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Canon XTi and how to set the Exposure Value #

Scott Lenz , Feb 10, 2008; 12:38 p.m.

I just recently purchased a Canon digital Rebel XTi and an EF-S 17-85 IS lens. I am learning about exposure and am using the Fred Parker "ultimate Exposure Computer" as my referense. (http://www.fredparker.com/ultexp1.htm)

I don't know if this is a well known technique , but it is basically a tutorial on how to use manual settings on my camera and eventually learn how to set the exposure intuitively. (If anyone has any other material that might be better, I'm all ears)

My problem is, I can't figure out how to set the Exposure Value Number on my camera. In M mode, shutter speed, Aperture, and film speed are pretty easy to set, but I can't find anything about setting the EV# in the manual. Is this set automatically even in Manual mode?

There is a EV+- number for correcting the EV# but how do I manually set it?

On a side note: I'm leaving for Fiji next week and was wondering what would be a good filter for bright sun and beach/ocean shots. I have a UV filter and a circular polarizer filter. Any suggestions on a fun or useful filter?

Thanks in advance for any advice. Its appreciated.



James Colwell , Feb 10, 2008; 12:47 p.m.

EV is defined by the combination of aperture and shutter speed, for any given ISO. The only camera that I've seen an EV display on is an old Olympus-35 SP. Many light metres do show EV, as well as aperture, shutter speed and ISO.

Speaking of intuitive exposures, have you heard of the "rule of 16"? On a sunny day, set the shutter speed to 1/ISO value and aperture to 16. If you want wider apertures, just increase the shutter speed (by double) for every extra stop opened up.

Scott Lenz , Feb 10, 2008; 01:01 p.m.

Thanks James, so if I understand you correctly, EV is a number that is the RESULT of the other settings, NOT something that can be set. I should not worry about EV and focus (so to speak) on ISO, aperture, and shutter speed. And I love the "rule of 16" great starting point.

James Colwell , Feb 10, 2008; 01:09 p.m.

Yes, and no. EV defines the appropriate exposure for the ambient light. You set ISO, aperture and shutter speed to get the right EV. Have a look at the EV calculator and guidance spreadsheet in the calculators and info section at my web site.

Mark U , Feb 10, 2008; 01:19 p.m.

Read all about the APEX system here:


Peter McKone , Feb 10, 2008; 04:42 p.m.

You probably already know this, but you CAN set exposure compensation. For outdoor work on a sunny day, I set my 350D to minus 2/3 of one stop. It prevents the sky from getting blown out. I lighten dark parts of the image in post-processing.

Keith Lubow , Feb 11, 2008; 08:07 a.m.

Exposure Value is a certain amount of light that is read by a meter. It is totally independent of your camera. It's simply a unit for measurement of an amount of light, just like a liter is a unit of measurement for volume. It's not something you can set on your camera.

ALL your meter does is measure light and figure out what Exposure Value to call it. Then, your suggested exposure by the camera (or on your calculator dial) is the combination of f stop and shutter time that will render that amount of light as middle grey.

It is like first measuring the size of an empty container, and then telling you how long to run the water at a certain flow rate to fill the liter bottle half way. How long to run the water is equivalent to T (shutter speed), and the flow rate is equivalent to A (f stop). You have the choice to fill the bottle half way by running a low flow rate for a long time, or a large flow rate for a short time, or any combination of the two.

The greatest part is that you also have the option to fill the bottle more than or less than half way. This is called overexposure or underexposure, exposure compensation, tonal placement, etc.

The reason to learn what exactly your meter is telling you is not so you can expose as it says every time...it's simply to give you a middle-toned reference value.


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