Light Meter Diffuser--Flat vs Spherical

[jcsorensen]

I just received a Minolta IV F light meter that I got off of E-bay. As I'm reading the owner's manual, it says you use the Spherical diffuser to take a flash reading and for ambient light readings.

However if you want to get the ratio of a main flash to fill flash , it says you need the flat diffuser on the meter. Can someone explain this to me as to why this is? Will the spherical diffuser get you in the ball park when working lighting ratios, or will it not even be close?

Look forward to playing with my new toy--just wish I didn't have to be at work so much so I could play a lot more.

[PacAce]

The spherical diffuser will read the light from all around so it'll have to had time giving your ratios from two different light or flash sources. The flat diffuser is more "directional". You have to point it towards the light source you want to measure and hence you can figure out the ration between the fill and the main light or flash sources.

[DaveG]

I just received a Minolta IV F light meter that I got off of E-bay. As I'm reading the owner's manual, it says you use the Spherical diffuser to take a flash reading and for ambient light readings.

However if you want to get the ratio of a main flash to fill flash , it says you need the flat diffuser on the meter. Can someone explain this to me as to why this is? Will the spherical diffuser get you in the ball park when working lighting ratios, or will it not even be close?

Look forward to playing with my new toy--just wish I didn't have to be at work so much so I could play a lot more.

With the flat diffuser the meter becomes very directional so the reading you get when you point it at one flash won't (or shouldn't be) influenced by a second flash.

But I use the same meter you have with the regular spherical diffuser to set up lighting ratios. I meter each light individually to calculate the lighting ratio, so the advantage of the flat diffuser (which I have) is pretty much moot. Even when I have both flashes firing, in order to get a combined exposure, I can get good individual light outputs by just flagging the meter with my hand.

That by the way is my work flow. Meter the main, set up the fill so it's almost a stop under the main (1:3 lighting ratio); then with colour slide or digital capture I measure them together which gives me my exposure. The limited latitude of slide or digital requires this approach and you still get a ratio that those media will handle.

[rodbunn]

The way my meter works is;

Flat is when I point the meter at a surface and measure the "reflected" light and Spherical is when I point the meter at the light source and measure "ambient" light.....

Rod

[DaveG]

The way my meter works is;

Flat is when I point the meter at a surface and measure the "reflected" light and Spherical is when I point the meter at the light source and measure "ambient" light.....

Rod

That's not the way to use the flat diffuser. The flat diffuser is for incident meter readings, as is the spherical one. You should use the spot meter attachment if you want to do reflective meter readings.

[rodbunn]

I'm loosing my mind. When I said "flat" I ment; on my meter you slide the "dome" over (off of the metering point) and then it's a spot meter that
you point at the surface . . .

Sorry, ever since I retired I've lost my mind ;-)


Later, Rod