There is so much duality in photography. On one hand, it’s the light and the subject, it’s the story we tell and the story the viewer sees, it’s a feeling, an emotion, a state, a symbol, a metaphor. Sounds poetic, doesn’t it? On the other hand, it’s pure science, every single bit of it – from the said light traveling through a complex lens design, all the way to the scene being imprinted whether on a piece of light-sensitive film or, temporarily, on a digital sensor. And that scientific part of photography brings all sorts of terms with it, terms that may not be necessary for the creative process, but as far as skillful execution goes, you can’t do without understanding them for very long. A painter needs to know his brushes at some point, right?
And so we are back to covering basics, something you surely must have noticed. In this article, I will talk about yet another, confusing-at-first-encounter term used in photography, more specifically – exposure stops. I will try to explain what they are and how stops of different exposure triangle parameters – shutter speed, aperture and ISO sensitivity – correlate, as well as give you examples of what are considered to be regular stop values of each parameter, and what are full, half and third-stops.
Table of Contents
Let’s Start From the Start
As most of you know, how much light or information a digital sensor or film receives during exposure to light (capture of an image) depends on three things – the shutter speed, aperture size and light sensitivity of the surface on which the image is captured. More than that, every one of these parameters is exactly as important. To make them directly comparable and to be able to compensate a change in one parameter with a change in another easily, something common had to be found between how long the light-sensitive surface is exposed to light (shutter speed), how much light is hitting the sensor at any given moment (aperture) and how sensitive the surface is to light in the first place (ISO value). A number, a measuring unit needs to be assigned. In other words, there has to be some sort of correlation between the three parameters, where a certain increase of one must equal a certain decrease of another in order to preserve the same overall exposure or brightness of the photograph captured.
Now, I say “needs to be found”, but it’s really quite obvious. You see, if you expose a piece of film of a certain sensitivity through an aperture of a certain diameter for, say, one second, and then expose another piece of the film under the same circumstances of the same sensitivity through the same aperture diameter for two seconds, the second piece of film will receive twice more light, simply because it was exposed to light two times as long. Likewise, if you expose two identical pieces of the film under the same lighting conditions for one second, but use a twice-as-big aperture (area-wise) for one of the pieces, that piece is, again, going to be twice as bright as the first one. Finally, if you expose two pieces of film through the same aperture for one second under equal lighting conditions, but with one piece of film being twice as sensitive to light as the other, the more sensitive piece of film will contain an image that is – you guessed it – twice brighter.
Have you noticed a pattern? Increasing any one of the parameters twice increases the amount of light hitting the surface twice (and, although technically changing sensitivity does not change the actual amount of light hitting the surface, it still has pretty much the same effect on exposure). And it doesn’t matter which parameters you change for the two pieces of film, too – increasing the size of the aperture twice for one piece of film is the same as exposing another piece of film for two times as long, and the resulting exposure of the image, all else being equal, will be the same. It’s not like compensating for a 2x increase in exposure time requires a 7.4-or-any-random-number times smaller aperture, correct?
That is the correlation we are looking for and a clear answer to what exposure stops are. So, a stop is two times the increase or decrease of light gathered during exposure. Adjusting any one of the three exposure parameters by one stop results either in twice more or twice less light captured. As such, a stop is a very convenient way of relating three different parameters that have different measurement units assigned to them by emphasizing not the measuring units, but the effect on exposure.
Making Sense of Numeric Values
Now that we know what a stop is in theory, it’s time to get acquainted with the numeric values and learn to compensate for a change in one parameter with a change in another.
Aperture Stops
To those of you who are yet unfamiliar with the definition of aperture or f-stop, in photography, reading our article on the subject is the very first step to take before continuing. Simply put, the aperture is the opening that the light goes through before reaching the sensor or film. The size of the aperture (its diameter) is controlled with diaphragm blades. The lower the numeric f-stop value, the larger the aperture, and the more light goes through at any given moment and vice versa.
