy to remove. I had thought of something like that, more like what they use on windshields. Normally I wouldn't stop down that far but it did make them easy to see. I suspect it has something to do with extending the DOF into the condensers as well. The deeper ding did show up at only 3 or 4 stops so it's something I feel should be addressed at some point. Then again it is a spare for a spare so I might just part it out if I decide it's taking up too much room.

 

[Ronald Moravec]

Get the product auto glass people use to repair windshield chips.

Polish removes surface and you can not retain proper curvature.

 

[Jim Jones]

Are both condenser lenses identical? The better of the two might work well enough when closest to the film, while the ding on the worst one might not show when further from the film.

Even if polishing out the dings slightly changes the contour of the condenser, it might not hurt. The condensers are in the light source path, not the image path.