# What is EI?

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• 12-06-2005, 07:41 AM
Trond
Quote:

Originally Posted by Mick Fagan
Thus, a lens set to f/1.4 allows twice as much light to strike the focal plane as a lens set to f/2.

Should be correct now. First time I´ve edited a Wikipedia article. It´s amazing that it can work...

Trond
• 12-06-2005, 08:09 AM
markbb
Quote:

Originally Posted by ErinHilburn
We were taught a b&w course, but 6 weeks is just not enough time to learn all there is to know. I don't recall my first professor mentioning this at all, however I do now remember my second professor performing this test for us,

Wow!! you get not one but two professors teaching a 6 week B&W course! That would be like Stephen Hawking running a class on wiring a plug. What college are you at?
• 12-06-2005, 09:54 AM
Ed Sukach
Another way to understand the concept of "f/stop" is to calculate the AREA of the aperture. An aperture of f/1.4 ("f" is the standard symbol for focal length; divide that by the aperture diameter) has an area twice that of an aperture of f/2 -thus allowing twice the amount of light to pass.

Let's see .. mathematics:

Area of a circle = pi (radius squared)
Given a focal length of 50mm:

(3.1416 ((50mm /1.4)/2)) squared = 3147.2 sq. mm
(3.1416 ((50mm / 2.0)/2)) squared = 1542.1 sq. mm

3147.2 / 1542.1 = 2.04086 : f/1.4 lets 2.04086 times as much light through as f/2.

Same way as calculating water flowing through a pipe of "x" diameter.
• 12-06-2005, 04:28 PM
ErinHilburn
No, not just two professors in six weeks its sixteen(sorry about the six rather large mistake ;)) weeks. The beginning photography is b&w and all photography contracts are required to take it. We only have one professor here as it is a small school in Alabama. But I also believe its one of the only schools here that offer a BFA in Photography other than montevallo. After that we take studio two which is a colorslide course, but we don't do any of our own processing or print making for that, so I am currently trying to learn how to do that on my own. After studio two I realized that it would improve my color work if I improved my b&w. The single professor we have feels that having only one professor leads to poor teaching, so he gets all these other photographers to teach classes under his name, so they aren't actually employed by the university. It was one of those photographers that I took a finite black and white course under which focused more on printmaking that the actual exposure of the film. I atted troy University. I think they just put up a design/art website if you care to see it. The photography examples are rather poor since they just threw what they had on there.

http://troy.troy.edu/artdesign/index.html

It's really not a bad school and one of the few here in alabama that still require you to start in the dark room. I know the professor in Auburn got rid of all the darkroom equipment and they all do digital now. I recently was in their gallery and so many of the photographs were just a poor picture with bad composition that had been highly photo manipulated, so that it would appear faintly interesting.

Sorry about the mistake with 6 instead of 16 next time I'll be sure to read over what I type (; I just don't feel that's enough time. I'm in my third year at the university and still I hesitate to call myself a photographer I am never satisfied with my work and the more I see it the less I like it. I feel that I know little to nothing about my chosen field andI want to know everything. Sometimes I get irritated with the classes and the fact that they must reiterate the same things in regards to fstop, shutterspeed, ISO, and proper exposure just because so many students are so lazy and dont' want to learn and instead shoot on automatic. I've purchased several books (some of which were suggested from apug), but without the equipment to try different techiniques I dont' really know them, I just know of them.

But now that I've gone on a really long tangent and talked forever. It's two professor in two different sixteen week sessions.

-Erin
• 12-06-2005, 05:14 PM
Mick Fagan
Erin, you must be doing something right if you won an award!

Mick.
• 12-06-2005, 05:40 PM
ErinHilburn
;) blind luck, I have a knack for night photography when it rains.
• 12-06-2005, 05:49 PM
Helen B
“So to summarise, what effect can I expect on skies if I lower box speed?”

