It time someone talked about WHY exposure is so confusing.

It's because of the way manufacture's label camera settings. They don't apply base 2 logarithms
consistently.

There are two reasonable rules:
1. Each detent on a control (aperture, shutter, ISO, exposure compenstation) must be EXACTLY
twice (or half) the exposure of the previous detent; and
2 Each should be labeled in integers: ... -3, -2, -1, 0, 1, 2, 3....

If you do this consistantly, you get the Additive Photographic Exposure System (APEX)
which was standardized way back in 1960 (ASA standard ASA PH2.5-1960) and was used
in industry and by the military (where confusion is not OK).

EC knobs (and menus) generally follow both rules: No compensation is labeled "0". Increasing
exposure by one stop is labled "1". Decreasing exposure by one stop is labeled "-1". Anyone
confused by this? Pretty simple, right?

F-numbers follow Rule 1, but not Rule 2. The sequence 1, 1.4, 2, 2.8, 4, 5.6, etc. is a lot more
complicated than 1,2,3,4,5... And you don't need to know the actual f-stop ratio unless you are
building a camera.

Shutter speeds are a mess. They follow neither rule. This sequence makes sense:
1, 2, 4, 8, 16, 32, 64, 128, 256, 512, .... This one doesn't: 1, 2, 4, 8, 15, 30, 60, 125, 250, 500, .....
What's the rule for latter sequence, pray tell?

ISO speeds are given in two different sysems: ASA and DIN. Both follow Rule 1, but only DIN
follows Rule 2. The ISO "standard" is to use BOTH! (Sure sign of a gutless committee trying to
please everybody.) The ASA number isn't even logarithmic. And ASA 100 is DIN 21 -- why 21?
"Historical reasons".

Finally, Exposure values follow Rule 1 but not Rule 2 -- again for "historical reasons".
"Historical reasons" is a polite way of saying S.N.A.F.U.

Exposure is confusing because of the silly, stupid, inconsitent way in which cameras controls
are labeled.

Here's the "Sunny 16" rule in the traditional Tower of Babel system:

At approx. EV 15 and f/16, use shutter speed 1/ASA speed
for example:
At approx. EV 15 and f/16 and ASA 100, use 1/100th sec

(which of course, isn't even a detent on the shutter dial-it only has 125.)

Here the general rule in APEX:

Does this math confuse anybody? Dang simple, if you ask me.
So by subtracting SensitivityValue from both sides:

As usual, people are willing to update their hardware and software (= buy stuff) but not their thinking.
Picture a cave man holding a Nikon. "Og like take photos. But Og confused by exposure." No wonder!


For reference, here's the basic system, as standardized in 1960.

APEX SYSTEM (per ASA PH2.5-1960)

Note: this may differ from EXIF Version 2.2.

APERTURE

SHUTTER SPEED

The original APEX standard kept the irregular shutter times: 1, 1/2, 1/4,1/8, 1/15, 1/30, 1/60, 1/125....

In fact, some cameras are already calibrated to 1/16, 1/32, 1/64... Shutters are rarely accurate enough
to tell the difference except at 1/15 <> 1/16.

FILM/SENSOR SPEED



BRIGHTNESS

Again, the original standard kept the irregular shutter speeds, so it had to have
irregular brightnesses as well.

Thanks to everyone for their responses. I appreciate the good comments from all sides.

Perhaps I should clarify: I'm not trying to get anyone to switch to APEX (although it would be
nice to have the option of buying an APEX-labeled camera).

My reason for creating this thread was to post the simplest forms of the exposure equation:

TimeValue + ApertureValue = SensitvityValue + Brightness

Brightness = TimeValue + ApertureValue - SensitivtyValue

Photographers use the concepts of "stops" (base 2 logarithms) all the time.
By converting everything to log2 the equation become simple artithmetic.
In other words, I posted this not because it is complex, but because it's the
simplest way to express the exposure equation.

Sometimes math doesn't make things more complex, it makes them simpler.
Doing photography without the concept of "stop" would be confusing, indeed!

Thanks to everyone for their responses. I appreciate the good comments from all sides.

Perhaps I should clarify: I'm not trying to get anyone to switch to APEX (although it would be
nice to have the option of buying an APEX camera). My reason for creating this thread was to
post the simplest forms of the exposure equation:

TimeValue + ApertureValue = SensitvityValue + Brightness

Brightness = TimeValue + ApertureValue - SensitivtyValue

Photographers use the concepts of "stops" (base 2 logarithms) all the time.
By converting everything to log2 the equation become simple artithmetic.
In other words, I posted this not because it is complex, but because it's the
simplest way to express the exposure equation.

Other posters are much better than I am at explaining things to beginners.
This post was to clarify what needs to be explained--as well as to explore
an interesting alternative way of labeling camera controls that actually
exists as ASA/ISO standard.

Sometimes math doesn't make things more complex, it makes them simpler.
Doing photography without the concept of "stop" would be confusing, indeed!