Aspherical Lenses and Field of View

Designing, making and testing the 50.1 PMMA ASPH has been a pain in the arse from start to finish. Annoyingly, most of it comes down to me and either my lack of concentration (the manufacturing error) or an oversight in understanding. The photos of the still scene were dire, show me that this lens just isn't appropriate for rendering images in a singlet form. Why is this? What went wrong?

The answer? Nothing went wrong. As has already been verified during manufacturing, the maths and the refractive index used to design the lens are spot on, and the machine that made it was CNC and calibrated to be working perfectly. Therefore there is no error. In actual fact, this lens does EXACTLY what it's supposed to do. It renders rays parallel with the optical axis to an exact point on the image plane, eliminating all spherical aberrations  But then why do the test images look so terrible? Well this is where my glaring oversight comes into play.

I am designing a photographic lens, which by nature has a field of view angle measured in degrees. Can you see the problem yet? My lens was designed to eliminate all spherical aberrations from rays entering parallel to the optical axis; aka 0 degrees. If the rays enter at a different angle..... well suddenly they aren't corrected. To explain, let me show you a ray trace through the lens as it was intended to be used:

And now let's show a ray trace of rays entering at the maximum angle for the field of view of a 50mm lens (as this lens was deigned to be) which is somewhere around +/- 23.4 degrees diagonally:

Oh..... Well... that doesn't look good. Lets trace a few incremental angles and see how quickly the aberrations creep into the image:

Wow. As you can see, image quality is just gone as soon as you leave the 0 degree entry path. The image is full of coma, so much so that any image quality would be totally destroyed. Just for proof, lets run an image render through the lens:

Total blur; it's just a mess! Exactly the same as the results I got from my tests. It's annoying that I had to make the lens to find out it didn't do what I needed it to do, but at the time I was designing it I didn't have access to the ZeMax optical design software. Now when I design lenses they will be checked over and over in simulations to ensure that they will give me good image quality when manufactured, and to help ensure that I haven't misunderstood or over looked anything. One thing is for sure, if I had have seen this simulation before then I wouldn't have bothered making the lens!

So what is this lens good for? Why do people bother designing lenses like this? Well i'm no expert but if I had to guess, for this exact type of plano-convex aspherical design, I would say lasers. Lasers create what seems like an extrusion of light, as if all the light rays are travelling at 0 degrees from the optical axis. There might be some useful application for an aspherical lens of this sort with in a laser array then. For aspherical lenses in general I think it is becoming more apparent as I continue designing that they belong in multi-element designs. I can see them providing a benefit to a multi-elemental designs where the unusual surface curvatures may help eliminate some aberrations. I will have to experiment with that, but for now I'm an going to treat this as a lesson learnt and move onto multi-elemental designs to see what I can do to build off of the success of the simpler 50.1 PMMA lens, and maybe implement an aspherical surface at the discretion of my optical design software.