Dispersion

2010.07.26 in personal and photography

I've been wearing glasses since third grade — approximately twelve years. I get new glasses about once a year or so, to adjust to changes in my prescription and fix scratches and such in the lenses.



I don't remember when I last got a new pair — it's been a few months, at least. Since I got them, though, I've noticed a significant degradation in something — initially, something I wasn't able to place. Eventually I noticed what it was: colors were moving! Different colors shifted different amounts depending on what part of the glass they passed through. As with a camera, the centers are perfect, and the edges are the problem areas.

The primary case in which I noticed this for the first few months was when looking at syntax highlighted code: brightly-colored keywords would appear to shift relative to the baseline, some in different directions than others. I eventually mentioned this to Dad, who pointed out the principle of dispersion, and I noted that this was something that most of my lenses strived to reduce (for obvious reasons) through the use of low-dispersion glass (Nikon calls it "ED", and 3 of my 5 lenses have it).

I'm somewhat intrigued by the fact that Nikon makes eyeglass lenses, but I think that's taking brand loyalty (and probably price) a little too far...

Today I stumbled upon a remarkable example of this phenomenon: one of those neon "OPEN" signs at a store near my apartment. I was able to completely remove the red lettering from its containing blue box as shown below, just by looking through the top of my glasses instead of the center — not even something one would consider unreasonable or strange.



The dispersion in the image above is not exaggerated (though it's not to scale, the open sign was quite a bit smaller than in the picture; call it two fingers high at arm's length, or so) — I could repeatedly get the top of the box to clear the bottom of the type.

At this point, I'm quite convinced that this is completely unacceptable performance: it's extremely irritating, to say the very least. I'm fairly sure that something that happened during my last optometric appointment (or, at least, with my most recent pair of glasses) made this much worse, and I will be sure to bring this up next time I visit. (There's another whole rant to be had about how much I detest the fact that there are no truly objective measurements involved in eyeglass prescriptions, and how broken that is...)

Yeah... so... let me know if you wear glasses and have a similar issue, I'd be interested to hear from you! Find a neon open sign and do your own experiments!

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