1 stop difference between ambient and reflective?

[PatrickMP]

<P>G'day group.

<P>I've run into a problem with my lighting setup and metering with a Minolta

Auto Meter IVf.

<P>As a test I set up a single flash head (Broncolor C70) at a gray card.

Taking an ambient reading with my meter I get 1/60th @ f/11. When I take a look

at the downloaded image on the LCD it always looks overexposed. To confirm,

I've tried to take a reflective reading with the spot attachment, and when I

meter off of the gray card I get 1/60th @ f/16! The 1/60th @ f/16 is confirmed

by the 10D's center weighted meter (full zoom to fill the frame) and with my

EOS-3's spot meter (aimed at the same point where I place the light meter when I

take an ambient reading).

<P>For my ambient reading I'm using the regular white dome that comes with the

IVf when you first buy it.

<P>The meter is about 8 years old, and I've never had to get it calibrated. I

just recently started shooting digital with studio flash which is why I was

running some tests. I'm confused because shouldn't a reflective reading from a

gray card yield the same result as an ambient reading?

<P>Attached is a sample. The image on the top is the meter reading (1/60 @

f/11) and the image on the bottom is the reflective reading (1/60 @ f/16).

<P>Thanks for any input.<BR />- Patrick<div></div>

[brian.]

I'm a little confused. Are you using the flash from the the flashead or just the modeling

light? I ask because you say you are using the camera's meter to verify exposure. I don't

think you can meter a flashead from your camera meter. Also I think your "overexposure"

is closer to correct than your f16 exposure is.

Your test might have flaws.

[PatrickMP]

<P style="border: groove">I'm a little confused. Are you using the flash from the the flashead or just the modeling light? I ask because you say you are using the camera's meter to verify exposure. I don't think you can meter a flashead from your camera meter. Also I think your "overexposure" is closer to correct than your f16 exposure is. Your test might have flaws.</P>

<P>If I take a reflective reading off of a gray card, and it reads 1/60 @ f/2.8 using a hot light, an equivalent reading using flash, say 1/60 @ f/16, should yield the same gray, shouldn't it? The meter reading should be independent of light source if you are measuring a gray card. Only the `brightness' of the light has changed, so for one source you need a larger aperture. Or have I completely missed something?

<P>- Patrick

[ronald_moravec1]

No they don`t match. Cards are 18% Meters are calibrated to between 12 and 18.

 

F stops on lenses can be off. My Niknon lenses are 1/3 stop less exposure than if I put Leica lenses on the same D200.

 

Flash output is not always exactly the same and you can`t go by the ready light. Some come on at 50%, some 75, and some 100.

 

Go by incident reading and actual taking lens. Then adjust meter trim inside the battery compartment or iso to get a good exposure reading.

[twmeyer]

I can't understand your description of what you are doing. <p>Tell us which meter/camera is used for which type of light, and if you are able to set the meter for flash and ambient light sources. Also, are you setting the aperture and shutter speed manually? or are those just the automatically indicated settings the camera recommends in an Auto mode? <p>I suspect you may be metering ambient light and then making the exposure with strobe, or using an auto metering mode on your camera with strobe lighting, but it's hard to tell from your description and the wording of your question... t

[Ed_Ingold]

Try nolding the grey card at an angle (30-45 degrees) to the light and take the spot reading from the direction of the light.

 

You may be getting a specular reflection from the grey card which affects the reflected light reading but not the incident reading. Whether the incident meter is calibrated at 18% or 13% reflectance only affects the exposure by about 1/3 of a stop.

[digitmstr]

Rule no.1:

<p>

when using a strobe as the MAIN light, <b>point the meter at the strobe, in incident mode</b>.

<p>

Flash strobe...

<p>

take reading...

<p>

...set camera accordingly.

<p>

Take picture.

[PatrickMP]

<P>Sorry to all if my original description was too confusing.

<P>To clarify:

<P>When I was using the strobes, I was metering with the meter in flash mode, using the CORD setting, and using the appropriate settings. I assure you, I know how to meter with my flashes. I've never had any problems metering, but this sudden one-stop difference has thrown me off. I normally use the incident meter only, but for testing I was trying to use a gray card and the results weren't what I expected.

<P>When I was using the reflective reading off of the gray card, I was using ambient light, <em>not</em> the strobe.

<P>My own confusion on the matter is that most everything I have been told and studied has stated that an incident reading should yield the same as a reflective reading from a gray card when the same amount of light is applied. What I've done is perform X tests:

<OL>

<LI>Taken an incident reading of my strobes using my meter in Flash mode.</LI>

<LI>Taken an incident reading of the ambient light using my meter in AMBI mode.</LI>

<LI>Taken a reflective reading off of a gray card with ambient light with the meter in AMBI, where the gray card was placed <em>at the same place my incident readings were taken</EM></LI>

<LI>Taken a reflective reading off of a gray card with strobe light, with the meter in NO-CORD mode, where the gray card was placed <em>at the same place my incident readings were taken</EM></LI>

</OL>

<P>Performing the above tests, #1 and #4 were one stop off, and #2 and #3 were one stop off.

<P>Now, if I take an incident reading a point A with my meter flat against a gray card so that the dome is exposed to the light source, then I should get an <em>identical</em> reading if I take a reflective reading pointing my spot meter at point A on the gray card.

<P>Now, according to Ronald M. above, they aren't necessarily the same, since gray cards are between 12 and 18%, which would coincide with my own results being off. Edward's description seems to be the most plausible. Finally, in reference to lens f/stops being off. Ronald, I tried the test with several lenses from three different camera bodies (two EOS based bodies and an older Pentax body). All bodies gave identical readings with the reflective reading from my meter using ambient light and the meter in AMBI mode.