# Photographic lenses from the physics point of view

First of all, we need to define the term lens for the question to be totally clear and accurate.

A camera lens (also known as photographic lens) is an optical lens or assembly of lenses. [Source]

I need to study photographic lenses and the photographic camera for a project for physics. I want to do some research by myself, but I need a starting point.

Below is the construction diagram of a Nikon 50mm f/1.4D:

My questions, because there are actually more:

1. What kind of lenses are L3 and L4?
2. The focal length of this lens (50mm) represents the focal length of the system of lenses, or something else?
3. How can I precisely analyze this system of lenses? I searched on Google, but seems to be no physics information about the lenses inside a photographic lens? I would like to actually draw the lenses system's diagram and analyze them mathematically/physically.

So what should be my direction?

P.S. My level of optics is not very high, because this is the second year I study it (I've just began high-school).

• 2) "When a photographic lens is set to "infinity", its rear nodal point is separated from the sensor or film, at the focal plane, by the lens's focal length." 3) you'd need to know the type of glass and it's properties, for each element. – RedGrittyBrick Dec 10 '14 at 20:44
• With regards to 1., do you mean aside from concave v convex shapes? – Kyle Kanos Dec 10 '14 at 20:47
• About one, the lenses I mentioned have a shape different than anything I studied at school. – Victor Dec 10 '14 at 20:51
• Victor, You have chosen an interesting and important project, as systems of lenses and mirrors are important far beyond the camera - they are at the heart of the manufacture of silicon chips, DVD and Blueray players, and much more. I don't know how much time you have, but I suggest you start by getting hold of some simple lenses, and if possible a ray-box. If you don't have a ray-box you could use a laser pointer (not one of the insane American variety!). You can then understand for yourself how images are formed, how moving the lens affects the focus of the image, and so on. – akrasia Dec 10 '14 at 21:06
• Actually the topic has been given by my teacher to everyone (randomly). I am a photographer so, since my lenses are all pretty expensive, they have also complicated lenses systems inside. I do not exactly know my direction right now and how I can create the diagram for a functional photo lens – Victor Dec 10 '14 at 21:22

L2 is a positive meniscus lens, L3 is a negative meniscus lens.

50 mm is the focal length of the entire system.

Detailed analysis is very difficult. Expensive commercial programs do it. To get approximate solutions, you can apply the matrix methods of Gaussian optics. Whether or not that will be good enough depends on your application. You will miss most of the aberrations, and your results for rays that are off-axis or far from the axis won't be good. But you will get pretty good results for the location of the focal plane, and for magnification.

• it should actually be detailed for my ninth grade level. I don't really know my direction now, this is why I am asking here – Victor Dec 10 '14 at 21:05
• For a ninth grade project, I think matrix ray tracing will be challenging enough. Do you intend to do theory for the project, or do you want to build the lens. The latter is difficult. In your example lens you have 13 surfaces and many air gaps. There are simpler lenses to consider, like the Gauss, double Gauss, Cooke Triplet, and Zeiss Planar that are serviceable lenses that are less complicated. – garyp Dec 11 '14 at 4:04
• I only intend to do theory for the project, and use my 3D Studios Max knowledge to create some beautiful animations according to the theory. If I had known the properties of the lenses inside that system (Nikon 50mm f/1.4D), it wouldn't have been so complicated to do the ray tracing. – Victor Dec 11 '14 at 8:28

A lens that is thick at the center than at the periphery is convex lens and will converge a parallel beam of light. Similarly a lens that is thin at the center and thick at the periphery is a concave lens which will diverge a parallel beam of light. Now L1 has one side plane so it is called plano-convex. L2 is double convex, L3 is double concave etc. 50mm represents the focal length for the entire system. Analysis means that you have to find the cardinal points which are the principal planes, the nodal points and also the focal point. Then you have to get entrance and exit apertures.

• No! You are a bit confused ... – garyp Dec 10 '14 at 20:56
• How am i confused? – SAKhan Dec 10 '14 at 21:01
• L2 and L3 are not double convex/concave lenses. They are meniscus lenses. – garyp Dec 10 '14 at 21:03
• Well was not confused rather couldnt recall. Did it time back. – SAKhan Dec 10 '14 at 21:09