Photography 101 – Lesson Four – ISO and EV
25-05-2007, 03:12 PM
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Photography 101 – Lesson Four – ISO and EV
About time for another "lesson" 
In the previous article (https://passionford.com/forum/viewtopic.php?t=264975) we talked about aperture and its effect on depth of field.
A couple of lessons ago, we also looked at exposure and touched on a number of terms and subjects that I promised to explain further. This is it !
This lesson is all about theory I am afraid, the next one will be more practical
First of all let’s introduce a term which is widely used in photography, ISO.
In the old days of film photography, the ISO (or ASA) speed of a film expressed how fast or slow negative or slide film was, another way of looking at this is to ask yourself how sensitive the film was.
In layman’s terms a fast film, is one that is able to capture small amounts of light very quickly, a slow film conversely requires a longer time to capture the same amount of light.
For those of you who were taking pictures many years ago, you might remember buying 100 ISO film for outdoor shots in the summer, and 400 ISO film for those family shots round the table at Christmas.
So, what is the difference between 100 ISO film and 400 ISO film, and what are the pros and cons of each I hear you ask.
film sensitivity
Film (negative or slide) is essentially a medium on which a chemical is applied. The chemical in question reacts to the light which is allowed through the lens, and, once developed in a laboratory (more chemical processes), stores the light that hit the film for ever (the negative, or positive for slides).
This chemical contains lots of “grains” that are responsible for receiving and storing this light, much like the pixels in today’s digital camera sensors.
In order to produce different film sensitivities, film manufacturer used different grades of “grains” in the chemicals, small ones for slow film, and large ones for fast film. This was based on the fact that the larger a grain was, the quicker it was able to absorb a given amount of light.
Traditional film sensitivities thus existed in the following range: 25, 50, 100, 200, 400, 800, 1600, 3200 and 6400 ISO.
As you can see from this list, the numbers double each time, this should be no surprise to you anymore… each increase in ISO number (from 100 to 200 for example), meant that for a given exposure, you could halve the shutter speed (e.g. 1/125s to 1/250s), or, close the aperture one stop further (F5.6 to F8).
More importantly, if your lens is limited to say F4.5 as a maximum aperture, and you are using a 210mm zoom lens for some sports photography inside a gym hall, you may not be able to correctly expose your pictures with 100 ISO film since F4.5 and 1/200s wouldn’t allow sufficient light through the lens to achieve correct exposure.
The temptation may then be to drop the shutter speed to 1/125s or 1/60s, but then, blurring would be likely, either because the subject moved too fast, or, because you couldn’t hold the long heavy lens steady enough for a clear sharp shot
The solution was then to get faster film (400 or 800 ISO), which would allow those pictures to be taken.
So, this is great isn’t it, just get faster film and there you go… well, remember, photography is about compromises, and here is another one…
Remember the larger grains in the faster film, how do you think these will translate when the picture is printed
Yup, the print won’t be quite a sharp and well defined, there is less detail in the picture, less resolution if you want, so larger prints look soft rather than crisp and clean.
And it gets even worse if you enlarge the print to A4 or more, the picture looks grainier and grainier as the film speed and print size increase.
I found the following descriptions for a few of these film sensitivities:
100 SUNLIGHT: 100 speed film is excellent color print film for sunny or bright light photo opportunities. It is good for close-ups, posed photos, and landscapes.
200 ALL-AROUND: 200 speed film is a general multipurpose film with extremely fine grain, producing soft, natural skin tones for people shots.
400 EXPANDED MULTIPURPOSE: 400 speed film is the most versatile film for compact, automatic 35mm cameras. It is great for candid snapshots and sports action. It can be used for low light or flash, outdoor or indoor.
800 FASTEST MULTIPURPOSE: 800 speed film has ultimate versatility for snapshots and fast action. It is ideal for use with zoom lenses. This film can be used for indoors, outdoors, and fast action.
