Knowledge check..

[LancsMak]

Just wanted to check my understanding/maths add up here as I was quite astounded. Tried explaining to someone the difference between indoor and outdoor photography in terms of light.

F stop from 3.2 to 5.0 is approx 1 full stop, so half the light.

Shutter from 640 to 1000 is double for easy maths, so half the light again.

Iso from 5000 to 500 is 10x less "light" /sensitivity.

So for two correctly exposed images, the difference in useful light level is 2x2x10=40 times light difference???

 

[TheBigYin]

500 > 5000 is just over 3 stops, not 10. Double the iso is 1 stop, so 500-1000 = 1 stop, 1000-2000 = 1 stop, 2000-4000 = 1 stop, 4000-5000 less than 1/3 of a stop so, pretty much immaterial

1/640th to 1/1000th is about 2/3 of a stop.

so no, its reallly not 40x the light intensity

 

[LancsMak]

Cheers

 

[Eucris]

Just wanted to check my understanding/maths add up here as I was quite astounded. Tried explaining to someone the difference between indoor and outdoor photography in terms of light.

F stop from 3.2 to 5.0 is approx 1 full stop, so half the light.

Shutter from 640 to 1000 is double for easy maths, so half the light again.

Iso from 5000 to 500 is 10x less "light" /sensitivity.

So for two correctly exposed images, the difference in useful light level is 2x2x10=40 times light difference???

My take on it is this.

Based on the proviso that the indoor shot was taken at f3.2, shutter 1/640 and ISO 5000, and the outdoor shot was taken at f5, shutter 1/1000 and ISO 500, then that will give you a 5.33 stop difference.

If one stop halves the amount of light and each subsequent stop halves the amount of light again (½, ¼, 1/8, 1/16, 1/32), then 5.33 stops will give approximately 1/40 of the amount of light.

 

[AndrewFlannigan]

If each stop halves the light falling on the sensor then the progression is...

1. f2 100%
2. f2.8 50%
3. f4 25%
4. f5.6 12.5%
5. f8 6.25%

...so stoping down 5 stops reduces the light hitting the sensor by roughly 90%.

More here...

f-number - Wikipedia

en.wikipedia.org

 

[Phil V]

...so stoping down 5 stops reduces the light hitting the sensor by roughly 90%.

Speaking percentages isn't really helpful. Seeing as the media constantly mangles the terminology*.

And photography already helpfully gives us an EV scale where 1 stop is a halving or doubling, Mark's first response was pitch perfect, adding the % adds no value at best, and at worst adds confusion.

*How often do we hear that Inflation going from 5% to 10% is a 5% increase ? When it's really not, it's a 100% increase, OR a 5 percentage point increase.

 

[Eucris]

500 > 5000 is just over 3 stops, not 10. Double the iso is 1 stop, so 500-1000 = 1 stop, 1000-2000 = 1 stop, 2000-4000 = 1 stop, 4000-5000 less than 1/3 of a stop so, pretty much immaterial

1/640th to 1/1000th is about 2/3 of a stop.

so no, its reallly not 40x the light intensity

Surely it is about light intensity. If you were to underexpose by 5 stops you would only be letting 1/32 of the light into the camera. So to get a correctly exposed image you would have to increase the light intensity 32 times, or I have misunderstood.

 

[Terrywoodenpic]

Conflating stops with percentages is a fools errand.
Which is why in photography we allways work in stops, moving one stop doubles or halves the exposure the light or even the iso value. Measure the light with an exposure meter and you will also be working in stops. It is no help to start working in lux or converting to some sort of percentage. That way leads to confusion and error.

You can not "set" a percentage on a camera or a light, so it is a pointless exercise.

 

[AndrewFlannigan]

You can not "set" a percentage on a camera or a light, so it is a pointless exercise.

The example I gave was simply to simplify the relation in a five stop difference. The f-stop scale was originally invented, if I recall correctly, to provide a geometric progression matching the doubling or halving of shutter opening times, which were being similarly adopted by manufacturers.

 

[Phil V]

Surely it is about light intensity. If you were to underexpose by 5 stops you would only be letting 1/32 of the light into the camera. So to get a correctly exposed image you would have to increase the light intensity 32 times, or I have misunderstood.

Photographers work in stops, because that's what we can control. We have no power over ambient light intensity, so it makes no difference how you'd describe controlling it.

And when we do have control over the light source; guess how we describe it? In stops.

