Help identifying/fixing a light

cmp914

Member
The school that I work for has two follow spots that I'm trying to get in working order. I've had to clean off what looks like decades of dust and rewire them since the plugs are for a type of outlet I have never seen before. Now I discovered that the placement of the lenses in the two of them don't match and I'm trying to figure out which is right. They have three lenses and I'm not sure which goes in the front, back and middle or which way each is supposed to face. The spots just say Altspot NY on them. It seems they are a discontinued product made by Altman, but I can't find any sort of pictures or diagrams to help me.

Anyone know how they are supposed to be placed? The picture is the three I pulled from one of the spots so I could clean them. Note that one of them has a blueish greenish tint.
 

Attachments

  • 20150326_133131.jpg
    20150326_133131.jpg
    73.9 KB · Views: 349
Post picture(s) of the fixture (both of the outside and of the lamp), so we can be sure, but here are my suspicions/assumptions.

The followspot is an Altman 902; see attached PDF.

The three lenses: The conza lens goes curves toward the lamp, both plano-convex go with curve toward the stage. The step lens (conza lens) goes in the back nearest the lamp. The two plano convex lenses are either 4.5x6.5 & 4.5x9, or 4.5x9 & 4.5x12.* In either case, the thicker lens goes in the middle, and the thinner toward the stage.
From the PDF:
altspot_lenses.jpg


There has been lots of discussion of these fixtures over the years; type "Altspot" into the search box. Here's one: http://www.controlbooth.com/threads/lotsa-questions-altman-1000q-followspot.10864 relating to the Altman 1000Q which is similar (or possibly the same) as your unit. "Altspot" was a somewhat generic term.

*When discussing plano-convex lenses, the first number is the diameter, and the second the focal length. To find a lens's focal length, take it outside in the sun (ideally at the equator at noon on an equinox--you want parallel rays entering the lens) and pretend to be burning ants, getting a dot of focussed light. The distance from the flat side (plano) to the surface is the approximate focal length.
 

Attachments

  • 902.pdf
    326.1 KB · Views: 180
Last edited:
Post picture(s) of the fixture (both of the outside and of the lamp), so we can be sure, but here are my suspicions/assumptions.

The followspot is an Altman 902; see attached PDF.

The three lenses: All lenses go with curve toward the stage. The step lens (conza lens) goes in the back nearest the lamp. The two plano convex lenses are either 4.5x6.5 & 4.5x9, or 4.5x9 & 4.5x12.* In either case, the thicker lens goes in the middle, and the thinner toward the stage.

There has been lots of discussion of these fixtures over the years; type "Altspot" into the search box. Here's one: http://www.controlbooth.com/threads/lotsa-questions-altman-1000q-followspot.10864 relating to the Altman 1000Q which is similar (or possibly the same) as your unit. "Altspot" was a somewhat generic term.

*When discussing plano-convex lenses, the first number is the diameter, and the second the focal length. To find a lens's focal length, take it outside in the sun (ideally at the equator at noon on an equinox--you want parallel rays entering the lens) and pretend to be burning ants, getting a dot of focussed light. The distance from the flat side (plano) to the surface is the approximate focal length.

Thanks for the help. As far as I can tell, the two Plano lenses are the same thickness. What do I do then? Also, is the tinted one supposed to be tinted?
 

Attachments

  • 2015-03-26 15.06.14.jpg
    2015-03-26 15.06.14.jpg
    94.7 KB · Views: 373
  • 2015-03-26 15.07.02.jpg
    2015-03-26 15.07.02.jpg
    83.1 KB · Views: 358
As far as I can tell, the two Plano lenses are the same thickness. What do I do then? Also, is the tinted one supposed to be tinted?
Put both back in the fixture and hope for the best.

