A narrow spot needed...

[Karel Bata]

Basically the mirrors spots will be portions of the original light source.

 

Not really. If you stand where the mirror ball is (or hang from a lighting bar next to it, but I recommend standing ) you will see all of the light source, not just a portion. This is what the mirrorball 'sees' and reflects.

 

The optics of this is quite complex and counterintuitive. I have a mirrorball next to window right here, and it's sunny. On the wall next to the window the images are rhomboids, distorted squares:

But on the wall opposite (behind the camera) they are circular - where the little mirrors act as pinhole cameras and create a blurred image of the sun. You can see the transformation as they turn into circles beginning in the pic on the right hand side.

So if your lamp has a circular exit for the light, as most do, you would see circular dots on the stage floor. If it's rectangular you should see squares. In theory, if you put a large star shaped cutout into the gel frame holder you should see stars. Anyone ever tried that? It would be like that trick for creating heart-shaped bokeh in a camera -

 

 

You should be able to do that with a mirrorball. I might give this a try.

 

Someone could write a book on this!

[sunray]

Yes very complex, not least due to the parrallax error created by the rear silvering of the mirrors.

'Portion' can be by brightness or by parts of the beam, depending on the beam type, state of focus [whether focussed on the ball or the final image position for example] and position of the light source.

In the case of the additional lens in the Patt23 the basic beam had a vague focus at the position of the ball. I've been trying to come up with with a description of the beam and the best I can do is compare it with a blowtorch flame with the outer flame and the focussed blue inner, although it then expanded after the focal point.

 

Where the centre part of the beam hit the balls mirrors the final image on the walls was a small version of the beam [a bright spot with a lighter halo]. But the outer edges of the balls reflections had almost no bright spot. Of course there were squares on the ceiling close to the ball as in the above pictures.

In my Disco days I used a 500W slide projector [with a selection of slides] fitted with a 300mm camera lens which was quite successful but not really bright enough for anything beyond 15ft so it was generally used to project on the surface behind the DJ rather than the hall.

Edited January 29, 2020 by sunray

[Karel Bata]

Interesting stuff.

It's fun to experiment isn't it? I think the mirrorball is a very underrated piece of lighting kit. I'm still discovering it's potential. (Geddit?) Gonna try out my star idea soon.

I wonder how much it would cost to get a front-silvered mirror ball made?

 

Edited January 29, 2020 by Karel Bata

[James Remo]

Have a chat with mirrorball paul... I’d be surprised if he didn’t already have one built.

https://www.mirrorballpaul.com

[bruce]

I hate myself for this!

 

Against my better judgement, I bought a couple of "10W LED Mini Pinspot Spotlight Spot Beam Light DJ Disco Stage Light White” from eBay. They look a bit like the Chauvet pinspots recommended above, and siren these ones are 10W and the Chauvets are 3W, they must be better.....

 

and they were only £12 fo a pack of 2!

 

They are truly awful.

 

Good round hard-edged beam. Not particularly bright. Moulded “fuse-free” 13A plug. No earthing, but internal gubbins cable tied to metal plate (with some heat shrink) which is directly connected to metal bracket.

 

I won’t be keeping them

[sunray]

I hate myself for this!

 

Against my better judgement, I bought a couple of "10W LED Mini Pinspot Spotlight Spot Beam Light DJ Disco Stage Light White" from eBay. They look a bit like the Chauvet pinspots recommended above, and siren these ones are 10W and the Chauvets are 3W, they must be better.....

 

and they were only £12 fo a pack of 2!

 

They are truly awful.

 

Good round hard-edged beam. Not particularly bright. Moulded "fuse-free" 13A plug. No earthing, but internal gubbins cable tied to metal plate (with some heat shrink) which is directly connected to metal bracket.

 

I won't be keeping them

I share your pain.