Source 4 ellipsoidals lenses

[JohnA]

While performing routine PM on a couple of S4 ellipsoidals, I noticed that the one of the lense tubes contained 2 lenses. The 26 degree piece was in its assigned 'slot'; but there was also a second lens in the tube-in the very first slot-- closest to the 'gate' end of the tube. What is the purpose of the second lens? Thanks for any info. John A

[Foxinabox10]

Does this happen to be an Enhanced Definition Lens Tube? Otherwise, standard 26 degree lens tubes should only have one lens.

[Van]

Pretty much all ellipsoidals use two lens to focus their light. Check out a photometrics chart or grab an intro to lighitng book. Typically they are two plano-convex lens, thickness of the lens, the angle of the curvature, and the distance they are apart dertermins the 'focus" or more accurately the beam angle of the lens tube. The lens tube is the only thing that makes a difference in what comes out of a S4, the "fixture" itself is inter- changable the tubes determine the beam angle.

[Foxinabox10]

However, in the S4, one lens is within the fixture unchanged regardless of what beam angle you want. The standard lens tube has the second lens in it. In addition, Enhanced Definition Lens Tubes (EDLT) have two lenses in them. Also, the new 70 and 90 degree S4 contain two lenses.

[Van]

Sorry, I'm living in the past, Obviously I'm been concentrating on carpentry too much lately. What you got there is an EDLT lens "Enhanced Definiation Len" beter for the projection of gobos. It goes back to the old school technology of getting a crisper beam from the photometrics of a two lens design.


Sorry I wasn't thinking earlier...... Can you all forgive me ?????

[mattm]

A 36 degree has 2 lenses in it. The cast housing for the lens tube has slots for every size beam, from 19 to 50. I haven't seen a 14, 70, 90, so I can't comment about those. From a manufacturing standpoint, it makes sense to cast only one tube. The reason for 2 lenses is to achieve the desired beam spread in a restricted space.

Matt McCormick
www.cablepick.com

[Foxinabox10]

You are correct. I mis-spoke. The 36, 70, and 90 degrees are the only standard (non-EDLT) lens tubes with 2 lenses.

[mbandgeek]

That happended at the local fine arts center, The TD, tfactech, just removed one of the lenses. The second lense gave the 26 degree fixture a 36 degree beam angle. upon removing, it returned to the specified 26 degrees.

[Footer]

You can not however simply move lenses around to get different degree spreads, it does no work. The lenses are all a bit different.

[kingfisher1]

cruise around the ETC site. they have a nice little diagram of teh different lens placements. also all the lens have a colored coded dot to signify their dergree, you can also find that info their too