Aperture size is defined by the so-called f-stops (as I’ve already mentioned, the lower the f-stop number, the larger the aperture opening). Now, the physical size of the aperture depends on the focal length of the lens as well as the actual f-stop, but for the purposes of this article that is largely irrelevant. What is important is that, in order to double the amount of light coming through, the area of the opening and not the diameter must be doubled. That is why calculating numeric aperture stop values is a tiny bit more difficult than that of shutter speed or ISO sensitivity, as you will see, and memorizing the numbers is perhaps more practical (if, arguably, unnecessary in most cases). Just as with shutter speed and ISO, there are certain f-stop values that are considered to be “default”, “round” or “standard”. Here is an illustration showcasing standard full-stop, half-stop, and third-stop values as well as a graphical representation of the size of the opening itself:
The illustration shows standard full-stop apertures values ranging from a very-large f/1.4 to really-rather-tiny f/32, with f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16 and f/22 in-between the two values. In total, the diagram spans the range of 10 full stops, but that does not mean that is all the stops you get. One stop wider than f/1.4 is f/1, go further than that and you will reach f/0.7, which is extremely large. Lenses with such parameters are extremely rare and exotic, however, so including them in the illustration really is not necessary. The same goes for the other end of the scale where aperture size gets smaller – f/44 or f/64 (not to mention even smaller apertures) are hardly ever applicable in today’s photography and there are few lenses that even allow such a setting (those that do are mostly designed for medium or large format film cameras).
Given that a difference of one-stop results in twice more or less light going through, calculating the difference in the amount of light going through between the two extremes of the scale is quite simple – f/1.4 opening lets in twice more light than f/2, eight times more light than f/4 and 512 times more light than f/32, at any given moment. Yes, that is a lot.
Shutter Speed Stops
I will not go into too much detail when talking about shutter speed and what it is, exactly – we already have a great article for that purpose and if you are yet unfamiliar with the term, I recommend you read it before continuing. In short, shutter speed defines the period of time during which light is allowed to go through the optical element (the lens) onto the light-sensitive surface (a digital sensor or a piece of film). Think of a beautiful mansion with a fence and a gate where a party is hosted: the sensor or film is the mansion itself, the light – guests flooding through the gate into the mansion, aperture – the width of the road leading to the gate while shutter speed is how long the gate remains open and allows the guests through so as to enough guests attend, but the place does not become overcrowded.
As you would imagine, shutter speed is measured in seconds or, rather more often, in fractions of a second. Much like with aperture, there are standard full-stops, half-stops, and third-stops. Here is an illustration showing a shutter speed range of 10 stops with values from one second all the way to 1/500th of a second:
Notice how the first shutter speed marking of the scale has a quotation mark – 1“. The quotation mark means that the marked shutter speed is in seconds and not fractions. It is necessary for distinguishing purposes because fractions are not marked as fractions – so the 250 stop is actually a shutter speed of 1/250th of a second. All this has been done purely for convenience.
It is also important to understand that, with today’s digital photography, the shutter speed scale is much larger than the ten stops shown in the illustration – photographers often use speeds as low as 30″ (seconds), which is 5 stops slower than 1″ shutter speed that I started with; and as high as 8000 (fraction of a second), which is another 4 stops higher than 500 shown in the graph. Certain cameras can go higher still. In other words, the range of practical shutter speed stops is much wider than that of aperture. Also notice that calculating stops is much easier with shutter speeds than it is with aperture – you just have to multiply or divide the number by two to get the value of the next or previous stop.
ISO Sensitivity Stops
Finally, we get to the last exposure parameter, and its stops. As with the other two parameters, we have a comprehensive article on the subject – there is a lot to know about ISO sensitivity. In this article, however, we are talking about exposure stops, so going too in-depth is not necessary. For our purposes, the following explanation is quite enough (but I do suggest you read that article if you want to learn more) – ISO is the level of sensitivity of your camera sensor (or film) to available light. The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. The component within your camera that can change sensitivity is called “image sensor” or simply “sensor”. It is the most important (and most expensive) part of a camera and it is responsible for gathering light and transforming it into an image. With increased sensitivity, your camera sensor can capture images in low-light environments without having to use a flash. But higher sensitivity comes at an expense – it adds grain or “noise” to the pictures.
