Feedback to 'Modes
and the User Interface' - Murphy's Law, May 2005
to Murphy's Law
Regarding the macro
mode on digital cameras, there is a good reason why this is used.
Most digital cameras use what is called a passive autofocus system,
which basically is a "try and see" method of autofocussing: the
camera adjusts the focal length through a range to find the sharpest
image, much like a human would do. This obviously takes some time
to do as the lens must be physically adjusted, the digital image
read out and evaluated, etc. Adding a macro mode allows the lens
to work over a much smaller distance. For example, when macro
is off, the lens doesn't have to move through the close-up range,
and when on, it need not check the more distant range. This saves
considerable time in the autofocus process. And since the autofocus
delay is usually the largest component of shutter lag (which manufacturers
are always trying to minimize), limiting focal distance reduces
shutter lag considerably. Of course, it is a trade-off vs. ease
Some cameras (typically
film point-and-shoot) use an active auto-focus method, where it
bounces a signal off the object to measure subject distance. This
method can be quite fast and would work well for a modeless macro
system, but it has its own set of drawbacks: easily fooled by off-center
subjects, windows, etc., less accurate, limited working distance,
higher cost to implement, etc.
Range finders seem much
less common in the world of compact digital cameras. Since they
already have a digital sensor and sophisticated microprocessor/DSP,
they can do the auto-focus without any additional hardware. Of course,
this leads to the shutter lag problem! The only digital cameras
that can autofocus really fast seem to be the DSLRs and other high-end
models that have a dedicated autofocus system in addition to the
main imaging sensor.
In the case of the compact
digital camera, the trade-off for the manufacturer is between making
the macro always present and eliminating the confusion and decreasing
the shutter lag. Since the vast majority of the customers aren't
shooting macro images but are very annoyed by shutter lag, I think
they made the right decision.
But none of this takes
away from the points in your article about making modes match user
Good Article. A small
slip - The example of a watch - seting time needs a mode switch.
Otherwise accidentlaly pressing the set switches will inadvetently
change the time. Concept is clear , but the exmaple is not valid.
(other examples are perfect).
Niall's Response: I
thought through the accidental change, and I wonder how valid that
is. On a wrist watch, it is very easy to accidentally press a button,
but the example I used was a clock, where I believe that hitting
a button accidentally would be unlikely. I have used many digital
clocks, but I can never recall accidentally putting one into the
'change-time' mode, which would be the result of accidentally pressing
one of the buttons in the current design, so I do not think I would
accidentally change the time if the design was modified to the one
suggested in the article.
I just came across
your article via an ACM newsfeed. Right on! I am passionate about
good, clean software design as well (so much so that I have put
together a modest website to espouse the idea). One example that
you might enjoy is the elevator panel outside the State Library
of Tasmania. You can see my description of it along with a terrible
photograph of it here (http://cleancode.sourceforge.net/wwwdoc/gallery/TasLibElevator.html),
but basically the numbers on the board go from top to bottom whereas
the floors are numbered--like all other elevators--from bottom
Michael Sorens, University
Niall's response: Excellent
site. The elevator example is a case using an incompatible mapping
between the interface and the real world. I make a brief reference
to this issue in an older article, 'Principles of User Interface
Design' available at http://www.embedded.com/2000/0012/0012ia1.htm.