Digital SLR as companion to your light meter?

[Devin Doyle]

Hi All,

I've been shooting 16mm a lot more and have begun to use my Rebel XTi in tandem with my Sekonic L-398 to get a rough visual representation of how light will read on the film. I simply match the ISO and shutter speed to my film stock/bolex, take a reading with the meter, set the appropriate t-stop on the XTi and snap a pic. I've seen other DPs do this for a bit of guidance on how the frame will read.

Well, on my virgin run with this new work-flow all the digital pics kept coming up 2 stops under-exposed. I wasn't using any filtration in front of the XTi (or the Bolex), and all the settings mirrored the Bolex perfectly.

I have faith in my old Sekonic (which has been calibrated), because the previous roll of 16mm I shot with it came out perfectly exposed.

Can anyone think of a reason why the Rebel would consistently come out 2 stops under? One would think that ISO 100 would be ubiquitous across the board - be it in an old light meter or a pro-sumer digital SLR. I've hypothesized that the sub-35mm sized CMOS chip in the camera requires more light to properly expose...but that idea seems flawed.

I suppose the true test will be when I develop the roll and see what the print looks like at both the Sekonic exposure and the internal light meter on the XTi.

Any ideas? I'd really appreciate any input!

[Michael Wisniewski]

1. Are you measuring reflected or incident light with the light meter? The SLR only measures reflected light.

2. The metering mode might be set to sample a different sized visual area than the light meter.

3. The manufacturer's ISO rating can be slightly different from actual ISO.

[Emre Safak]

You may be using matrix metering, rather than spot or center.

[Devin Doyle]

Thanks for the replies!

Michael, I'm using an incident meter which can't be very selective in what it reads. However, I attempt to frame up an area comparable to what the Sekonics light meter reads in order to get a similar reading. I considered that the ISO ratings may differ, but I'm hoping that those standards may be shared between the two tools.

I did some investigating after reading the posts and changed the internal metering in the camera to partial as opposed to evaluative (matrix metering) and I've been met with success. It seems fairly obvious that evaluative metering involves internal computations by the camera to determine what it thinks the best exposure is - not what the archaic Sekonic light meter determines. This partial metering setting seems to read a smaller area of the image (as the incident meter does) and delivers exposures that match.

Thanks to all for their input. I appreciate it!