Condensers and film strip projector question at DVinfo.net

Leo Mandy · July 25th, 2005, 06:31 PM

I have finally taken apart an old film strip projector that I had lying around (I thought I might have a use for it, but alas the use came in the form of destroying it to get the lenses!). Now here is the question. The setup in the project is like this :

LIGHT - |) (| filmstrip LENS

Why are there two in sequence? In fact, one is crystal clear like glass and the other is slightly bluish green in tint. Any ideas?

Aaron Shaw · July 26th, 2005, 02:46 PM

These are just guesses so bear with me :)

The lens that seems to be colored might be due to an optical coating. Often these coatings will appear as a fine blue/green/purple film on the lens which can be seen better at some angles than others.

The reason for the two sequential lenses is to eleminate distortion. When you have two lenses in that sort of setup the distortion created by the first lens will usually be corrected well enough by the second (of the same type) to use in projection etc.

Leo Mandy · July 26th, 2005, 02:48 PM

Thanks, its weird though, why two lens in sequence just to make the light less distorted? There is nothing between the light and the two lens, so that is why I was curious.

July 25th, 2005, 06:31 PM	#1
Leo Mandy Major Player Join Date: Dec 2004 Posts: 749	Condensers and film strip projector question I have finally taken apart an old film strip projector that I had lying around (I thought I might have a use for it, but alas the use came in the form of destroying it to get the lenses!). Now here is the question. The setup in the project is like this : LIGHT - \|) (\| filmstrip LENS Why are there two in sequence? In fact, one is crystal clear like glass and the other is slightly bluish green in tint. Any ideas?

July 26th, 2005, 02:46 PM	#2
Aaron Shaw Major Player Join Date: Jul 2004 Posts: 587	These are just guesses so bear with me :) The lens that seems to be colored might be due to an optical coating. Often these coatings will appear as a fine blue/green/purple film on the lens which can be seen better at some angles than others. The reason for the two sequential lenses is to eleminate distortion. When you have two lenses in that sort of setup the distortion created by the first lens will usually be corrected well enough by the second (of the same type) to use in projection etc.

July 26th, 2005, 02:48 PM	#3
Leo Mandy Major Player Join Date: Dec 2004 Posts: 749	Thanks, its weird though, why two lens in sequence just to make the light less distorted? There is nothing between the light and the two lens, so that is why I was curious.