Thurs Feb 21, 5p

We covered astigmatic corrections, including power-cross, the idea of crossing 2 cyls to obtain any spherocylindrical dioptric power, axis transposition, with- and against-the-rule astigmatism & it's physiological origins, as well as basic design of spectacle lenses. A water melon from Pete's Frootique helped. Here's the whiteboard - a bit cryptic I fear.



We then tried all the spex sent by Giese Optical International and none of them provided the clear vision we had all looked forward to. But the 200 pairs from VAO arrived this afternoon and are currently soaking in my bathtub (I have two, if you want to visit). I will distribute packs of those to you, together with trial case lenses, for you to practice neutralisation and mark-up of optical centres etc. This is a very useful exercise, methinks, and I promise to include something similar in your April exam. The first step is to figure out what type of lens you're dealing with, the second is to estimate power etc. Here's the whiteboard:



Last, I showed you how to calibrate a focimeter. The blasted thing was broken and I electrocuted by right eyelid. Remember, keep both eyes open and slowly reduce the telescope down until the graticule image first becomes clear.

Get an updated script with an added step-along problem from http://myweb.dal.ca/partes/O4iP_22Feb08.pdf.

Oh, and there is a new treat from the Scary Monkey under Valentine's Day.