In photography you will find that on your SLR will be a shutter speed called
“15”. This represents 1/15th of a second, and for many
photographers you would think that 1/15th is something
akin to a long time exposure. It is not, and even without optical image
stabilization electrotrickery, offered on many DSLR’s, this shutter speed can
actually be hand held, as long as some basics steps are adhered to.
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, but I think is a carry-over from Box Brownie days.
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 the picture.
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 ฝ 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 ration, 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.
The continuously variable aperture cameras slowly
disappeared, with ‘click-stopped’ aperture became a common feature in the 1960s;
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! Understand the
numbers 15 and 16 and how they affect your final image, and you will expand your
photographic abilities.