Ever sensor has a “base” ISO – a value when it does not need to increase or decrease its sensitivity to light. Some cameras start at ISO 200, like older Nikon models and current Fujifilm mirrorless cameras. Others start at (arguably more preferable) ISO 100, and that is where our ISO sensitivity stops illustration starts:
As with shutter speed stops, calculating ISO sensitivity stops is very easy – one just needs to divide or multiply the value by 2 to add a stop or go one stop down. The standard stops are also very easy to memorize. While most modern cameras can go lower than ISO 100 or higher than 51,200, because of the limitations that are imposed when increasing sensitivity too much, the illustration shows the most useful and usable ISO stops with the last two or three highest full-stop values bordering on hardly-ever-used for most photographers.
As with the previous two illustrations, this one also shows half- and third-stop values. I’ve not talked about them yet for one reason – there is a caveat.
Standardization
If you take a look at one of the illustrations again, but focus this time not on the full-stop values, but rather on half-stops and third-stops, you will probably notice that the scale contains some inconsistencies. For example, the half-stop between f/11 and f/16 is f/13, but then the first third-stop is also defined as f/13. How could it be, if a third is less than a half? Shouldn’t the value be less, too? Well, theoretically, yes. But from a practical standpoint, manufacturers chose differently.
You see, only the full-stops are completely standardized and manufacturers are doing their best to stick to such full-stop values, be it the ones you see in the aperture, shutter speed or ISO sensitivity illustrations. But for third- and half-stops, some rounding up was unavoidable. More than that, different camera manufacturers choose to round up differently, too. For example, the first third stop between f/5.6 and f/8 on my Nikon D700 is specified as f/6.3, as shown in the illustration, but my Fujifilm specifies f/6.4 instead. In this particular case, the margin of error appears because, mathematically, you need to multiply an f-stop value by the square root of 2 to add a stop to it, and square root of 2 is not a round number (1.414 is just the start). So, theoretically, the third stop between f/11 and f/16 should actually be marginally less than f/13, while half-stop should be marginally more. For convenience, manufacturers round up the values, and so the marked values are the actual values used during exposure. In practice, this is hardly relevant. Bottom line is, third- and half-stops may appear differently in your camera than in these illustrations. That is perfectly normal.
Compensating One Parameter Change With Another
All three of the parameters have exactly the same effect on exposure. Increasing either one by one stop will let in twice more light to the sensor (not strictly true with ISO sensitivity, but you get my meaning), while decreasing will have an opposite effect. This also means that an increase of one parameter by a stop can be compensated by decreasing another by the same stop, or two others by half-stop each. So, for example, if you are doing some sports photography and coming up with slightly blurry images while your current settings read f/5.6, 1/250, ISO 400, you need to speed up the shutter to capture quick motion more crisply, but keep the overall exposure the same. What’s the best way to do it? Provided that the lens allows this in the first place, opening up the aperture by one stop to f/4 and bumping up the ISO value by another stop to ISO 800 will let result in four times more light coming in, which in turn gives you two full stops to compensate with shutter speed and normalize the exposure of the image. So by opening up the aperture by a stop, increasing sensitivity by a stop, and increasing the shutter speed by two stops as a result of that, you end up with f/4, 1/1000, ISO 800, sharply captured images and correct exposure, at the expense of a slight increase in noise and slightly shallower depth of field. There is always some trade-off, but it’s not always a meaningful one.
From Theory to Practice
Now that we have the whole theory before our eyes, time to do some basic experiments to see if it really does work that way. Coming up with unpretentious photographs for illustrative purposes proved to be simple – I found an immeasurably cool, green and old Land Rover Defender to show what a roughly two-thirds of a stop and over one stop of difference in shutter speed does to exposure, and some archways to help me out with compensating a change in one setting with another. Let’s start with the latter.
