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Archive 2013 · Exposure Value question

Jamison Hurst
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p.1 #1 · p.1 #1 · Exposure Value question

I am trying to learn to know what the EV of a given scene is the old-fashioned way.

I am using this site as a way to learn-

https://www.fredparker.com/ultexp1.htm#top

I am also using a Minolta III F meter as a crutch backup to test my guesses while I learn.

Now, I just took a reading from indoors near a window, and my meter indicates ISO400, f4 at 1/60th. The meter also provides EV's, and it indicates for this reading EV 10.

If I look at the above link, and scroll down to the Exposure Factor Relationship chart, for ISO400 f4 at 1/60th, it indicates an EV of 8.

Is there a standard for EV's? Which is correct, and why the discrepancy?

Edited on Sep 04, 2013 at 09:41 PM · View previous versions

Sep 04, 2013 at 12:03 PM

jcolwell
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p.1 #2 · p.1 #2 · Exposure Value question

Yes, there is a standard definition. One Exposure-Value (EV) is the amount of light to provide correct exposure for an exposure time of t = 1 sec., with a lens at f/1.0, and at ISO 100.

The relationship between shutter speed, aperture and ISO is shown below,

EV = (log(Tv)/log(2)) + (log(Av)/log(sqrt(2)) - log(ISO/100)/log(2)

where, Tv is Time value (for t = 1/60 sec, Tv = 60), Av is aperture value (for aperture f/4, Av = 4), and ISO is ISO.

When shooting large and medium format film cameras, I often used the following "guidance tables", which show my interpretation of information in the "Exposure Value Chart", at the same site that you linked.

I've also attached EV tables for ISO 100 and 3200.

P.S. I agree with Fred Parker: t = 1/60 sec, f/4, ISO 400, corresponds to 8 EV. Maybe your meter is set for ISO 100.

Sep 04, 2013 at 12:35 PM

Jamison Hurst
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p.1 #3 · p.1 #3 · Exposure Value question

Thank you for the reply.

Yes, I thought it was the meter, but it is set correctly to asa 400. It gives very consistent readings exactly 2 EV's greater than what the tables say. hmmm.

I don't imagine the tables have changed in the 30 years since the meter came out.

Sep 04, 2013 at 02:14 PM

jcolwell
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p.1 #4 · p.1 #4 · Exposure Value question

Jamison Hurst wrote:
...I don't imagine the tables have changed in the 30 years since the meter came out.

Sep 04, 2013 at 02:26 PM

Toothwalker
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p.1 #5 · p.1 #5 · Exposure Value question

jcolwell wrote:

The meter has not changed either, since 1983.

Sep 04, 2013 at 02:44 PM

Bifurcator
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p.1 #6 · p.1 #6 · Exposure Value question

G-Zus, do you really need all that? My brain is throbbing after clicking on your link. Can't you just stuff an exposure triangle into your head and do with that?

Maybe something like one of these:

http://4.bp.blogspot.com/-tK5ww8YoCO8/ULo93q2AEFI/AAAAAAAABhw/AK6JhHnOosw/s1600/Esthetic_Exposure_Triangle2.jpg

http://mamaneedsahobby.files.wordpress.com/2012/09/slide1.jpg

http://www.exposureguide.com/images/exposure/exposure-triangle.jpg

http://g-ecx.images-amazon.com/images/G/01/BOOKS-TXTB-PEAED-AA-/-APlus/ExposureTriangle._V391966108_.jpg

Sep 04, 2013 at 04:24 PM

philip_pj
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p.1 #7 · p.1 #7 · Exposure Value question

Colour me impressed - Venn diagrams and a photographic food pyramid or maybe a Maslow pyramid of imaging needs!

You might like to read on LVs also, more the reality of actual light levels than EV:

http://www.kenrockwell.com/tech/ev.htm

Sep 04, 2013 at 06:49 PM

Jamison Hurst
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p.1 #8 · p.1 #8 · Exposure Value question

Your reply is excellent, great info in those triangles. That info I have in my head from experience, but a picture is worth a thousand words.

Sep 04, 2013 at 07:43 PM

Jamison Hurst
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p.1 #9 · p.1 #9 · Exposure Value question

It's a curious thing, but I have discovered the reason behind my confusion.

The meter delivers different EV's for equivalent exposures.

At ASA 100 here in my office with average light the reading is f/1.4 at 1/15th giving an EV of 5 which corresponds to the chart(s) I linked.

Changing the ASA on the meter to 400, the reading is f/1.4 at 1/60th (equivalent to the above exposure), but the EV reads 7.

So different EV's are given based on the ASA setting in the meter, which is the part I need to reread in the manual!

In any case, thanks to all who replied. I can now merrily master the Ev charts as they correspond to a given light condition and set my meter-less camera appropriately for (hopefully) a confident exposure!

Sep 04, 2013 at 07:58 PM

Jamison Hurst
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p.1 #10 · p.1 #10 · Exposure Value question

Thank you for the link. Very helpful.

Sep 04, 2013 at 09:45 PM

LightShow
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p.1 #11 · p.1 #11 · Exposure Value question

As a tangent there is also Ansel Adams Zone System for evaluating exposure.
http://en.wikipedia.org/wiki/Zone_System
http://www.luminous-landscape.com/tutorials/zone_system.shtml

Sep 04, 2013 at 09:56 PM


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