Pentaxuser,
This is something that is best answered by testing in the typical conditions you are referring to, using your normal printing method. Colour print materials are usually designed to respond to a fixed density range on the negative (and that density range is only a portion of the potential negative density range), so doing a straight print to capture shadow details is likely to burn out the highlights (in the print) and vice-versa. It’s worth finding out, by personal experiment, how your particular materials and technique respond to changes in exposure: how it affects the different representations of shadows, mid-tones and highlights.

If the print material were capable of responding to the entire density range that negative film is capable of having, the result with most scenes would look very flat. Tonal compression equivalent to thirteen stops of scene brightness condensed into seven stops of image brightness on the paper. So, without resorting to unmentionable techniques, dodging and burning, or masking are necessary. Unless you fix it at the taking stage with a grad.

“Wow!! you get not one but two professors teaching a 6 week B&W course!”

Sounds very impressive. ‘Professor’ means very different things in US and UK English: in the UK a professor is typically a department head at a university and thus rarely to be caught teaching, or doing anything else that even faintly resembles real work. In the US a professor can be the equivalent of a teacher in the UK.

“f/1.4 lets 2.04086 times as much light through as f/2.”

Ed,
Small nitpicking point, but the f-numbers that aren’t equal to two raised to an integer power (ie 0.5, 1, 2, 4, 8, 16 etc) are quoted to two significant figures, and the last one may not be correct (eg 5.6 should be 5.7 and 22 should be 23 but it doesn't really matter) so calculations to more than two sig figs are a bit meaningless. Example: ‘1.4’ is the shortened form of the square root of 2, so it is 1.41421 if you want six figure accuracy. Not that aperture settings are ever likely to be anywhere near that accuracy, of course.

Best,
Helen
(and thanks to Mick for the kind comment)
• 12-06-2005, 06:52 PM
pentaxuser
Quote:

Originally Posted by Helen B
“So to summarise, what effect can I expect on skies if I lower box speed?”

Pentaxuser,
This is something that is best answered by testing in the typical conditions you are referring to, using your normal printing method. Colour print materials are usually designed to respond to a fixed density range on the negative (and that density range is only a portion of the potential negative density range), so doing a straight print to capture shadow details is likely to burn out the highlights (in the print) and vice-versa. It’s worth finding out, by personal experiment, how your particular materials and technique respond to changes in exposure: how it affects the different representations of shadows, mid-tones and highlights.

If the print material were capable of responding to the entire density range that negative film is capable of having, the result with most scenes would look very flat. Tonal compression equivalent to thirteen stops of scene brightness condensed into seven stops of image brightness on the paper. So, without resorting to unmentionable techniques, dodging and burning, or masking are necessary. Unless you fix it at the taking stage with a grad.

“Wow!! you get not one but two professors teaching a 6 week B&W course!”

Sounds very impressive. ‘Professor’ means very different things in US and UK English: in the UK a professor is typically a department head at a university and thus rarely to be caught teaching, or doing anything else that even faintly resembles real work. In the US a professor can be the equivalent of a teacher in the UK.

“f/1.4 lets 2.04086 times as much light through as f/2.”

Ed,
Small nitpicking point, but the f-numbers that aren’t equal to two raised to an integer power (ie 0.5, 1, 2, 4, 8, 16 etc) are quoted to two significant figures, and the last one may not be correct (eg 5.6 should be 5.7 and 22 should be 23 but it doesn't really matter) so calculations to more than two sig figs are a bit meaningless. Example: ‘1.4’ is the shortened form of the square root of 2, so it is 1.41421 if you want six figure accuracy. Not that aperture settings are ever likely to be anywhere near that accuracy, of course.

Best,
Helen
(and thanks to Mick for the kind comment)

Thanks Helen. Sounds as if a ND grad is favourite. However I must try the same scene at different speeds to check the effect first. Nothing ventured nothing gained as they say.

Pentaxuser
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