The following image was taken at f/1.4, 1/800, ISO 200:
Here is how it compares to the same scene (don’t mind the slight framing changes, I shot hand-held) captured at f/2, 1/800, ISO 400:
As you can see, after compensating a one-stop increase in ISO sensitivity with one-stop decrease in aperture size, the overall exposure (or brightness) of the photograph remained exactly the same. Even though closing down the aperture by a stop ensured twice less light was making its way onto the sensor, a one-stop increase in sensitivity did the exact opposite. Now, let’s make a comparison with shutter speed change:
The before image was captured at f/1.4, 1/800, ISO 200, while the after image was captured at f/1.4, 1/1600, ISO 400. Again, compensating a one-stop faster shutter speed with a one-stop increase in ISO sensitivity proved to render the exact same exposure.
It is important to understand that, in practice, photographers (and the cameras, too) rarely stick to full stops. It is not too likely that the correct exposure for a particular scene will require standard full-stop values from every parameter, is it? And so the sample images that you will see now will showcase larger or smaller adjustments than a full-stop.
A side note: I took these sample images without using a tripod. Any weird perspective changes you might notice are a side-result of using Photoshop’s Layer Align tool.
The following photograph is what I (and the Fujifilm X-E2) consider to be well-exposed:
X-E2 + XF23mmF1.4 R @ 23mm, ISO 400, 1/680, f/1.4[/caption] X-E2 + XF23mmF1.4 R @ 23mm, ISO 400, 1/680, f/1.4[/caption]
Now let’s see what a shutter speed change from 1/680 to 1/1700 (roughly 1.3 stops of difference) does to the brightness:
The difference is significant – the sensor definitely received over two times less light due to the shutter being open for a much shorter period of time. Now let’s see what happens if we decrease the shutter speed by two-thirds a stop instead – from 1/680 to 1/420:
The difference is, again, clearly noticeable, although nowhere near as prominent as before. Still, this proves that even two thirds of a stop is a lot. What it also proves is that “correct” exposure is very subjective – one could prefer any of the three images in terms of exposure.
Namasthe,
A useful article with matching example.
Thanking you.
Namasthe.
22-09-20
Hello I am a beginner in photography , I find this article helpful and confusing as well. The examples which you gave above with full f stop completely makes sense theoretically however I tried following the full f stop concept practically on field but that didn’t make sense even though I did the math as per full f stop and compensated , I didn’t get the correct exposure :. please tell me how professional photographers click such amazing pics and does following full stop concet gives you correct exposure. Is there any specific rules to follow to get good picture or its just trial and error method trying different combination on camera and then editing in light room? please help me with this
Thanks for the article. I didn’t know wich were the full “F” stops, and now I know them.
Romanas, as a relatively new photographer with a very solid technical foundation I found your article to be a perfect compromise between sticking strictly to the technical facts, and giving us just enough of them to have us understand what we are doing. Although I was able to understand and follow most of the nitpicking in the comments that followed the article, they did not really add anything to what I gained from your explanation. Thank you for a well written and comprehensive article!
Thank you for helping us beginners!
Another great article Romanas!
It’s nice because it doesn’t get all technical, it gets to the point without confusion and boredom setting in. it is exactly what is needed to teach beginners about the subject! This is the kind of thing that will help people to move from using the auto settings on the camera to having much more control.
Regards,
Daniel
Daniel, since you mentioned it, that’s sort of my goal with these beginner series. I have my mind set on a few more articles such as this :)
What Model is that Defender Romanas? I mean do you know what year this model came out?
