Alright, so I've noticed a few things in some of the lens design diagrams in the lens reviews, and I'd like to know what they are.
I'm using the diagram of the Pentax-M 28mm F3.5 as the example because it has the things I'm unsure of. I'll attach a photo with colored circles around what I'm talking about.
On the line that runs down the center of the elements, there are several 'breaks' with small dashes in them. What are these for, if anything? They are circled in
RED.
There's an oddly-shaped element in some of these wider-angled lenses. does this type of element have a name? I assume it's what allows the lens to have a focal length lesser than the flange distance, but correct me if I'm wrong. The element is circled in
GREEN. I've also seen arrangements of multiple elements in other wide angle lenses that appear to have a similar purpose. Does this type of grouping have a name?
On the element circled in green, there are small indents on the top and bottom. Do these provide any optical function, or is it more of a groove to hold the element by? The indents are circled in
ORANGE.
Thank you!