'Stops'

[Pinpho]

So I know what F stops are. I know the basics and the exposure triangle. What I don't understand is when people are referring to aperture and shutter speed and say stuff along the lines of 'you can calculate how many stops between settings x and settings y'. Could someone please explain this to me and explain how this knowledge will affect my photography skills? If possible could you provide links?

Cheers, Danny

 

[PMN]

Hi Danny,

Any chance you could explain a little more in depth which bit you're having difficulty with? The question seems a little vague to give a clear answer!

 

[Pinpho]

Hi Danny,

Any chance you could explain a little more in depth which bit you're having difficulty with? The question seems a little vague to give a clear answer!

It's a little hard to explain without being able to link you to one of the parts I am confused with - have seen it on a few threads a while ago but can't remember which ones.

Basically when people say, you can calculate the stops between say f5, 1/200 & f9, 1/400. I don't really know how to word this so forgive me, but is this simply referring to the aperture F stops and disregarding the shutter speed entirely?

Sorry that I couldn't be clearer

EDIT: So say for example I have seen people saying things like 'Setting X is 5 stops from setting Y'. My thought is that it is the amount of 'clicks' on the wheel that you turn to change the shutter speed/aperture settings? Really don't know how to word this and quite possibly what I'm asking is very silly.

 

[HoppyUK]

So I know what F stops are. I know the basics and the exposure triangle. What I don't understand is when people are referring to aperture and shutter speed and say stuff along the lines of 'you can calculate how many stops between settings x and settings y'. Could someone please explain this to me and explain how this knowledge will affect my photography skills? If possible could you provide links?

Cheers, Danny

Understanding stops is vital, but easy.

The term has its historical roots in aperture control (as in to block or 'stop' the light) but today 'a stop' or 'one stop' refers to any halving or doubling of exposure settings.

In the exposure triangle, shutter speeds are obvious (eg 1/125sec is twice as long as 1/250sec) and so is ISO (ISO200 is half as sensitive to light as ISO400). The tricky one is f/numbers that also pass half or double the amount of light, but are linked by the square root of two (ie 1.4 - there is a mathematical reason for this) and are further confused by lower numbers passing more light than higher numbers. Eg, f/4 passes twice as much light as f/5.6, which is double f/8 and so on.

These are 'whole stops' but there are also intermediate settings. You just have to learn this.
1/1000sec, 1/500, 1/250, 1/125, 1/60 etc.
ISO100, 200, 400, 800, 1600, 3200, 6400 etc.
f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16,22 etc.

From the tutorial section on here, this is a good guide by Pookeyhead http://www.talkphotography.co.uk/forums/showthread.php?t=440126

 

[Andy_S]

One stop is the doubling, or halving, the amount of light reaching the sensor*.
Easy to work out with changes of shutter speeds. 1/200, 1/100, 1/50, 1/25 etc...
1/200 to 1/25 is 3 stops.
Apertures are a bit harder to work out, have a look at the chart here: http://www.digitalcameraworld.com/2012/03/17/free-f-stop-chart-master-your-aperture/
f2.8, f4, f5.6, f8 each cover 1 stop.
The same with iso, 100, 200, 400, 800... (*Not really light reaching the sensor, but doubling/halving the sensors output with each step.)

To go from one shot: 1/200 f2.8 iso 200. to another 1/50 f8 iso400.
You gain 2 stops from the slower shutter speed, lose 3 from the smaller aperture and gain 1 from the increase in iso. Total change = 0.
The exposure should be the same in both shots. BUT the longer shutter speed may cause blurring from camera shake, or a fast moving subject, and you will have a much larger depth of field from the f8 aperture.
HTH

 

[Steve Smith]

Aperture settings are usually in a sequence 2.8, 4, 5.6, 8, 11, 16, 22, etc. Going from one setting to the next will either double or halve the exposure. e.g. f2.8 lets in twice as much light as f4 and f16 lets in half as much light as f11.

Equally, standard shutter speeds are 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, etc. Going from one setting to the next will also either double or halve the exposure. e.g. 1/60 will let in twice as much light as 1/125 and 1/1000 will let in half the light of 1/500.

You can maintain the same exposure by chnging one setting in one direction and the other in the opposite direction.

e.g. if you are at f8 and 1/125, you will get the same exposure if you open up the aperture by two stops to f4 and increase the shutter speed to 1/500.

