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A moderately Technical Discussion about f stops.


Henricvs

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I'm sure all of this makes it crystal clear to a beginner exactly what the effect on the picture is if they change the aperture number from 2 to 8.

 

Getting bogged down in theory and technical nitty-gritty is the enemy of making good pictures. Nobody needs to know the area of the aperture 'hole' to apply f-numbers practically. The numbers are what they are, and could just as easily be marked 1, 2, 4, 8, 16 etc. like they are on some old enlarging lenses.

 

The point is to make the association of a particular number with its visual effect, and secondarily how it affects the exposure. And nobody needs to know how the numbers were arrived at to do that.

 

They just need to know that f/4 lets in twice as much light as f/5.6, and that f/2.8 lets in twice as much light again. A simple relationship like - 'If you make the aperture number bigger by a step, you need to make the shutter speed smaller by a step' is about all that's needed. Apart from by the terminally curious.

 

We're not living in the stone age. We can (mostly) leave the tedious calculations to the camera now, and concentrate on the important bit of what's in front of the camera and seen through the viewfinder.

 

@ Rodeo_Joe --

Does knowing the technical stuff make you a better photographer? Maybe not but it doesn’t hurt. Knowing the technical stuff brought fame and riches to Ansel Adams. Possibility a kid with a camera phone will win the Pulitzer Prize by just being there and taking a praiseworthy picture. In-between is the casual photographer and the professional photographer. Some pros just naturally get it. Some pros get it by osmosis. Some pros study for years to get it. As for me, never famous but 55+ years of being well employed and enjoying every minute.

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@ Rodeo_Joe --

Does knowing the technical stuff make you a better photographer? Maybe not but it doesn’t hurt. Knowing the technical stuff brought fame and riches to Ansel Adams. Possibility a kid with a camera phone will win the Pulitzer Prize by just being there and taking a praiseworthy picture. In-between is the casual photographer and the professional photographer. Some pros just naturally get it. Some pros get it by osmosis. Some pros study for years to get it. As for me, never famous but 55+ years of being well employed and enjoying every minute.

I enjoy learning new things and understanding how and why on just about all my interests, including photography. I'm a slow learner, but I never give up.

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Area varies as the square of the linear measure. Even engineers sometimes forget that.

 

"This 4 inch diameter water line is plugged. I will use two 2 inch lines to bypass it." Sorry that will provide for only 1/2 the flow. You would need four 2 inch lines to bypass and get the same area and flow as the 4 inch line.

 

4^2 = 16

 

2^2 = 4

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James G. Dainis
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Yes, I see. Okay, that is helpful. Thanks.

 

Do the math (its easy).

 

Pick a focal length. It really doesn't matter. Let's say 50mm.

 

Calculate the area of the circle formed by the iris at f/1.4. A = ((50/1.412)/2)**2 * pi (the answer is 984 mm**2)

 

Now calculate the area of the iris at f/2 A = ((50/2)/2)**2 * pi (the answer is 490 mm**2), or half the area of the circle at f/1.4.

 

So, an aperture of f/2 admits exactly half the light per unit of time that an aperture of f/1.4 does. Conversely, f/1.4 admits twice the light that f/2 does.

 

It is left as an exercise for the interested student to perform similar calculations for f/2.8, f/4, f/5.6, f/8 and so on. You will find that, at each step, the area is half (allowing for rounding) the area of the previous step.

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Knowing the technical stuff brought fame and riches to Ansel Adams.

 

- And that's why he thought that Zone VIII - described as white with detail, which could realistically have no more than 100% Lambertian reflectance - was 3 stops more than Zone V, which is firmly stated as having 18% reflectance?

 

By my calculation 3 stops (8x) more than 18% = an improbably high 144% reflectance.

 

So much for Ansel's technical prowess.

 

What brought him fame and riches was his eye for a good landscape composition, being an excellent printer, and all the books he wrote off the back of it.

 

I'm sure that trying to follow the Zone system has led to far more wrong exposures than right ones, and only B&W film latitude has saved the wrong 'uns.

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- And that's why he thought that Zone VIII - described as white with detail, which could realistically have no more than 100% Lambertian reflectance - was 3 stops more than Zone V, which is firmly stated as having 18% reflectance?

 

By my calculation 3 stops (8x) more than 18% = an improbably high 144% reflectance.

 

So much for Ansel's technical prowess.

 

What brought him fame and riches was his eye for a good landscape composition, being an excellent printer, and all the books he wrote off the back of it.

