glasses

Just like a new pair of glasses, your brain has to ADAPT to the presented image. I have moderate astigmatism, plus a HUGE difference in refraction between my two eyes. I have to adjust the two eyepieces to the opposite limits before I get both eyes to focus at the same time. So, give ONE specific microscope some time to get used to. If you are nearsigted, use the microscope without glasses. You may have to adjust the eyepieces a lot. But, without the glasses, you get a HUGE increase in field of view. Oh, and of course, you have to adjust the eyepieces for interpupillary distance, too. The trick is to move your head slightly side to side. When both eyes see the same vignetting, the IP distance is set right.

But, when all this is set right, you can see stuff that you'd never be able to see with the viewer hoods.

For electronics, of course, a microscope with a big working distance is also a big help. 100 mm is the BARE minimum, 150 mm is probably the best.

Jon

VERY interesting! I use all optical instruments without glasses. We're talking binoculars, telescopes, microscopes. Well, of course, I am not reading text with those, but I don't seem to notice any astigmatism effect. All of these instruments make stuff BIGGER, however, so maybe the astigmatism is just not evident when objects appear large.

Jon

It's pretty easy. Off-axis, lenses are prisms.

Hold the lens away from your face, with some vertical reference line or feature in the background.

If the lens is off-axis, the lens will appear to "break" the vertical reference line. Negative lenses shift the 'broken' line segment toward the lens' optical axis, positive lenses shift it away.

Shucks, he stole my technique.

Grrr.

Cheers, James Arthur

Which one? The technique where you set fire to the prescription with sunlight, or the one where you etch marks in the lenses with a permanent marker?

You stole my growl.

I didn't say it was hard, just a bit harder than burning holes in paper on a sunny day. ;)

Light passing through the centre of a thin lens is undeviated, which is one of the bases of high school optics. (I still use high school optics quite a lot--it's an approximation, but a very useful one.)

Cheers

Phil Hobbs

The fire technique burst my suspension-of-disbelief when I was a kid reading "Lord of the Flies." Piggy was near-sighted.

Your video guy didn't mention that lens height is important too, and the technique works to find the len axis in X and Y.

If the lens' optical axis is wonky or mismatched to your pupil height, it'll drive you batty.

But horizontal alignment is more critical, because your eyeball-pointing control system (vergence) is hard-wire tied to your eyeball-focusing system ("accommodation"), and vice versa.

So, if your eyes are commanded to a certain convergence anticipated for a particular task, but external optics displace the images from their expected positions requiring a different vergence, your extra-ocular muscles (the pointing muscles) clash between the predicted and feedback- driven positions, producing eye strain, headache, and fatigue.

Arrr, ye' don't say, matey?

Cheers, James Arthur

It's Pi Day, not Pirate Day.

(In other words, your pi don't rate.) ;)

Cheers

Phil Hobbs

They never struck me as particularly impatient, but the capacity for being able to detect that an image is slightly out of focus isn't uniform or cons istent.

I once had to get my eyes tested after about a week of more or less continu ously refocussing and destigmating images on a particularly baulky electro n microscope, and was congratulated by the optometrist on detecting small d ifferences in focal strength quickly and consistently (which had never happ ened to me before, and hasn't happened since).

Tell that to my patched eye(rate), matey!

In the old days sailors lost their vision to sun-sighting through sextants, but my squinted eye is due to optometrists' +/- 0.25 diopter precision(*) making it too maddening to use both sides of my specs at the same time!

(*) I can measure my own Rx to 0.1D easily, 0.05D if I really try.

I've had the same experience as John. I recently had an O.D. Rx me some new specs, ignoring (and well different from) my casual measurements, insisting on her own.

I was right and she was wrong. Beyond the erroneous Rx, the lab's work was off too--one lens' optical axis is off center, and the cylindrical correction I didn't want, isn't correctly oriented.

It's probably all within spec, so to speak. Their industry's standards aren't very high.

The resulting two pair are unusable, but she was spectacular enough that I didn't mind.

Cheers, James Arthur

If James Arthur comes across to optometrists as the same kind pompous self-satisfied nonsense-peddling snake oil merchant as he presents as here, it's not surprising that the prescription he got didn't suit him.

His political prescriptions are bad news for the lower 99% of the US income distribution, so it can't come as a surprise that the 99% are getting their own back.

We had all-company-folks pizza and pie today, in room 3.14.

Avast, were she a square pizza matey? Because then ye c'ld saye, "The pie arrrh squared!"

Cheers, James

I'm talking about the eyeglass+lens seller, not optometrist.

If you were here, that would get you 22/7 in the face.

Yes, but I'd have dodged 355/113rds to the left, making your 22/7ths a clean miss.

Cheers, James "~3.141592653589793238462643383279" Arthur

I used to know pi to 100 places.

During our pi lunch, one conversation drifted to rational approximations of pi, which then drifted to generalized rational approximations of real numbers. That came up in the programming of the LMX2571 synthesizer, where, to hit a target frequency, you have to find the best N/M ratio. That gets us bogged down in all sorts of number theory and subtleties. I think the guys have worked it out.

TI has an eval board, and PC code to talk to it, but they won't show us the code to program their chip!

These might help you memorize more digits for Pi:

I didn't memorize Pi intentionally. I noticed it one afternoon in a list of handy constants on the back flap of my junior-high math text, read through it, and have just remembered it ever since. I was surprised as anyone.

Some pals didn't believe me, so I recited it for them, starting a mad competition of them each trying to memorize more digits than the other. We'd often catch them between classes, violently disagreeing over what the n-th digit was (or wasn't).

(Did I mention that they turned out to be Forth programmers?)

Brains are weird.

Cheers, James Arthur