Just to complicate things further, the sensor or film's sensitivity is also scaled in stops. In the sequence 50, 100, 200, 400, 800, etc. ISO 200 is twice as sensitive (needs half the light) of ISO 100.

The important thing to remember is that a difference of one stop is either a doubling or halving of exposure or sensitivity.


Steve.

 

[Pinpho]

Thank you all for the excellent replies, absolutely perfect! I love how much I can learn from you guys, it really is a pleasure!

This seems fairly difficult to grasp at the minute but I get the concept, its just a case of reading up more and putting it into practice. Just having a play around with my camera to work out stops and the standard f#'s you mention above seem different for my lens.

f5.3, 5.6, 6.3, 7.1, 8, 9, 10, 11, 13, 14, 16, 18, 20, 22, 25, 29, 32, 36

When in 'A' mode, when the aperture is adjusted, so too is the shutter speed (a given). So let me see if I am understanding this:

Original; f9, 1/200 -> f8, 1/250 = Would this be 0 stops difference? Gain 1 from the increased aperture, and lose one for a faster shutter speed?

It seems very difficult for me to determine the stop amounts as when shooting in aperture mode, I will need to hold the camera on a subject with unchanging light conditions as the shutter speed automatically adjusts. Confused.

Steve: I don't know how to adjust both settings? Would that be on the 'P' or 'M' functions? I haven't used those yet as I haven't read that section of the manual.. which I will do now!

 

[Rockman]

The figures given by Steve are whole stops, modern lenses give se intermediate options.

Mike

 

[HoppyUK]

Danny, your camera is set to one-third stops increments (standard default) and that is confusing things. For the purpose of learning, go in to the menu and change it to read in whole stops only.

For example, instead of one click on the dial moving the aperture from say f/5.6 to f/6.3, f/7.1 and f/8, it will go straight from f/5.6 to f/8 - missing out the 1/3rd stop and 2/3rds stop increments.

You need to be in manual M to change all these settings independently. And check the link I gave above.

 

[Pinpho]

Danny, your camera is set to one-third stops increments (standard default) and that is confusing things. For the purpose of learning, go in to the menu and change it to read in whole stops only.

For example, instead of one click on the dial moving the aperture from say f/5.6 to f/6.3, f/7.1 and f/8, it will go straight from f/5.6 to f/8 - missing out the 1/3rd stop and 2/3rds stop increments.

You need to be in manual M to change all these settings independently. And check the link I gave above.

Will change to read in whole stops now for while I am learning thanks for the advice! will check the link also. Would you say that M is a better mode to shoot in than either A or S (which I normally use)? It seems that it gives more control but requires more knowledge to use (which I am determined to learn)!

Thank you all for the wonderful input, very much appreciated!

 

[Ivan S]

M mode will take longer to use for shots, depends on what you are shooting really, once in M mode you will use the in built light meter, have you looked at the light meter yet?

 

[HoppyUK]

Will change to read in whole stops now for while I am learning thanks for the advice! will check the link also. Would you say that M is a better mode to shoot in than either A or S (which I normally use)? It seems that it gives more control but requires more knowledge to use (which I am determined to learn)!

Thank you all for the wonderful input, very much appreciated!

I would only set the camera to whole stops increments while you're sitting with it trying to learn the relationships between the various settings. It just simplifies things for learning, but out in the field you will get better exposure accuracy by being able to make finer adjustments with one-third stops changes.

The different modes A, S, M and P are just different ways of setting the same exposure, allowing you to lock some (according to the result you want) while the camera automatically balances the others. None is better than the other - just speed of use, convenience, personal preference, whatever.

 

[Pinpho]

M mode will take longer to use for shots, depends on what you are shooting really, once in M mode you will use the in built light meter, have you looked at the light meter yet?

Haven't looked at that yet, haven't even touched on this setting, seems I have a lot of reading up and experimenting to do

 

[EOS_JD]

the triangle also involves ISO
50, 100, 200, 400, 800, 1600, 3200, 6400, 12,800, 25600 etc.

I would not change to full stop settings. No matter what setting you are on for SS or Aperture, 3 clicks is a stop of light - You don't need to worry about full stops (although they are useful to use - and easy to remember).

