Making Lenses With Shorter Focal Length from Cheaper Materials

**fred_radmehr** · 13-Apr-2021, 00:12

Hi everybody and glad to be here again,

I have a system of lens and wanted to remake them one by one from polycarbonate (or other transparent and easily available materials) but want them to have 4 times shorter focal length (advice given by the gentleman Nodda Duma).

My question is that I can, based on lens making formula, change the R1 or R2 and the thickness and I do not know which one I should consider.

Any hints or advices?

I have access to 3d printers and CNC and zeemax software at my workplace.

Thanks a lot in advance

**fred_radmehr** · 13-Apr-2021, 00:46

Sorry forgot to mention that my original lens system is the Cooke triplet(or it seems to be so).

**OTS Matt** · 17-May-2021, 17:39

Hi Fred.

Unfortunately, switching materials is not so simple. Each optical glass (or plastic) has a refractive index and dispersion that's taken into account in the Cooke triplet design so that the aberrations are carefully balanced. When you change the materials, the shapes and spacings will also need to change. I'd recommend redesigning with the materials you've selected in Zemax.

As for making the polycarbonate (or other material) lenses, how are you doing the shaping and polishing?

**Eric Woodbury** · 17-May-2021, 18:32

And don't forget temperature coefficient of expansion (which I believe is quite high in plastics) and lens coatings.

Fluorite lenses for use into the UV spectrum are lighter, but these have their own problems.

If you are looking to trim weight, there is probably an easier path.

**fred_radmehr** · 19-May-2021, 00:36

Hi everybody and thank you so much for your replies.

I am aware of these difficulties and am trying to do my best to at least learn from some failures.

About polishing and shaping I should say that it is going to be made by a gentleman at work who is good at these stuffs and he was talking about making master model from CAD files which I do not know in detail but I promise to post and upload my results.

please stay tuned.

**Nodda Duma** · 19-May-2021, 02:54

I think my advice was good luck. I have not seen 3D printed lenses implemented in the professional optical design world. I have seen attempts — funded research and simple prototypes — but attempts only which failed to go anywhere for fundamental, real reasons. The 3D printed lens technology is not mature enough.

But, perhaps your friend can help you explore the possibilities. What is possible will not be much. I would start by making a landscape lens, with proper shape to correct spherical aberration. This should set your expectations correctly.