 

I'm sure that trying to follow the Zone system has led to far more wrong exposures than right ones, and only B&W film latitude has saved the wrong 'uns.

 

[uSER=2403817]@rodeo_joe|1[/uSER] -----

 

Actually an 18% gray card expressed as a decimal fraction = 0.18.

This is because percent means per 100.

Thus the math

Double 18% = 0.18 X 2 = 0.36 = 36% (a 2X change = 2 f-stops delta (4X)

Double again 0.36 X 2 = 0.72 = 72% (another 2x change = 3 f-stops delta (8X)

 

Perhaps Ansel Adams and is partner Fred Archer nailed the zone system they conceived in 1930. The 18% gray target became the de facto calibration point for most all light measuring instruments. A tip of the hat to the men who provided a bridge between the science of sensitometry (film measurement) and exposure determination.

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[uSER=2403817]@rodeo_joe|1[/uSER] -----

 

Actually an 18% gray card expressed as a decimal fraction = 0.18.

This is because percent means per 100.

Thus the math

Double 18% = 0.18 X 2 = 0.36 = 36% (a 2X change = 2 f-stops delta (4X)

Double again 0.36 X 2 = 0.72 = 72% (another 2x change = 3 f-stops delta (8X)

 

Perhaps Ansel Adams and is partner Fred Archer nailed the zone system they conceived in 1930. The 18% gray target became the de facto calibration point for most all light measuring instruments. A tip of the hat to the men who provided a bridge between the science of sensitometry (film measurement) and exposure determination.

 

He actually gave Zone VII 3 stops more exposure than Zone V but the resulting negative density is only about 1.8 stops denser or in other word 0.54 density more. So it's still well within the film dynamic range.

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He actually gave Zone VII 3 stops more exposure than Zone V but the resulting negative density is only about 1.8 stops denser or in other word 0.54 density more. So it's still well within the film dynamic range.

@BeBu Lamar -- You are spot on. The slope or gamma of pictorial film is 0.8. In other words, if it were 1, the slope angle would be 45 degrees and you would get full value for each f-stop change. A gamma of 1 has proven to be too contrastry so pictorial films have on average a slope angle reduced to about 36 degrees which works out to be 0.8. Thus for each 1 f-stop change you only get 0.24 density units not the 0.30 density units if the film had a gamma of 1.0

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@BeBu Lamar -- You are spot on. The slope or gamma of pictorial film is 0.8. In other words, if it were 1, the slope angle would be 45 degrees and you would get full value for each f-stop change. A gamma of 1 has proven to be too contrastry so pictorial films have on average a slope angle reduced to about 36 degrees which works out to be 0.8. Thus for each 1 f-stop change you only get 0.24 density units not the 0.30 density units if the film had a gamma of 1.0

 

There is an article in wikipedia that says that negative fiims have gamma less than one, and reversal films more than one.

 

For negative films, besides the reasons you say, less than one give more exposure latitude that you can undo

with appropriate gamma in printing. Lower gamma makes film exposure easier, but printing harder.

 

But for slides, there is no printing step, so it has to have the appropriate gamma in the first place.

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-- glen

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@ Bebu & Alan.

Read Ansel Adams' books!

It's quite clear from the technical sections that each zone is equated to exactly one stop difference in exposure. This is quite obviously shown on the H&D graphs that he had John Sexton produce.

 

It doesn't matter how you express the reflectance of a surface; as a decimal or as a percentage. Multiplying 18% or 0.18 by 8 still gives you 144% or 1.44, either of which is way above the reflectance of fresh snow, a whitewashed wall, a fluffy white cloud, or any other matt white surface you care to name. In short Zone VIII is overestimated by one half stop.

 

The density produced on film is irrelevant to the metering and exposure process, and as is also clear to anyone familiar with the zone system, is regulated by the development time. That's the whole point of the zone system. Or it would be if based on accurate data.

 

However, if the zones as described aren't actually one stop apart - and they're not - then it puts a big question mark over the whole over-complicated procedure.

 

The error is easily tested by using a digital camera these days. Applying +2.5 stops compensation to an exposure reading taken from an 18% grey card takes it to white, and just short of overexposure. While 3 stops compensation induces overexposure 'blinkies'.

Conversely, metering from a matt white surface and applying -2.5 stops compensation renders the surface as 18% grey.

 

My theory is that Adams' background as a concert-standard pianist puts everything in perspective: That the zone system has a parallel in music notation, and is just as arcane and illogical to other than its initiates.