But I have a digital camera, and you are talking about film, should I care about all this…
Well, you should really, your digital camera (be it a compact or SLR) sports an ISO setting which tries to replicate what was available in the good old film days, but, it does so at a potentially much greater cost than grainy pictures… Read on…
One of the disadvantages of film was that if you were taking pictures outdoors, then indoors, then outdoors, etc… you could easily find yourself with the wrong film in the camera and needed to change it, or, make do, or, carry two cameras, etc… Never mind having to make sure you had enough stock of each film with you
Problem with digital is that you are stuck with a 6, 8, 10 megapixel sensor, and to date, no one has come up with a swappable sensor, not at a reasonable price, or, practical enough for you and I do it in any case, that’s assuming that for a given sensor size, a 6MP is less sensitive to light than a 10MP one which isn’t strictly the case.
So, camera manufacturers have replaced an analogue process (grains in chemical solution) with an electronic one, and given us a range of ISO settings on our shiny digital cameras. Usually the range is 100 to 3200 these days.
How ? Well, by putting an amplifier on the CCD output, thus amplifying the signal received by the CCD and artificially increasing sensitivity… Changing ISO settings on your digital camera will not physically change the characteristics of your sensor – unlike changing film
And as always there is a catch… The higher the ISO setting you choose, the more amplification takes place, and as with any amplification, you get to the stage where distortion starts to take place. In digital photography, this is known as noise.
To prove this, try taking a picture at night, without the flash on 1600 or 3200 ISO, the picture will most probably look very grainy, possibly even show red dots in places where they shouldn’t be.
Some cameras are more or less prone to this problem though so mileage will vary depending on model and equipment.
Note: the longer the shutter speed (1s, 2s, etc…) and the more likely additional noise will creep in too, this is because the sensor is energised for such a long time that it heats up sufficiently to affect the quality of the image it captures.
So, I hope you now fully understand what these three mysterious letters mean
Lastly, let’s look at another term used by photographers, EV.
EV is a unit used to measure exposure, it stands for Exposure Value. Much like meters, inches, degrees (Fahrenheit or Celsius), etc… a base line has been established by the photography community many many years ago.
The base line is that EV 0 corresponds to an exposure of 1 second at F1.
We’ve seen previously that changing speed or aperture effectively doubles or halves the amount of light reaching the film or CCD, well, this difference is 1 EV.
Thus, every time you double exposure time, you double available light and therefore increase exposure by 1 EV.
Conversely, if you halve exposure time, you half available light therefore decreasing exposure by 1 EV or changing the exposure by -1 EV.
The same applies to aperture and changing F-stops.
Why is that important you may ask, well… should you delve into your camera’s menus, or dials, you might find references to exposure compensation and flash compensation, and these are shown in EV values.
Also, in your viewfinder, there should be an exposure scale, showing whether your current choice of speed and aperture will under or over exposure the image, again, the scale is shown in EV.
So every time we change speed or aperture settings, we halve or double the available light ? Well, no, not always…
If you remember back to the exposure lesson, I said that shutter speeds on cameras were usually 1/8s, 1/15s, 1/30s, 1/60s, 1/125s, 1/250s, 1/500s, 1/1000s, 1/2000s, 1/4000s, 1/8000/s, etc…
And, apertures were usually, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, etc…
Each change from one value to the other in the list above is indeed halving or doubling, however, you might find that your camera has speeds such as 1/750s or 1/1500s, now those don’t fit into the halving or doubling scale do they ?
The reason is that modern cameras have much more refined capabilities in terms of exposure, and, limiting yourself to 1 EV for each possible change can result in less than optimum exposure. In the old days, the electronics used for exposure were quite rudimentary and 1EV was deemed sufficient. Not so anymore
Cameras are now able to set speeds of 1/2 EV (1/750s and 1/1500s) and even 1/3 EV (1/600s and 1/800s) which explains how these strange numbers have come about.
That’s it for now, in the next lesson I hope to cover flashes and their uses in photography, but I first need to dig my camera out and take lots of example pictures for you
As usual, any questions, feel free to ask
In the previous article (https://passionford.com/forum/viewtopic.php?t=264975) we talked about aperture and its effect on depth of field.
A couple of lessons ago, we also looked at exposure and touched on a number of terms and subjects that I promised to explain further. This is it !