 

[ernesto]

I would not change to full stop settings. No matter what setting you are on for SS or Aperture, 3 clicks is a stop of light - You don't need to worry about full stops (although they are useful to use - and easy to remember).

Thats a confusing post and sounds like you are suggesting 3 clicks from 1.8 is one stop, 3 clicks from 1/500 is one stop?

(Just trying to clear it up as it could be misleading)

 

[Major Eazy]

When in 'A' mode, when the aperture is adjusted, so too is the shutter speed (a given). So let me see if I am understanding this:

Original; f9, 1/200 -> f8, 1/250 = Would this be 0 stops difference? Gain 1 from the increased aperture, and lose one for a faster shutter speed?

It seems very difficult for me to determine the stop amounts as when shooting in aperture mode, I will need to hold the camera on a subject with unchanging light conditions as the shutter speed automatically adjusts. Confused.

Basically something like that.

Let's just say that you need f11 at 1/125 to get a photo at the right exposure levels as an example, so....

If your camera is in A mode and you chose to go from f11 to f8 which is one stop faster allowing in more light, making the exposure (the photo image) much more lighter, the camera will change the shutter speed from 125 to 250, which is one stop faster to cut the time the camera lets in the light, so the exposure will be back to the same exposure level instead of your hoping to make it lighter, so yes, there is no different in stop settings, just different in depth of field and movement sharp/blur.

Somewhat similar to as if you up the volume on the PlayStation/Xbox/Sky/whatever (the aperture) by 5 levels (1 stop faster) to make the music 5 times louder (overexposure by 1 stop) but someone else turned the volume on the television set down (the camera automatically changing the shutter) by 5 levels (1 stop faster) to cancel out your 5 levels louder music (your image will be back at right exposure).

So if you use M mode, and you chose to change from f11 to f8 which is one stop faster, but you did not change the shuttle and it stays the same, then the camera will let in more light, making the exposure one stop lighter, so yes, you can say it is one stop, this is because you have control over both aperture and shutter, so you change the aperture but the camera did not change the shutter.

As if you up the volume on the PlayStation by 5 levels (1 stop) but there is nobody to change the television volume down by same 5 levels, so you are 5 levels louder (therefore your image is 1 stop overexposure).

In either A mode or S mode, if you change settings to one or two or three stops, the other half will automatically change too to same number of stop settings, so in effect cancelling out your changes. Zero stop different (assuming we leave film speed out of it).

Manual setting is your best option. If you want to change light levels, you just change either the aperture OR shutter, for example, change from f11 to f8 which is one stop faster but leave the shutter, so your images will be one stop overexposure, or if you change from f11 to f5.6 which is two stops faster, but leave shutter, so your image will be two stops overexposure.

However, if you change aperture one stop faster (ie f11 to f8) to let in more light and you chose to change shutter one stop slower (ie 125 to 60) to give camera more time to let in yet more light (where normally camera in A mode would change it one stop faster (ie 125 to 250)) so you are in effect two stops overexposure. 1 stop from your aperture plus 1 extra stop from your shutter = 2 stops.

 

[Major Eazy]

Thats a confusing post and sounds like you are suggesting 3 clicks from 1.8 is one stop, 3 clicks from 1/500 is one stop?

(Just trying to clear it up as it could be misleading)

I agree with ernesto.

Never mind how many clicks of the wheel or the aperture ring or the shutter dial is needed as everyone use different settings, some prefer full stops, some prefer 1/3 stops, so for [EOS_JD] three clicks could be 1 stop but for me three clicks is 3 stops. Our modern digital cameras can have the thumb wheels programmed to our likeing such as if we want 1/3 stops or full stops. Even on my manual focus lens for my 35mm Minolta camera, to turn the aperture ring from say f11 to f16, I can feel two clicks to get there, so 3 clicks would mean I end up between f16 and f22, which is in effect one and a half stops.

 

[redhed17]

Thats a confusing post and sounds like you are suggesting 3 clicks from 1.8 is one stop, 3 clicks from 1/500 is one stop?

I agree with EOS JD.

If the camera is set to adjust in third Stops. Each click on the wheel is one third of a Stop, so three clicks is one whole Stop. If you had a f1.8 lens @ f1.8 and clicked the adjustment wheel three clicks it would go to f2, f2.2 to f2.5, one Stop.