 

If you think of Zone V as 'middle C' then Zone VIII is equal to note F, which is only 2 tones and a semitone up. Not 3 whole tones.

 

I suspect Adams' was confusing musical notes with zones, and just failed to mentally scribble in the sharps and flats.

 

"There is an article in wikipedia that says that negative fiims have gamma less than one, and reversal films more than one."

 

Wikipedia is correct, but that has absolutely nothing to do with exposure determination. Non-sequiter arguments that distract from Adams' blatant error just don't wash I'm afraid!

Edited by rodeo_joe|1
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Does knowing the technical stuff make you a better photographer? Maybe not but it doesn’t hurt

I certainly don’t think it has to hurt, but I do think it can hurt. For some, these technical discussions can supplement and support an artistic vision. For some, concentration on technique can very well overwhelm or substitute for it. I think Adams was a master technician and printer and gave a lot to photography and photographers. I think he was less an artist. Whether his love for printing and photographic techniques took away from more creative visual potential, I do not know, but I don’t think the two went hand in hand for him.

There’s always something new under the sun.
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I certainly don’t think it has to hurt, but I do think it can hurt. For some, these technical discussions can supplement and support an artistic vision. For some, concentration on technique can very well overwhelm or substitute for it. I think Adams was a master technician and printer and gave a lot to photography and photographers. I think he was less an artist. Whether his love for printing and photographic techniques took away from more creative visual potential, I do not know, but I don’t think the two went hand in hand for him.

@ The Shadow --

 

Ansel Adams and his cohorts lived and worked in an era void of camera automation. The hand-held electric light meter had just emerged. They chose to use giant cameras because film and enlargement techniques were not up to snuff. The point is, getting the exposure “right” was paramount. They needed to acquire the technical stuff -- otherwise they used trial-and-error. 21st century photographers can concentrate on composition, ignoring the technical, it’s OK if you let the camera do the thinking.

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I take a gray card reading and it reads 1/500 - f/16 which is Zone V.

I take a shot at 1/250 - f/16 and that is one stop more or Zone VI.

I take another shot at 1/125 - f/16 and that is another stop more or Zone VII.

I take another shot at 1/60 - f/16 and that is another stop more or Zone VIII.

 

Going from Zone V to Zone VIII is a three stop difference. Ansel is quite clear about this in his book, The Negative.-

 

..."we define the one-stop exposure change as a change of one zone on the exposure scale, and the resulting gray in the print is considered one value higher or lower on the print scale."

As far as I can tell, 99% of his references to exposure/Zones is given as direct exposure stops not sensitivity readings.

James G. Dainis
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@ Bebu & Alan.

Read Ansel Adams' books!

It's quite clear from the technical sections that each zone is equated to exactly one stop difference in exposure. This is quite obviously shown on the H&D graphs that he had John Sexton produce.

 

It doesn't matter how you express the reflectance of a surface; as a decimal or as a percentage. Multiplying 18% or 0.18 by 8 still gives you 144% or 1.44, either of which is way above the reflectance of fresh snow, a whitewashed wall, a fluffy white cloud, or any other matt white surface you care to name. In short Zone VIII is overestimated by one half stop.

 

The density produced on film is irrelevant to the metering and exposure process, and as is also clear to anyone familiar with the zone system, is regulated by the development time. That's the whole point of the zone system. Or it would be if based on accurate data.

 

However, if the zones as described aren't actually one stop apart - and they're not - then it puts a big question mark over the whole over-complicated procedure.

 

The error is easily tested by using a digital camera these days. Applying +2.5 stops compensation to an exposure reading taken from an 18% grey card takes it to white, and just short of overexposure. While 3 stops compensation induces overexposure 'blinkies'.

Conversely, metering from a matt white surface and applying -2.5 stops compensation renders the surface as 18% grey.

 

My theory is that Adams' background as a concert-standard pianist puts everything in perspective: That the zone system has a parallel in music notation, and is just as arcane and illogical to other than its initiates.

 

If you think of Zone V as 'middle C' then Zone VIII is equal to note F, which is only 2 tones and a semitone up. Not 3 whole tones.

 

I suspect Adams' was confusing musical notes with zones, and just failed to mentally scribble in the sharps and flats.

 

"There is an article in wikipedia that says that negative fiims have gamma less than one, and reversal films more than one."

 

Wikipedia is correct, but that has absolutely nothing to do with exposure determination. Non-sequiter arguments that distract from Adams' blatant error just don't wash I'm afraid!

