java disabled or no main menu showing above - use links
| The whole field of
photography is full of matters like, ''exposure'',
''f stops'', ''shutter speeds'', ''depth of field''
..... and so on. Because of so much automation now
available in the modern camera, much of this does
not need to be very deeply understood.
However - many cameras, including some digital, do
give options for a certain amount of manual control.
This then can put the photographer more in creative
control and for that reason some of the more ''technical''
aspects are worth understanding so as to better exploit
the manual options.
Many books have been written on this subject - it
is also possible to find much information on the web.
I will though here just try as briefly as I can, to
touch on various aspects through example and analogy
- after which further reading is recommended.
Try and read through this section first (sorry, I
know - more text!) and then take a look at some diagrams
that will hopefully further clarify what we are discussing.
is an ''f'' stop?? -
Simply put, it is a size of aperture (hole!) in
a lens - mostly controlled by a mechanical iris
If a lens of 50mm focal length was wide open,
then it would have an aperture of f1 and
transmit its maximum amount of light. Reduce that
aperture to 25mm and we have f2, reduce
further again, to 12.5mm and this will be
Now, if we halve the diameter this way in each step,
we in fact invoke the inverse square law .... meaning
that f2 will transmit 1/4 the amount
of light compared with f1. By the time we
get to f4 we are down to 1/16 the
amount of light.
This is too large a jump and so an intermediate
aperture designation is needed, so that each step
halves the light each time. As this is a logarithmic
process, we can multiply the cross sectional area
of the 50mm (f1) aperture (1963.5 mm squared)
by .71, which gives us 1402 sq mm. If we
use that to now work out the new aperture diameter,
(2 x [sq root, area divided by Pi]) we arrive at
42mm. The inverse of .71 is 1.4 and this
is the new f number ...... f1.4 ...... letting
through half the light compared with f1
but twice the light of f2.
The progression of these ''intermediate'' f stop
numbers follows on by being a series modified (nominally)
by factor 2 ..... so, 1.4, 2.8, 5.6, 11,
22 ... each altering the light transmission
by 1/4, as with the whole numbers we looked at first.
The whole sequence then of usual and familiar f
stop numbers would be ........
1, 1.4, 2 ,2.8, 4, 5.6, 8, 11, 16, 22, 32
This is the common scale ... rarely going smaller
than f32, but sometimes intermediate numbers
are added if required. So - go up the scale
in numerical value and you go down the light
transmission scale by factors of 1/2 for
each step. Obviously the reverse is also true.
| Shutter Speed
This is a little less involved compared with apertures!
Quite simply, shutter opening times are either halved
or doubled .... corresponding to halving light input
or doubling light input. Easy!
The usual scale starts conveniently from 1
second ... and then down in halving increments .....
1/2 sec, 1/4 sec, 1/8 sec, 1/15
sec, 1/30 sec, 1/60 sec, 1/125
sec, 1/250 sec, 1/500 sec and 1/1000
sec. Each halving of time, halves light input - but
you will notice here, there is a small concession
to ''rounding off'' the figures, to maintain a convenient
How though do we make choices for shutter speed if
our camera has manual options? This is discussed later
on this page where we consider the importance
of movement (camera and subject) and the effects of
different focal length lenses.
| Aperture vs shutter
We can now hopefully consolidate a vital relationship
here. If we halve the light entering through the lens
but double the duration of shutter opening - we have
not changed the overall light transmitted. For example
We have a setting on the camera of 1/125 at
f8 ...... one of the all round ideal ''compromize''
settings. We could halve the amount of light the aperture
lets in and then double the amount the shutter allows
through ...... giving a new exposure set of - 1/60
at f11 sec.
Going the other way - we might double the light allowed
through the aperture but half the time the shutter
is open - so our new exposure set would then be 1/250
at f5.5. All these three settings will let
exactly the same amount of light through - the exposure
value is the same.
The differences tho will affect how well movement
is stopped (shutter speed)
...... and how much depth of field/focus we have (aperture),
see next section. Thus, choices need made for any
given subject matter based on those requirements.
These factors are further expanded below.
| Depth of Field
(Zone of sharpness) -
When taking distance shots with normal focal length
lenses, this is rarely an issue. As soon however as
we close in on subject matter we have to become more
concerned as to what will and what will not be in
Imagine you wish to photograph a snubbie revolver
with the muzzle in front, but want also to try and
keep the cylinder in focus and even too, the grips.
To obtain the best depth of field you will need the
smallest aperture available and the shortest focal
length of lens ... no zoom. Even then it may be difficult.
Sometimes the best solution is to shoot at high quality,
move back a ways and then later crop the picture to
select the central portion of required subject matter
- this will have improved (''stretched'', or expanded)
your depth of field.
At the other end of the scale, we may in fact want
shallow focus, such that the subject is sharp but
what is behind is well blurred - for this we choose
a much larger aperture if possible. Add to that choosing
to zoom in so that lens focal length increases and
at the same time probably moving away somewhat.
For an example which well illustrates the relationships
between aperture size and depth of field, take
a look here.
All this juggling with aperture will mean compensating
through shutter exposure, the ''time'' factor. This
may induce other potential problems - see following
| Shutter Speeds,
Movement and Lenses -
If as in the above description of depth of field relative
to aperture - we have selected a small aperture to
maximize depth of field - we will be necessarily obliged
to use much slower shutter speeds.
If the subject is stationary and does not need to
be ''frozen'' by a fast shutter speed, all may be
well. Except - there is now still serious potential
for picture blurring due to camera shake. The
way around this will usually be to support the camera
somehow, a sturdy tripod being far and away the best
Camera shake and low shutter speeds also become more
serious as lens focal length increases - remember
how shakey a target looks when viewed through a scope!!
Long focal length (zoomed in) shots always present
problems because you not only want enough shutter
speed to compensate for camera shake when hand held
but - as you increase shutter speed, so you must further
open the aperture - and that will shorten your focal
There might be occasions when a fast shutter speed
is needed however - for instance you want to take
a picture of your buddy firing his auto, and maybe
hope to catch a case in the air! Now - you will have
to use the fastest speed available in the hopes that
it will ''freeze'' motion enough. This would tho necessitate
a large aperture in order to still have a suitable
exposure value - and bearing in mind what is written
above re depth of field .... this just might make
your focus very critical. Something to remember.
It will possibly be apparent by now - there is much
need for compromize ...... you have to decide which
aspect of your picture matters most for a given exposure
- focal depth or, stopping movement and camera shake.
Not always easy!
| "Film Speed"
This is only really relevant when related to films.
They are usually rated by ''DIN'' number or ''ASA''
rating. For example, 100 ASA film is quite slow but
good definition. 200 ASA is twice as fast but with
slightly less resolution. And 400 ASA is twice as
fast again ..... with resolution being further reduced.
With digital cameras however, we are not too interested
in this as most functions are automated. However,
some cameras do have a setting which works like an
equivalent of film ASA, and gives some sort of guide
to choice of flash distances and powers, as well as
sometimes giving the option to make a choice based
on desired results.
plodding though the above, and if you have reached
here - congratulations! I hope maybe you have learned
a little more, even if somewhat fatigued!
If your camera makes provision for manual settings,
including aperture and shutter priority options
- you can maybe now relate what you have read, to
how best those options might assist you in taking
the shots you want.
For some diagramatic reinforcement of all this,
go look at this
page and perhaps it will further help consolidate
Back to Top