View Full Version : Optical theory primers?

David R Munson
12-Jun-2007, 16:07
I'm looking for an elementary introduction into multi-element optics. Specifically, something that would be useful for the tinkerer. I'm debating trying to adapt the lens from my Holga to my Mamiya 645, but this would require making the lens retrofocus to make room for the mirror. Also there are some ideas floating around in my head for LF optics. Suggestions for online guides or books one might find on Amazon would be much appreciated.

Mark Sawyer
12-Jun-2007, 17:04
Go to amazon.com and do a search under "Rudolf Kingslake". Probably "Lenses in Photography. The Practical Guide to Optics for Photographers" would come closest, although "A History of the Photographic Lens" is (I think) the most useful and informative for large format users...

But most of his stuff is a bit dry and presumes a fair amount of basic knowledge. Kingslake was definitely more an optics expert than a writer...

Bob Jones
12-Jun-2007, 17:30
Another possibility you might want to look at is the CD book "Exploring Simple Lenses" by John Evans. It's currently $19 and despite being mainly about single-element lenses it may be of interest. When I bought it a month or two ago it shipped from the UK in about a week.

Available from http://www.AlternativePhotography.com There's a short review posted there too.

Paul Metcalf
13-Jun-2007, 13:55
Online freebe http://www.mellesgriot.com/products/optics/toc.htm

13-Jun-2007, 16:24
A serious book on the subject is "Applied Photographic Optics" by Sidney Ray. It discusses in quite some detail every aspect of lenses and lens systems and how they work. Not a light read or an easy book but if you have mastered all the material there, you should be working for Schneider or Rodenstock. It won't be the first place you look to learn something about photographic optics but will probably be the last. It is expensive, you might want to have your library borrow a copy for you before you commit to buying it.
Dave B.

David R Munson
13-Jun-2007, 20:03
Thanks for the suggestions. The Holga/Mamiya mod is something I've been toying with for a while, and figure it's about time I actually start figuring out how to do it right. Now I just have to find a junked 645 lens to gut to graft the Holga lens into!

Emmanuel BIGLER
14-Jun-2007, 00:02
Thanks for the suggestions. The Holga/Mamiya mod is something I've been toying with for a while, and figure it's about time I actually start figuring out how to do it right. Now I just have to find a junked 645 lens to gut to graft the Holga lens into!

Hi !
If I understand well, the goal is to allow a mamiya 645 to focus with the Holga lens when the subject is located at infinity.
The first thing you can experiment easily is to mount the lens by any means in frot of teh camera body and see that you can actually focus at a certain distance. For this you do not need any book, you just need a piece of paper and may be a pocket calculator to compute the position of the image for a given position of the subject using Newton's formulae or similar classical formulae of paraxial geometrical optics.
Then you want to be able to focus at infinity with the Holga lens. This might no be possible as you mention, however taking into account that it is for experimental purpose, you can apply the principle of the retrofocus lens by adding a negative lens element in front of the Holga lens. I have no idea of the Holga lens design, if it is a single lens element, you'll have to play with a two element system.
You could find some help by using a real lens design software like OsloŽ for which a free version, Oslo-eduŽ is available, the free version allows to design up to a 4-element lens. A group of my students in engineering just played with Oslo-edu they re-started from the 1902 tessar design patent and were able to re-compute everything with Oslo. they had absolutely no knowledge of lens design, however they did have some basic knowledge about single lens elements.
Oslo-edu is perfect to play with perfect single lens elements, just enter the focal length of each element and spacing between them and Oslo will compute everything for you.
No need even to know anything about Mr Snell's, (Descartes' in France) or Newton's formulae ;-)

Emmanuel BIGLER
14-Jun-2007, 07:03
Even if this is not at all a 'primer' and even if you have no use of the OsloŽ software, I have found the (freely downloadable) Oslo Reference Manual to be an excellent reference textbook on optics.

Chapter 3 on paraxial optics contains the answer and basics about most things photographers can need when trying to adapt a 60mm Holga lens to a 645 SLR ;-)


"Chapter 3, Paraxial Optics"

David R Munson
14-Jun-2007, 10:34
Excellent info, guys. Many thanks.

Emmanuel BIGLER
15-Jun-2007, 02:34
If we do not care for aberrations, there is a simple solution to the problem by adding a negative lens element in front of the Holga lens.
The focal length of the coupound will be 75 mm and the clearance behind the holga lens increased to 88 mm.
Sure, the aberrations will be terrible, but with a Holga, as far as I know, this is part of the game ;-)

A good example of what Oslo-eduŽ can do, very easily, just playing with perfect lens elements.

Dr Klaus Schmitt
15-Jun-2007, 15:12
I have used the same idea Emmanuel used, but I placed a negative lens behind the lens which also worked quite well, esp. stopped down.

David R Munson
19-Jun-2007, 16:00
A bit of an update! First of all, thank you for all the help, everyone. This is going to be very helpful. I have completed the initial stage of the project, having gutted a Mamiya 80mm f/2.8 and chopped up my Holga into a number of pieces. I was able to cut up and reconfigure the original Holga lens housing to screw directly into where the rear element of the Mamiya lens once sat. I then backed it up until the mirror hit the assembly, and screwed it back in a little so it cleared again. At this point, max focus distance was about two feet. I then took an exacto knife and pared down the back end of the assembly, removing a few millimeters worth of plastic, then repeated the positioning procedure so that the mirror clears the back of the lens, but just barely.

At this point, the lens will focus from about six inches to about four feet. I went out and shot one roll's worth of 220 with this arrangement and will develop the film tonight. One issue was focusing with the effective aperture of being around f/11 or so, as the dimness combined with the not-so-stellar crispness of the Holga lens making focusing tricky. It was workable, though. Without any aperture behind it, ie wide open, the plastic lens has aberrations to no end, moreso even than is desirable for this sort of lo-fi adventure. However, f/11 is a little on the dim side and further limits the usefulness of the lens. If I enlarge the aperture to be around f/5.6 or f/8, I think I'll still keep enough of the aberrations at bay and have just enough more light to make a decent difference in usability. I will experiment with different optics and see about making the assembly focus to infinity, but in the mean time at very least it will be fun for close-ups of various things and some creative portraiture. Should be interesting.

I'll update more as this progresses.

David R Munson
19-Jun-2007, 18:45
Here's a couple photos of the beast as it stands. Yes, the actual lens is positioned so far back as to practically not even be in the lens body, but that empty body makes one hell of a lens hood and there's no vignetting to speak of.