 

I will give you full explanation after I reread the books. But I know Adams didn't care for subject reflectance only his prints.

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Ansel Adams and his cohorts lived and worked in an era void of camera automation. The hand-held electric light meter had just emerged. They chose to use giant cameras because film and enlargement techniques were not up to snuff. The point is, getting the exposure “right” was paramount. They needed to acquire the technical stuff -- otherwise they used trial-and-error. 21st century photographers can concentrate on composition, ignoring the technical, it’s OK if you let the camera do the thinking.

@ alan_marcus|2,

 

Though Adams and his contemporaries had certain types of equipment available to them and may have, therefore, shared some needs and approaches, I would still say Adams towered above many in his understanding of and expertise in important techniques and technical dimensions of exposure, processing, and printing. I would also say his creative and artistic eye was not as significant to me as others of his day.

 

I would likewise differentiate among many later 20th and early 21st-century photographers who vary greatly in their technical acumen, who place different emphases on subject, composition, narrative, emotion, and other things, and who also vary in their willingness and desire to let the camera “do the thinking,” which I think is a flawed way of considering even the most automatic of cameras, cameras which still depend, as Adams rightly reminded us, on the most important component of photography, which is “the twelve inches behind the camera.”

 

In any case, my original point to you was to say that, in some cases, knowing technique can hurt, if it’s over-emphasized to a point where it can actually have a negative effect on the creative photographic eye. In some technical discussions, it does seem like interest in the technical aspects of photography for their own sake far outweighs aesthetic interest in photography. That does not happen across the board but I think it does happen.

Edited by The Shadow
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@ Rodeo_Joe --

Does knowing the technical stuff make you a better photographer? Maybe not but it doesn’t hurt. Knowing the technical stuff brought fame and riches to Ansel Adams. Possibility a kid with a camera phone will win the Pulitzer Prize by just being there and taking a praiseworthy picture. In-between is the casual photographer and the professional photographer. Some pros just naturally get it. Some pros get it by osmosis. Some pros study for years to get it. As for me, never famous but 55+ years of being well employed and enjoying every minute.

 

It's interesting to understand the math behind the f numbers. I think the main thing to know is given the use of modern aperture numbers that each number represents either double the amount or larger aperture number next to it. (+ or - 1stop, ie., F2.8 lets in half the light of F2). Next is to also realize that shutter speed numbers on modern cameras also represent 1 stop of light more than the speed setting to the next larger number. (ie 1/125 allows one stop more of light in than 1/250). So the importance for any photographer is to be able to create equivalent exposures using the combination of aperture stops and shutter speeds. Knowing the relationship there allows you to have some control over the Depth of Field and how that will effect the photo. For example, given that a photo is properly exposed at a speed of 1/125 (125 on the camera shutter dial assuming it has one) at an aperture setting of f/8, you can find equivalent exposures for a set of apertures/speeds so exposure wise 1/125 at F/8 = 1/60 at F/11; 1/30 at F/16; 1/250 at F/5.6 and 1/500 at F/4 and 1/1000 at f/2.8; 1/2000 at F/2 etc. Lastly, there is the + or - EV. Each EV whole number = one stop of light. Changing the EV number when shooting can give you a way to change exposure without changing either shutter speed or aperture setting. This is basic functioning and something that is used on basically any photo I take in some fashion. Hope this helps:)

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@ alan_marcus|2,

 

Though Adams and his contemporaries had certain types of equipment available to them and may have, therefore, shared some needs and approaches, I would still say Adams towered above many in his understanding of and expertise in important techniques and technical dimensions of exposure, processing, and printing. I would also say his creative and artistic eye was not as significant to me as others of his day.

 

I would likewise differentiate among many later 20th and early 21st-century photographers who vary greatly in their technical acumen, who place different emphases on subject, composition, narrative, emotion, and other things, and who also vary in their willingness and desire to let the camera “do the thinking,” which I think is a flawed way of considering even the most automatic of cameras, cameras which still depend, as Adams rightly reminded us, on the most important component of photography, which is “the twelve inches behind the camera.”

 

In any case, my original point to you was to say that, in some cases, knowing technique can hurt, if it’s over-emphasized to a point where it can actually have a negative effect on the creative photographic eye. In some technical discussions, it does seem like interest in the technical aspects of photography for their own sake far outweighs aesthetic interest in photography. That does not happen across the board but I think it does happen.

