Do you read in cm or cf? If you read in cm, you reading give over exposure? The formula is for candles per square FOOT. He based this formula upon the use of the Weston Master light meters and others such as that which provided c/ft2 on the dial of the meter.
Yes modern light meters use foot candles. I use a Sekonic 758C and it uses foot candles.
I hope someone who actually understand the formula can offer some advice instead of people trying to say it's not useful; you're just making it for harder for other people to find out the answer. Just because you don't find it useful doesn't mean it's NOT useful.
@Chris: Yes. CF on the Sekonic 758C.
I used this converter:
EV 14 = 213.676992 foot-candle = 2300 meter candle.
EV 14 = 1/125 @ f/11 at ISO 100 as we all know.
Formula: with square root of ISO, you use f/10.
The formula you post suggests 1/214.
That's not that off the mark. 1/214 @ f/10 instead of 1/125 @ f/11. The formula gives you an exposure which is a bit closer than what we would expect as normal. I reckon about 1/3 of a stop closer.
I suppose your problem is in your light meter which does not really give you candles per square meter, but something else. (Or maybe you should check if it is set at ISO 100).
Parenthesis without polemic.
I still don't get the practical reason for this exercise. In photographic units each EV corresponds to "twice" the luminance. In meter-candle or foot-candle "twice" the luminance is expressed in "twice" the number. If you want to know the contrast of illumination of the scene, in foot-candles you just divide the two numbers and then derive the stops of difference.
For instance, if two light sources are measured as EV 14 and EV 11, you know there is a three stop difference.
If the same sources are measured as 1600 fc and 200 fc, you divide 1600 by 200, obtain 8, know that 2^3 = 8 so there is a 3 stops difference.
EDIT the equivalence above between meter-candles and EV is taken from my light meter's instruction booklet, so that might be a bit approximated and the formula in foot-candle might be a bit closer to the "normal" exposure value.
EDIT maybe you are using your lightmeter with the dome in front of the cell? If I understand it right, this kind of measurements are reflected light measures.
Thanks for the example. I will continue to do more tests under different conditions.
Originally Posted by davidave
I'm sure it's useful in some strange way but at the end of the day, you're just making it harder on yourself to go out, take that picture by simpler means and turn it into a masterpiece in the darkroom. Of course this is just my humble opinion and not meant to offend or lecture anyone.
Again, I certainly don't have the answer for you but my question remains: aside from personal preference, endless thirst for knowledge, and the need for various forms of sadomasochism and torture, why would anyone want to complicate matters to achieve the same results, which depending on someone's overall skills can be utter crap or genius?
This is more of a general question but I do often wonder... :)
I think answer is to try to walk in shoes of great master. If you want to learn painting , you might able to copy a masters painting. Of course you can buy a print but as Shaw says unreasonable people makes the progress.
There is of course validity to that but I don't believe it lies in emulating/replicating the strictly technical aspects of photography, but in studying the creative side of an artist's point of view, while nurturing and progressing one's own. I constantly see too many people getting wrapped in technicalities and getting lost in endless tests and quests for magic bullets. But I digress here :). Sorry..
Originally Posted by Mustafa Umut Sarac
I believe the S.E.I. has a scale that reads in foot-candles, thus accounting for the incorporation of that unit of measurement into Ansel's heuristic.
I understand that in general, but in this case the great master might have substituted the figures on the dial of his light meter to read in EV instead of foot-candle. It really is only the painting of the dial that changes.
Originally Posted by Mustafa Umut Sarac
If the dial is painted in EV, you make a subtraction.
If the dial is painted in foot-candles, you make a division and then extract the base-2 logarithm.
The result is the same, but one of the two cases is more immediate :)
Adams should have bought a light meter with the proper dial :) or have it rewritten with the "proper" scale.
EDIT: I read now on Wikipedia the EV concept (I would say convention) was developed in the '50 in Germany. That would mean that before that epoch light meters did not indicate EVs. I find EV the best invention since the iron thread to cut eggs. I memorize and read on the instruments EV15, EV12 that's much easier to remember. EV 12.3 is easier to memorize than 1/125@f/5.6 + 0.3 stop.