 

[Garry Edwards]

The example I gave was simply to simplify the relation in a five stop difference. The f-stop scale was originally invented, if I recall correctly, to provide a geometric progression matching the doubling or halving of shutter opening times, which were being similarly adopted by manufacturers.

(My bold). Actually no, although language evolves with time and usage, and "one stop" now generally means either halving or doubling the exposure, whether that's achieved by changing the shutter speed, the ISO setting or the lens aperture (which which is where the term originated)

The lazy way for me to explain this is to reproduce a bit from my beginner book . . .

"In the very early days of photography, there wasn’t any way of reducing the amount of light, so all photos had to be taken with the lens “Wide open” – no control at all - which made life difficult for the photographer.

After a while, it became possible to unscrew lenses, allowing photographers to insert a “stop” – basically a washer – into the lens to restrict the amount of light. And then, in 1858, John Waterhouse improved on this idea with a series of drop-in constrictions with various size holes, later followed by a metal strip with different size holes drilled into it, and his invention was known as the Waterhouse Stop. See https://en.wikipedia.org/wiki/Waterhouse_stop. This idea was developed and improved by the lens maker Carl Zeiss in 1906 and eventually developed into what we have today, the Iris diaphragm, which is a mechanical device that mimics our own eyes, letting in more light in dark conditions and less light in bright conditions. Look at the illustrations on this page, which demonstrate the process very well https://en.wikipedia.org/wiki/Diaphragm_(optics)

The very old camera lenses had a visible iris diaphragm, which made it much easier to understand than the current ones, which can hardly be seen at all, at least on the very popular DSLR cameras simply because, when we look through the viewfinder to compose our shots we want a bright, clear image, which means that the lens is “wide open” until we press the magic button, at which point the iris diaphragm closes to the chosen setting, the shutter then opens and closes for the length of time of the chosen setting and the iris diaphragm then fully opens again."

 

[AndrewFlannigan]

(My bold). Actually no, although language evolves with time and usage, and "one stop" now generally means either halving or doubling the exposure, whether that's achieved by changing the shutter speed, the ISO setting or the lens aperture (which which is where the term originated)

It's entirely possible I put the cart before the horse in my description but, as you indicate, the outcome is the same.

By the way, I'm sure you already know, given your occupation (but others may not) that both the Germans and the French experimented with that very means of locomotion in the late 19th and early 20th centuries...

Cart before the horse - Wikipedia

en.wikipedia.org

 

[Terrywoodenpic]

The example I gave was simply to simplify the relation in a five stop difference. The f-stop scale was originally invented, if I recall correctly, to provide a geometric progression matching the doubling or halving of shutter opening times, which were being similarly adopted by manufacturers.

It came first in Waterhouse stops for lenses which doubled between individual stops. Shutter speed followed suit but not equally. They were first usually 1, 1/2, 1/5,1/10, 1/25, 1/100, 1/200,1/300 and may be 1/500 this did not fit the doubling very well.
The later 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250.1/500 fitted rather better but did not become normal till the 50's

Digital speed and apertures first added the the one third intervals but now mostly show decimal intervals. So newbies are not seeing the doubling pattern at all. And seem to be pretty confused between the relationships of shutter, aperture and iso. Which makes life for them more difficult.

 

[Eucris]

Photographers work in stops, because that's what we can control. We have no power over ambient light intensity, so it makes no difference how you'd describe controlling it.

And when we do have control over the light source; guess how we describe it? In stops.

You are of course quite correct, photographers do work in “stops”, however, the fact remains that if you were to underexpose by 5 stops only 1/32 (3.125%) of the light would hit the sensor. Using fractions and percentages is a very easy and simple way to express the effect that changing the settings has on the amount of light hitting the sensor, in fact it is the only way to express it. It is no different to saying that 1 stop will either double or halve the amount of light, which would be expressed as 2 (200%) or ½ (50%).

 

[Phil V]

You are of course quite correct, photographers do work in “stops”, however, the fact remains that if you were to underexpose by 5 stops only 1/32 (3.125%) of the light would hit the sensor. Using fractions and percentages is a very easy and simple way to express the effect that changing the settings has on the amount of light hitting the sensor, in fact it is the only way to express it. It is no different to saying that 1 stop will either double or halve the amount of light, which would be expressed as 2 (200%) or ½ (50%).

I can’t disagree more.
But you’re entitled to your opinion. However genuinely unhelpful I think it is to add language that can be misconstrued to a situation where simple language already exists.