As soon as I left, I regretted not taking a closer look – the engine, trim, anything would have given me an idea, but I really can’t say. It definitely was not one of the oldest models. An honest thing, isn’t it? :)
Yes. It sure is beautiful. Maybe you should photograph old cars and vehicles from time to time. The front is the cutest part of this beast
I’ve seen a few such cars in Vilnius. There is an old Alfa Spider, found it where I least expected to. And an old SL Merc, I believe. Then I came across this Defender. I also saw a beautiful XJ. Overall, though, it is a rare catch. Very rare.
Romanas,
A very good explanation at the beginner level. Two additional points that I have always included when explaining this concept to beginners came from questions from students. First is that the peculiar numbers we use to describe aperture come from the need to include the focal length of the lens into the formula that produces the number. Doing this results in the f-stop number applying to any lens, no matter what the focal length or the physical size of the film/sensor. Given the same length of exposure and the same sensitivity of film, f4 will always produce an image of the same brightness no matter what camera or what lens is used. The second point is the origin of using the word ‘stop’ to measure aperture size and shutter speed. This comes from the design of older fully manual cameras where the dials that controlled the aperture and the shutter has physical detents, or stops, to control the settings. A perhaps more modern term is EV (Exposure Value) i.e. one stop equals one EV.
Donald,
thank you for the input. I did not even think about the origin of the word “stop”, but it makes perfect sense. And I do prefer it to EV, sentimental as I am. :)
Donald,
It definitely does matter what camera or what lens is used. Given the same length of exposure and the same sensitivity of film, f/4 will NOT always produce an image of the same brightness.
Be careful in speaking with such absolutes.
Ultracrepidarian,
would you like to elaborate a little bit?
Gladly! If you compare two cameras with identical settings for shutter, aperture and ISO, the exposures will vary for a number of reasons. Truth be told, though, ISO doesn’t even belong in the conversation with exposure since it has no effect on exposure.
In any event, the first reason is the actual transmission of light for a given lens at a certain f-stop differs from lens to lens (see T-stop). Next is that lens manufacturers round to the nearest stop when stating aperture, which may not be the same from lens to lens. Third, and most typically, the accuracy of ISO varies from manufacturer to manufacturer. ISO 800 on one camera may give the same exposure as ISO 640 on another, all else being equal.
As I stated before, it’s important not to speak in absolutes and oversimplifications.
All of what you said makes a certain amount of sense, of course. And yet at the same time perhaps you are digging a little too deep trying to find faults in the statement which, in essence, is correct – Donald was talking not about differences in sensor technology, light transmittance, t-stop and so on, which we should assume to be exactly the same, but rather difference in sensor size and whether we can and should use an f/4 APS-C lens on APS-C sensor the same way we would use an f/4 full-frame lens on full-frame sensor when it comes to exposure. But if you want to dig that deep, I can rephrase his words – given the same sensor technology, same light transmittance and other factors being equal, so long as the sensor size used with the lens is not larger than the one supported by the lens, exposure at the same shutter speed, ISO sensitivity and aperture will lead to the same brightness of the image regardless of the sensor format used.
As for the ISO playing a part in exposure, it certainly does. Exposure in photography is not only the light that goes through a lens and the shutter, it is also how the light is received. It’s called exposure triangle for a reason. Otherwise, we would not even have such a parameter.
It certainly does not! The so-called Exposure Triangle is a holdover from film days when variations in ASA/ISO definitely had an effect on exposure. However, with digital, this is no longer the case. With digital, only three factors have a bearing on exposure:
– Scene luminance
– Shutter speed
– Aperture
As stated previously, ISO in digital (stop thinking film) comes into play only AFTER the image sensor has been exposed to light.
Look, I know this flies in the face of conventional wisdom and longstanding teachings, but it is based on fact – not conjecture or popular opinion. We have to stop thinking film exposure and digital exposure are the same. They are not, and our teachings need to reflect that.
