Spot on Bob. You need a page for posts like this for easy reference, i cant even find the last good explanation you gave to pass on to another member .
April 10, 2023
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Another common way, set the shutter and aperture, and it will tell DIN/ASA/ISO. Helps selecting film and / or development.
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You set the ISO on the exposure meter to tell it the exposure you're trying to set? But i don't know what exposure to set. That is why I am using an exposure meter to find out. Nor do I know how ISO relates to exposure. How do I decide what ISO to set?
And [the exposure meter] tells you the EV (combination of shutter and f-number) that you need to set to get the exposure that ISO says you should set? ISO says what? Where does ISO say what exposure I should set? Does it speak to us in some way?
I am sorry, professor, but that is just gibberish. Not only could no-one use an exposure meter in the manner you describe but they would not know where to start. Set the ISO to tell the exposure meter the exposure you're trying to set? You are having a laugh! Have you actually used an exposure meter? -
I told you that what you said here was all cow manure 😄
In any case,
ISO is the relationship between image lightness and exposure* with the aim to output an average 18% grey image. It basically sets the pixel value in the jpeg data for the number of photons that were recorded at the corresponding pixel/photosite on the sensor for the ISO setting
Personally, I don't need to consider ISO when setting the exposure*. I set the widest aperture to suit my DOF and the slowest shutter speed to meet blur constraints. I let the camera set ISO where it likes as long as important highlights are not clipped. If at base ISO important highlights are clipped then I compromise on dof or blur. It really is that simple for me 😊
For me ISO has no say at all in the exposure* I set.
Setting the ISO before setting the exposure* tells the digital camera to bias its meter to target the exposure* appropriate for that ISO setting. The higher you set ISO the smaller will be the exposure* the digital camera sets.
* exposure - amount of light that struck the sensor per unit area while the shutter was open
** optimal exposure - the maximum exposure* within dof and motion blur requirements without clipping important highlights.
*** under exposed - more exposure* could have been added with the DOF and blur constraints still being met without clipping important highlights. -
Exactly. Very well put.
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A light meter measures light. An exposure meter measures light, but also suggests f-stops and apertures. How much light you want on the film/sensor is a function of the ISO setting. The dial on the meter, once the ISO is set and the light is measured, will show you the pairs of f-stops and apertures which will achieve the desired exposure. So, yes, the ISO setting on an exposure meter tells the meter what exposure (in lux-seconds) you want.
As to deciding what ISO to set, you can use the ISO on a digital camera, or the ISO rating on a film camera, or any Exposure Index that you have decided works for the film and development chosen, or the ISO setting chosen for a particular digital camera.
Although phrased unconventionally -- for effect, I presume -- what Bob said is correct.
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ISO=10/Hm where Hm = average exposure in lux-seconds. Now you know.
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Although phrased unconventionally = Totally divorced from reality.
Are you seriously proposing telling beginners that "the ISO setting on an exposure meter tells the meter what exposure (in lux-seconds) you want."?
Madness. -
Are you being deliberately obtuse? Yes, of course you are.
bobn2 said: "So you set the ISO on the exposure meter to tell it the exposure you're trying to set.".
What exposure am I trying to set and why?
