The "Exposure Triangle"?

[raydm6]

Is the "Exposure Triangle" (relationship between aperture, shutter speed, and ISO) a new term/concept that has recently appeared?

I must admit, with over 40+ years practicing amateur photography, I have never heard of this term. I have practiced it with my manual cameras over the years without calling it that.

I came across the term when doing some research on purchasing an XT-2 (which I don't need because I have way too many cameras as is ), and came across this concept several times.

I did a search on RFF and have not been able to see any reference to it although there are numerous websites/articles on the 'net describing this relationship.

Curious, your thoughts...

 

[Mcary]

I think those of us who started out shooting with 35mm film cameras where once you loaded the media"film" you were pretty much stuck with that ISO/ASA, yes you could change rolls mid-roll but it was a pain. Just got use to thinking of aperture and shutter speed as the things one could adjust to get the desired exposure for a give situation so that's the way a lot of us still think. So even though I know I can and do changes ISO as needed I generally only do so when/if change the aperture and/or shutter speed doesn't give me what I need for the given situation.

 

[css9450]

I think those of us who started out shooting with 35mm film cameras where once you loaded the media"film" you were pretty much stuck with that ISO/ASA.... Just got use to thinking of aperture and shutter speed as the things one could adjust to get the desired exposure for a give situation so that's the way a lot of us still think.

I am sure you are correct. The advent of digital added a third element you can adjust to vary the exposure and since there were now three, instead of just two, suddenly it could be described as a "triangle".


I remember prior to buying my first digital, in my naivete I assumed that if I changed the ISO on the camera, it would globally change the ISO for every photo already on the memory card. So if I shot my first photos at ISO 100 but later switched the camera to ISO 1600, I thought the first photos would then suddenly become grossly overexposed on the memory card. It was mind-boggling to me when I realized I could change the ISO for each and every photo if I wanted to, with no harm done.

 

[Ko.Fe.]

I started to understand what is going on only after getting DSLR. To me exposure is shutter speed, aperture and ISO combination. Some could call it triangle, troika and so on.

 

[David Hughes]

or it could be called the exposure settings...


Regards, David

 

[davidnewtonguitars]

Iin the article by Colin Barey on Stand Development https://www.japancamerahunter.com/2013/10/black-white-film-development-lazy-people/
he made the earth move, for me anyway, when he wrote that rolls shot at different speeds could be developed together using 1:100 dilution of Rodinal. Taken to its logical conclusion, multiple iso's could be shot on a single roll of film, with acceptable results, using stand development.
So now all three of the variables are at the command of the film user, just like in the digital process. A "triangle" is ours.

And I tried it, at least enough times to know it wasn't going to be for me.
Now I am happy when I shoot HP5 and FP4 at box speed, I can develop them together, thanks to the scientists at Ilford.

 

[peppard]

Now I am happy when I shoot HP5 and FP4 at box speed, I can develop them together, thanks to the scientists at Ilford.

David: Can you please explain how you do that?

Thanks,
Giorgio

 

[charjohncarter]

There has always been this triangle but nobody called it that. Maybe because of what the first poster wrote. What surprises me is how digital photographers don't have any idea what aperture or shutter speed they are using or know the relationships. Even when most of us started we quickly learned (by mistakes) what DOF and slow shutters cause. I'm not talking about RFF members just my children and grandchildren. I gave up on one grandson finally just told him to use auto.

 

[ptpdprinter]

I think those of us who started out shooting with 35mm film cameras where once you loaded the media"film" you were pretty much stuck with that ISO/ASA, yes you could change rolls mid-roll but it was a pain. Just got use to thinking of aperture and shutter speed as the things one could adjust to get the desired exposure for a give situation so that's the way a lot of us still think. So even though I know I can and do changes ISO as needed I generally only do so when/if change the aperture and/or shutter speed doesn't give me what I need for the given situation.

Yep. With 35mm film, once loaded, one leg of the triangle was fixed. Now with digital, all three are in play. Within a few stops, I use ISO as a variable which allows me to maintain a minimum shutter speed. Lack of sharpness is more affected by camera shake than a lack of lens resolution.

 

[airfrogusmc]

The law of reciprocity still stands. We used it all the time. In fact Hasselblad Zeiss lenses had a lock to lock it in.

