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scratch removal on lenses (front)

9272 Views 16 Replies 10 Participants Last post by deronmoped, May 22, 2007

nidi

Discussion Starter · May 19, 2007

Hello guys,

a friend of mine has moderately scratched lenses (HD-10F)

scratches are visible on the front element.

is it possible to polish them ?

Thanks for any help

Michael

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1 - 17 of 17 Posts

DO NOT POLISH THEM.

There is an anti-reflective coating on most lenses if you "polish" them you will remove this useful coating.

Scratches on the OUTSIDE lens element make NO IMPACT WHATSOEVER on the image. I have had, literally, GOUGES approximately a mm deep in some lenses, and when I removed the paint from the gouges, they were totally invisible on the screen.

Really, don't worry AT ALL about scratches on the outer most lens element.

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garyfritz

· #3 · May 19, 2007

Right. Try an experiment: gently stick a 1" square piece of post-it on the front of your lens. You will NOT be able to see it on the screen. The only change is that your image will be a bit dimmer.

If a 1" square "hole" doesn't hurt the image, you can be sure a small scratch won't. Polishing it will do more harm than good.

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klover

· #4 · May 19, 2007

Quote:
Originally Posted by garyfritz /forum/post/0

Right. Try an experiment: gently stick a 1" square piece of post-it on the front of your lens. You will NOT be able to see it on the screen. The only change is that your image will be a bit dimmer.

If a 1" square "hole" doesn't hurt the image, you can be sure a small scratch won't. Polishing it will do more harm than good.

I've never understood why doing something like that doesn't cause a major obstruction.

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garyfritz

· #5 · May 19, 2007

The lenses' focal point is at the REAR of the lenses -- on the face of the tube. Any small detail (like your video signal!) there is visible on the screen. But in the middle (between CRT and screen) the light sort of "spreads out" and then focuses again at the screen. I don't know enough about optics to describe exactly what the light path is, but basically the light path only focuses at the CRT and at the screen.

Consider what happens if you put your hand in front of the screen. If your hand is an inch from the screen, the shadow is sharp. As you move it farther and farther away, the shadow gets fuzzier and fuzzier. It's about maximally fuzzy at the front of the lens, so your picture is getting through (/around) your hand, or finger, or whatever.

Dunno if that makes any sense, but bottom line the front of the lens is not much of a concern for scratches &etc.

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NateTTU

· #6 · May 20, 2007

I have some hd-18 lenses that the anti-glare coating is coming off. Sounds like to me that I shouldn't worry about this then? I'm pretty anal about having everything "perfect", but certainly don't want to spend $200+ for a new set.

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none74

· #7 · May 20, 2007

Quote:
Originally Posted by NateTTU /forum/post/0

I have some hd-18 lenses that the anti-glare coating is coming off. Sounds like to me that I shouldn't worry about this then? I'm pretty anal about having everything "perfect", but certainly don't want to spend $200+ for a new set.

Having the anti-reflective coating is more important than getting scratches out. If you lose the coating, there will be a reduction in your contrast ratio since some light will be reflected BACK to the tubeface from the outer layer of your last lens element....I think...

I'm fairly sure that coating is meant to stop light that is going out of your lenses from being bounced back on its way out...

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barcoed

· #8 · May 20, 2007

I completely agree with all of the above advice.

I once had a binocular with a stone chip in the front of one objective (the big lens at the front) - it was completely invisible from bird watching to astronomy. Same with projectors.

And remember: If it looks good, it IS good!

Enjoy.

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NateTTU

· #9 · May 20, 2007

Quote:
Originally Posted by none74 /forum/post/0

Having the anti-reflective coating is more important than getting scratches out. If you lose the coating, there will be a reduction in your contrast ratio since some light will be reflected BACK to the tubeface from the outer layer of your last lens element....I think...

I'm fairly sure that coating is meant to stop light that is going out of your lenses from being bounced back on its way out...

Can anyone else confirm this? Thats a bummer if its true, means I need to get a "new" pair.

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Curt Palme

· #10 · May 20, 2007

Quote:
Originally Posted by NateTTU /forum/post/0

I have some hd-18 lenses that the anti-glare coating is coming off. Sounds like to me that I shouldn't worry about this then? I'm pretty anal about having everything "perfect", but certainly don't want to spend $200+ for a new set.

Well then I guess you've set a price on your 'anality'

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NautikaL

· #11 · May 20, 2007

You can't just reapply the anti-reflective coating?

This is a good diagram of a converging lense. You can see that the rays are converged at the tube face, diverge at the lense, and then converge again at the screen. Everything is inverted by the lense however.

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dav99

· #12 · May 20, 2007

"I'm fairly sure that coating is meant to stop light that is going out of your lenses from being bounced back on its way out..."

Yes, the coating works as an impedance transformation device, just like using the proper

impedance coax cable. If the impedance is'nt right there will be reflections in the signal.

Weather it's a radio wave or light wave it all works the same.

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NateTTU

· #13 · May 20, 2007

Quote:
Originally Posted by NautikaL /forum/post/0

You can't just reapply the anti-reflective coating?

Some companys provide this service but I imagine its a pretty penny. I didn't want to buy another pair but I guess I will. However, would the pair that I have right now with some of the antiglare coming off be worth anything?

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NautikaL

· #14 · May 20, 2007

How can you tell if the coating is coming off?

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NateTTU

· #15 · May 20, 2007

I will post a couple of pics later this evening but its just the same as when the antiglare coating comes off anything. You can see the spots where its just glass and doesn't have that film anymore.

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