Understanding lens diagrams

[Orio]

I am curious if there is someone here who can understand a lens diagram.

Let's take the Planar diagram for instance:

http://en.wikipedia.org/wiki/Zeiss_Planar

Is anyone able to tell the purpose of each glass in the diagram?

i am really curious, and would like to learn how to understand a lens diagram.

[LucisPictor]

Good question, Orio!

I also would like to understand that, since I only know a little bit about the difference between a concave and convex lens.

But, I suppose, the complete lens design is really complicated.
People learn this at university.

Let's hope someone comes up with a quick'n'dirty summary...

Carsten

[Borges]

I can't explain, but erwin puts can...

This is a wonderful 80-side publication from leica written by erwin puts. It's a kind of image brochure, so intended as advertisment. But this publication opens your mind if optical theories are new for you. You will found something about history of lens design, about the work of a designer, the different glass types, thickness, the aberrations - I read it many times the last weeks. This is no concrete explanation why a specific lens has this a concave glass there and a convex here and so on, but he describes the process and the theories behind it.

I am sure you will love this!


english:
www.leica-camera.us/assets/file/download.php?filename=file_139.pdf

german (for carsten):
www.leica-camera.de/assets/file/download.php?filename=file_116.pdf

Michael

[LucisPictor]

Thanks, Michael!

Just downloaded it. Will have a look at it (at both versions ) as soon as I find the time.

And I'm going to post the link in the German forum.

Carsten

[Rob Leslie]

I don't think we need to understand and would go as far to say it wont help your photography any, even if you do. The time and effort is best spent taking photos and a study of what your lens will do and how it behaves with different subject matter and lighting. This also applies to Lens test charts OK as a rough guide but they often bear no relation to how a lens behaves when you come to us it in anger.
Put another way what's the point of understing how a Sigma APO element works if the lens is no good when you take it out and use it!

[Orio]

[dnas]

I'm new to this forum, but I post on various other ones. I know this is an old topic, but it doesn't seem to have been answered in very simple terms.

When you have two transparent media at a common boundary (a lens in air, for example), the light bends at the boundary(glass surface) between glass and air. This is called refraction.

If the light stikes at 90 degrees to the surface, it doesn't bend. However, if it strikes on an angle, it does bend.
Convex lenses are wider in the middle, while concave lenses are wider at the edges.

If we take a single convex lens, then light passing through it will bend a little TOWARDS the center. The further the light rays are from the center, the more the light will bend. Concave lenses work the other way around, bending away from the center.

In a perfect world, we would only need just this one lens element. However, the amount the light bends, depends on the color or the light. For example, blue bends more than green, which bends more than red. If we use just one lens element, then the different colors will not focus on the same point. The lenses also have spherical surfaces, which contribute to the problem.

So lens designers use other glass elements (both convex and concave) to modify the paths of the light rays, in an attempt to focus the different colors on the same point. With glass of the same type, this is a little difficult, and even more so when you have a zoom lens.
That's why low dispersion (SD, UD, etc) glass is used in some lenses for some of the elements, and because it has a different refractive index, it's easier to correct for the different colors.

Also used are aspherical lens elements which do not have a spherical surface, which bends the light in a more correct direction because of its shape.

So to trace the light ray patterns, draw some parallel lines towards the lens. Bend the rays slightly towards the center for convex, and slightly away from the center for concave. The further from the center, the more it will bend. When the ray leaves the lens element, it will bend again towards the center for convex or away for concave. The lines will bend less for the low dispersion elements.

Hopefully, you will find all of your lines converging to a single point!!!

[Attila]

NIce to see you here! Many thanks for this explanation! We all look forward more posts from you!

[kds315*]

Good to read:
APLLIED PHOTOGRAPHIC OPTICS, Sydney F Ray:
http://books.google.com/books?id=cuzYl4hx-B8C&dq=photographic+optics+Ray&pg=PP1&ots=n_PsxXyzLz&sig=SZlovoRVrm-mKBCBlTHz2p7SKnk&prev=http://www.google.com/search%3Fhl%3Den%26safe%3Doff%26client%3Dopera%26rls%3Den%26hs%3DAIN%26sa%3DX%26oi%3Dspell%26resnum%3D0%26ct%3Dresult%26cd%3D1%26q%3Dphotographic%2Boptics%2BRay%26spell%3D1&sa=X&oi=print&ct=result&cd=1&cad=legacy

and
http://www.vanwalree.com/optics.html

and
http://photo.net/photo/optics/lensTutorial

and the "classic" Kingslake:
http://www.amazon.com/Lens-Design-Fundamentals-Rudolph-Kingslake/dp/0124086500