Light

Discussion in 'Digital Photography' started by rda, Oct 9, 2004.

1. rdaGuest

I understand the effect on exposure with regards to different exposure
times; 1/250 allowing half the light of 1/500.

But I am still unsure how this relates to "stops". I often hear people talk
about altering exposure by a number of stops either way, but just how does a
"stop" equate to amount of light getting exposed?

Also I am unsure about aperture settings; does f2 allow double the light of
f4 which allows double that of f8?

Any help or pointers to websites would be great.

--
RDA
300D

rda, Oct 9, 2004

2. Joseph MeehanGuest

rda wrote:
> I understand the effect on exposure with regards to different exposure
> times; 1/250 allowing half the light of 1/500.
>
> But I am still unsure how this relates to "stops". I often hear people
> talk
> about altering exposure by a number of stops either way, but just how does
> a
> "stop" equate to amount of light getting exposed?

"Stops" ... Interesting word. It started out as "Waterhouse stop"

http://www.skgrimes.com/wat/

>
> Also I am unsure about aperture settings; does f2 allow double the light
> of
> f4 which allows double that of f8?
>
> Any help or pointers to websites would be great.

More than you ever wanted to know:

http://www.uscoles.com/fstop.htm

In short f stops are reciprocals of the square root of 2.0 (1.4+) So
you get 1.4, 2.0, 2.8, 4.0, 5.6, each one representing double the light
gathering capability of the prior number and every other number double of
the prior.

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

Joseph Meehan, Oct 9, 2004

3. NostrobinoGuest

"rda" <> wrote in message
newsaN9d.5311\$...
>I understand the effect on exposure with regards to different exposure
> times; 1/250 allowing half the light of 1/500.

It's the other way around: 1/500 is half the length of time of 1/250, and so
passes half the amount of light at any given lens opening.

>
> But I am still unsure how this relates to "stops". I often hear people
> talk
> about altering exposure by a number of stops either way, but just how does
> a
> "stop" equate to amount of light getting exposed?

A stop more is twice as much light, a stop less is half as much light. Two
stops more is four times as much light, and so on. While "stop" originally
referred to lens opening, it is now generally taken to mean altering the
amount of light by a factor of two (in either direction) whether by changing
the aperture or the shutter speed.

>
> Also I am unsure about aperture settings; does f2 allow double the light
> of
> f4 which allows double that of f8?

No, f/2 passes FOUR times as much light as f/4, which passes FOUR times as
much light as f/8.

The f-numbers are literally fractions of f, the focal length. So an f/2
aperture is half the focal length in diameter, f/4 is a quarter of the f.l.,
and so on. Since area is proportional to the square of the diameter of a
circle, an f/2 lens opening has four times the area of an f/4 opening and
therefore passes four times as much light (in the same period of time).

The usual sequence of f-stops is based on multiples of the square root of 2,
approximately 1.414, so that each successive stop changes the amount of
light passed by a factor of two. This sequence in descending order of
aperture size is usually given as f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11,
f/16 and so on. Of course there are intermediate f-numbers as well, and also
there are some lenses with maximum apertures larger than f/1.4, though they
are not very common.

N.

>
> Any help or pointers to websites would be great.
>
> --
> RDA
> 300D
>
>

Nostrobino, Oct 9, 2004
4. rdaGuest

"rda" <> wrote in message
newsaN9d.5311\$...

OOPS! this was meant to read.

> I understand the effect on exposure with regards to different exposure
> times; 1/250 allowing DOUBLE the light of 1/500.
>

--
RDA
300D
>
>

rda, Oct 9, 2004
5. Don Stauffer in MinneapolisGuest

Some of the first cameras that had aperture control did not have
completely variable aperture- rather they had plates with various
sized holes. Even on continuous variable aperture, the lever that
controlled the size of the aperture had detents or 'stops' on it. At
first there was no standard for the ratio of one 'stop' to another.
Soon, however, the standard became such that each stop let in twice as
much light as the next smaller one. Since the amount of light is
proportional to the square of the diameter, the aperture DIAMETER
(which is how f/stops began to be labeled) had a ratio of square root
of two, or 1.41. Thus the difference between f/11 and f/8 is
approximately 1.4, and the areas of the two stops differ by two, and
let in two times (or 1/2 times) as much light, equivalent to doubling
(or halving) the shutter speed.

"rda" <> wrote in message news:<paN9d.5311\$>...
> I understand the effect on exposure with regards to different exposure
> times; 1/250 allowing half the light of 1/500.
>
> But I am still unsure how this relates to "stops". I often hear people talk
> about altering exposure by a number of stops either way, but just how does a
> "stop" equate to amount of light getting exposed?
>
> Also I am unsure about aperture settings; does f2 allow double the light of
> f4 which allows double that of f8?
>
> Any help or pointers to websites would be great.

Don Stauffer in Minneapolis, Oct 9, 2004
6. Joseph MeehanGuest

Gary Eickmeier wrote:
> Joseph Meehan wrote:
>
>> More than you ever wanted to know:
>>
>> http://www.uscoles.com/fstop.htm
>>
>>
>> In short f stops are reciprocals of the square root of 2.0 (1.4+)
>> So
>> you get 1.4, 2.0, 2.8, 4.0, 5.6, each one representing double the light
>> gathering capability of the prior number and every other number double of
>> the prior.

>
> I think his problem is more basic than that; 1/250th does not allow half
> the light of 1/500th.

????? I would hope not. It sound be twice.

>
> Gary Eickmeier

--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math

Joseph Meehan, Oct 9, 2004
7. Gary EickmeierGuest

Joseph Meehan wrote:

> More than you ever wanted to know:
>
> http://www.uscoles.com/fstop.htm
>
>
> In short f stops are reciprocals of the square root of 2.0 (1.4+) So
> you get 1.4, 2.0, 2.8, 4.0, 5.6, each one representing double the light
> gathering capability of the prior number and every other number double of
> the prior.

I think his problem is more basic than that; 1/250th does not allow half
the light of 1/500th.

Gary Eickmeier

Gary Eickmeier, Oct 9, 2004
8. rdaGuest

"Gary Eickmeier" <> wrote in message
news:ILV9d.674\$...
>
>
> Joseph Meehan wrote:
>
> > More than you ever wanted to know:
> >
> > http://www.uscoles.com/fstop.htm
> >
> >
> > In short f stops are reciprocals of the square root of 2.0 (1.4+)

So
> > you get 1.4, 2.0, 2.8, 4.0, 5.6, each one representing double the light
> > gathering capability of the prior number and every other number double

of
> > the prior.

>
> I think his problem is more basic than that; 1/250th does not allow half
> the light of 1/500th.

Thats what happens when I post in a hurry ;-)

--
rda
300D

rda, Oct 9, 2004
9. Frank essGuest

Don Stauffer in Minneapolis wrote:
> Some of the first cameras that had aperture control did not have
> completely variable aperture- rather they had plates with various
> sized holes. Even on continuous variable aperture, the lever that
> controlled the size of the aperture had detents or 'stops' on it. At
> first there was no standard for the ratio of one 'stop' to another.

I am forever envious of the photographer who chose as his 'nome de
frame'

"F. Stop Fitzgerald".

--
Frank ess

Frank ess, Oct 10, 2004