a57 v d5100 for first DSLR

Started Apr 6, 2013 | Questions thread
Wally626
Senior MemberPosts: 1,707
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Re: a57 v d5100 for first DSLR
In reply to Fat Dragon, Apr 9, 2013

Fat Dragon wrote:

Wally626 wrote:

Checked my A77 versus a light meter in a very unscientific test.

Camera multi spot mode says 1/50 at f/2.8 ISO 1600

Camera spot meter mode on small 18 percent grey card centered in the scene says 1/15 at f/2.8 ISO 1600

Incident light meter says between 1/30 and 1/60 at f/2.8 ISO 1600

In the image the one using the camera spot meter was too bright the multi spot and incident meter shots were exposed corectly. Base on rough approximation the meter was probably about 1/40 versus the 1/50 the camera gave so pretty close.

The Sony camera is probably calibrated for a 12 percent gray card which would be why the scene was a bit over exposed using an 18 percent gray card.

To help a layman out, would this test indicate differences in actual ISO levels between various cameras, or simply a different approach to metering in the SLT as compared to an SLR or incident light meter?

To measure the difference in the cameras ISO setting you would need a calibrated test lab. Essentially take a picture of an object with known brightness under well controlled conditions. Using an incident light meter you can measure exactly how much light is illuminating the object of interest. Set the camera to the shutter speed aperture and ISO combination that should provide a well exposed image. If the image is well exposed then the camera ISO is set correctly. I have an incident light meter but it is not a calibrated model and cannot be used to get absolute numbers.

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