This lesson is all about theory I am afraid, the next one will be more practical
First of all let’s introduce a term which is widely used in photography, ISO.
In the old days of film photography, the ISO (or ASA) speed of a film expressed how fast or slow negative or slide film was, another way of looking at this is to ask yourself how sensitive the film was.
In layman’s terms a fast film, is one that is able to capture small amounts of light very quickly, a slow film conversely requires a longer time to capture the same amount of light.
For those of you who were taking pictures many years ago, you might remember buying 100 ISO film for outdoor shots in the summer, and 400 ISO film for those family shots round the table at Christmas.
So, what is the difference between 100 ISO film and 400 ISO film, and what are the pros and cons of each I hear you ask.
film sensitivity
Film (negative or slide) is essentially a medium on which a chemical is applied. The chemical in question reacts to the light which is allowed through the lens, and, once developed in a laboratory (more chemical processes), stores the light that hit the film for ever (the negative, or positive for slides).
This chemical contains lots of “grains” that are responsible for receiving and storing this light, much like the pixels in today’s digital camera sensors.
In order to produce different film sensitivities, film manufacturer used different grades of “grains” in the chemicals, small ones for slow film, and large ones for fast film. This was based on the fact that the larger a grain was, the quicker it was able to absorb a given amount of light.
Traditional film sensitivities thus existed in the following range: 25, 50, 100, 200, 400, 800, 1600, 3200 and 6400 ISO.
As you can see from this list, the numbers double each time, this should be no surprise to you anymore… each increase in ISO number (from 100 to 200 for example), meant that for a given exposure, you could halve the shutter speed (e.g. 1/125s to 1/250s), or, close the aperture one stop further (F5.6 to F8).
More importantly, if your lens is limited to say F4.5 as a maximum aperture, and you are using a 210mm zoom lens for some sports photography inside a gym hall, you may not be able to correctly expose your pictures with 100 ISO film since F4.5 and 1/200s wouldn’t allow sufficient light through the lens to achieve correct exposure.
The temptation may then be to drop the shutter speed to 1/125s or 1/60s, but then, blurring would be likely, either because the subject moved too fast, or, because you couldn’t hold the long heavy lens steady enough for a clear sharp shot
The solution was then to get faster film (400 or 800 ISO), which would allow those pictures to be taken.
So, this is great isn’t it, just get faster film and there you go… well, remember, photography is about compromises, and here is another one…
Remember the larger grains in the faster film, how do you think these will translate when the picture is printed
Yup, the print won’t be quite a sharp and well defined, there is less detail in the picture, less resolution if you want, so larger prints look soft rather than crisp and clean.
And it gets even worse if you enlarge the print to A4 or more, the picture looks grainier and grainier as the film speed and print size increase.
I found the following descriptions for a few of these film sensitivities:
100 SUNLIGHT: 100 speed film is excellent color print film for sunny or bright light photo opportunities. It is good for close-ups, posed photos, and landscapes.
200 ALL-AROUND: 200 speed film is a general multipurpose film with extremely fine grain, producing soft, natural skin tones for people shots.
400 EXPANDED MULTIPURPOSE: 400 speed film is the most versatile film for compact, automatic 35mm cameras. It is great for candid snapshots and sports action. It can be used for low light or flash, outdoor or indoor.
800 FASTEST MULTIPURPOSE: 800 speed film has ultimate versatility for snapshots and fast action. It is ideal for use with zoom lenses. This film can be used for indoors, outdoors, and fast action.
But I have a digital camera, and you are talking about film, should I care about all this…
Well, you should really, your digital camera (be it a compact or SLR) sports an ISO setting which tries to replicate what was available in the good old film days, but, it does so at a potentially much greater cost than grainy pictures… Read on…
One of the disadvantages of film was that if you were taking pictures outdoors, then indoors, then outdoors, etc… you could easily find yourself with the wrong film in the camera and needed to change it, or, make do, or, carry two cameras, etc… Never mind having to make sure you had enough stock of each film with you
Problem with digital is that you are stuck with a 6, 8, 10 megapixel sensor, and to date, no one has come up with a swappable sensor, not at a reasonable price, or, practical enough for you and I do it in any case, that’s assuming that for a given sensor size, a 6MP is less sensitive to light than a 10MP one which isn’t strictly the case.