 

[LancsMak]

Wow I didn't think this would be such a discussion! Thanks to everyone. I certainly expected that I was missing something with my logic but wasn't expecting this level of debate.

 

[Phil V]

Digital speed and apertures first added the the one third intervals but now mostly show decimal intervals. So newbies are not seeing the doubling pattern at all.

I hadn’t realised that this was happening. How mad is that?

 

[Phil V]

Wow I didn't think this would be such a discussion! Thanks to everyone. I certainly expected that I was missing something with my logic but wasn't expecting this level of debate.

As is so common on the internet. The first response nailed it. And if I was you; I’d ignore everything that follows it. There’s no value, just noise (and I’d include my posts in that)

 

[Eucris]

I can’t disagree more.
But you’re entitled to your opinion. However genuinely unhelpful I think it is to add language that can be misconstrued to a situation where simple language already exists.

Ok, so let me ask you a question. If you were to take an exposure reading and then underexpose that reading by two stops how much light would there now be hitting the sensor. The answer is one quarter (25%). As far as I am aware there is no other way to express this, if there is then please tell me what it is and how it is calculated.

If any of the calculations in my previous posts are incorrect then again please tell me what is wrong with them and how I should have calculated them.

 

[Phil V]

Ok, so let me ask you a question. If you were to take an exposure reading and then underexpose that reading by two stops how much light would there now be hitting the sensor.

Two stops.

As @Terrywoodenpic stated previously. My cameras don’t have any controls with a % label, but I can alter the ISO, SS or aperture by 2 stops with ease.

 

[Terrywoodenpic]

You are of course quite correct, photographers do work in “stops”, however, the fact remains that if you were to underexpose by 5 stops only 1/32 (3.125%) of the light would hit the sensor. Using fractions and percentages is a very easy and simple way to express the effect that changing the settings has on the amount of light hitting the sensor, in fact it is the only way to express it. It is no different to saying that 1 stop will either double or halve the amount of light, which would be expressed as 2 (200%) or ½ (50%).

Originally, adjusting exposure by a full 'stop' was pretty much the minimum change to get a noticeable and useful difference in density on the film. Any further refinement was more easily done at the printing stage. This was partly so because shutters were neither very accurate nor consistent. Photographers have leant to think in stops, and is part of the inevitable learning curve for all newbies. It is the only way to have a direct relationship between shutter seed aperture and sensitivity, and the resulting 'exposure'. Percentages can not achieve this.

When. I had my first adjustable camera at age ten in 1945 I too had real difficulty coming to terms with these relationships..
However after a few tears my eldest brother got me sorted.

I suggest that you go with the flow and learn to think like a photographer, just like the millions before you. You will not persuaded any one to reinvent the wheel. The one we have works so well and solves so many problems in thinking about exposure. And even more so when balancing flash with ambient light. Or with long extensions in macro work.

It is all based on stops and the inverse square law. Even Iso sensitivity is based on a log scale so that it's additive. (Doubling the value equals one stop) On the Din Scale adding three adds one stop (doubles the value) which is equally easy.

We all know about percentages and they are not helpful, or we would have found a way to use them long since,
Many great scientist and mathematicians. Have studied the problems of simplifying and expressing and working with exposure and and sensitivity. They are the ones that settled on using stops.

Cine photographers invented T stops to take into account comparative light transmission through complex lenses, but that is another story. They also almost always use incident light measurement rather than reflected for pegging exposure and tonal values... But they still work and think in stops.

 

[Phil V]

If any of the calculations in my previous posts are incorrect then again please tell me what is wrong with them and how I should have calculated them.

At no point did I suggest that your calculations were incorrect.

Just that they’re unnecessary and unhelpful

 

[Phil V]

Sorry to labour the point but here’s why percentages just don’t work, and why ‘stops’ do.

If my image is underexposed by 2 stops, and I work out that means I only have 25% of the light I need, then to get the correct exposure I have to increase my light catching capability by 200%. BTW that’s 2 stops, exactly the same thing I started with.

So can anyone explain the relationship between 25% and 200%?

Then can you tell me how I convert that to aperture values?

Please now can we see how unhelpful this is?

I know that 100 ISO to 400 ISO is two stops
That 1/125 to 1/500 is two stops

And that f2.8 to f5.6 is two stops

I appreciate that the last one is a bit more tricky but only when you first hear it.

