Steel Gobos

[sabian186]

We have some rosco brand steel gobos that we just bought size b. I put them in a 1000w ellipsoid and in about 5-10min it had got so hot that the gobo "melted" and the design got messed up.

Are they not supposed to be used with 1000w? I would use 500w lamps but I'm trying the gobo with a congo blue gel and it's just not that visible with the lower wattage lamp. Any thoughts?

,Jacob

[waynehoskins]

Is the fixture in question in bench focus? Are 575-watt lamps available for this fixture?

Now, even in perfect bench, good luck being able to see Congo, especially a pattern in Congo, even with 1K lamps. Congo is half a percent transmissive, so for every KW you put into the back of the gel, you get 5 watts coming through the front of it, give or take. (Ignoring that the watt is a measure of power and not light, but the analogy holds well enough for the big picture comparison)

Also, since 99.5 percent of your light is being absorbed by the Congo and turned into heat, you may have color burnout problems. Is there another color, more transmissive, that might fit your design concept?

[Steve Vanciel]

What is the brand/model of light fixture you are using?

[sabian186]

Yes, the spot is in bench focus. It can take 500w bulb but I'm not sure about a 575w. I haven't tried the gels out yet on it yet either so It might not work out anyways with a 1k lamp.

What I'm trying to accomplish projecting crosses on the sanctuary side walls of our church and I thought hey congo blue is a very attractive color for doing some atmosphere lighting because I don't want these crosses sticking out like soar thumbs and distracting from the stage or anything else going on. Any other color suggestions?


I don't know the fixture brand/ model I just know they are pretty oldish late 80's maybe early 90's. I'll try to find out and take a picture of the fixture.

Also do you think that congo blue would be ok in 1k par 64's?

[Steve Vanciel]

Originally Posted by sabian186

It can take 500w bulb but I'm not sure about a 575w.

If this unit takes a medium 2pin lamp (FEL-1000W, EHG-750W, EHD-500W) there are some newer 575W @ 115V lamps (such as an FLK) that could work as well.

What I'm trying to accomplish projecting crosses on the sanctuary side walls of our church and I thought hey congo blue is a very attractive color for doing some atmosphere lighting because I don't want these crosses sticking out like soar thumbs and distracting from the stage or anything else going on. Any other color suggestions?

Either using a lower wattage lamp or dimming the fixture could keep it from being too distracting. This could also let you use a less saturated color. As Wayne noted, Congo is very saturated and thus passes very little light.

Also do you think that congo blue would be ok in 1k par 64's?

Any blue will work in any light. It is just a question of how bright it will be and how long before it burns or fades out. Tungsten lamps have very little of the blue spectrum and therefore the gels must absorb a lot of energy to produce a little bit of blue.

Returning to your original question, a quality (Rosco) steel gobo should work fine in a 1KW ellipsoidal light that is properly adjusted. A simple cutout of a cross should last a long time compared to a more intricate pattern like branches or window panes. Is the fixture benched for a peak or a flat field?

SteveV

[waynehoskins]

Back in college Les and I used Congo bax in one show. Two or three units, old 8" Fresnels. 1Ks, I think. They only saw use in one scene. I believe we had to change the Congo more than once during tech and the one weekend run. Plus, you couldn't really see it anyway.

The melty gobo sure sounds like it's uber-peaked.

[sabian186]

So here is a picture of the fixture, I believe it is an altman 360 Q.




Here in lamp compartment it says 360 Q so that's why i'm guessing that.





Here is the Gobo I'm trying to use as you can see it is somewhat brittle because of the outline of the cross.



The fixture is bench focused for flat field focus. So I tried the 500w lamp and it seemed to be ok for the gobo but I didn't have any gel on it. Does that FLK 575w lamp put out more lumens for the wattage?

As for the congo blue and the par 64's I'm wanting to create an atmosphere lighting look. Any other gels you guys would recommend for wall washing for the side walls besides congo blue?

[Esoteric]

A few things about gobos:

1. If your unit is not in bench focus they will burn up
2. With a 1K lamp anything with small lines will eventually burn
3. When I use congo blue I usually have at least 36k of PARs behind it, otherwise it is a waste of time
4. If you have to have a pattern with really fine lines you have two options, either use a projection or when using a 1k lamp have a glass litho made
5. Yes the FLK is more efficient and will give you more output
6. I would look into R80 or R78

Mike

[waynehoskins]

Yep, that's an Altman 360Q-6x22. Note that 360Qs were never rated for a 1K lamp, only 750 maximum. Put a GLA in there and see if that doesn't help things.

[Steve Vanciel]

Originally Posted by waynehoskins

Altman 360Q-6x22

A very narrow angle, long throw fixture.

GLA

One of several 575W retrofit lamps. They are more efficient due to being rated at 115V (typical dimmer output level) rather than 120V (typical wall outlet level). This class of lamp uses a compact filament popularized by ETC's HPL lamps. They will project a sharper gobo image since there is more of a point source to the filament than the older series of lamps with a long filament (FEL, EHG).

The gobo pattern you showed does have some fine lines that will be very prone to melting. If it gets bad enough, you could remove the inner parts and just go with the main cutout for a simple cross image. This could be projected with a light color (gold, amber, or straw) over a deeper color background from a PAR. The contrast could be very effective.

SteveV