Wednesday, May 31, 2006

Tools for Old Eyes

I got my first pair of glasses at 30. Though the opthamologist said she didn't usually write a prescription for such a small correction, I insisted. You see, I had started spending a lot of time in front of a CRT and I had noticed a curious thing, the periods looked like little ringed planets, and the rings—parallel to the ground with a level head—moved to whatever angle my head was tilted.

This was disturbing to me. I'd always had excellent vision. I had to do something about it. So, off I went, to the opthamologist. It turns out, no surprise, that my problem was astigmatism. Combined with a need for considerably more light and some presbyopia, I now find that I need visual tools for everyday life.

The Bigger Picture

I have my glasses of course, but I also carry a Bausch & Lomb 10X Loupe with a Hastings Triplet lens. It is a lovely little piece of glass.

A 7X Version of the B&L Loupe, Which I also Own

A triplet is a compound lens, three separate lenses cemented together. This technique produces an exceptionally flat field and minimal chromatic aberration (distortions of color). A 10x loupe requires a bit of skill to use because it has a very short working distance. The B&L glass has a focal length 2.5 cm. This is the distance from the center of the lens to the point of focus. The working distance, measured from the face of the lens closest to the subject works out to only 2 cm, though, and your eye must be symmetrically placed on the other side of the glass. The depth of field is small, about 3 mm, so the position is critical. Learning to use it is well worth the effort, though. You can see things that are literally invisible otherwise. This approaches the magical. Aside from the practical benefits, there are new and interesting things about otherwise very familiar objects. Fun, fun, fun.

The B&L glass will run about $40.00 USD, but it is worth the investment. The ~$15.00 USD Belemo Triplet Loupe has excellent reviews, though I have never used it. It has a larger field, but in photos I detect aberrations at the edges so it may not be usefully larger. Still, the low price makes it attractive.

Shedding Some Light

As I mentioned before, I have become progressively dependent on more light (and the resulting higher contrast). Reading serial numbers, part numbers, and the like—particularly in the poor lighting of ordinary rooms—has become impossible.

The best solution I have found so far is my other constant companion, a Streamlight Stylus with a white LED. The 12 candela of lovely photon flux does the trick. The unreadable becomes readable, the indistinguishable becomes distinguished. It takes a good 10 years off my eyes.

The Stylus is a slim, pen-like light that will set you back around $15.00 USD including a set of batteries. At about 15 cm, it is somewhat longer than most pens, but it isn't so long that it can't find a home in your pocket. It is very well made with a drawn aluminum body with a machined brass threaded section for the screwdown aluminum top. It is certainly rugged and will stand up to being treated without special care and probably some abuse.

White LEDs are wonderful things, though they are so common today we take them for granted. A white LED is really a blue LED with a phosphor that is excited by the LED output. You can see the yellowish goop over the LED die, that is the phosphor. The tendency of white LEDs to be bluish, especially at the center is due to the underlying blue chip.

White LEDs require relatively high voltage to operate. Most LEDs are happy at 3V, which can be supplied by two cells. The white guys want at least 4V. This leaves manufacturers two options: use 3 cells in the light or a charge pump that trades current for voltage and steps up the 3V to something that makes the white LED more happy.

The Stylus takes the easier way out and uses three cells. Unfortunately, to make it slim enough to be a real pocketable light, Streamlight chose decidedly oddball and disturbingly expensive AAAA battery. Yes, that's four A's. You've probably never seen one, but imagine the next step from AA to AAA to... really small. The low current-hunger of the LED means a set of these little guys lasts a reasonably long time. Still, at around $4.00 USD for a set of 3, the battery situation is almost a show-stopper. Almost. Fortunately, there is a hackish solution.

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Anonymous Anonymous said...

Very interesting, but the link at the end is broken.

Wed Oct 17, 07:15:00 PM EDT  
Blogger Yaakov said...

It certainly was but now it is fixed.


Wed Oct 17, 07:20:00 PM EDT  

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