60's era Klieglight (ERS) Step Lenses

[pianoman]

I just acquired two 1960's era Klieglight ERS instruments, but they have two different lenses in them. One has a step lens with more steps than the other lens. Both are mounted in the position closest to the edge (which from what I understand is where the step lenses are supposed to be). However, the instrument with the step lens with more steps will not focus, or at least not at about 25 feet, which is all I've been able to try it out at thus far. The other instrument creates a very nice round beam that can be made slightly fuzzy or nice and sharp with the adjustment of the focus, but the one with more steps basically covers a whole wall, and has about as much focus as a fresnel on flood. I can trade out for a matching lens, but my question is what is wrong with this instrument with the higher stepped lens? I tried moving it to the outer position like the other and that didn't help at all. Is it just that the beam angle is much larger than the other? I can't test it on a large wall as of yet; all I have is my basement, so the distance is not so great and the wall height is only about 8 feet or less. I have attached pictures of the lenses and instruments as well in case you're not sure what I'm talking about.

-Dan

[ship]

most likely yep. Different beam spread and wrong for the lens tube if both lens tubes are the same.

Extract the lenses and look at the OD size. Remember that step lenses are a lens that has the insides cut away, yet the radius of the lens remains the same as if it were a solid lens. Potentially one with more steps is of a larger magnifiction.

Than of course I have no experience with wrong step lenses in a fixture. Could have been a replacement lens mis-sized. Could be but doubtful that one lens brand to another, one has more steps than another but I seriously doubt this.

Most likely it's the wrong lens size in the fixture for the focal length of the lens train.

Also, if you note your photos, there is some dirt and funkeyness going on inside the fixtures. Might want to look into it.

[pianoman]

Yeah, I need to clean them all out. The two others I just got are covered in sawdust. I don't mind using the non-focused lenses really, and I suppose at the time they kind of made sense, as the concept of stage lighting was still in development, as well as the real place of an ERS fixture in the theatre. So I find it believable that they just had two different lens focus patterns basically. From what I'm told, these instruments could have plano convex or the two different kinds of step lenses in them. The theatre I got them from only had one of the plano convex lenses; the rest were the two kinds of step lenses. I will mess around with the lens position some, since there's actually two lens positions in the lens tube: one up close to the front and another toward the back. But then again, since I don't have any fresnels anyway, these could work out rather nicely.

-Dan

[Logos]

Have you checked the trim (relation of lamp to reflector) on the lantern with more steps in the lens. In these older lamps that can have quite an effect on the beam spread as well.
I've just acquired two Strand(UK) Patt 23N lanterns which look as though they are related in the design world to your lanterns. I suspect similar period. My lanterns are mid 60's UK manufacture. These however both have ordinary plano convex lenses. I have seen the lantern fitted with both Fresnel and step lenses though and I am currently seeking lens tubs with those lenses to experiment.
These lanterns were still aroung quite a lot when I started in this busines but I had little opportunity to use them in those days.

[pianoman]

That is something to check; I doubt it's been really adjusted at all, ever. I'll have to see about doing that; I don't know how it works as I don't have a manual but if it's something fairly obvious then I might be up for it.

-Dan

[Logos]

In European and UK lights it is usually a screw or small knob on the bottom of the rear body of the lantern but be very careful when adjusting with the lantern powered up. I have blown more lamps that way.

[pianoman]

Update: I decided last night to clean out all the instruments and primarily the lenses. What I discovered was that the paint that lines the sides of the steps on the inside of the lenses had deteriorated and was just powdering on contact. I popped 3 out of 4 lenses out (the last one broke actually) and cleaned them in oxy clean overnight. They're much cleaner now, but most of the paint is gone. Is this something I should be concerned about?

-Dan

[Logos]

I assume that the paint you're talking about was coating the inside of the lens tube? If it has powdered away it may marginally affect the amount of random reflection you get. What colour is the unpainted metal and what colour was the paint that has come off?
I have resprayed the interior of lens tubes with the sort of paint you use on engine blocks in a matt black but it isn't a cheap proposition. I don't really know the lantern you are working on so I don't know how hot it gets.
I hope this is helping.

[pianoman]

Actually the paint I'm referring to is actually on the glass lens. On the inside of the step lens there are ridges at each step, if you will, and on the part of the step that is perpendicular to the fixture, the step was painted black/grey. If you think of this in terms of an actual stairwell that you would walk on, think of each "step" as the part you walk on to go on the stairs, and so then the part that you do not step on, which is the toeboard of each step, is the part that is painted. Does this make sense? It looked like it was a method of masking off the bits of the step that one doesn't want light coming through.

-Dan

[Logos]

Fascinating. I haven't seen that but I guess it makes sense. I have no idea what effect it's absence will have. Maybe Ship or one of the other guys who knows american fixtures better than I do can help.