The effect of the ISO dial setting on camera metering

[GeorgianBay1939]

The dog has been dead for a while. If it was ever alive..

"You are changing one of the three brightness variables so that you'll have to change either f/ or ss to get a proper exposure. The ISO dial is calibrated to give you optimum exposure in varying light conditions. Turn ISO down in bright conditions, up in dark conditions. Increasing the ISO setting increases the sensor's gain to compensate for lack of brightness in the scene."

Set up an imaginary quote (or a real one from one person, not indicative of any widespread believe), then spend 1000 words shooting down a straw dog that no one else believes in, replacing one wrong opinion with something that, if not wrong, is certainly more convoluted and less useful

I am looking forward to your suggestion, less convoluted and more useful than my simple attempt.

Others have made some very useful, concise suggestions. You're welcome to try.

The above is paraphrased and shortened from a conversation that took place at Henry's, a camera store in Sudbury Ontario Canada. Although the term "exposure triangle" was not mentioned the concept of ISO being a part of exposure was used. The terms exposure and brightness were used interchangeably.

Although I do not have near the seniority that you do here, I have often seen the triangle used to explain how to set ISO. Here is an example:

http://www.digitalcameraworld.com/2...gle-aperture-shutter-speed-and-iso-explained/

After thinking about it, I realized that the above explanation would limit the growth of the youngster and contemplated how I would answer such a question when asked by a developing (!) photographer.

"Two functions of a camera's ISO dial" was my first attempt at forming such an answer. After reading the thread I realize that both parts, metering and mapping, of the answer needed improvement. Since the metering portion seemed to be almost ok, I would ask that you limit your comments to the metering portion of the answer in this thread. I will start a thread to deal with the (much more controversial) mapping portion later.

------------------->lots of stuff cut out<-----------------------

How did any of this help your imaginary youngster?

No help yet. I don't know if or when I'll ever see him again. But I won't venture forth until I have a solid grasp of what the ISO dial really does and how it can be used to capture optimal raw files.

Certainly a case were the cure is worse than the disease. If it takes this much to explain ISO, I would expect the next step, pressing the shutter release, to take full chapter!

No fear. I already know what that button does. No chapter is contemplated.

 

[xpatUSA]

I use the Additive Photographic Exposure System (APES or APEX) as my framework for such discussions.

Nice. Most folks don't know what a logarithm is any more!!!

In that framework metering is simply the camera measuring scene Brightness.
(So ISO setting does not affect camera metering in my terminology (your title implies otherwise to me.) )

Perhaps my title should be "The effect of ISO dial setting on camera exposure recommendations".

Exposure Compensation (EC) is a biasing of the metered Brightness value.

Brightness, EC, and the ISO Speed setting comprise the Exposure Value (EV).
[ Clearly this use of the ISO speed setting is independent of how it affects the sensor circuitry. ]

https://en.wikipedia.org/wiki/APEX_system#Exposure_equation



Definition of EV: (log = log to base 2) and above equation:

EV = log(A^2)/T = log B + log Sx [+ log EC ] ? (meter calibration constant??)

To "zero" the meter you need an Aperture Value and Time Value that equals this EV.

Graphically this is illustrated in my Exposure Waterfall - A Simple Graphical Explanation of Exposure article and the accompanying Exposure Waterfall chart.

Nice! To zero the chart select EVx (exposure compensation so that) EVa +EVt =EVb + EVsx + EVx

Nice use of combining EVx (Exposure Compensation) with the exposure metering equation above.

Personally I find this presentation better than the "exposure triangle" but my feelings aren't universally held

I can see why. Although more complex yours is correct while the ET is generally false. I suspect folks will take the easy, but false, way out instead of learning what log base 2 means.

Regards,

--
Bill ( Your trusted source for independent sensor data at http://www.photonstophotos.net )

Good stuff. I am trying to avoid EV because it is also widely misunderstood and misused.

This post bothers me a little. It contains statements that are demeaning in spite of their intent.

As to the "ET", it is inappropriate for those like myself who choose the so-called base ISO and superglue the knob in that position :-D

Anybody remember nomographs ? I visualize one with an ISO scale in the middle and A and t scales, one on each side of it. Says it all . . could even have EC incluida by making the the ISO scale be on a slider.

I like that old stuff:



So much simpler . . .

--
Ted

 

[mostlyboringphotog]

... snipped to save server space

Good stuff. I am trying to avoid EV because it is also widely misunderstood and misused.