So, camera manufacturers have replaced an analogue process (grains in chemical solution) with an electronic one, and given us a range of ISO settings on our shiny digital cameras. Usually the range is 100 to 3200 these days.
How ? Well, by putting an amplifier on the CCD output, thus amplifying the signal received by the CCD and artificially increasing sensitivity… Changing ISO settings on your digital camera will not physically change the characteristics of your sensor – unlike changing film
And as always there is a catch… The higher the ISO setting you choose, the more amplification takes place, and as with any amplification, you get to the stage where distortion starts to take place. In digital photography, this is known as noise.
To prove this, try taking a picture at night, without the flash on 1600 or 3200 ISO, the picture will most probably look very grainy, possibly even show red dots in places where they shouldn’t be.
Some cameras are more or less prone to this problem though so mileage will vary depending on model and equipment.
Note: the longer the shutter speed (1s, 2s, etc…) and the more likely additional noise will creep in too, this is because the sensor is energised for such a long time that it heats up sufficiently to affect the quality of the image it captures.
So, I hope you now fully understand what these three mysterious letters mean
Lastly, let’s look at another term used by photographers, EV.
EV is a unit used to measure exposure, it stands for Exposure Value. Much like meters, inches, degrees (Fahrenheit or Celsius), etc… a base line has been established by the photography community many many years ago.
The base line is that EV 0 corresponds to an exposure of 1 second at F1.
We’ve seen previously that changing speed or aperture effectively doubles or halves the amount of light reaching the film or CCD, well, this difference is 1 EV.
Thus, every time you double exposure time, you double available light and therefore increase exposure by 1 EV.
Conversely, if you halve exposure time, you half available light therefore decreasing exposure by 1 EV or changing the exposure by -1 EV.
The same applies to aperture and changing F-stops.
Why is that important you may ask, well… should you delve into your camera’s menus, or dials, you might find references to exposure compensation and flash compensation, and these are shown in EV values.
Also, in your viewfinder, there should be an exposure scale, showing whether your current choice of speed and aperture will under or over exposure the image, again, the scale is shown in EV.
So every time we change speed or aperture settings, we halve or double the available light ? Well, no, not always…
If you remember back to the exposure lesson, I said that shutter speeds on cameras were usually 1/8s, 1/15s, 1/30s, 1/60s, 1/125s, 1/250s, 1/500s, 1/1000s, 1/2000s, 1/4000s, 1/8000/s, etc…
And, apertures were usually, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, etc…
Each change from one value to the other in the list above is indeed halving or doubling, however, you might find that your camera has speeds such as 1/750s or 1/1500s, now those don’t fit into the halving or doubling scale do they ?
The reason is that modern cameras have much more refined capabilities in terms of exposure, and, limiting yourself to 1 EV for each possible change can result in less than optimum exposure. In the old days, the electronics used for exposure were quite rudimentary and 1EV was deemed sufficient. Not so anymore
Cameras are now able to set speeds of 1/2 EV (1/750s and 1/1500s) and even 1/3 EV (1/600s and 1/800s) which explains how these strange numbers have come about.
That’s it for now, in the next lesson I hope to cover flashes and their uses in photography, but I first need to dig my camera out and take lots of example pictures for you
As usual, any questions, feel free to ask
14-08-2007, 02:25 PM
#5
Testing the future
only just seen this - great work again greg 
don't suppose you fancy a day out teaching a group of us some of these things and getting in some practical experience? i would love it and gladly pay for any expenses and a slap up meal at the end just a day around windsor would be great, plenty to take shots of there in the parks, town centre, river, castle etc
don't suppose you fancy a day out teaching a group of us some of these things and getting in some practical experience? i would love it and gladly pay for any expenses and a slap up meal at the end
just a day around windsor would be great, plenty to take shots of there in the parks, town centre, river, castle etc
14-08-2007, 05:15 PM
#7
Testing the future
excellent - when is good for you? a weekend or a weekday evening? would there be enough time in an evening before light is too low? don't think so really, so weekend is better eh?
need better weather than this though
need better weather than this though
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18-08-2007, 05:01 PM
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Originally Posted by foreigneRS
excellent - when is good for you? a weekend or a weekday evening? would there be enough time in an evening before light is too low? don't think so really, so weekend is better eh?
need better weather than this though
need better weather than this though
Can't think of when just yet, need to check with nats
18-08-2007, 05:03 PM
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Originally Posted by cossiemen
Very nice job mate, well done but ...
can you translate this into Dutch please?
can you translate this into Dutch please?
