Optics for dummies

[photorat]

I, like many on this forum, know pretty well how to handle my camera. But I realised the other day that I really know jack s*** about how it actually works. Why, for instance, are the dust particles on the rear element of my 15 heliar only ever a problem at f/16 or f/22 and otherwise invisible? Stupider still, why is it that when you close the aperture ring you can still capture the whole field of view and not just a tiny circle in the centre of the frame? Why does it increase DOF?

Can anyone refer me to resources that explain all this (for dummies)?

Cheers and thx!

 

[David Murphy]

Fundamentals of Optics by Jenkins and White (many editions) is a classic. You need about a year of basic physics, and some basic college math to take this book on.

 

[wolves3012]

Any of the more general books on photography should give you a non-technical explanation on depth of field. If you want to convince yourself about the field of view when closing the aperture, take a lens and focus a bright light (spotlight or something) onto a piece of white paper. Close the aperture down while keeping the lens in focus and you'll just see it get dimmer not smaller. As for *why* this happens, it'd take more than a short post on here to explain!

I'm guessing that dust specks on a rear element are significant at small apertures for either or both of 2 reasons: firstly they are a greater proportion of the effective lens area and secondly the depth of field may actually be great enough to bring them towards focus even from behind the lens node. Ok, so the second one is very much a guess on my part, I'm no lens expert!

 

[wyk_penguin]

I think the first part of the answer is valid enough but the second part I can't agree simply for the fact that something can't be "in focus" when there is only air between it and the film.

Sometimes you just have to believe the physics people, just as I believe that striking leys on my computer will allow someone somewhere else to see this message even though I don't know a **** about how a computer works.

 

[akptc]

Here is another optics(?) question that's been keeping me awake at night: why does the RF patch seem vertically misaligned when I look through the viewfinder at a certain angle but otherwise it seems spot on? This only happens on my M bodies, i.e. not on any fixed lens rangefinders. Is it my eyes? an optical illusion? or do all my cameras need adjustment? 😱

 

[bmattock]

"Lenses in Photography" by Rudolph Kingslake. No degree in physics required.

It is out-of-print, you'll have to look for it, but plenty of copies are available. Best book on the subject you'll find.

 

[bmattock]

A freebie, written long ago by an important figure in lens design - a lot has happened since then, but the basics are there.

http://books.google.com/books/pdf/O...YC&output=pdf&sig=0ADvvqrXT8svMiHBs_TNtD6Ja00