 

Well stripping out the long explanations behind the creation of the numbers is less important then knowing how the speeds and aperture settings work in relationship to each other to create exposure is pretty basic to photography and after using it should be as second nature as breathing. Difficult to do photography without having a working understanding of exposure, at least in my view. Knowing that doesn't in any way inhibit the creative aspects of picture making I don't think, and its probably ok to discuss the nuts and bolts of photography on its own merits without a danger of minimizing the creative aspects.

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Simply stated, if one thoroughly understands the fundamentals of an art or craft, they can go far in any direction. Both Picasso and Dali were classically trained.

 

In photography, if the lighting is perfect and you let the camera do the thinking for you, a good eye for composition will let you get amazing photographs every time.

 

Knowing what's actually happening in the camera, though, lets you navigate tricky or less than perfect light, as well as make the most of a composition. Yes, being an expert on what's going on in the camera but not recognizing or understanding good composition is a great way to get technically perfect but very boring photographs. Still, though, I'm a firm believer in BOTH aspects being important.

 

Aside from that, the scientist in me WANTS to know what's happening.

 

With the Picasso and Dali comparison, there's also a lot of validity to classical artistic training as to what makes and doesn't make a good composition.

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Difficult to do photography without having a working understanding of exposure,

Did you take me to be saying otherwise? If so, read what I wrote again. This discussion has gone WAY BEYOND what one would need to know of exposure in order to take a good photo. It’s the WAY BEYOND point I was suggesting could create enough of a distraction where creativity might get a bit stifled though, of course, it doesn’t have to. I’ve seen folks discuss mathematical details about photo exposure and lens performance who can’t speak nearly as articulately about aesthetic aspects of photography and whose photos show little more than an ability to expose well. That’s all I’m saying. Now back to our regularly scheduled program ...

There’s always something new under the sun.
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I just got around to reading this thread. My impression is that it should have started off by defining f-number, the ratio of focal length to diameter of the lens opening. The intensity of light collected by a lens is proportional to the diameter of the lens opening squared, and the intensity of light collected by film or image sensor is proportional to the intensity of light collected by the lens divided by focal length squared (the further away from the lens the lower the intensity). This is why equal f-numbers for different focal length lenses produce equal exposure values, and why f-number decrease produces exposure increase. Most of what is discussed in this thread evolves from the simple basic definition of f-number.
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Did you take me to be saying otherwise? .

 

No I didn't However, If people want to give beginners information about nothing else but the physics of photography, why shouldn't they? Did we really need a cautionary warning about losing a focus on the meaning and aesthetics or stifling creativity? The info Glenn imparted is absolutely great for beginner photographers in my opinion, I don't think providing the info will endanger their artistic aspirations. There are other threads we can have about other aspects of making a photograph.

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Both Picasso and Dali were classically trained.

Since it’s the science of exposure being discussed, I think DaVinci would be a better painter analogy, whose background in math and science had a profound influence on his work. Dali was “classically trained” in the history and aesthetics of art. Dali is known to have utilized his study of Freudian theory in developing the dream and hallucination content and style of his painting. Dali’s art is also influenced by his knowledge of and affinity for Classical and Renaissance art. This can especially be seen in his later work’s use of religious symbolism. Dali’s training is a very different matter from studying the math or science of exposure.

 

There were painters who had an in depth knowledge of scientific aspects of paint and pigmentation, as well as the study of light. The ones we’ve heard of and whose work has become celebrated through the ages probably utilized that technical knowledge to good advantage. I’m sure there are plenty of unheard of painters who absorbed themselves in the more technical aspects of their art to little positive effect on their work.

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its probably ok to discuss the nuts and bolts of photography on its own merits without a danger of minimizing the creative aspects.

Right, but is that what’s happening here at PN? I’ve been around PN since 2007 and there’s noticeably much more about technical matters and gear than about the art, creativity, critique, or history of photography than there used to be. The redesign to PN2.0 alone saw much more support for and fluidity of use on the forum side than on the critique side of the site, which was barely usable at first and still performs at a subpar level in today’s Internet world. Participation in critiques is way down for other reasons as well. Browse through the forums and you’ll find very little discussion of the aesthetic, creative, or historical sides of photography relative to much, much more about gear and process. I think the latter has definitely come at the expense of the former and I think PN is a photographically poorer and diminished place as a result. For me, it shouldn’t be a matter of either/or but it is a matter of relative energy and emphasis.

There’s always something new under the sun.
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