Exposure

[smoothassilk]

Is there a trick or formula for getting exposure equivalents?

[LanceHaynie]

Well, if you want a formula I believe it is: log2(A^2/S) where A is your aperture, and S is your shutter speed.

However, I find that my light meter can do that a lot more quicker than I can. :D

[smoothassilk]

Is there a way to do it without a light meter?

[KJ Smith]

Originally Posted by smoothassilk

Is there a trick or formula for getting exposure equivalents?

On most Canons you can set it in P, Tv, Av roll the dial and watch them go by.

Or just memorize how they go. When you are talking full stops, they are either double or half depending on which way you go.

15--30--60--125--250--500--1000
22--16--11---8----5.6---4-----2

All those are equivalents for that particular exposure.

In terms of light volume.

15, is twice as much as 30. 30 is twice as much as 60. 60 is twice as much as 125. These are fractions of a second.

60 is also half of 125. 30 is half of 60. 15 is half of 30.

And.

16 is twice as much as 22. 8 is twice as much as 16. and so on. This is a number that represents the actual aperture size. Bigger number, smaller hole.

16 is half of 8, 22 half of 16 and so on.

Now for the bonus question. If this was an exposure of the bright North sky, not into the sun, what is the ISO the camera is set on?


ON Edit, OK should be fixed

Edit again for ISO.

And even though you didn't ask, ISO goes the same way

50, 100, 200, 400, 800 ect.

Each being either twice as much or half as much light.

50 needs twice as much as 100, 100 needs twice as much as 200.

or 200 needs half of what 100 needs, 100 needs half of what 50 needs.

[PhotoByLeal]

Put the camera on P and take a test shot and look @ your settings and work with that!
Then you should start leaning your lighting conditions from there.....like your f/stop + shutter speed= Manual Exposure on a GREAT PICTURE!

This is a cheap mans version of a light meter, I hope this helps!

good luck!

[merock]

The Sunny 16 rule!!! In mid sunny day, f/16, 1/250 iso 200. Then go from there.

[Some Idiot]

EQUIVALENT EXPOSURE

[venchka]

Aren't we talking about EV?
Ken Rockwell knows.......
What are EV and LV © 2005 KenRockwell.com
Lenses and shutters on Rollei & Hasselblad cameras have a feature that locks shutter speed and aperture together. Turn the EV dial and you get perfect exposure for any of the related pairs of shutter speed & f/stop. This works well with exposure meters that offer readout in EV values.
Assuming of course that you are trapped in a time warp somewhere in a parallel universe and using a manual camera and manual exposure meter.

[jfoureyes]

Originally Posted by merock

The Sunny 16 rule!!! In mid sunny day, f/16, 1/250 iso 200. Then go from there.

I been using it since 1968...still works with digital too

[venchka]

The Sunny 16 Rule and EV scale are apples and oranges. Kinda.

EV mechanism on a Zeiss lens.

[ronocnikral]

Originally Posted by KJ Smith

In terms of light volume.

15, is twice as much as 30. 30 is twice as much as 60. 60 is twice as much as 125. These are fractions of a second.

60 is also half of 125. 30 is half of 60. 15 is half of 30.

And.

16 is twice as much as 22. 8 is twice as much as 16. and so on. This is a number that represents the actual aperture size. Bigger number, smaller hole.

16 is half of 8, 22 half of 16 and so on.

isn't the aperature on a geometric scale? e.g., if you square the f stop number, the result should be twice the amount or half of the previous f-stop^2.

1^2 = 1
1.4^2 = 2
2^2 = 4
2.8^2 = 8
4^2 = 16
5.6^2 = 32

so on and so forth...

[LanceHaynie]

I am not sure if we are making this more complex or simplifying it! :-/

[venchka]

Y'all sure can make simple things difficult.
Cameras are set up so that each change in aperture or shutter speed is one full f/stop. If you change one you have to change the other in the opposite direction to maintain the same EV value.
Example:
Aperture changes from f/5.6 to f/8.
The shutter must change from 1/125 to 1/60.
The reverse is true.
If I change the shutter speed from 1/250 to 1/1000,
I must change the aperture from f/11 to f/5.6.
That was a 2 stop change. Just to make sure y'all are awake.
If you turn the EV ring on a Hasselblad or Rollei the relationship between aperture and shutter speed remains fixed. Piece of cake.

[ronocnikral]

complex? all math i learned in the 5th grade.

another rule of thumb for aperture, if you double the f stop number, the product is two full stops difference.

simple, a little wheel on the side of my spotmeter is simple. or count the clicks one way, change other parameter same number of clicks the other way...

[Bruce M. Morris]

in answer to the original post... if some of this is repeat knowledge for you, just bear with me...
Exposure is determined by 3 elements: ISO, Shutter Speed and Aperture. For any given ISO(say ISO 200), you have an exposure for your scene (say 1/200 @ F/16). Equivalent exposures would be determined by keeping one of the 3 elements constant; as you change the Second element(say increasing or decreasing shutter speed), the third (Aperture) is changed in in the opposite direction. From our example, if you change S/S to 1/100, Aperture changes to f/22.

Mark, I hope this helps some.