A Question About Stops

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mrphilk

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Phil
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Some of you might have read my previous threads so thanks for your patience.

I just purchased a DSLR and am in feet first trying to learn everything. Im getting myself confused with all the jargon.

Stops, is this for example 1" or 0.5" exposure times?

Or is the the scale using the `Av` button on my camera that goes from -2 - +2?

Ive tried a few searches but either im missing sometihng or not quite getting it.

For examplle I read about doing HDR imagery (maybe a bit advanced for me i know) and it said take 7 pictures at different stops.

Does this mean start at -2 and work up, or start at 1" and work faster?
 
I've been shooting with my dslr now for year and I still don't know all of the jargon so I wouldn't worry about it.

I am not sure but I've always taken a stop to refer to the aperture.

For instance, on my old 50mm f/1.8 the apertures are:

1.8. 2.8. 4, 5.6, 8, 11, 16 & 22.

So to drop a stop would be going from 8 to 5.6.

However, modern cameras and lenses can do this in 1/3s so:

8, 7.1, 6.3, 5.6

I can't tell you if a modern stop equals one complete drop or whether it includes the 3rds as well.

I am sure we'll find out soon when someone more knowledgeable comes along :D
 
The expression 'stops' has become a bit confusing so I can sympathise.

The expression 'stop's, comes from the very early days of photography when photographers had metal plates with different sized aperture holes in them which they used to adjust exposure by sliding them into a slot behind the lens. They literally thought of it as stopping or admitting light - hence the expression 'f stops' which crept in for different aperture sizes and the term continued in use long after the metal plates were replaced with the adjustable diaphragm as we know it today.

If you open up the aperture from f4 to f2.8, you open up by one whole stop, effectively doubling the amount of exposure by one whole stop. Similarly ,if you close down the aperture from f2.8 to f4 you reduce the amount of exposure by one whole stop - effectively halving the exposure.

Just to confuse the issue though, when we talk about adjusting exposure by a given number of 'stops' we aren't necessarily talking about using the apertures to achieve it -it can just as easily be done by adjusting the shutter speeds which have the same halving and doubling sequence as the apertures, and the same effect on exposure.

In other words through common usage,the term 'stops' has come to mean a given amount of exposure adjustment, but not necessarily referring to aperture changes.

See if this tuturial helps at all....

CLICKY
 
One stop is equivilent to a doubling or halving of the exposure (also known as 1 EV - exposure value).

You double or halve the exposure by doubling or halving the exposure time using the shutter,

OR by doubling or halving the light getting thru the lens using the aperture settings, that familiar sequence of f2, f2.8, f4, f5.6, f8, f11 and so on. Shifting from one to the next being a one stop change.

The exposure compensation settings you refer to are normally calibrated to show whole stops and 1/3 stop increments.

All the best John
 
As said above, a 'stop' nowadays refers to any halving or doubling of exposure - aperture, shutter speed or ISO.

Shutter speeds and ISO are obvious, but the key to understanding f/numbers is to multiply by the square root of two, ie 1.414. Also, the higher the number, the less light is passed, eg f/2.8 x 1.414 = 4 (rounded) which is half the light. There is a mathematical justification for this, but it confuses the heck out of most newcomers ;)

Try this - 1/125sec at f/4 and ISO200 is the same exposure as 1/250sec at f/5.6 with ISO 800.
 
I think I get it now :-) read a little bit of that turorial (ive saved it to read fully later) and I think its `clicked` :-)

As if it wasnt complicated enough without using the same name for 2 things that can be quiet confusing on their own lol
 
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