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| This PMMA block was made as part of a student exercise at AGSB. It is hand polished and was completed in 40 minutes. There are no scratches visible to the eye. This level of finish is required as a MINIMUM in my lens designs. However, while it is fairly easy to hand polish flat surfaces to this standard, a convex/cave lens surface simply has to be polished using computer controlled machine. |
It's been 3 months since I finished my last round of prototyping. The intention was to design and manufacture 2 prototype multi-element systems. I encountered a range of problems which slowed me down drastically, but ultimately led to a greater understanding of what it takes to make lenses of this kind. I learnt to program CNC G-code scripts, made a new cutting tool for the lathe, made multiple new collets of various types, and experimented with multiple methods of cutting tight concave surfaces. In the end, although I learnt a lot from the process, I ended up being a little short on time and the resultant lenses suffered from poor surface finishes.
It's the 6th of Septmeber 2013 and there is just under a month before I return to my university to officially start my project. Therefore I really don't have a lot of time to spend on this, a week maximum. In reality, optics may only form a minor component of my actual designs. However, it is essential that I can demonstrate the ability to make functioning optical systems if I am even to consider incorporating them in anyway into my designs. Therefore the aim of this next prototyping phase, I want to finally produce an optimised multi-element lens with minimal aberrations which actually functions in reality in accordance to it's design. This means my previous problems with surface finishes has to be fully resolved.
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| Wobbles in the optical image are signs of an uneven surface, even though it was hand polished with great care on a high speed lathe. Every element in the system adds errors like this to the final image. Put simply, these imperfections CANNOT be present in a working multi-element system. |
With little time and lots of pressure to get this one absolutely spot on, I have decided to design a new lens to manufacture. It needs to be as simple as possible while showing improvements over the original singlet lens. The new design will feature:
- The least amount of elements possible while solving image aberrations, which happens to be 3.
- 6 surfaces, 1 aperture stop, 4 controllable air spaces. 11 aberration control variables in total.
- Cooke-triplet design, utilising two PMMA elements sandwiching a PC element.
- Preferably an interchangeable aperture stop.
- Aluminium housing as already manufactured from the previous prototyping phases.
- Nikon and Canon mounts.
Using my knowledge, notes, books on optics, and ZEMAX, I am going to attempt to design and optimise a Cooke triplet in 2 days, ready to be manufactured next week.