Ulltracrepidarian, it makes total sense to explain exposure in traditional way with ISO, Aperture and Shutter Speed. I have never seen anyone teach exposure with Scene Luminance instead of ISO (as being film ISO / sensitivity to light), because it is hard to explain and understand for a beginner. On top of that, given that many photographers shoot with digital and perhaps might want to experiment with film at some point, thinking of ISO as sensitivity makes perfect sense. Why should one think of ISO one way with film and a totally different way with digital? The whole point of ISO was to keep digital simple for film shooters to transition to. Manufacturers knew very well that ISO does not change the sensitivity of the sensor and yet ALL of them choose to show it the same way. If you look at any tutorial by Nikon, Canon or any other manufacturer, ISO is always explained the same way, similar to what Romanas has done in this article. I do not see the point in trying to change all that…only confuses people more.
Maybe this will help
www.clarkvision.com/articles/iso/
Ulltracrepidarian, why is it so important to you to knock out ISO from ‘exposure thinking’ in digital when the effect of using it is similar to what you had in film (including graininess despite how it originates in both), even though ISO in digital is surely post-exposure process? Perhaps you could make a bigger deal out of it if you had control over ISO in RAW file, but you do not, and ISO is applied during overall capture (after exposure before RAW file is created)! I totally agree with Romanas and Nasim, explaining such details is only confusing for beginners and to be honest not even practically useful for advanced photographers.
It has a bearing on how you post-process, as explained in this article: www.digitalphotopro.com/gear/…an-you-go/
Whether one thinks of ISO as an integral part of exposure or post-exposure process have nothing to do with how one does post-process!
That’s not why they’re called “stops.” There were no dials with physical detents. Instead, there were interchangeable diaphragms, called Waterhouse Stops, which were plates with different size holes drilled hole in the center. These plates stopped a certain amount of light from entering, which is where the name “stop” came from. Lens makers provided slots in lens barrels for the insertion of the chosen stop. This type was known as an “aperture stop.” There were also “field stops,” akin to lens hoods, which stopped stray light from causing things such as lens flares.
There is a factual error in this article regarding ISO. A sensor does not and cannot change its sensitivity to light. There is no setting whatsoever on a digital camera, including ISO, that can modify a sensor’s sensitivity to light. ISO in digital is a level of post-capture analog amplification that occurs. In other words, exposure has already taken place before amplification of data, i.e. ISO, is applied. This amplification of the analog signal simply modifies the brightness of the exposure. While various films had different sensitivities to light, a digital sensor has one – and only one – sensitivity to light.
If I recorded sound and amplified the sound after the recording took place, I’ve done nothing to modify the sound level as it was being recorded, nor did I do anything to alter the microphone’s sensitivity to sound. Amplification takes place after the recording, just as ISO setting is applied after recording, i.e. exposure.
PodViewer, you are absolutely correct about this. However, my experience teaching beginners for the past few years has shown me that it is much easier to understand ISO when one thinks of it as “sensitivity” – it makes much more sense than amplification. I received similar feedback on my “What is ISO?” article from some people, but if you look at the comments in that article, a lot of people are thanking me for it, because they finally understood what ISO meant.
We will write an article someday about how ISO works in digital cameras with factual data (for advanced photographers), but for now, these are articles for beginners that are designed to be easy to understand :)
Hi Nasim, thank you for the reply. I can certainly understand the need to clarify potentially complex topics, but not at the expense of using false statements. Given the choice, using analogies (such as the one of recording sound) would be much more preferable than using falsehoods. Doing so goes much further in getting the point across. When a beginner becomes more advanced, how will we ever be able to teach correct concepts when they’ve only been taught mostly false ones?
On the other hand, it also might have been better to preface the concept of ISO in this article with something like “…it’s as if you were able to change the sensor’s sensitivity to light,” rather than “…it changes the the sensor’s sensitivity to light.”
