Aperture/Shutter Speed/ISO Tutorial

[LensofNature]

The Camera Exposure: Aperture, ISO and Shutter Speed tutorial was one of the most helpful methods I have come across for explaining these core concepts of photography. The use of the water bucket analogy aided my visualization of the relationship between shutter speed, aperture and ISO, as did the sample photos depicting the effects of shutter speed and aperture. A visual representation of "noise" (which is very difficult for me to detect and understand) was much appreciated. The shutter speed and aperture charts were a treasure given my mathematical learning disability, and I've recorded the information for reference when I'm "in the field". It converted abstract theory to concrete examples with specific values, which gave me a frame of reference for which I had been searching for many years. The article was well written, with no spelling or grammatical errors to distract me. The tutorial was based on an experiential adult learning model that incorporated multiple modes of learning. Excellent job!

[xpatUSA]

The Camera Exposure: Aperture, ISO and Shutter Speed tutorial was one of the most helpful methods I have come across for explaining these core concepts of photography. Excellent job!

Denise, the tutorial is technically incorrect in one place:

ISO speed: controls the sensitivity of your camera's sensor to a given amount of light

In fact, the response of the buckets (i.e. their sensitivity) to a given amount of light can not be changed by the ISO setting. Although the "exposure triangle" is said to be useful, beware that applying more and more ISO under-exposes the sensor which, in turn, can adversely affect the quality of your image.

Less well-known is that, with the standard CMOS photocell circuit, the ever-popular "buckets" start out full and get emptied at a rate depending on the illumination and for a time equal to the shutter period. Thus a "full bucket" is quite dark! Of course the following circuitry sets that to rights with inversion and stuff.

Pardon my pedantry, and do ignore the above technical comment if you find it confusing in any way ...

[William W]

Denise - I reckon it is fantastic that you have gained a practical tool which you can use in the field.

I think that knowing the 'limits' of Shutter Speed, Aperture and ISO for any given shooting scenario is also useful.

For example, if you want to capture kids running around squirting each other with water pistols, then you probably would choose to prioritize a faster shutter speed as the main ingredient of your exposure triangle - you probably would like to be pulling around 1/500sec to capture that action.

On the other hand for a rural landscape you might want a large DoF and using F/11 might be your priority, and, provided a stable tripod or support were available, then 1/60sec could be quite adequate.

I think, regarding 'ISO' (and referencing Ted's reply) - part of his message (I think) was to warn you to be careful not to pump the ISO too high, unless necessary, because doing so renders more the appearance of noise. To this end, cameras' and peoples' tolerances vary; so you need to make your own choices as to what is acceptable noise for your images.

***

Only on ISO and also referencing Ted's commentary:

It is useful to mention that there are some photographic terminologies which traversed the passage from analogue to digital (i.e. were used for film and have been adapted to digital).

Arguably “ISO” is one.

The term “ISO” when used as a photographic term and applied to film photography, uses two numbers, separated by a forward slash, and these do indeed represent that film’s sensitivity to light. (e.g. ISO100/21°)

The choice of the term “ISO” to describe ‘sensitivity’ in digital photography (in my opinion) seeks to make a backward link to films’ ‘sensitivity’, basically, for an easily understood explanation and continuation of the easily explained exposure triangle model.

***

Noted, and also pedantically, the term “ISO” (pronounced ‘eye-so’) when used as a word to describe film’s sensitivity to light was hijacked from the organization's name - “ISO”. (See Note*1)

ISO (eye-so) became a commonly used word in photography circles when it essentially replaced the ‘ASA’ (ay-ess-ay) and ‘DIN’ (din) standards in 1974. ‘ASA’ and ‘DIN’ were the two more common standards to measure film’s sensitivity, however there were more – and ‘ISO’ replaced all of those, too.

ISO (eye-so) is now the commonly word to describe the digital camera’s sensitivity to light, albeit that not being technically correct.

Historical Context -

If we look back at (or if we were part of) the early days of digital camera’s entry into mainstream photography, one exhilarating moment for every photographer was the realization that carrying two three, four or even five or cameras bodies (specifically loaded with DIFFERENT film) was no longer necessary – for a different ‘speed’ between frames, we need only simply twiddle the ISO knob and needing to load the various cameras with both colour and monochrome films was not passé, it simply was dead in the water.

