Beam Angle & Lux?

[Talvik]

What determines the beam angle in a moving head fixture? I presume it's the lens.

My main question is, is it possible to change the lens of a moving head to tighten the beam dramatically?

Also would this increase the lux at a given distance?

In addition, with lights with a range of beam angles, is it accomplishing a tighter beam usually by just using a smaller gobo? and does this decrease lux?

 

For example I've seen lights like the blizzard torrent with a 15 degree beam angle accomplish a very tight beam like a sharpy,

is it just accomplishing this with a small circular gobo? Versus a sharpy that has a tight beam lens?

[fliggygeek]

What determines the beam angle in a moving head fixture? I presume it's the lens.

My main question is, is it possible to change the lens of a moving head to tighten the beam dramatically?

Also would this increase the lux at a given distance?

In addition, with lights with a range of beam angles, is it accomplishing a tighter beam usually by just using a smaller gobo? and does this decrease lux?

 

For example I've seen lights like the blizzard torrent with a 15 degree beam angle accomplish a very tight beam like a sharpy,

is it just accomplishing this with a small circular gobo? Versus a sharpy that has a tight beam lens?

 

The beam angle is determined by the lenses in the head, on a standard fixture its normally just the zoom lens and the front lens.

Yes, for example, Martin used to stock various replacement lenses for lights like the Mac 250 series and the Mac 500.

They could reduce, from memory, the 21.5 degree standard beam to 16.5 degrees or something.

Its been a while since I've seen one though, most lens replacement kits are to convert wash fixtures to beam fixtures.

 

Yes it is definitely possible to change the beam angle of fixtures dramatically. Within certain boundaries, it does increase the lux, the boundaries being that the optics can have a big negative effect on total lux.

 

Small aperture gobos are not beam angle changers. They simply decrease the size of the beam opening, having no effect on total lux, because its simply blocking part of the beam.

 

Think of the beam coming off your fixture as a solid cone. A gobo simply makes the cone smaller. A lens makes it wider or thinner.

 

From the brief look at the Blizzard Torrent, it would be hard to fit the correct lens to it to make a 1-5 degree beam similar to a sharpy, not to mention that the beam would only be 2 inches round at 1 degree when exiting the fixture.

The best lights to make a beam mod to are usually wash fixtures due to the large lens opening, it gives you a fatter beam.

Blizzard do make a Torrent Beam, have a look at the lens on that for an idea of what I'm talking about.