The law was; say you had an EV that would give you say 1/500 at 2.8, it would give you the same density on the negative( if the shutter and aperture were functioning properly) as 1/250 at f/4, 1/125 at 5.6, 1/60 at f/8, 1/30 at f11, etc. It still is a law. One difference is with film the law would treat down with really long exposures and different emulsions would have different characteristics. Adams referred to this as the reciprocity effect but most referred to it as reciprocity failure. With digital that effect or failure of the law to work no longer exists. There ia always a relationship between ISO, shutter speed and aperture. They are some of the basic controls we have as photographers.

 

[willie_901]

There Is No Exposure Triangle

There Is No Exposure Triangle

But there is a brightness triangle!

Exposure and the rendered rendered image brightness are not synonymous. Exposure and the rendered image brightness are only identical when a camera's ISO parameter is set to the base (native) sensitivity setting.

For digital cameras, exposure is the amount of energy measured by the sensor when the shutter is open. This is determined by only three things:

• Scene luminance
• Shutter time
• Aperture

Exposure determines the S/N for the data which in turn determines the information-content's uncertainty. Optimizing exposure minimizes uncertainty and maximizes perceived, rendered, image quality.

ISO is irrelevant. ISO has no affect on the sensor sensitivity(1). The raw file data S/N may or may not depend on the camera ISO setting(2). The camera ISO parameter is a simply calibrated exposure index based on one of five industry standards.

However, for any combination of shutter time and aperture, the meter will estimate the appropriate amount of gain (ISO) required to render a bright image when exposure is limited by camera motion, subject motion and, or DOF. This change in gain is not necessarily required to maximize perceived image quality(3).

Over exposure occurs when one or more sensor photo-diode sites generates enough photoelectrons to exceed their maximum electrical charge capacity. All useful information for that pixel is lost.

Under exposure occurs when the opposite happens. Some amount of sensor under exposure is almost always unavoidable. However, unnecessary under exposure always degrades perceived image quality. The most common cause of unnecessary under exposure is not using the lowest practical camera ISO setting.

After the shutter closes the photo-diode sites' electrical charge is emitted as a spatial array of DC voltages. Those voltages are digitized as integers and written to an in-camera raw file.

When the shutter time and aperture are set for optimum exposure, the result is a rendered image with an aesthetically appropriate brightness. Optimum exposure means the shutter and aperture were set to retain highlight region information required to achieve the photographer's goals. This means unimportant highlight regions can be intentionally over exposed.

Often convenience, subject motion, or depth of field mandates the sensor be under exposed. The result would be a rendered image that is too dark. Now, the gain DC voltages' gain can be increased before digitization. Changing the camera ISO parameter changes the gain level. As long as the gain does not exceed the maximum ADC's signal level threshold, the image brightness will be aesthetically appropriate.

The role of ISO is to achieve a useful image brightness.

The triangular relationship between ISO parameter, shutter time and aperture holds as for rendered image brightness. It doe not apply to exposure.


1. Recently sensors with dual conversion gain became available. In bright light the phtotodiodes' conversion gain is set for maximum dynamic range. In low light (higher ISO settings) the gain is changed to increase sensitivity.

2. For newer cameras increasing signal gain (ISO) does not significantly decrease the electronic noise levels. These cameras are described as ISO invariant or ISO-less. For older cameras increasing gain can decrease the electronic noise levels. With the former, image noise is dominated by photon noise. For the latter electronic noise increases as exposure decreases.

3. With raw files increasing signal gain after the shutter closes does not significantly increase perceived image quality. This is not the case for in-camera JPEGS.

 

[Steve M.]

Diafine developer can be used as David mentioned. One shot on the roll could be at ISO 200, another at 1600, etc. I guess it just developed to completion, like prints. You tend to get flat negs though, and can't vary the look by using over or under developing.

I don't know a thing about digital cameras, but I'm pretty sure they work like film cameras in regard to exposure, and w/ film, brightness IS exposure. Under expose the shot, and it gets dark, over expose a shot, and it gets blown out (too bright). Or vice versa. I get that mixed up a lot because I think of the positive image, not the negative.

 

[oftheherd]

I was always fascinated with math, especially geometry, but I just never wanted to take the time to learn it properly.

