First thing to do on Wednesday morning was to get my first ever lens turned out! With the collet finished and ready to do, I used to to grip the billet into the machine chuck in reverse. It held a treat! It's amazing to think that only 1mm area ring can hold the part in place well enough to be machined, pure magic! Anyway, unfortunately in order to turn down the back side of the lens we have to chew through a huge amount of material. This wouldn't be the case in an optimized manufacturing setup, but turning a single element from a single billet will always produce a high percentage of wastage. This would have to be worked on if the manufacturing routine was to stay the same just scaled up.
Anyway, using the same surface mapping in CAD, I was able to plug in the new numbers for the billet protrusion offset and run the program and let the machine cut. Below you can see the machine at work, and the resultant rough lens which was released from the slightly crushed collet:
Holding the lens like this in my hand for the first time was brilliant. Just getting to this stage ticks one of my boxes for this week. Using modest equipment, a lens with a programmed surface can be turned out quickly, easily, with little expense and modest machinery. Manufacturing a collet to hold a billet in reverse is a perfectly viable solution if this was going to be scaled up into mass manufacturing.
The next obvious thing to do is polish it! :D There's nothing better than seeing rough acrylic become gradually more clear as you polish it up. Same process as last time, except this time with much more care and on both sides of the element. 1000, 6000, 12000, buffing wheel, with constant inspection with a high power ultra bright LED maglight. Any deep marks or scratches caused by the tool, or more likely by waste material getting trapped below the tool as it's being turned, are slowly eliminated. It is important to polish the element evenly so that the surface profile isn't altered. I decided to use the abrasive papers on the element while secured in the collet and spinning at high speed on a manual lathe. The results can be seen below:
So with the lens element finished, the next step is to get it ready to test. Placing it in front of a camera body with it's lens removed is a quick way to work out if the lens element resolves to the desired focal length (which it did), but other than that it's not good for much more. Light can get in from behind the element and there's no chance of being able to hold it on the desired plane, so to test it properly, I needed to make a proper lens housing. I would have loved to make the housing from aluminium, but with limited resources I ended up using a block of nylon turned down into a cylinder and then turned in accordance to a quick design I knocked up.
By the end of the day I hadn't got as much done as I had wanted, which was frustrating. I ended up leaving the block in over night so that I could finish it the next day. Before I left however I was able to make the mount which I had turned down on Monday fit perfectly onto the back of the block.
One last photo; my corner of the room! I ended up setting up my own desk with the CNC and manual metal lathe next to me, it was a designer-makers dream!