This post bothers me a little. It contains statements that are demeaning in spite of their intent.

As to the "ET", it is inappropriate for those like myself who choose the so-called base ISO and superglue the knob in that position :-D

Anybody remember nomographs ? I visualize one with an ISO scale in the middle and A and t scales, one on each side of it. Says it all . . could even have EC incluida by making the the ISO scale be on a slider.

I like that old stuff:



So much simpler . . .

--
Ted

Really, really cool stuff - I'm insanely jealous of your "exposure calculator" ;-)

Really, other than getting used to the f-stop sequence, what does it take to get ET?

BTW, I mentioned nomograph here http://www.dpreview.com/forums/post/57229585

 

[Jeff]

snip

This post bothers me a little. It contains statements that are demeaning in spite of their intent.

As to the "ET", it is inappropriate for those like myself who choose the so-called base ISO and superglue the knob in that position :-D

Anybody remember nomographs ? I visualize one with an ISO scale in the middle and A and t scales, one on each side of it. Says it all . . could even have EC incluida by making the the ISO scale be on a slider.

I like that old stuff:



So much simpler . . .

--
Ted

Ted ... absolutely love this!

--
Jeff

jck_photos’s albums | Flickr

www.flickr.com

 

[xpatUSA]

... snipped to save server space

Good stuff. I am trying to avoid EV because it is also widely misunderstood and misused.

This post bothers me a little. It contains statements that are demeaning in spite of their intent.

As to the "ET", it is inappropriate for those like myself who choose the so-called base ISO and superglue the knob in that position :-D

Anybody remember nomographs ? I visualize one with an ISO scale in the middle and A and t scales, one on each side of it. Says it all . . could even have EC incluida by making the the ISO scale be on a slider.

I like that old stuff:



So much simpler . . .

--
Ted

Really, really cool stuff - I'm insanely jealous of your "exposure calculator" ;-)

No need, mbp, I downloaded the image from an article long ago - I don't actually own it.

Really, other than getting used to the f-stop sequence, what does it take to get ET?

Phone home? Move to New York? (just kidding). I don't really understand the question, probably due to my simple life, but my MO is:

ISO: always "base"

Aperture: set for required DOF

Speed (so-called): set to put the needle in the middle plus an appropriate offset dictated by the scene content (black cats, snow, blah-di-blah).

If I run out of adjustment, e.g. speed ends up in 'bulb', I don't take the shot.

BTW, I mentioned nomograph here http://www.dpreview.com/forums/post/57229585

Well done :-D

--
Ted

 

[GeorgianBay1939]

I use the Additive Photographic Exposure System (APES or APEX) as my framework for such discussions.

Nice. Most folks don't know what a logarithm is any more!!!

In that framework metering is simply the camera measuring scene Brightness.
(So ISO setting does not affect camera metering in my terminology (your title implies otherwise to me.) )

Perhaps my title should be "The effect of ISO dial setting on camera exposure recommendations".

Exposure Compensation (EC) is a biasing of the metered Brightness value.

Brightness, EC, and the ISO Speed setting comprise the Exposure Value (EV).
[ Clearly this use of the ISO speed setting is independent of how it affects the sensor circuitry. ]

https://en.wikipedia.org/wiki/APEX_system#Exposure_equation



Definition of EV: (log = log to base 2) and above equation:

EV = log(A^2)/T = log B + log Sx [+ log EC ] ? (meter calibration constant??)

To "zero" the meter you need an Aperture Value and Time Value that equals this EV.

Graphically this is illustrated in my Exposure Waterfall - A Simple Graphical Explanation of Exposure article and the accompanying Exposure Waterfall chart.

Nice! To zero the chart select EVx (exposure compensation so that) EVa +EVt =EVb + EVsx + EVx

Nice use of combining EVx (Exposure Compensation) with the exposure metering equation above.

Personally I find this presentation better than the "exposure triangle" but my feelings aren't universally held

I can see why. Although more complex yours is correct while the ET is generally false. I suspect folks will take the easy, but false, way out instead of learning what log base 2 means.

Regards,

--
Bill ( Your trusted source for independent sensor data at http://www.photonstophotos.net )

Good stuff. I am trying to avoid EV because it is also widely misunderstood and misused.

This post bothers me a little. It contains statements that are demeaning in spite of their intent.

I don't mean to demean! So please let me try to justify my comments:

"Nice. Most folks don't know what a logarithm is any more!!!"