I adjust my aperture in stops (half stops in reality)

My shutter speed in stops

My ISO in stops

My light meter gives me a readout in stops (both in camera and hand held)

My speedlights and battery powered studio flash gives me readings in stops.

The only thing that doesn’t give me stops is the mains studio lights, and they use a digital scale so stupid that I revert to ‘turn it down 2 clicks’

 

[Terrywoodenpic]

Ok, so let me ask you a question. If you were to take an exposure reading and then underexpose that reading by two stops how much light would there now be hitting the sensor. The answer is one quarter (25%). As far as I am aware there is no other way to express this, if there is then please tell me what it is and how it is calculated.

If any of the calculations in my previous posts are incorrect then again please tell me what is wrong with them and how I should have calculated them.

You can of course convert stops to fractions decimals or percentages, but why would you want to, it serves no practical purpose. The adjustments you must make are in stops.

 

[AndrewFlannigan]

You can of course convert stops to fractions decimals or percentages, but why would you want to, it serves no practical purpose. The adjustments you must make are in stops.

I think part of the problem with "stops" is that the concept is alien to many newcomers, so they sometimes need an explanation that relates what's happening to what they already know. The other part of the problem is that the "explanation" too often confuses rather than enlightens.

 

[Phil V]

I think part of the problem with "stops" is that the concept is alien to many newcomers, so they sometimes need an explanation that relates what's happening to what they already know. The other part of the problem is that the "explanation" too often confuses rather than enlightens.

Of course it does. Because it makes no sense to convert something quantifiable (a stop) into something unquantifiable (%) and then have to convert it back.

none of the controls have a % setting.

 

[hunnymonster]

If my image is underexposed by 2 stops, and I work out that means I only have 25% of the light I need, then to get the correct exposure I have to increase my light catching capability by 200%. BTW that’s 2 stops, exactly the same thing I started with.

So can anyone explain the relationship between 25% and 200%?

Am I missing the point here? 200% is only a single doubling - therefore 1 stop... 400% (therefore quadrupling/4x) would be 2 stops, no?

 

[Phil V]

Am I missing the point here? 200% is only a single doubling - therefore 1 stop... 400% (therefore quadrupling/4x) would be 2 stops, no?

If you increase by 100% you’re doubling.

If you increase something ‘by’ 200% that means you’re adding twice as much as you originally had, if you’re increasing something ‘to’ 200% then you’re just doubling it.

Again %’s are really really unhelpful because the language around their use is very important.

 

[Cockney]

(My bold). Actually no, although language evolves with time and usage, and "one stop" now generally means either halving or doubling the exposure, whether that's achieved by changing the shutter speed, the ISO setting or the lens aperture (which which is where the term originated)

The lazy way for me to explain this is to reproduce a bit from my beginner book . . .

"In the very early days of photography, there wasn’t any way of reducing the amount of light, so all photos had to be taken with the lens “Wide open” – no control at all - which made life difficult for the photographer.

After a while, it became possible to unscrew lenses, allowing photographers to insert a “stop” – basically a washer – into the lens to restrict the amount of light. And then, in 1858, John Waterhouse improved on this idea with a series of drop-in constrictions with various size holes, later followed by a metal strip with different size holes drilled into it, and his invention was known as the Waterhouse Stop. See https://en.wikipedia.org/wiki/Waterhouse_stop. This idea was developed and improved by the lens maker Carl Zeiss in 1906 and eventually developed into what we have today, the Iris diaphragm, which is a mechanical device that mimics our own eyes, letting in more light in dark conditions and less light in bright conditions. Look at the illustrations on this page, which demonstrate the process very well https://en.wikipedia.org/wiki/Diaphragm_(optics)

The very old camera lenses had a visible iris diaphragm, which made it much easier to understand than the current ones, which can hardly be seen at all, at least on the very popular DSLR cameras simply because, when we look through the viewfinder to compose our shots we want a bright, clear image, which means that the lens is “wide open” until we press the magic button, at which point the iris diaphragm closes to the chosen setting, the shutter then opens and closes for the length of time of the chosen setting and the iris diaphragm then fully opens again."

Very interesting about the origins and evolution, thanks for that.

 

[hunnymonster]

If you increase by 100% you’re doubling.

If you increase something ‘by’ 200% that means you’re adding twice as much as you originally had, if you’re increasing something ‘to’ 200% then you’re just doubling it.

Again %’s are really really unhelpful because the language around their use is very important.

