Incident metering exposure different with flash than ambient

I've been calibrating my camera bodies and lenses with my Gossen Digisky meter. I'm getting a about a 2/3 difference in exposure reading between metering ambient and metering flash.

my set up is in my small studio using a large SB for flash and overhead tungsten for ambient.
I'm using my X-Rite color checker for an exposure target.
I bring the RAW files into LR and us a zero preset, then fix WB.

weird.
I must be missing something.

'Tis weird. Are you getting different wrap from the two sources on the hemisphere? Also, is one source achieving a little extra environmental bounce registering on the hemisphere?

which is higher?

The flash exposure registers higher. I've got to add compensation to the ambient reading.

windpig wrote in post #17862643
The flash exposure registers higher. I've got to add compensation to the ambient reading.

Just to be clear, are you saying that your flash shots are consistently exposed correctly using the meter readings, and your ambient-only shots are coming out 2/3-stop underexposed if you use the meter-recommended f-stop? In other words, is the issue only with ambient light metering?

absplastic wrote in post #17862945
Just to be clear, are you saying that your flash shots are consistently exposed correctly using the meter readings, and your ambient-only shots are coming out 2/3-stop underexposed if you use the meter-recommended f-stop? In other words, is the issue only with ambient light metering?

Yup

You are making assumptions about what Canon programming should produce - and they do not agree with you! NEVEC and AFR demonstrate how Canon have made exposuree calculations work. Even Wilt has been caught with tests that by chance were right in the crossover point of the two effects, so was misled. Search this forum for more details.

The effects are as intended and may or may not suit a specific requirement; we must work around them.

I have posted this previously. It summarises the concepts and interactions. A light meter does NOT perform these calculations.

(Sorry for disappearance of table formatting... it makes it hard to see the combined effect. The figures for ISO 100, 400, 1600 are EV. )

CliveyBoy wrote in post #17863392
You are making assumptions about what Canon programming should produce - and they do not agree with you! NEVEC and AFR demonstrate how Canon have made exposuree calculations work. Even Wilt has been caught with tests that by chance were right in the crossover point of the two effects, so was misled. Search this forum for more details.

The effects are as intended and may or may not suit a specific requirement; we must work around them.

Nevic wouldnt apply to manual flash measured with a meter.

only thing that comes to mind is that with the tungsten overhead, and the flash, i'm assuming, coming more from in front of the x-rite, maybe the angle of incidence thing is coming into play.

i.e. light falling on the subject from overhead is mostly being reflected to the ground while the globe on the light meter, and maybe even the angle you have held the light meter at relative to that light is different than that of the flash to meter.

damn, i can't even tell if that makes sense. LOL gotta go run and errand or 5 will add more words later if it doesn't make sense.

gonzogolf wrote in post #17863440
Nevec wouldn't apply to manual flash measured with a meter.

But it does, I understand, depending on the EV contributions of ambient alone and flash alone.

CliveyBoy wrote in post #17863465
But it does, I understand, depending on the EV contributions of ambient alone and flash alone.

How can nevec apply if the camera is unaware of the flash?

If flash is in camera hot-shoe, the camera knows, especially if the flash is powered on, including not set to fire. It also know, if an intelligent radio trigger is in the camera's hotshoe.

However, I have not tried the tests you seems to be setting up, because the manufacturer has said that there is more to it than that. Your results are as I would expect, given the info we have.

I'm using a non hot shoe flash. By "exposure compensation" I mean I have to manually adjust exposure to compensate. I'm shooting fully manual.
In other words if I'm my meter says f11 at 1/160, ISO 200 when incident metering flash using my 5DIII and 135L, I have to shoot at F9, 1/160, ISO 200 for proper exposure. When I shoot with the same set up but metering using the over head tungsten light source my incident metering is spot on.

Left Handed Brisket may be on to something with the angle of incidence. I think I'll set up the tungsten source lower and see how it meters. 2/3 stop is fairly significant.

This is with the hemisphere aimed at the camera.

Thanks for the input from all of you. I appreciate you taking the time.

Ah! It was I who made too many assumptions