question for Darryl

[harry a saake]

when blocking up lenses that are st,s, it is common on some to notice that the line does not appear straight across, but rather has a sag in the middle. Do they, or is this an illusion created by the blocker and in some cases the lens?

[shanbaum]

Harry, imagine for a moment that Darryl is a ball. A nice spherical one. Draw the largest possible circle around him on his surface. Now hold him so that you're viewing the circle straight-on and horizontally - as though Darryl were the Earth, and your circle the equator. The line's nice and straight, isn't it? Now, rotate Darryl downwards along the vertical. What happens to your line?

[harry a saake]

Shanbaum, i don,t know, can you make Darryl available for test purposes

[Darryl Meister]

"Imagine Darryl as a ball... Rolling down the hill, toppling over innocent bystanders as they gather to admire his sphericalness..." ;)

I can't say that I've ever given this a great deal of thought. Robert makes a very good point. It seems to me that the curved appearance might also be affected by the base curvature of the major (distance) portion of the lens.

Best regards,
Darryl

[eyesguy]

Hi Harry:

A slight curve in the seg line is perfectly normal. As Shanbaum and Darryl have suggested, it's a geometry thing dealing with angle of view of a straight line on a spherical surface. The amount of curve you see depends on both base and add AND somewhat by the way the casting mold was manufactured.

Regards,

eyesguy

[harry a saake]

:D i can see the first two points, explain what the casting mold would do to effect this.
...PS what would it look like if shanbaum was spherical?

[shanbaum]

I am spherical.

[eyesguy]

It's hard to explain if you are not familiar with ST mold production methods. It has to do with cutting the face angle on the fusing segment or bar stop on one-piece molds In both cases, you're cutting a angled flat on the edge of a sphere which can lead to a curved face. Like I said, it hard to explain -- sorry!

eyesguy

[harry a saake]

Shanbaum, your not spherical, Spiritual would fit.

MALO MORI QUAM FOEDARI

[shanbaum]

I'll be sure to tell my Rabbi, if I ever get one.

[harry a saake]

SHANBAUM, I THOUGHT YOU WERE ONE