Which makes it even less useful... Increasing by 200% means you end up with 300% of the original - which isn't 2 stops either... Which is why we all use stops (and/or logarithms)

 

[Phil V]

Which makes it even less useful... Increasing by 200% means you end up with 300% of the original - which isn't 2 stops either... Which is why we all use stops (and/or logarithms)

Yeah you have to increase by 100% and then by 100% again.

It really isn’t a useful method (and yes my maths was incorrect 1st time).

 

[AndrewFlannigan]

Am I missing the point here? 200% is only a single doubling - therefore 1 stop... 400% (therefore quadrupling/4x) would be 2 stops, no?

Correct.

If F8 is the original stop, then F5.6 would double the area, allowing 200% of the light transmission. F4 would then double the area again allowing 400% of the light to pass through the lens. Going the other way: F11 will allow 50% of the light to fall on the sensor and F16 will allow 25%. Percentage or F-number, the principle is identical.

The F-numbers themselves are the result of the simple calculation {Focal Length / Diameter of opening}.

Far more than you probably want to know can be found on the Wikipedia page I referenced above.

 

[dekeyboy]

This discussion started on Saturday at 12.30 pm. The last input was Sunday at 3.47 pm. This means that some of you decided to not take any photographs, but to look up various ways of not agreeing with someone. This continued to the point of making photography sound quite boring. Some of the responses were right on point and some were disruptive from WILLY WAGGING people. I can only hope that one day we will see a post that one person gives a correct response and at least 90% of others can agree with.

 

[Cockney]

This discussion started on Saturday at 12.30 pm. The last input was Sunday at 3.47 pm. This means that some of you decided to not take any photographs, but to look up various ways of not agreeing with someone. This continued to the point of making photography sound quite boring. Some of the responses were right on point and some were disruptive from WILLY WAGGING people. I can only hope that one day we will see a post that one person gives a correct response and at least 90% of others can agree with.

I thought it was quite an interesting discussion.

 

[Ed Sutton]

This continued to the point of making photography sound quite boring.

Boring and complicated. I've been taking photos for almost 50 years now and haven't understood any of it!

I have taken lots of photos over the weekend though, don't know what f stops or shutter speeds I used, the camera sorted them out for me.

 

[Garry Edwards]

This discussion started on Saturday at 12.30 pm. The last input was Sunday at 3.47 pm. This means that some of you decided to not take any photographs, but to look up various ways of not agreeing with someone. This continued to the point of making photography sound quite boring. Some of the responses were right on point and some were disruptive from WILLY WAGGING people. I can only hope that one day we will see a post that one person gives a correct response and at least 90% of others can agree with.

People are always going to disagree, that's human nature, and it's generally healthy to disagree, except when people become unpleasant.

Photography is an interest that involves experience, knowledge, creativity, equipment and science, but the science is "soft" rather than hard and immutable. It doesn't always travel in straight lines and can confuse us, and different people are bound to have different backgrounds and different levels of knowledge etc, which means that we won't always agree with each other.

Boring and complicated. I've been taking photos for almost 50 years now and haven't understood any of it!

I have taken lots of photos over the weekend though, don't know what f stops or shutter speeds I used, the camera sorted them out for me.

That's fine if it works for you, after all we don't need to be a mechanical engineer to drive a car well

But the fact that you're happy to trust technology doesn't mean that the more technical aspects of photography are boring.

In short, let's play nice!

 

[Ed Sutton]

But the fact that you're happy to trust technology doesn't mean that the more technical aspects of photography are boring.

A tip for reading my posts - don't take them all literally.

 

[Terrywoodenpic]

It has been suggested that photography is a art form, however it is also a craft and a science,
This does not mean that photographers must be interested in only one of these aspects.
Many of us are interested in everything connected with photography,
Nothing need be boring or out of bounds
The RPS, was for instance, founded to advance the Art and Science of photography.
Amen.

 

[AndrewFlannigan]

People are always going to disagree, that's human nature, and it's generally healthy to disagree, except when people become unpleasant.

This is true.

Using the {ignore} button is just one way to stop people from winding you up.

 

[TheBigYin]

Using the {ignore} button is just one way to stop people from winding you up.

unfortunately not all of us have that luxury - Garry and myself for instance would be a bit remiss in our duties on here if we were ignoring people, wouldn't we...

(plus, the very cockwombles we'd probably LIKE to ignore are also the ones that as mod's we need to be looking out for...)