Do you remember those books of (mathematical and physical) tables we used to carry around with our log log duplex or log log trig vector K&E slide rules during our years at engineering schools? Thank goodness all of that freight has been replaced by hand-held gear that doesn't even require Reverse Polish Notation! I had lunch with a bunch of land surveyors a couple of weeks ago. Times have changed. Even aircrew don't need baggy flight suits to carry E6B "computers" any more!




The back, used for wind triangles, was even sexier! See link.

"I can see why. Although more complex yours is correct while the ET is generally false. I suspect folks will take the easy, but false, way out instead of learning what log base 2 means."

While engineering/scientific pedants (MBP's descriptor of me) will keep struggling until they are satisfied that they have it right, most photographers are more interested in taking pictures. If the ET works for them, why bother with all of that logarithmic stuff. More power (!) to them.

"Good stuff. I am trying to avoid EV because it is also widely misunderstood and misused."

I use EV in the formal sense. EV = log_2 (N^2)/t and I make the distinction between EV and EV(ISO 100) which is often called LV, Light Value. The former is a camera setting pair, the latter is a measure of lighting conditions .

I apologize if my tone was demeaning. Not my intent.

As to the "ET", it is inappropriate for those like myself who choose the so-called base ISO and superglue the knob in that position :-D

Not quite super glue in my case. I use contact cement to that I can break it in circumstances like this one: http://www.dpreview.com/forums/post/57163812

Anybody remember nomographs ? I visualize one with an ISO scale in the middle and A and t scales, one on each side of it. Says it all . . could even have EC incluida by making the the ISO scale be on a slider.

I like that old stuff:



So much simpler . . .

--
Ted

--
Tom
The best part of growing old is having the opportunity to do so.

Brtthome's Blog

photos, prose, prattle and possibilities

brtthome.wordpress.com

 

[xpatUSA]

This post bothers me a little. It contains statements that are demeaning in spite of their intent.

I don't mean to demean! So please let me try to justify my comments:

"Nice. Most folks don't know what a logarithm is any more!!!"

Do you remember those books of (mathematical and physical) tables we used to carry around with our log log duplex or log log trig vector K&E slide rules during our years at engineering schools?

Yes, I had a book of Castle's 5-figure tables long ago. I started out with a log-log slide rule as a assistant controls engineer in 1969, before calculators appeared for all. Had a watch with a circular slide rule bezel for years until my aging eyes couldn't read the numbers :-(

Thank goodness all of that freight has been replaced by hand-held gear that doesn't even require Reverse Polish Notation!

I once built a Sinclair "scientific" calculator: RPN, 5-digit (fixed point) plus exponent. So for 12345.6789 you had to enter <1.2346 E 4> (glurk). No fun at all. Much later, I got into the Forth programming language which was also RPN. Always a glutton for punishment, eh?

I had lunch with a bunch of land surveyors a couple of weeks ago. Times have changed. Even aircrew don't need baggy flight suits tocarry E6B "computers" any more!

Still got mine:

I apologize if my tone was demeaning. Not my intent.

OK. I do it myself quite a bit, mainly railing against "Real Worlders". They often answer a technical post with "but in the real world . . . blah-di-blah".

As to the "ET", it is inappropriate for those like myself who choose the so-called base ISO and superglue the knob in that position :-D

Not quite superglue in my case. I use contact cement so that I can break it in circumstances like this one:http://www.dpreview.com/forums/post/57163812

I remember that post - pretty good!

--
Ted

 

[bclaff]

... I use EV in the formal sense. EV = log_2 (N^2)/t ...

This is twice you have made the error with the parentheses, so this time I'll point it out.

It's log_2(N^2/t) == log_2(N^2) + log_2(1/t)

Regards,

 

[bclaff]

Anybody remember nomographs ? I visualize one with an ISO scale in the middle and A and t scales, one on each side of it. Says it all . . could even have EC incluida by making the the ISO scale be on a slider.

I like that old stuff:



So much simpler . . .

Yeah, a photographic slide rule.
Naturally I simply see a wooden version of my Exposure Waterfall

It occurs to me that what is at work here is the power of logarithms, the oxymoron makes me smile.

Regards,

--
Bill ( Your trusted source for independent sensor data at http://www.photonstophotos.net )

 

[mostlyboringphotog]

snipped to save server space

Yeah, a photographic slide rule.
Naturally I simply see a wooden version of my Exposure Waterfall

Is there an App for that?? ;-)

It occurs to me that what is at work here is the power of logarithms, the oxymoron makes me smile.