***

(Note*1) ‘ISO’, per se, is the alternative world-wide, abbreviated name (not an acronym) for the international organization which brings together various national standards to an international agreement. These standards are not exclusively standards for photography.

The organization's full name (in English) is: The International Organization for Standardization.

ISO (as applied to the international organization) comes from the Greek word “isos” meaning ‘equal’.

There is a recent discussion here at CiC about the term/word ‘ISO’: LINK

WW

[DanK]

Although the "exposure triangle" is said to be useful, beware that applying more and more ISO under-exposes the sensor which, in turn, can adversely affect the quality of your image.

I'm going to restate this in a way that is equivalent but I think easier to understand.

Increasing ISO on your camera doesn't make the sensor more light-sensitive. It simply amplifies the signal coming out of the sensor. It's very much like turning up the volume on a radio or TV.

However, all of these devices--the camera, the TV, the radio--have noise as well as the signal you want. When you increase ISO, you boost both the signal and the noise. I'm sure you've experienced this. If you get a very faint signal on a radio and turn up the volume to compensate, you don't get a nice, pure sound. You get static, crackling, etc. You also get reduced dynamic range in the music itself, which is related. The camera is analogous. This is why you will see endless discussions online about getting noisy images from shooting at a high ISO.

Different people handle this differently. My approach is to start with what Bill describes: what aperture and shutter speed to I want, given whatever I'm photographing? If there is so little light that I can't get those settings with base ISO, I raise ISO--as little as I can. Otherwise, I leave it at the base level.

[LensofNature]

Well, this is a surprise - giving positive feedback and receiving a "bucketful" of criticism and correction. Well, at least it keeps me on my toes.

[DanK]

It was not intended as criticism or correction. One of the characteristics of this forum is that people teach each other things. So speaking for myself, that's all I was trying to do. I thought that restating the ISO issue in another form would make it clearer.

This happens all the time here, even for more experienced photographers. I've been a photographer for half a century and have been doing digital for perhaps a dozen years, but the way I dodge and burn was taught to me by someone here just a few years ago. It was clear to me that his method was superior to mine, so I adopted it. Similarly, I've learned a lot about problems of oversaturation from a different participant. IMHO, that's much of the value of this forum.

In my experience, not understanding that ISO is amplification, not an increase in exposure, causes people a lot of confusion in other respects. I hoped to help with that. If my comment bothered you, I apologize.

[LensofNature]

Thank you, point taken.

[LensofNature]

Thank you, William, this is most helpful and interesting, especially the ISO history and examples of settings for action versus landscape photography.

[LensofNature]

Increasing ISO on your camera doesn't make the sensor more light-sensitive. It simply amplifies the signal coming out of the sensor. It's very much like turning up the volume on a radio or TV.

I like your analogies; I can relate to radio, and to take it a step further, I'll expand that analogy to hearing aids. If the volume is amplified too much it creates "feedback" or screeching; doesn't improve the quality of the sound or the clarity.

[William W]

I concur with all the points Dan made in Post #6, this one, is especially important -

. . . restating the ISO issue in another form would make it clearer. . .

because we all learn in different ways, our individual 'light bulb moments' come from different sources, so, here at CiC often the commentaries are similar, sometimes nit-picking, sometimes questioning, sometimes calling out an error, yet (99%) always each is intended to forward the conversation.

I would always rather be told something that I already know fifty times, than miss out on something new that I can learn.

WW

[William W]

. . . not understanding that ISO is amplification, not an increase in exposure, causes people a lot of confusion in other respects. . .

+1 This is a very important concept/premise.

[lunaticitizen]

I was unsure if it's ever appropriate to criticize my host... but just like Ted said the particular tutorial about camera exposure is incorrect and misleading.

IMHO when you found any literature mentioning "exposure triangle" with ISO as one of its elements, you'd better take it with a metric ton of salt.

It's not easy to explain what ISO is in purely layman's terms, but I believe this article from DPReview is very clear and concise.

If you're a hardcore like Ted, then there's no better source to understand what ISO is than the standard itself.

If you don't have time to read, just remember that exposure simply depends on your shutter speed and aperture choice (plus scene illuminance).

[xpatUSA]

I rather like and still use the mighty Sekonic which is a classic illustration of exposure in itself:



Once upon a time, there was a circular slide rule for everything technical. As a fearless aviator, I never left home without my trusty E6B "computer" ...

I imagine that there are apps for smartphones or tablets these days that do the same thing but probably not as well and they do need batteries ...