Crossed Cylinder Concept (HELP)

[John@OWDC]

Does anyone have a VISUAL, mechanical, or "3D" teaching aid for crossed cylinder?
OR
Does anyone have a clear step-by-step "Crossed Cylinders for Dummies (me)"

If you do would you please just email me direct at: johnseegers at laramyk dot com.

Thanks

[rbaker]

If you Google "Jackson cross cylinder" you will find about a million citations.

[John@OWDC]

If you Google "Jackson cross cylinder" you will find about a million citations.

I'm looking for how it relates to the optical cross, toric transposition and drawing lens power/position.

Not the refraction - optometry stuff.

Plenty of three-step drawings of sphere (combined with) cylinder becomes this ________

But nothing that really explains why our sphere becomes 0.00 and power (combined with) 0.00 and power.

A sphere is a sphere - and a cylinder is a cylinder.

I'm missing the point where a nice -2.00 sphere transforms to being 0.00 -2.00 for the sake of cross-cylinder.

I'm missing something and if I can't visualize it I can't grasp it.

I don't even have a rational starting point to build from.

Could someone give me a realistic day-to-day example of it?

Let's say you received the following ________________________.

How would you take that information and create a working Rx that another optician would recognize

I have some worksheets but nothing that gives me a good reason WHY we do it or need it.

Sure I can follow the steps as outlined and end up back at the Rx given but that doesn't help explain the why just the how.

I need the why!

Sorry - hope that helps.
John

[Chris Ryser]

Determining cylinder power

Two questions should be asked to determine thecylinder power:

1. In what direction on the number line is traveloccurring (on the number line) from the sphere to thecylinder (either in the negative direction or in thepositive direction)?

2. What is the distance traveled from the sphere to thecylinder power (the amount of cylinder present in theprescription)?

see also:
http://www.ooa.org/aws/OOA/asset_man.../110761?ver=83

[Chris Ryser]

This one has several solutions, take your pick


https://www.google.ca/search?q=cross...w=1280&bih=592

[John@OWDC]

Page 1: Example from a student notebook. Sure, follow the steps and you end up back at the Rx. So what. WHY do you need to do this?

Page 2: Example from Geometric Optics book. Sphere COMBINES WITH Cylinder the usual three-step drawing.

Now can we put these two together some how?

A real-world example?