I think you are being too pedantic here. The result of the amplification of the signal is to increase the sensitivity of the camera to light. Yes? Simplifying that to referring to the sensor is just a simple way of comparing it to the sensitivity of film. It is no more a false statement than “the diameter of the aperture is determined by dividing the focal length by the f-stop”, which is the common understanding. It is of course not factual. The aperture diameter that is used to determine the f-stop is a theoretical one based on the diaphragm being located at the front element of the lens. When this system of standardizing measurements was devised that was, indeed, where the diaphragm/aperture was. This theoretical aperture diameter is retained to allow lens designers to place the diaphragm anywhere they want in the lens barrel without messing up the calculations. So the actual aperture diameter in a 300mm lens at f2.8 is not 107mm (4.2 in) as the arithmetic would indicate, but something less depending on where in the lens barrel the designer elected to put the diaphragm.
OK, let’s put the name calling aside for a moment. My point was NOT to explain complex topics using technical, esoteric terms. Rather, my point was that, given the choice, there are better ways than using incorrect statements. That’s hardly being pedantic.
Nasim, is there theoretically the possibility to perform two or more amplifications of the same signal? As in duplicate the signal and perform one amplification at ISO 800 while keeping the second Version at ISO 100?
I’m sure it is technically not possible (or too difficult with current technology) but it would greatly enhance a cameras DR if someone was able to pull it off.
OK, if we are being picky…The sensitivity of the CCD/CMOS sensor is best described by its detective quantum efficiency, which depends on exposure value and reaches the limit of quantum efficiency at higher exposures (due to less signal-to-noise). So in principle, this inherent property of digital sensors means that their actual sensitivity is not fixed and will depend on different amounts of light captured. This of course does not have anything to do with ISO and, yes, ISO setting does not change sensor’s sensitivity to light. As you said, ISO is simply an analogue gain applied electrically by an amplifier circuit. These amplifications (different ISOs) are applied after exposure and simply result in more electric current generated from the same number of photoelectrons originally knocked out by light striking the sensor during the exposure. After this, the signal is digitized in camera and then digital gain can also be applied. Importantly, however, this post-exposure ISO processes cannot be mistaken with post-processing that you may do on a computer. In other words ISO is an integral part of the capture after which camera spits out first usable image – RAW file (after all you cannot access and change the ISO setting in post-processing in RAW file).
Yes, film is different because higher speed films can indeed capture more light during exposure (digital sensors with higher ISO cannot). Interestingly, however, the process of obtaining first useful image in film stretches from film exposure to its subsequent development into negative (first usable, i.e. visible image, kind of RAW equivalent in digital). Development of latent image to negative is nothing else as amplification where you use ‘chemical’ electrons (rather than photoelectrons) to faster reduce silver ions in emulsion. And so in film you also take advantage of post-exposure amplification process because you develop latent image into negative. So the speed of film is actually determined not only by bigger silver halide crystals in emulsion (directly lowering the amount of light needed during the exposure) but also by development to negative.
And now that we’ve established all that, how is this actually relevant to photographers? :) Exactly, it’s not. So while technically sensors can’t “bump” their sensitivity, I suggest we don’t get that technical and look at certain things a bit more simply. Mind, I am simply amazed to find we have such knowledgeable readers. I should really just keep quiet!
Spot on Romanas! Often you give camera to person with passion for art who does not know anything about how the ‘box’ works just to see way better photographs (taken using auto and scene modes) than from a technical guy who will think and think and think until the moment is gone…:)
So very true!
To not mislead anyone, in the first bracket above there should be ‘thanks to decreasing noise or increasing signal-to-noise ratio’…
Hi Romanas
From what I always learnt any f-stop such as F1.4 means that the opening of the lens is of a diameter equal to : (lens dia) / (Fstop value) for instance a 50 mm lens F1.4 the blades gives a dia of 50/1.4 = 35.714 mm when the aperture is set to F1.4, at F16 the diameter of the blades is 3.125 mm
regards
Luc, please see my comment above – the article is for beginners, which is why some terms are over-simplified. Roman wrote “Now, the physical size of the aperture depends on the focal length of the lens as well as the actual f-stop, but for the purposes of this article that is largely irrelevant”, which is correct and the same thing you pointed out.