Thursday, April 18, 2013

Accurate Metering for the right exposure.

Good Thursday from Prospect.

Today I want to extend a bit I touched on two posts ago. I'm referring to using an exterior meter to gain correct exposure.

You can see here what the correct exposure should be here.
All shots, except this one were shot with Canon EOS 5D mk1
with a Sigma 50mm f1.4 (best 50mm ever)
As I hinted, rather openly, incident light meters are the only way to accurately measure the light hitting your subject. Reflective meters, which reside inside todays cameras,  measure the light that has bounced back from your subject and assumes the brightest area is 18% grey. This is just the way these meters are engineered. Don't ask me why.

What then happens it compensates for that and setting that to white and usually over exposes the shot making it look like midday bright. When in fact the shot was taken late afternoon and overcast. The result may look pleasing but it's wrong.

So let me show you the difference between reflective meter readings and incident readings and their results. I have included a shot of my Sekonic L-398 studio meter with the resulting reading.
The camera gave me a reading of 2 stops brighter. I set the aperture and ISO in cement so the only change would be shutter speed. Film rules here.

Now my habit has always been to over expose by 1/2 to 1 stop for reversal film (I said usually, it goes back to film days when you couldn't chimp the shot and had to rely on your experience to get it right).

The shot of the meter shows my reading 20 feet away from the scene but is reading the available light reaching the subject.

Accurately exposed based on the environment
and time of day
You'll notice at ISO 50 we should be set at 1/3 stop open from 5.6 and 1/500th. The reflective meter gave me a setting of 1/125th for shutter.

Quick note here I've deliberately cemented the ISO at 50 to demonstrate the changes on a level playing field. ISO 50 is the slowest sensitivity I have ever shot film. As well my Hasselblad only has a max shutter speed of 1/500th which dictates I use slow film to stay inside the limitations of that shutter for outdoors. (It's great in the studio since, being a leaf shutter it syncs at all speeds).

The point here is, you may think the reflective meter shot seems okay but it's over exposed in relation to the true lighting of the scene. That shot left our grey in the foreground completely blown while the sekonic gave us a better balanced exposure we can use.

If you think this just isn't so then here's a challenge for you. Turn off your preview, stop chimpping, and just set your exposures manually by the built in meter in your camera and check them after you have shot all day. If you aren't upset with the results then let me know. Heck, even if you're unhappy with the days results let me know that too.

May look right but way too bright
for the time of day and lighting conditions.

I look forward to hearing from you.

Note: all the shots are as shot in camera as RAW, opened in photoshop camera raw, tags added and saved for web at 1920 px, long edge.

I hope this helps you make better shots. Enjoy, Derek

Aperture at f5.6,
underexposed but still usable.
It's easier to lighten the shadows then
recover blown high lights.

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