Een paar lessen geleden, bekeken wij ook blootstelling en hadden over een aantal termijnen en onderwerpen betrekking die ik beloofde om verder te verklaren. Dit is het! Deze les is allen over theorie ik bang ben, volgende zal praktischere Clin d'oeil zijn Eerst en vooral leg een termijn voor die wijd in fotografie, ISO wordt gebruikt. In de oude tijd van filmfotografie, snelheid drukte de van ISO (of ASA) van een film uit hoe de snelle of langzame negatieve of diafilm was, een andere manier om dit te bekijken is te vragen hoe gevoelig de film was. In de termen van de leek is een snelle film, één die kleine hoeveelheden licht kan zeer snel vangen, vereist een langzame film omgekeerd een langere tijd om de zelfde hoeveelheid licht te vangen. Voor die van u die beelden vele jaren namen geleden, zou u zich kunnen herinneren kopend 100 ISO film voor openluchtschoten in de zomer, en 400 ISO film voor die familieschoten om de lijst bij Kerstmis. Zo, wat het verschil tussen 100 ISO film en 400 ISO film is, en wat pros en cons. van elk zijn hoor ik u vraagt.
the rest is on http://babelfish.altavista.com/
20-08-2007, 03:54 PM
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Originally Posted by foreigneRS
frog sorry greg, was away in norway getting some pics at the gatebil meet. i'll post something up if i got anything good.
did you buy a camera then ? what is it ???
21-08-2007, 07:40 AM
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Originally Posted by foreigneRS
not a dSLR, only a Fuji finepix S6500fd. i want to learn a bit more before i spend a bit more
28-09-2007, 12:08 AM
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Originally Posted by frog
Originally Posted by cossiemen
Very nice job mate, well done but ...
can you translate this into Dutch please?
can you translate this into Dutch please?
Een paar lessen geleden, bekeken wij ook blootstelling en hadden over een aantal termijnen en onderwerpen betrekking die ik beloofde om verder te verklaren. Dit is het! Deze les is allen over theorie ik bang ben, volgende zal praktischere Clin d'oeil zijn Eerst en vooral leg een termijn voor die wijd in fotografie, ISO wordt gebruikt. In de oude tijd van filmfotografie, snelheid drukte de van ISO (of ASA) van een film uit hoe de snelle of langzame negatieve of diafilm was, een andere manier om dit te bekijken is te vragen hoe gevoelig de film was. In de termen van de leek is een snelle film, één die kleine hoeveelheden licht kan zeer snel vangen, vereist een langzame film omgekeerd een langere tijd om de zelfde hoeveelheid licht te vangen. Voor die van u die beelden vele jaren namen geleden, zou u zich kunnen herinneren kopend 100 ISO film voor openluchtschoten in de zomer, en 400 ISO film voor die familieschoten om de lijst bij Kerstmis. Zo, wat het verschil tussen 100 ISO film en 400 ISO film is, en wat pros en cons. van elk zijn hoor ik u vraagt.
the rest is on http://babelfish.altavista.com/
22-11-2007, 08:11 PM
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Photography 101 - Lesson five – Flash photography here:
https://passionford.com/forum/viewtopic.php?p=4326747
Enjoy
https://passionford.com/forum/viewtopic.php?p=4326747
Enjoy
28-11-2007, 11:10 AM
#19
..BS Motorsport..
Got to say this has been one of the most informative reads ive seen on here, seriously hats off to you for sharing this. Great way of putting things across mate roll on christmas
roll on christmas
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