If you are adjusting the the Shutter, and the camera was at 1/500th and clicked three times faster it would go to 1/640th, 1/800th to 1/1000th. One Stop. If you went slower from 1/500th, each click would be 1/400th, 1/320th to 1/250th. One Stop.

The same would be true if you adjust the ISO too.

It's easy enough to check for yourself. :shrug:

I also agree with Hoppy that it is easier to get your head around if you think of it all in whole Stops. I had to look up the intermediate third Stops between f1.8 and f2.5, and didn't know that f2.5 was one Stop from f1.8. :shrug: If I had my camera in front of me though I wouldn't need to, because three clicks is one Stop.

I would never set the camera to adjust half or whole Stops because your are limiting what the camera can do for you. :shrug: Although it may help at home while you are coming to grips with Stops.

However, much easier to play about here on the Camerasim site to try and get your head round Stops. You can also see the simulated effect of the changes you make.

 

[redhed17]

Somewhat similar to as if you up the volume on the PlayStation/Xbox/Sky/whatever (the aperture) by 5 levels (1 stop faster) to make the music 5 times louder (overexposure by 1 stop) but someone else turned the volume on the television set down (the camera automatically changing the shutter) by 5 levels (1 stop faster) to cancel out your 5 levels louder music (your image will be back at right exposure).

That only works as an analogy if each adjustment of 'one' is equal on each device, which is unlikely imho. It certainly isn't equal adjustments on my Media Player and PC volumes, as they do not make similar adjustments for the percentage changed. And you are always limited by, in my case the volume of the PC. If I have your PC volume set to 90%, I have Media Player adjustment from 0-100% over that PCs 90%. If I have the PC volume set to 10%, I can never go louder than the 10% PC volume.

Stop values (and the half or third Stops in between) in the exposure triangle are designed to change the same amount of light. If I go to the smallest Aperture, I can always get the correct exposure by using longer Shutter speeds, and even have too much light if I go too long. In your analogy you are always limited by one master volume.

 

[HoppyUK]

Hoping this is helpful to the OP...

'One stop' is any halving or doubling of exposure setting.
A 'whole stop' or a 'full stop' refers to the numbers below (also in post #4).

Eg, f/4 to f/5.6 is one stop difference, and both are whole stop values.
F/6.3 to f/9 is also one stop difference, but neither of those values is known as a whole stop.

WHOLE or FULL stop values:
f/1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32 etc.
1 second, 1/2 sec, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000 etc.
ISO 50, 100, 200, 400, 800, 1600, 3200, 6400 etc.

Note there are some rounding of numbers going on!

 

[Major Eazy]

That only works as an analogy if each adjustment of 'one' is equal on each device, which is unlikely imho. It certainly isn't equal adjustments on my Media Player and PC volumes, as they do not make similar adjustments for the percentage changed. And you are always limited by, in my case the volume of the PC. If I have your PC volume set to 90%, I have Media Player adjustment from 0-100% over that PCs 90%. If I have the PC volume set to 10%, I can never go louder than the 10% PC volume.

Stop values (and the half or third Stops in between) in the exposure triangle are designed to change the same amount of light. If I go to the smallest Aperture, I can always get the correct exposure by using longer Shutter speeds, and even have too much light if I go to long. In your analogy you are always limited by one master volume.

It's just an example, something to give an illustration idea.

 

[Suvv]

Going back to basics
What helped me with f numbers in the old days when you only had full stops, was realising that if you start with f1 (which I have never seen on a lens) and remember the 1.4 factor and split the list into 2 groups you get:

f1 f1.4 f2 f2.8 f4 f5.6 f8 f11 f16 f22 f32

Notice how the 2 groups are a doubling of the previous number in that group (going L to R) with a rounding up when you double f5.6 to get f11 (rather than f11.2).

 

[sk66]

IMHO, this is "nice to know" stuff and not really critical in any sense. It was more important back when you could use a camera without a battery or meter and we used things like the "sunny 16 rule" and the "zone system." These days the math doesn't really matter.

What DOES matter is that you understand how they interact, and probably more importantly is how changing each setting will impact the final photograph.

 

[ernesto]

It helps if you have some understanding of them when trying to understand how they interact though.

 

[Major Eazy]

No matter what setting you are on for SS or Aperture, 3 clicks is a stop of light

Nope.

3 clicks of the wheel for either aperture or shutter is one stop if your camera's setting is set up for 1/3 stops.

