Light meters, ratio lighting

Setting up some lighting for portraits and instead of my usual thinking
of "2 stops down on one side" I decided to do it per "ratio" (same thing
of course) using my meter.

My flash meter has a mode for ratio light metering, however the manual
for the meter suggests the flat disk difuser be used in lieu of the
dome. (Minolta VF meter). I have no idea why (and I don't have the flat
disk either).

I meter off the shaddow side and off of the key side (with opposing
light off) and then off the subject nose with both lights on. The ratio
I typically aim for is 4:1 from key side to shaddow (2 stops). I set
the aperture per the highest of the three readings (usually the nose,
sometimes the keyside if the softbox is really close to the subject).

The background light is set anywhere from 2 stops below to a stop and
half above the aperture depending on what I'm trying to do.

What I don't understand is how the flat disk is going to be "better"
than the dome for ratio readings (as the Minolta meter manual suggests).

Any comments?

Cheers,
Alan.
--
--e-meil: there's no such thing as a FreeLunch.--

Alan,
I have an old minolta meter with the disc. Anyway I think the meter
guide be asking you to do reflective metering as opposed to incident
metering. The relective should give you more accurate numbers but could
be a bit tricky even with the disc for the meter. I think it's supposed
to be 10 degrees of coverage. You could always try a home-made disc and
tape it in place. I think the newer meters have spot/reflective flash
metering? not sure.
Hope that helps,
Jack

Alan Browne wrote:


Setting up some lighting for portraits and instead of my usual thinking
of "2 stops down on one side" I decided to do it per "ratio" (same thing
of course) using my meter.

My flash meter has a mode for ratio light metering, however the manual
for the meter suggests the flat disk difuser be used in lieu of the
dome. (Minolta VF meter). I have no idea why (and I don't have the flat
disk either).

I meter off the shaddow side and off of the key side (with opposing
light off) and then off the subject nose with both lights on. The ratio
I typically aim for is 4:1 from key side to shaddow (2 stops). I set
the aperture per the highest of the three readings (usually the nose,
sometimes the keyside if the softbox is really close to the subject).

The background light is set anywhere from 2 stops below to a stop and
half above the aperture depending on what I'm trying to do.

What I don't understand is how the flat disk is going to be "better"
than the dome for ratio readings (as the Minolta meter manual suggests).

Any comments?

Cheers,
Alan.

On Tue, 04 May 2004 22:41:03 GMT, Jack Germsheid
wrote:

Alan,
I have an old minolta meter with the disc. Anyway I think the meter
guide be asking you to do reflective metering as opposed to incident
metering. The relective should give you more accurate numbers but could
be a bit tricky even with the disc for the meter. I think it's supposed
to be 10 degrees of coverage. You could always try a home-made disc and
tape it in place. I think the newer meters have spot/reflective flash
metering? not sure.
Hope that helps,
Jack

There are several disks made for the meter. The reflective disks are
made entirely of black plastic and have holes in the middle. The disk
for reading light sources in the studio is made of white diffusion
plastic. The metal pin in the Minolta head tells the meter what disk
is on the meter so if you just tape a piece of cardboard over the head
you may not be getting correct readings.

McLeod wrote:

On Tue, 04 May 2004 22:41:03 GMT, Jack Germsheid
wrote:



Alan,
I have an old minolta meter with the disc. Anyway I think the meter
guide be asking you to do reflective metering as opposed to incident
metering. The relective should give you more accurate numbers but could
be a bit tricky even with the disc for the meter. I think it's supposed
to be 10 degrees of coverage. You could always try a home-made disc and
tape it in place. I think the newer meters have spot/reflective flash
metering? not sure.
Hope that helps,
Jack



There are several disks made for the meter. The reflective disks are
made entirely of black plastic and have holes in the middle. The disk
for reading light sources in the studio is made of white diffusion
plastic.

I don't agree that you can only use the incident dome in the studio.
I've used my disc in the studio to record refelective readings. Worked
fine. Slightly differnt readings than incident of course but the
photographer must evaluate all this info and make their exposures
accordingly.

The metal pin in the Minolta head tells the meter what disk
is on the meter so if you just tape a piece of cardboard over the head
you may not be getting correct readings.


This I did not know(pin), so that's why I read here on occasion.

Hey, anyway. Why bother with the disc. Stick with what has been working
for you - unless of course it hasn't been working.
Regards,
Jack

Setting up some lighting for portraits and instead of my usual thinking
of "2 stops down on one side" I decided to do it per "ratio" (same thing
of course) using my meter.

My flash meter has a mode for ratio light metering, however the manual
for the meter suggests the flat disk difuser be used in lieu of the
dome. (Minolta VF meter). I have no idea why (and I don't have the flat
disk either).

I meter off the shaddow side and off of the key side (with opposing
light off) and then off the subject nose with both lights on. The ratio
I typically aim for is 4:1 from key side to shaddow (2 stops). I set
the aperture per the highest of the three readings (usually the nose,
sometimes the keyside if the softbox is really close to the subject).

The background light is set anywhere from 2 stops below to a stop and
half above the aperture depending on what I'm trying to do.

What I don't understand is how the flat disk is going to be "better"
than the dome for ratio readings (as the Minolta meter manual suggests).


the dome can catch light coming from the side that a flat disk won't. you
could probably use the dome and just shield it from the fill or other light
with your hand.

btw, two stops difference is a 5:1 ratio. I know it doesn't make sense but
it does if you understand the principle behind the system. This system of
ratios is built on the fill based lighting concept. Where your fill light
determines the base or threshold exposure of the image, with the key light
added on to that, works much better with black and white films where you can
alter the processing times.

So you meter your fill, it is supposed to be even and shadowless, so each
side of the subject gets the base exposure, that's one unit of light,
whatever it is.

so the score is:
1 : 1

now we add our key light and make it 2 stops brighter, which is 4 times the
amount of light reaching the subject than the fill light.

so now the score is:

1+4 : 1 or 5:1

It really isn't that important except for one thing, if you ever take a PPA
test to become a certified photographer that ratio thing will screw up
enough questions to kill your results.

the dome can catch light coming from the side that a flat disk won't. you
could probably use the dome and just shield it from the fill or other light
with your hand.


When I first got a flash meter it seemed counter intuitive to me to do
incident metering after years of reflective metering with 35mm
equipment. So I used the disc with hole on the meter from the camera
position pointed toward the subject. First metering the main with all
light sources off and then the fill in the same fashion. Yes this works.
Probably more suited to product photography with uncertain reflective
values - as opposed to more familiar flesh tones where incident metering
does just fine. Colour or Black and White would also be consideratins
for metering techniques.Wher's Heinz Richter when you need him?
AFAIK the hole in the disc meteres aprx 10 degrees of the field and
shouldn't need sheilding from other strobe light sources for individual
metering. Cumulative metering shouldn't be an issue with the disc
either. I don't use a fill light anymore or reflective metering, opting
for the large reflector and large softbox options and incident metering.
Alan doesn't have the disc for the meter anyway and Z's ratio
explantation and PPA admission test spoiler does just fine for use with
incident.
Jack