Good integrating lumisphere material?

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BetterSense

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I'm building an incident light meter and need a good lumisphere. It should be hemispherical, it might as well be white, and should let light pass through it easily, but scatter it thoroughly.

A ping-pong ball would be just about perfect, but a ping-pong ball is too big. I need something with about 7/8" diameter. Any ideas on what I could use?
 

jeffreyg

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See if an existing meter has the right size sphere and maybe you can get a non functioning one for the part or get a replacement sphere from their parts dept.
 

Rick A

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I'm building an incident light meter and need a good lumisphere. It should be hemispherical, it might as well be white, and should let light pass through it easily, but scatter it thoroughly.

A ping-pong ball would be just about perfect, but a ping-pong ball is too big. I need something with about 7/8" diameter. Any ideas on what I could use?
Possibly something from a gumball machine that has a cheap necklace or whatever in it--some are all clear,some have a clear half with a white half--usually 50cents. My kid always has to spend a couple of quarters in them when we go to the store--worth a try.

Rick
 

paul ron

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Ping Pong ball.
 

Steve Smith

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Why does it have to be hemi-spherical? A piece of white Perspex (or Plexiglass as it's called where you are) should be fine. My Zeiss Ikophot has a flat piece for ambient measurement.


Steve.
 

chriscrawfordphoto

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Buy a dome for the Minolta meters, they're the size you need and are available separate from the meter, or were when the Minoltas were still being made, you can probably get a used one.
 
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BetterSense

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Actually I found a box of miniature Christmas tree ornaments that are made out of white plastic. Cut in half and the sparkles sanded off, it looks like about the perfect thing.

Why does it have to be hemi-spherical?
I'm not sure; it seems most incident meters have hemispherical domes so they have very gross directionality. A flat piece would be more convenient by a long shot, because it wouldn't stick out.
 

winger

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I'm not sure; it seems most incident meters have hemispherical domes so they have very gross directionality. A flat piece would be more convenient by a long shot, because it wouldn't stick out.
My meter (Sekonic L-718) has both. The pieces are interchangeable (also with one for measuring reflected light), so maybe you can figure out a way to do this?
 
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BetterSense

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I'm sure a flat piece would work. I can calibrate the meter to whatever I choose to use. I'm just not sure what I want. I found the Sekonic user's guide online, and it says

Use Lumisphare (sic) when you wish to measure incidend light for portraits and 3-dimensional subjects...point the Lumisphare accurately toward the camera...

Use Lumidisc when you wish to measure lighting contrast and lux as well as exposure of single-dimensional objects...point the Lumidisc accurately toward the light source...

I'm not sure what a single-dimensional object is and why you would be photographing it.

To be honest I'm not sure how one uses an incident meter. I always figured you held it in the light you were interested in, I just am not sure what direction you are supposed to point the 'dome'. If I'm outside in the daytime shooting 'street', I would point the dome straight up toward the sky I suppose. But if I have someone sitting in a chair, side-lit by a window, do I point the dome at the window, or back toward the camera?

It makes sense to me that a flat piece is going to be significantly more directional than a hemisphere would. I don't know if that's a good or bad thing.
 
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John Koehrer

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The flat disc is used to measure the evenness of light on a two dimensional object(copywork). Measure from corner to corner and verify the light is the same across the surface.
With a hemisphere it's most commonly used pointed at the camera from the subject.
The dome shape allows the meter to evaluate light falling onto a 3 dimensional subject and average the reading from top, bottom both sides and front.
 
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