Bradford E. Anechiarico
EV meter vs. exposure
I have an old Polaroid EV meter that is used to register/meter the exposure values for a scene in order to set aperture, speed, etc. I am aware of how this works and how it compares to modern light meters, but my question is if there is any direct correlation to the modern meters that allow you to meter the scen and it tells you the shutter speed, aperture, etc. to use?
This old meter allow you to set film speed and then dial in to match the current EV of the scene and I use it for pinhole photography mainly after finding a shutter speed in my SLR and then comparing it to a higher f/stop for the pinhole based upon a chart.
Just wondering if there is an easier way to do this instead of having to carry around the SLR to compare to the EV meter? Are there direct comparisons for EV readings and the TTL reading in the SLR?
Any help would be appreciated.
John A. Lind
I wrote a tutorial about exposure and a good portion of it explains the EV system. Your "EV" meter is measuring EV in terms of BV (brightness value) and SV (film speed value). What you are looking for is how to translate this into AV (aperture value) and TV (time value; shutter speed). The very basic equation for exposure is:
EV = BV + SV (what your meter measures)
EV = AV + TV (what you set on your camera)
BV + SV = AV + TV
For the reading your light meter gives you, any combination of AV and TV that adds up to the EV reading on your meter will give you the exposure you metered.
To see the translation of lens aperture f-numbers to AV numbers, and the translation of shutter speeds to TV numbers, see my tutorial:
In particular, see the discussion about AV and TV down the page under "Exposure Settings." There are two tables there you can copy. One translates f-stops to AV numbers and the other translates common shutter speed stops to TV numbers. As long as AV + TV = EV from your meter, you have the exposure your meter is giving you.
|Bradford E. Anechiarico||
Thank you, John, for your response.
Your site pretty much explained it all to me and in quite a bit of detail. I knew it would be a little harder than I hoped to simply try and get the two to come to some easy correlation so it seems that it is up to me to do a bit of figuring in order to get the values I am looking for between such readings.
As always, your information is quite complete and very helpful.
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