Regards,

--
Bill ( Your trusted source for independent sensor data at http://www.photonstophotos.net )

 

[xpatUSA]

I like that old stuff:

Yeah, a photographic slide rule.
Naturally I simply see a wooden version of my Exposure Waterfall

I thought that table was pretty informative and I especially like the row for Manual Mode where the camera determines nothing!

It occurs to me that what is at work here is the power of logarithms, the oxymoron makes me smile.

More of a pun, I'd say, increasing our pedantry exponentially ;-)

--
Ted

 

[gollywop]

... I use EV in the formal sense. EV = log_2 (N^2)/t ...

This is twice you have made the error with the parentheses, so this time I'll point it out.

It's log_2(N^2/t) == log_2(N^2) + log_2(1/t)

== 2log_2(N) - log_2(t) ;-)

 

[bclaff]

It occurs to me that what is at work here is the power of logarithms, the oxymoron makes me smile.

More of a pun, I'd say, increasing our pedantry exponentially ;-)

I'm sticking with oxymoron as opposed to pun.

Fun fact: my current employer is Precision Estimating.

 

[bclaff]

snipped to save server space

Yeah, a photographic slide rule.
Naturally I simply see a wooden version of my Exposure Waterfall

Is there an App for that?? ;-)

No app, yet, just the interactive chart

 

[Detail Man]

It occurs to me that what is at work here is the power of logarithms, the oxymoron makes me smile.

More of a pun, I'd say, increasing our pedantry exponentially ;-)

I'm sticking with oxymoron as opposed to pun.

Fun fact: my current employer is Precision Estimating.

Many tend to conflate Standard Error of the Meme with Standard Deviancy ... as if they were the same (!) I speak with an accurate uncertainty, merely saluting the horizonal expanse of vast and deep mysteries.

 

[xpatUSA]

It occurs to me that what is at work here is the power of logarithms, the oxymoron makes me smile.

More of a pun, I'd say, increasing our pedantry exponentially ;-)

I'm sticking with oxymoron as opposed to pun.

OK

Fun fact: my current employer is Precision Estimating.

Now that is an oxymoron

 

[GeorgianBay1939]

... I use EV in the formal sense. EV = log_2 (N^2)/t ...

This is twice you have made the error with the parentheses, so this time I'll point it out.

It's log_2(N^2/t) == log_2(N^2) + log_2(1/t)

Thanks for pointing that out.

Actually I should've written log_2[(N^2)/t] to let the brackets establish the order of priority as I didn't recall the priority when using transcendental functions.

It has been about 50 years since I coded FORTRAN, so I am a bit rusty. I didn't want to take the chance of dividing the exponent, 2, by t before exponentiating N. Hence that bracket.

Thanks for the correction.

Regards,

 

[GeorgianBay1939]

... I use EV in the formal sense. EV = log_2 (N^2)/t ...

This is twice you have made the error with the parentheses, so this time I'll point it out.

It's log_2(N^2/t) == log_2(N^2) + log_2(1/t)

== 2log_2(N) - log_2(t) ;-)

 

[gollywop]

... I use EV in the formal sense. EV = log_2 (N^2)/t ...

This is twice you have made the error with the parentheses, so this time I'll point it out.

It's log_2(N^2/t) == log_2(N^2) + log_2(1/t)

== 2log_2(N) - log_2(t) ;-)

 

[GeorgianBay1939]

Snip

I had lunch with a bunch of land surveyors a couple of weeks ago. Times have changed. Even aircrew don't need baggy flight suits tocarry E6B "computers" any more!

Still got mine:

I apologize if my tone was demeaning. Not my intent.

OK. I do it myself quite a bit, mainly railing against "Real Worlders". They often answer a technical post with "but in the real world . . . blah-di-blah".

As to the "ET", it is inappropriate for those like myself who choose the so-called base ISO and superglue the knob in that position :-D

Not quite superglue in my case. I use contact cement so that I can break it in circumstances like this one:http://www.dpreview.com/forums/post/57163812

I remember that post - pretty good!

--
Ted

I was lucky to have a back seater in the CF-101B. He ran the radar and the ECCM machinery and kept tabs on where we were. I was able to get away with Mental DR (1 in 60 rule solved everything) using navaids and radar. Also M X 10 ~ NM / minute . Much easier than the E6B.

Little different than Situational Awareness helmets, eh?

--
Tom
The best part of growing old is having the opportunity to do so.

Brtthome's Blog

photos, prose, prattle and possibilities

brtthome.wordpress.com