How big is a 'stop' and a ND filter question

Nicola.P

Nicola.P

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Nicola
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In relation to Aperture and shutter speed. I know you get full stops and half stops but I am never sure when using my camera what 1 stop is and what half a stop is?

Also I have seen in magazines and the like people using Nd filters say to meter with it off and then adjust the aperture/shutter speed by x amount of stops. Why? Why can't you just meter with it on? (I normally use matrix metering)
 
ill let someone else answer ND as i never use them

but f stop in full increments is

f1.4, f2.0, f2.8, f4, f5.6, f8, f11, f16, f22

thirds and halves are obviously in between
 
Each full stop equals either double or half the light of the previous/next whole stop.

The following are 1 stop apart ...

F/
1.4 2 2.8 4 5.6 8 11 16 22 32 45 64

Each one is 1.4* the previous - i.e. it's related to the Sqaure root of 2, i.e. from 1 to the one after the next the value doubles or halfs - not too confusing I hope.

n.d's are usually marked in 1/3 stops or multiples of full stops - depends on maker, it's best to check each

You can't just stick the filter on the lens and meter, it won't make much difference unless it's a grad nd and you'e trying tio retain detail in the sky and you're meter is working mainly to the foreground light values - this does depend on composition.
 
Thanks :)

How do stops work with shutter speeds or are stops just for aperture?

So with ND filters if I had say a 7 stop ND filter I would meter with it off and then adjust the shutter/aperture by 7 stops? Or is it more complicated than that?
 
Stops work for both but the numbers are different.

leaving the aperture unchanged each of the following are a full stop apart

1/

15 30 60 125 250 500 1000 etc

Don't forget that 1/125 at F/4 gives you the same exposure value as 1/15 @ F/11 but the depth of field changes (due to the aperture) and so goes subject movement (and camera shake) due to the shutter speed.

Re the 7 nd, this is either a 7 stop (unlikely) or 7 * 1/3rd stop, i.e. 2 1/3 stop - check with the maker which it is - or just try each - the beauty of digital being you'll know straight away.
 
I think probably the easiest way to picture stops is that both shutter speed and aperture has an effect on the amount of light getting to your sensor without taking into account the aesthetic qualities involved in changing aperture/shutter speed.

A whole stop means either doubling or halving the light getting through. Most cameras allow changes in 1/3 stops but some have 1/2 stop changes.

I guess the easiest way to figure out you are changing the light getting in by a stop is to move your shutter speed three places.
 
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