The day you bought your computer will always be the day it booted and ran the fastest. As you add hardware, software, drivers, etc., you increase the load on the machine. USB and other external devices don't arbitrarily affect the efficiency of how your computer runs, although they affect power use. I turn them off to save power (especially when using a laptop).
I also do things like remove CDs from drives to speed things up at bootup. This helps the disk operating system, since it won't have to spin up the CD when it first looks at the computer directories. And when I'm editing images and I want maximum performance, I reboot my computer and start up only my image-editing application. Rebooting helps defrag RAM and makes sure I don't have any other hidden applications running.
The EV Answer
A) In the February HelpLine, I asked: "If the explicit value of EV=0 is ƒ/1 at 1 sec., can you think of another value of EV=0?" Rich Kolson from Verona, Pa., sent in the answer:
"Based on the EV value of 0 being defined as 1 sec. at ƒ/1, equivalent exposures for EV 0 should be: ƒ/1.4-2 sec.; ƒ/2-4 sec.; ƒ/2.8-8 sec.; ƒ/4-16 sec. I don't believe that reciprocity failure comes into effect since EV is a numerical exposure value rather than a required exposure to produce a properly exposed photo."
Great, Rich, you win the prize: a copy of the new PCPhoto Best Tips and Techniques for Digital Photography, a collection of articles, stories, how-to tips and more from the pages of PCPhoto.
You're right on the reciprocity failure (plus, the original question dealt with digital cameras). For those of you unfamiliar with the term, reciprocity failure is when film doesn't respond to light as quickly during long exposures. In other words, as exposures get longer, more light is required to hit the film in order to create an image. Film manufacturers publish correction factors to counteract this effect.
What's In A Name?
In the January/February issue of PCPhoto, a minor error crept into the "Digital Camera Fundamentals" glossary: JPEG stands for Joint Photographic Experts Group not Joint Pictures Expert Group. Another term on the video side of compression (not in the glossary) is MPEG. It stands for Moving Picture Experts Group (many people think the "M" stands for motion, but the group wanted to make a point that they were working on compression for everybody, not just the movie studios).