3 meters read differently from my dslr... Why???

[Heespharm]

So here's the setup.... Gossen Luna pro, soligor digital 1* spot and sekonic 400 series 1* spot... Canon t2i dlsr VS 18% grey card under even light


I use the reflective mode on the gossen and the two spot meters on the middle of the grey card... All reads EV 9 then I take a picture of the grey card under evaluative and spot metering with the dslr and the equivalent shutter speed and aperture readings equals EV8 (histogram shows peak in the middle of the middle zone)

What gives???? I think I did the tests pretty scientifically and either all my meters are wrong or the dslr reading are based on a different light scale?

[engl]

The look of the histogram in the camera is going to depend on the JPEG settings used, as well as the tone curve inherent to the camera. ISO is also not very well specified for digital cameras, or rather, there are several conflicting specifications. One is related to the light needed to saturate the sensor, while one is based on the resulting output levels after processing (for some setting).

In short, if you want to use a digital camera as your meter (which I do), you are going to have to experiment and find how it relates to the rest of your workflow (film, developing etc.).

[Mark Woods]

Great response Stefan.

[Ivan J. Eberle]

Was the angle of reflectance of the light the same off the card for each? Spot metering v. incidence has that variable.

Too, what color temperature was the ambient lighting? There was a long recent thread here about how many modern meters are tuned for a particular color temperature with results varying widely outside that window. Not having a Canon Rebel I can't speak to that, but my Nikon DSLRs and F5 have RGB sensor array meters which don't suffer this, they're color-temperature agnostic. These and my Pentax 645N spot meter are extremely accurate, and agree closely with one another (and my old General Electric DKW-58 selenium meter usually agrees with them. The DKW-58 is probably all I'd ever need for shooting color negative films from dawn to dusk outdoors, incidentally).

Ignore histograms for film metering purposes--except as quick and dirty indicators of subject brightness ratios. (You won't know or see what's being clipped by the .jpg algorithm, and if exposure is on the edge of blowing out a transparency film highlight, you can too easily miss it looking at a histogram.)

Or shoot color negative film and don't sweat occasionally being a stop over or under. (It's what the newsies gravitated to before abandoning scanning film for DSLRs en masse.)

[Leigh]

Metering systems in dSLRs are NOT "light meters". They're analytic systems that use complex algorithms in an attempt to determine what kind of scene you're shooting, and what exposure is most likely to result in an acceptable image.

The algorithms are designed around the characteristics of the camera sensor, not the characteristics of film.

Since a gray card is not in the scene library, they're not likely to interpret it correctly.

You have three real meters that agree. Believe them.

- Leigh

[engl]

Metering systems in dSLRs are NOT "light meters". They're analytic systems that use complex algorithms in an attempt to determine what kind of scene you're shooting, and what exposure is most likely to result in an acceptable image.

The algorithms are designed around the characteristics of the camera sensor, not the characteristics of film.

Since a gray card is not in the scene library, they're not likely to interpret it correctly.

The analytic system part only applies to matrix metering, most DSLRs also have "dumb" center weighted and spot metering. However, as you say, the metering systems are in all modes tweaked for the characteristics of the sensor and the processing used by the camera.

[Heespharm]

Angle of reflectance was same height aimed from me standing withe meter at eye level aimed at direct center of grey card....

I don't shoot much slide film but I do have 115 sheets of rvp50 4x5 so good to know...

I'll just trust my light meters... And the zone system...

I guess the camera settings in dslr are just for the dslr and doesn't actually measure luminance in an objective way... More just in relation to the sensor??? Am I thinking correctly??

[Jack Dahlgren]

Angle of reflectance was same height aimed from me standing withe meter at eye level aimed at direct center of grey card....

I don't shoot much slide film but I do have 115 sheets of rvp50 4x5 so good to know...

I'll just trust my light meters... And the zone system...

I guess the camera settings in dslr are just for the dslr and doesn't actually measure luminance in an objective way... More just in relation to the sensor??? Am I thinking correctly??

The dlsr is reading light at the sensor plane - so there is some loss through the lens and perhaps a bit of bellows compensation required unless you are focusing at infinity. Both of those together are probably not a full stop, but they are definitely non-zero.

[Tony Evans]

My Spot Meter reading of the Grey Card on the Pentax K20D varies with which lens I have on (view adjusted to cover Grey Card). Same for a big uniform lit wall. For analogue shooting, I always go with my Soligor Digital 1 degree Spot, which I get calibrated every 1 -2 years. I`m surprised by the EV 8. Most DSLRs under-expose by about one- to two-third stops, presumably to prevent overblown highlights.

[Ivan J. Eberle]

Using consumer-grade DSLR model to use as a spot meter begs the question of whether you were trying to use it in a manual metering mode with a kit lens-- perhaps one not having a constant aperture? Some of these drop lose two full stops from one end of the zoom range to the other.