Exposure

[KJ Smith]

I think I covered the simple way with my first line.

Leave it in one of the programed modes and the camera will handle it.


As far as the math, I don't know if that was the reasoning behind it or not.

I do know that the diameter of the apeture divided into the lenght of the lens will give you the f-stop.

IE: a 50mm diameter apeture on a 100mm lens is a f 2.
a 25 mm diameter on a 100mm is a f 4

A 50mm diameter on a 200 is a f 4

and so on.

[ronocnikral]

Originally Posted by KJ Smith

I do know that the diameter of the apeture divided into the lenght of the lens will give you the f-stop.

IE: a 50mm diameter apeture on a 100mm lens is a f 2.
a 25 mm diameter on a 100mm is a f 4

A 50mm diameter on a 200 is a f 4

and so on.

this is true. and the reason why you need to square the f-stop number. the exposure is based on the area of the aperture opening, not the diameter. the old PI*r^2. or pi/4*d^2. or pi/4*(focal_length/f-stop)^2. or you can just do f-stop^2 since everything else is a constant...

[Jake]

photography is hard.

[KJ Smith]

Originally Posted by thejakestir

photography is hard.

Nope, talking about photography is hard.


All you need is an eye, finger and a heart............. and maybe a camera.

[KJ Smith]

Originally Posted by ronocnikral

this is true. and the reason why you need to square the f-stop number. the exposure is based on the area of the aperture opening, not the diameter. the old PI*r^2. or pi/4*d^2. or pi/4*(focal_length/f-stop)^2. or you can just do f-stop^2 since everything else is a constant...

I guess that makes sense..

[venchka]

Originally Posted by thejakestir

photography is hard.

If that were true, old Pharts couldn't do it.

[venchka]

Following the link above........

EVs are a great idea: by talking about an EV you are talking about any one of many different combinations of aperture and shutter speed that give the SAME exposure. Cameras started to use these numbers in the 1950s, but today only the Hasselblad retains them. With every other camera one needs to use the scales on light meters to determine the EV values. Some cameras can be adapted, as I did to my Plaubel Makina 67, which simplifies their use with spot meters.

Zero EV is defined as f/1.0 at one second. Therefore, EV0 is a pretty long exposure. This is the same exposure as f/1.4 at 2 seconds, f/2.0 at 4 seconds, f/2.8 at 8 seconds and so on. EV1 is one stop less: f/1.4 at 1 second. EV 2 is two stops less: f/2.0 at 1 second or equivalent EV is a camera setting. It was popular in the 1950s to couple camera controls together so that once one set an EV one could rotate locked f/stop and shutter speed rings to choose between different equivalent settings. Today only Hasselblad continues the tradition. It is much easier to remember typical light conditions as a single EV number than combinations of camera shutter and aperture settings.

So what's the correct exposure for Velvia (ASA/ISO 50) in side-lit daylight? That light is LV14. Since Velvia is one stop slower than 100 we need to give it one more stop exposure, or SUBTRACT one EV from the LV to get the EV. Therefore, LV14 - 1EV= EV13. EV13 is 1/125 at f/8 or 1/15 at f/22. Light meters that read in EV have scales on the side that show you all the equivalent camera settings for any EV.

What tricks does this tell us? Well, in nature nothing gets brighter than something lit by full sun, which is LV15. If you see LV17 in your meter you know that that must be a white object in daylight. Guess what: that's how evaluative and matrix meters know that, too!

Ken Rockwell

[tml]

Are we on a math forum? Tri

[venchka]

Math is absolutely NOT required for photography.

[ronocnikral]

my wife can attest to that.

[venchka]

Arithmatic once in awhile. Like when you are at the Co-op and trying to figure out how much stuff you can buy.

[ronocnikral]

my wife doesn't seem to do that math either...

[venchka]

Grinning.