1 click of the wheel for either aperture or shutter is one stop if the camera's setting is set up for full stop. Same as 2 clicks if set for 1/2 stops.

You made it sounds like no matter if my camera's setting is set to either 1/3 stops or 1/2 stops or 1 full stop, I still need 3 clicks to get 1 stop. Sorry but my camera had been set up for full stop and I checked it out, when I tried what you said, no matter what setting I am on for shutter or aperture, 3 clicks still result in my camera getting 3 stops.

It is not a case of "no matter what" as the number of clicks of the wheel vary depending on what set up you chose, which in turns vary from person to person.

Therefore one person's "three clicks of the wheel to get one stop" is another person's "one click of the wheel to get one stop".

Bad example to suggest to someone something like: "Set your Aperture/shutter/ISO by three clicks." which for you would be 1 stop but for me would be 3 stops (for those who prefer 1/2 stops would be one and a half stop).

Because everyone have their camera set up differently, it makes sense to say "Set your Aperture/shutter/ISO by one stop." which for you would be three clicks and for me only need 1 click.

So, after all, it do matters what setting you are on.

 

[HoppyUK]

Default setting for all cameras is one-third stop increments, so unless someone has deliberately changed it...

 

[Suvv]

IMHO, this is "nice to know" stuff and not really critical in any sense. It was more important back when you could use a camera without a battery or meter and we used things like the "sunny 16 rule" and the "zone system." These days the math doesn't really matter.

What DOES matter is that you understand how they interact, and probably more importantly is how changing each setting will impact the final photograph.

Except when you are given advise about altering the meter reading by changing stops
If you are taking shots of snow you may be advised to open up by (say) 3 stops.
If you have not got a grey card you may told to meter off the palm of your hand and add 1 stop, if you have white skin, or subtract 1 stop, if you have black skin.
If you do not know what a stop is, then what do you do?

- ask a question on TP of course

 

[Major Eazy]

Default setting for all cameras is one-third stop increments, so unless someone has deliberately changed it...

I agree but it still doesn't mean 3 clicks of the wheel = 1 stop, anyone can change their settings to either 1/2 or full stop increments before joining this wonderful website and read someone advised 3 clicks of the wheel is 1 stop.

 

[redhed17]

IMHO, this is "nice to know" stuff and not really critical in any sense.

It can become critical when you start to use ND filters and need to work out shutter speeds. Too strong a filter and the camera is not going to work the settings out for you. :shrug:

 

[Phil V]

It's a little hard to explain without being able to link you to one of the parts I am confused with - have seen it on a few threads a while ago but can't remember which ones.

Basically when people say, you can calculate the stops between say f5, 1/200 & f9, 1/400. I don't really know how to word this so forgive me, but is this simply referring to the aperture F stops and disregarding the shutter speed entirely?

Sorry that I couldn't be clearer

EDIT: So say for example I have seen people saying things like 'Setting X is 5 stops from setting Y'. My thought is that it is the amount of 'clicks' on the wheel that you turn to change the shutter speed/aperture settings? Really don't know how to word this and quite possibly what I'm asking is very silly.

1 stop more is twice as much light.
So in shutter speeds its double the time but in apertures there a little more difficult to understand. ISOs follow the rules like shutter speeds.
So lets assume a sunny day: ISO 100 at 1/100sec f16 is correct.

ISO 200 at 1/100sec f22 is also correct.

ISO 100 at 1/200sec f11 is also correct.

ISO 100 at 1/400sec f8 is also correct.

ISO 200 at 1/50sec f11 is 3 stops more, 1 stop of ISO 1 stop of shutter speed and 1 stop of aperture.

The aperture is the hole the light comes through and is a proportion of the focal length. Due to the maths they look odd:
F1 f1.4 f2 f2.8 f4 f5.6 f8 f11 f16 etc (multiply the last number by 1.4)

 

[sk66]

Except when you are given advise about altering the meter reading by changing stops
If you do not know what a stop is, then what do you do?

Adjust the settings in LiveView...WYSIWG.
Or take a picture and chimp...that's what most do anyways.

You pretty much have to do one of those anyways because putting in an offset is just a SWAG...but hopefully closer than not.

More often than not the "right answer" is to properly meter a scene.

If you have not got a grey card you may told to meter off the palm of your hand and add 1 stop, if you have white skin, or subtract 1 stop, if you have black skin.

