and do not want to be burdened with technical details. There are,
however, three such foundational technical details that will make your
life easier if understood. There are also some easy and free guides to
helping you take usable photos. The key to good exposure, exposing your
film to light, is based on the three pillars of shutter speed, aperture and
film speed or ISO. Lets look at each of these briefly.
Shutter Speed
The shutter speed is simply the amount of time that the shutter is open,
letting light into the camera. Often, this is marked in whole numbers
on your camera, e.g. 15, 30, 60, 125, etc. Usually, these are fractions
of a second, e.g. 1/15th of a second, 1/30th of a second and so on.
With mechanical shutters, these are not precise numbers, so 1/25th is
pretty much interchangable with 1/30th. Part of using a vintage camera
is getting a feel for how close the inscribed shutter speed is to
actuality.
Note that for the most part the numbers double each step. This means
that the shutter will be open for half the time each step, letting in
half as much light. This is useful to keep in mind when applying the href="#reciprocity">Rule of Reciprocity and using f-stops. This
brings us to the next pillar of exposure, aperture.
Aperture
Aperture is simply the size of the opening or iris in the lens. The
numbers on your lens, e.g. 4, 5.6, 8, 11, 16, etc. indicate the ratio of
diameter of this opening to the focal length, bigger numbers mean a
smaller hole or iris opening. These are called f-stops or just stops.
So, f/1.0 would be a wide opening that lets in lots of light while f/22
would be a small opening. Like shutter speed, each step to a larger
number (stop up) lets in half as much light. Knowing this and for the
conditions that Rule of Reciprocity holds,
you can trade a step up of shutter speed with a stop down in aperture,
or vice versa. To make an exposure, you need one more item, the speed
of the film.
Film Speed or ISO
One cannot choose a shutter speed or aperture until the speed of the
film is known. The ISO number tells you how sensitive the film is to
light. The higher the ISO number, the more sensitive the film is,
leading to shorter shutter times or smaller apertures or both for the
same lighting situation. There is also a corresponding increase in
graininess of a film with higher ISO, though this differs with films and
is dependent on the developer used to process the film.
So, for darker situations, Ilford Delta 3200 (nominally
ISO 3200) or CineStill[1] 800T (nominally ISO 800 in incandescent
light) might be preferred, while for daylight an ISO 100 film might be
fine. Alternatively, If a coarse grain is desired an ISO 400 or higher
film might be chosen. While if a fine grain is desired a film of
ISO 100 or less might be chosen, like Adox[2] CMS 20 II
(ISO 20 in Adotech developer), Ilford Pan F (ISO 50) or
Kodak Ektar 100 (ISO 100). Note that tabular grain films
tend to be finer grained than traditional grain films.
So, how do we put together these three elements to get an exposure?
Well, with an exposure guide, of course!
Exposure Guide
The simplest exposure guide is the Sunny 16 Rule. This rule
simply states that on a typical sunny day an hour after sunrise to an
hour before sunset, set the shutter speed to the ISO of the film (e.g.
to 1/100th of a second for ISO 100 film) and an aperture of f/16. There
are extensions to this rule that say open up a stop for hazy sun
(f/11), another stop (f/8) for cloudy or overcast situations and so on.
SLR Lounge lists href="http://www.slrlounge.com/photography-essentials-the-sunny-16-rule/">a
table of Sunny 16 light conditions amongst other tips.
While the Sunny 16 Rule can save the day, you may have questions about
other lighting conditions or applying the Rule of Reciprocity. For these,
handy paper calculators can be had for free or a small cost. There is
even a calculator for covering situations where reciprocity fails. This
and others will be covered in the next post on Ag+ Process.
Rule of Reciprocity
The Rule of Reciprocity simply states that the product of illumination
and time of exposure is a constant. In clear terms, if you open up one
f/stop or close down one f/stop, then you must halve or double the
shutter speed, respectively. To illustrate the correspondence, say for
an ISO 50 film using the Sunny 16 Rule:
| Shutter Speed | Aperture | |
|---|---|---|
| 1/25 | f/22 | -1 stop |
| 1/50 | f/16 | Sunny 16 |
| 1/100 | f/11 | +1 stop |
| 1/200 | f/8 | +2 stops |
| 1/400 | f/5.6 | +3 stops |
Interactive Exposure Tool
Check out the interaction between ISO, shutter speed and aperture with
This great tool by Tony
Catalano
shows how these three elements interact for correct exposure,
stopping motion or causing blur and changing depth of field, respectively.
First try using the Shutter Speed Priority and vary the shutter speed.
Notice how the fan seems to stop with higher shutter speed. Then try
Aperture Priority and vary aperture, note the lamps in the background and the
effect on bokeh and depth of field. Finally, go Manual mode and vary the ISO
and one other setting at a time to see the effects.
That's it for now. Stay tuned for the next article on exposure guides!
Update, 2016-01-30:
[1]: http:/2015/07/cinestill-film.html
[2]: http:/2015/10/profile-adox-fotowerke-of-berlin-germany.html
Update, 2016-01-30:
[1]: http:/2015/07/cinestill-film.html
[2]: http:/2015/10/profile-adox-fotowerke-of-berlin-germany.html