Don't worry about the greenie. While not original, based on the PDF, it won't be an issue.
Re: Lenses



Les is onto something here, as indeed earlier versions of the 360Q used a soda lime glass (thus the greenish tint when viewing the lens) while the later version employed the use of a clearer crown glass. The thickness of this lens type will certainly affect the output of the fixture, and the amount of dirt, dust, grime, etc will exacerbate the problem. (Can I say that on this forum? Exacerbate just doesn't seem, well... proper.)



Wikipedia states in part:

http://en.wikipedia.org/wiki/Crown_glass_(optics)
Crown glass (optics) is produced from alkali-lime (RCH) silicates containing approximately 10% potassium oxide. It has low refractive index (≈1.52) and low dispersion (with Abbe numbers around 60); crown glass is one of the earliest low dispersion glasses...

Soda-lime glass - Wikipedia, the free encyclopedia
Soda-lime glass is prepared by melting the raw materials, such as sodium carbonate (soda), lime, dolomite, silicon dioxide (silica), aluminium oxide (alumina), and small quantities of fining agents (e.g., sodium sulfate, sodium chloride) in a glass furnace at temperatures locally up to 1675 °C...

Soda-lime glass is divided technically into glass used for windows, called float glass or flat glass, and glass for containers, called container glass. Both types differ in the application, production method (float process for windows, blowing and pressing for containers), and chemical composition. Float glass has a higher magnesium oxide and sodium oxide content as compared to container glass, and a lower silica, calcium oxide, and aluminium oxide content.
 
Last edited:
Do note that the conza lens is supposed to curve in toward the lamp (it appears correct in your photo).

The asbestos is hazardous to work with but won't be an issue once you seal the fixture back up. I don't believe this unit has a fan, so you shouldn't have to worry about the fan exasperating the issue by making the asbestos airborne. Remediation of the wiring would likely just stir things up so I'd leave it.

I agree that I'd close the fixture up and hope for the best. If it looks wrong, we can go from there. Are you basically saying that between your spots the sets of lenses don't match, or do they match each other, just not the PDF?

Measure the exact thickness of the lens by placing it curved-side down on a smooth, flat surface. Then measure the gap between the table and the flat surface of the lens.
 
Do note that the conza lens is supposed to curve in toward the lamp (it appears correct in your photo).

The asbestos is hazardous to work with but won't be an issue once you seal the fixture back up. I don't believe this unit has a fan, so you shouldn't have to worry about the fan exasperating the issue by making the asbestos airborne. Remediation of the wiring would likely just stir things up so I'd leave it.

I agree that I'd close the fixture up and hope for the best. If it looks wrong, we can go from there. Are you basically saying that between your spots the sets of lenses don't match, or do they match each other, just not the PDF?

Measure the exact thickness of the lens by placing it curved-side down on a smooth, flat surface. Then measure the gap between the table and the flat surface of the lens.

I mean that between the two of them, the positioning doesn't match. The conza lens is facing one direction in one and the other way in the other. Both have one greenish lens and one white and in one the greenish is in front, the other in the middle. The all four plano lenses are the same thickness unless my ruler just isn't precise enough to read the difference.
 
The three lenses: The conza lens goes curves toward the lamp, both plano-convex go with curve toward the stage. The step lens (conza lens) goes in the back nearest the lamp. The two plano convex lenses are either 4.5x6.5 & 4.5x9, or 4.5x9 & 4.5x12.* In either case, the thicker lens goes in the middle, and the thinner toward the stage.
From the PDF:

.

Derek

I've never heard of the term 'conza' lens. ( it looks like a step lens from what I can see ). Whats the definition of a conza lens, or was it just an Altman affectation ?

Ok after I posted I see the link to Control booths definitions. But I still don't understand what is special about it.
 
The only time I've heard it called a "conza" is in Altman documents... But they are pretty consistent about calling it that.

OP - the conza lens is supposed to face the lamp (belly towards the lamp).

