Cycles is relatively simple path tracer without MLT so I did not try to simulate lenses in Cycles, and do not recommend it for this purpose. LuxRender is much better choice for this, it is free and open source, and integrates with Blender very well. With LuxRender it's possible to simulate fish-eye or normal lenses focusing light (image) on film (with translucent matte material and camera behind it). You could simulate chromatic aberration too. You could model half of each aspherical (or spherical) surface profile precisely with XYZ Math Surface, then spin 360 degrees, then delete all doubles and set smooth shading. This way, it is possible to model even achromatic doublet (you will need three surfaces with properly defined interior/exterior volumes). But more lens elements you have between film and the scene, the more issues you will encounter. When done modeling lens elements, enclose them in completely black container.
Simulation of simple lenses (1-2 elements) is almost without issues, complex lenses with many elements (4-6) may have weird noisy artifacts (but result usually good enough "to get overall idea"). If number of elements is too many (for example, 18), simulation may fail (just render few fireflies on black screen). Another limitation is that LuxRender as far as I know cannot simulate AR coating yet.
You did not mention how good you are with lens modeling and underlying math describing their surface, and how many elements you plan to have in your lens simulation(s). I think there are no good tutorials about this yet. If you need one please comment, I could expand this answer with much more details (but please note that it may take few weeks because if I do this, I would like to do it with good examples, and only if somebody actually interested in more detailed answer, and if using LuxRender is acceptable option).