Imagine how much better a photographer I could have been if I had applied myself more to geometry!

I wish I hadn't come across this threat. sigh.

 

[davidnewtonguitars]

Hi Giorgio,
I am using I'ford's Photo Processing Chart times for D76 1+1, which is 11 min. for HP5@400 and FP4@125.
With FP4@50, where I like it, it is a different story.

David: Can you please explain how you do that?


Thanks,
Giorgio

 

[cz23]

I hadn't hear the triangle concept before, but I like it. But I'm not sure it's a literal representation. You can change any exposure variable without affecting the others (over or underexposure), but you cannot change the length of a triangle side or any one angle without affecting the others.

Maybe the fact that a triangle is always 180° could relate to CORRECT exposure. Then, for correct exposure, changing one would always require a change of one or both of the others, but always equal to 180° (correct exposure). Just not sure if the doubling and halving of exposure relate to side lengths or angle values.

I took geometry fifty years ago, and am sure I'm taking this too literally.

John

 

[peppard]

David,

Thank you for the explanation.

Giorgio

 

[ellisson]

But there is a brightness triangle!

Exposure and the rendered rendered image brightness are not synonymous. Exposure and the rendered image brightness are only identical when a camera's ISO parameter is set to the base (native) sensitivity setting.

For digital cameras, exposure is the amount of energy measured by the sensor when the shutter is open. This is determined by only three things:

• Scene luminance
• Shutter time
• Aperture

Exposure determines the S/N for the data which in turn determines the information-content's uncertainty. Optimizing exposure minimizes uncertainty and maximizes perceived, rendered, image quality.

ISO is irrelevant. ISO has no affect on the sensor sensitivity(1). The raw file data S/N may or may not depend on the camera ISO setting(2). The camera ISO parameter is a simply calibrated exposure index based on one of five industry standards.

However, for any combination of shutter time and aperture, the meter will estimate the appropriate amount of gain (ISO) required to render a bright image when exposure is limited by camera motion, subject motion and, or DOF. This change in gain is not necessarily required to maximize perceived image quality(3).

Over exposure occurs when one or more sensor photo-diode sites generates enough photoelectrons to exceed their maximum electrical charge capacity. All useful information for that pixel is lost.

Under exposure occurs when the opposite happens. Some amount of sensor under exposure is almost always unavoidable. However, unnecessary under exposure always degrades perceived image quality. The most common cause of unnecessary under exposure is not using the lowest practical camera ISO setting.

After the shutter closes the photo-diode sites' electrical charge is emitted as a spatial array of DC voltages. Those voltages are digitized as integers and written to an in-camera raw file.

When the shutter time and aperture are set for optimum exposure, the result is a rendered image with an aesthetically appropriate brightness. Optimum exposure means the shutter and aperture were set to retain highlight region information required to achieve the photographer's goals. This means unimportant highlight regions can be intentionally over exposed.

Often convenience, subject motion, or depth of field mandates the sensor be under exposed. The result would be a rendered image that is too dark. Now, the gain DC voltages' gain can be increased before digitization. Changing the camera ISO parameter changes the gain level. As long as the gain does not exceed the maximum ADC's signal level threshold, the image brightness will be aesthetically appropriate.

The role of ISO is to achieve a useful image brightness.

The triangular relationship between ISO parameter, shutter time and aperture holds as for rendered image brightness. It doe not apply to exposure.


1. Recently sensors with dual conversion gain became available. In bright light the phtotodiodes' conversion gain is set for maximum dynamic range. In low light (higher ISO settings) the gain is changed to increase sensitivity.

2. For newer cameras increasing signal gain (ISO) does not significantly decrease the electronic noise levels. These cameras are described as ISO invariant or ISO-less. For older cameras increasing gain can decrease the electronic noise levels. With the former, image noise is dominated by photon noise. For the latter electronic noise increases as exposure decreases.

3. With raw files increasing signal gain after the shutter closes does not significantly increase perceived image quality. This is not the case for in-camera JPEGS.

Can the electronic noise level be selectively suppressed to some degree when signal gain is increased, or, in other words, are there in-camera algorithms to detect random signal in the sensor pixels and to not increase gain in these areas?