Strangely (according to the WIKI entry), the 1000Q has a conza lens. However both my 1000Q's contain only two plano convex lenses. The conza lens is used to homogenize the output pattern of a lamp against a spherical reflector. If you were to replace the spherical reflector with an ellipsoidal reflector and turn the lamp axial, the conza lens would no longer be needed. Since the 1000Q uses an ellipsoidal reflector in combination with an FEL (or similar) lamp, the conza lens would be redundant. My guess is that the Altman document reference was for a previous version of the 1000Q.
 
Last edited:
Thanks for the help. As far as I can tell, the two Plano lenses are the same thickness. What do I do then? Also, is the tinted one supposed to be tinted?
In that picture, it looks like the lamp is either not seated correctly or the socket may be off. The filament plane should be flat but in the picture it almost looks to be at an angle.
 
@JChenault I, too, have only heard of a conza lens in relation to older Altman (and Capitol) followspots.
Strangely (according to the WIKI entry), the 1000Q has a conza lens.
I, too, was surprised by finding two slightly different conza lenses listed in an Altman parts list from 11/08, reinforced by the snippet of pdf I included above in post #2.

"Rear lens: 4.5 x 2.5 x 6.5 conza for both [902 and Dyna-Spot] follow spots". As @Les said, it's a condensing lens needed due to the spherical reflector. I don't know what the extra "2.5" refers to, but its more than a simple step lens. The only google reference turned up this thread http://forums.prosoundweb.com/index.php?topic=142682.0 and isn't much help. Kinda makes it sound like the lens gives an oval beam, and that rotation orientation matters, perhaps to homogenize the filament lines, as @Les said.

It's a mystery, and sadly, I'm not sure there's anyone still living at Altman who knows.
 
...its more than a simple step lens. The only google reference turned up this thread http://forums.prosoundweb.com/index.php?topic=142682.0 and isn't much help. Kinda makes it sound like the lens gives an oval beam, and that rotation orientation matters, perhaps to homogenize the filament lines...

It has been years since I have looked at a conza lens, but I do recall seeing very slight ripples in the "bullseye" of the belly side of the lamp. I never stopped to think about whether or not it was a "feature", but it looks like there is a purpose and that it wasn't just my imagination.

I've been lending a hand at my local community theatre lately and they do have an old Little F-10 Opto sitting up in the "loft". I recall it using the following optics: spherical reflector - mogul prefocus lamp - conza lens - ~4.5" plano convex lens - ~8" plano convex lens (kind of a mashup between the Dyna-Spot and the 1000Q). Maybe I will try rotating the conza lens and reporting what happens.
 
I'm not totally sure I get what you mean. Are you saying the filament should be parallel to the lenses? Or perpendicular?

Should be parallel from what I remember (broadside facing the lens) . It does look like the lamp could use a little more (or less) "twist", but that could be a trick of the light (get it? :) ).
 
Last edited:
One other nit-picky issue:
It appears that the main power cord has been replaced with a yellow extension cord cable at some some point. It looks like 16 gauge SJ cable. That's not heavy enough to run a 1500 watt lamp for any amount of time without danger of insulation melting. If you're planning on only using 1000 watt lamps, it's not an issue (except that they don't make them any more…)
For safety's sake, that should be replaced with at a minimum 14 gauge cable. To be extra-safe and make sure it's absolutely code-compliant, use 12 gauge SO rated cable.
 
One other nit-picky issue:
It appears that the main power cord has been replaced with a yellow extension cord cable at some some point. It looks like 16 gauge SJ cable. That's not heavy enough to run a 1500 watt lamp for any amount of time without danger of insulation melting. If you're planning on only using 1000 watt lamps, it's not an issue (except that they don't make them any more…)
For safety's sake, that should be replaced with at a minimum 14 gauge cable. To be extra-safe and make sure it's absolutely code-compliant, use 12 gauge SO rated cable.

I don't have a clue who did that or how long it's been like that. Is there any way I could easily check the cable to see if it is 12 gauge or 14 gauge?
 

Users who are viewing this thread

Back