What problem is caused by a scratch on a fresnel lens?

<p>What effect/problem can be caused by a scratch on a fresnel lens?</p>

<p>Thanks,</p>

<p>Francesco</p>

<p>What sort of fresnel lens, used in what way? Are you talking about a glass fresnel, used on something like high-powered cine lighting? A scratch there might throw a bit of light out, as a sort of tiny diffuser, instead of quite as cleanly focusing it all where it's supposed to go. Without knowing more about what you're <em>really</em> asking, it's almost impossible to respond constructively.</p>

<p>Sorry, I thought that placing my question in the "tungsten lighting" section it wouldn't have been necessary to specify. <br>

Anyway yes, I'm talking about fresnel lens lights, as Mole-Richardson, Arri etc.</p>

<p>thanks</p>

<p>Well obviously it's going to depend on the scratch. If it's deep and leaves jagged facets in the glass, you're going to get some stray light heading out in directions you may not intend. If you're trying to create careful puddles of light that don't stray onto (for example) a backdrop, a deep scar in the lens could pollute the scene a bit. I doubt that a superficial scratch would matter in the least.</p>

<p>Compare the depth and area of the scratch to the depth and area occupied by all the circular steps intentionally put on the Fresnel lens to make it work. The intentional steps also scatter light, so this comparison will give you some idea how much additional scattering will result from the accidental scratch. </p>

<p>My guess is that unless it is a huge, deep scratch, you'll never see any difference.</p>

<p>Tom M</p>

<p>I agree with Tom. Unless it's large in relation to the size of the lens it will probably have no noticable effect at all. And even if it does, it is highly unlikely to render the lighting unit useless. Much less impact than a scractch on a camera lens.</p>