This week’s column is
dedicated to the DSLR users, rather than the compact users and certainly not
the camera-phone folk. Don’t get me wrong, compacts and camera-phones will
give you images, but not the equipment you can experiment with.
Let’s take the number
15 as an example. The simplest 15 is shutter speed, and almost every camera
ever made has a setting called “15” which stands for 1/15th of a second.
This is probably the most underused shutter speed ever, and yet it can help
make your photographs very much better.
There seems to be an
idea in the photographic world that anything slower than 1/60th of a second
cannot be hand-held, and you must use a tripod. This is tripe - unless you
have some medical condition resulting in uncontrolled shaking spasms.
The reason to use
1/15th is to expand the light range in which you can take shots without
flash, such as sunsets for example, or to bring out the background, even
when using flash. You know the shots taken at a function where you get
someone looking like a startled rabbit in blackness, where if you had used a
1/15th shutter speed you would have got a nice mellow background to soften
Of course there are a
few tricks to hand-holding at the slower shutter speeds. The first is to
steady yourself and that can be done easily by leaning against a wall or a
pole (preferably not a chrome one attached to a go-go dancer). The second is
to hold the camera firmly in both hands, take a breath in and hold it and
then gently depress the shutter button. I have even shot at ½ a second by
holding the camera firmly pressed down on the back of a chair. Take a few as
some will have obvious camera shake, but you will get at least one good one.
Still on the number 15.
There is a theoretical f stop which could be called f 15. F stops after all
are only a way of measuring the diameter of the aperture inside the lens, to
bring it to its simplest terms. As you go through the usual f stops of f 8
to f 11 to f 16, you are actually cutting the light down by one half each
time. The f stop scale is also an inverse ratio, as the bigger the number,
the smaller the diameter. There is a good mathematical reason for this, but
just believe me.
If you really want to
get technical, for example, f/16 means that the aperture diameter is equal
to the focal length of the lens divided by sixteen; that is, if the camera
has an 80 mm lens, all the light that reaches the film passes through a
virtual disk known as the ‘entrance pupil’ that is 5 mm (80 mm/16) in
diameter. The location of this virtual disk inside the lens depends on the
optical design. It may simply be the opening of the aperture stop, or may be
a magnified image of the aperture stop, formed by elements within the lens.
The f stop scale is a
sliding one, allowing for fractional differences in the light allowed
through to the film (or the digital sensors). Most old cameras had an
aperture scale graduated in full stops but the aperture was continuously
variable allowing the photographer to select any intermediate aperture, and
thus it would be possible to shoot at f 15.
variable aperture cameras slowly disappeared, with ‘click-stopped’ aperture
became a common feature in the 1960’s; the aperture scale was usually marked
in full stops, but many lenses had a click between two marks, allowing a
gradation of one half of a stop.
On modern cameras,
especially when aperture is set on the camera body, f-number is often
divided more finely than steps of one stop or half a stop. Steps of
one-third stop (1/3 EV) are the most common, since this matches the ISO
system of film speeds. Enough technical details! Time to just believe me
Finally, a rather
obscure photographic 15. The AA lithium batteries that power many cameras
and flash units weigh 15 gm.