Steve Richfield wrote: > Alan, > > On Sat, Jul 28, 2012 at 11:44 AM, Alan Grimes <[email protected] > <mailto:[email protected]>> wrote:
> Steve Richfield wrote: > > Glasses do LOTS of things besides making images sharp. They make > images > > larger or smaller. They introduce pincushion or barrel distortion. > They > > introduce differences in responses to maintain eye tracking. All of > > these things "warp" your sense of where things are in your world. > =\ > I had to go without glasses for a week or two. When I got my new pair, > they made me feel like I was 3 feet tall! =\ > That is because they got your interpupillary distance (IPD) wrong. I > make my own measurements using a precision steel machinists ruler and a > mirror. The gizmos that most eyeglass places have are usually badly > miscalibrated. Profoundly improbable because I had my P.D. checked with three different machines at 3 different opticians as I searched for a new pair, all of the machines agreed exactly. > Note that http://EyeBuyDirect.com has some fancy software where, if you > create an account (no purchase is necessary) and enter in your photo, it > computes your IPD from your photo!!! I tried it. We disagreed by ~1 mm, > which sounds better than your eyeglass place is doing, unless your > prescription is EXTREMELY strong. My astigmatism is 2.0 in one eye and 1.75 in the other. > BTW, the quick test for IPD being correct is to look at an object that > is ~4 meters or ~13 feet away, and flip your glasses up and down to see > if the object seems to jump toward and away from you as you alternately > look through your glasses, and look under them. Your present glasses > would obviously fail this simple test. > I suggest going back and getting them to make their glasses right. Due to financial limitations, I got the cheapest bargain-barrel pair I could find and obtain reasonably quickly. -- E T F N H E D E D Powers are not rights. ------------------------------------------- AGI Archives: https://www.listbox.com/member/archive/303/=now RSS Feed: https://www.listbox.com/member/archive/rss/303/21088071-c97d2393 Modify Your Subscription: https://www.listbox.com/member/?member_id=21088071&id_secret=21088071-2484a968 Powered by Listbox: http://www.listbox.com