Or just meter the grass. Green grass is usually about mid gray.

 

[sk66]

It can become critical when you start to use ND filters and need to work out shutter speeds. Too strong a filter and the camera is not going to work the settings out for you. :shrug:

Ive never seen an ND stop the camera from metering... Focusing yes...
I use a 10stop variable ND focus first, shut it down and let the camera set the exposure. Pretty much the same as I would do with an IR filter (focus then add the filter/meter).

 

[sk66]

F1 f1.4 f2 f2.8 f4 f5.6 f8 f11 f16 etc (multiply the last number by 1.4)

I find it's easier for most to just remember 1 and 1.4. Double them and alternate...
1-----2-----4-----8---16---32
--1.4---2.8---5.6--11---22

 

[redhed17]

Ive never seen an ND stop the camera from metering... Focusing yes...
I use a 10stop variable ND focus first, shut it down and let the camera set the exposure. Pretty much the same as I would do with an IR filter (focus then add the filter/meter).

I don't know about your camera, but if I measure the scene without a 10 Stop ND filter attached, and I get a reading of 1/8th sec @ f16 and then put the ND filter on, I may change the shutter to the maximum 30 sec shutter speed in camera speed, and the meter may say it is correctly exposed or not, probably not, but any image taken at 30 sec will be under exposed.

The correct exposure in that situation would be 2 minutes if I want to keep the f16 aperture. I know that because 10 stops from 1/8th sec is 2 min. 1 stop = 1/4, 2 stop =1/2, 3 stop = 1 sec, 4 stop = 2 sec, 5 stop = 4 sec, 6 stop = 8 sec, 7 stop = 16 sec. 8 stop = 30 sec, 9 stop = 1 min, 10 stop = 2 min. The camera couldn't have worked that out because the longest shutter is 30 seconds on most DSLRs.

 

[sk66]

The camera couldn't have worked that out because the longest shutter is 30 seconds on most DSLRs.

That makes sense... I've never taken a shot that long with an ND.

 

[EOS_JD]

Thats a confusing post and sounds like you are suggesting 3 clicks from 1.8 is one stop, 3 clicks from 1/500 is one stop?

(Just trying to clear it up as it could be misleading)

3 clicks of ss (in one direction) from any SS value is a stop of light

3 clicks of aperture (in one direction) from any aperture value is a stop of light

3 clicks of ISO (in one direction) from ANY ISO value is a stop of light.

What is confusing?

 

[EOS_JD]

I don't know about your camera, but if I measure the scene without a 10 Stop ND filter attached, and I get a reading of 1/8th sec @ f16 and then put the ND filter on, I may change the shutter to the maximum 30 sec shutter speed in camera speed, and the meter may say it is correctly exposed or not, probably not, but any image taken at 30 sec will be under exposed.

The correct exposure in that situation would be 2 minutes if I want to keep the f16 aperture. I know that because 10 stops from 1/8th sec is 2 min. 1 stop = 1/4, 2 stop =1/2, 3 stop = 1 sec, 4 stop = 2 sec, 5 stop = 4 sec, 6 stop = 8 sec, 7 stop = 16 sec. 8 stop = 30 sec, 9 stop = 1 min, 10 stop = 2 min. The camera couldn't have worked that out because the longest shutter is 30 seconds on most DSLRs.

In those situations you switch to Bulb more where you can control the shutter speed to any value you wish. You are not limited to 30 seconds in Bulb mode

 

[EOS_JD]

I find it's easier for most to just remember 1 and 1.4. Double them and alternate...
1-----2-----4-----8---16---32
--1.4---2.8---5.6--11---22

I like that lol

 

[Uneducated_Rick]

3 clicks of ss (in one direction) from any SS value is a stop of light

3 clicks of aperture (in one direction) from any aperture value is a stop of light

3 clicks of ISO (in one direction) from ANY ISO value is a stop of light.

What is confusing?

it is only 3 clicks if your camera is set to 1/3 stops increment - some people have it set to 1/2 or whole stop increments

 

[Steve Smith]

If you have not got a grey card you may told to meter off the palm of your hand and add 1 stop, if you have white skin, or subtract 1 stop, if you have black skin.

People's palms are usually of the same reflectance regardless of skin colour. This would only be correct for the back of the hand.


Steve.