We got a new Ocean Optics spectrometer to the lab today and naturally I had to play around with it a bit in the evening. Compared to our 20+ year old Jobin Yvon rotating-grating thing this one is a very small tidy box, with data transmission and power over USB, and an SMA-connector for light input through a 600um core fiber.
Some sample spectra below (the filenames describe the light-source).
Seeing something with the Ronchi test was easy, but the Foucault test proved a bit more demanding. The light-source and the knife-edge need to be securely bolted to the table, and they need to be finely adjustable along the optical axis and perpendicular to the optical axis. The final piece of advice needed to make it work was to sand down the LED used as the light source. The LED then becomes a diffuse suorce, and the knife edge is placed half-way across the LED also.
It turns out that the room we were using for this doesn't have very good 'seeing'. After turning off a printer and some computers that created visible air-current there still remains a lot of disturbances. About the only thing in the photo above that is 'real' and doesn't change with the air-currents is the round spot in the middle.
This is our Foucault tester. The knife edge and light source move along the optical axis using a 50mm-travel translation stage, and everything moves up/down to place the knife edge at the correct height using a small lab jack.
By popular demand, a schematic which roughly shows the electrical connections of our cnc-mill setup. Most of it fits inside one box (also shown here). The m5i20 I/O connectors are on the left, followed by the optoisolator cards. E-stop chain in the middle, servo-amplifiers and motors to the right. Jog wheel at the bottom. The small VFD board I made later is not shown.
I'm fitting some more equipment around a Nikon TE-2000 microscope, and the stock objective turret is in the way. Machined this objective holder in steel yesterday.
An ISO100 1/100s exposure of the moon through my Synta 80ED. An easy target during last night, but moonlight also lit up most of the rest of the sky preventing any serious deep-sky photography.
A single 8 minute iso800 exposure of Cassiopeia through a Canon 17-40/4L lens at 17mm and F/5.6. The Andromeda galaxy (M31) is visible at the bottom center.
From the same night as my earlier Cygnus photo. This one is not as good with some light pollution or dew-problems at the left. The red artifact in the lower right corner is the same amplifier noise that's visible in the cygnus photo. My home-made lens hood causes vignetting.
Veikko Rihu from Provoke has produced these two 1:17-scale radio controlled yachts modeled after Volvo Open 70 boats.
The boats are moulded in carbon and feature a 45-degree canting ballast. Length is 1339mm and beam 350mm. The displacement is 6.3kg with about 4.7kg in the keel, fin, and canting-electronics.
Polishing is hard work compared to fine grinding. There is much more friction between the lap and the mirror - it's nice to take a break after 15 to 20 minutes of polishing. Possibly due to insufficient pressing our mirror started to polish at the outer edge first. We did about 2 hours of polishing the first evening. Today we started with hot-pressing, i.e. leaving the lap and mirror under hot water for a while and then pressing the two against each other to achieve good contact. After about 1 hour today we did a first Ronchi test, which clearly shows the less well polished spot in the middle. One more hour of polishing and we are up to about 4 h in total. There's still a hint of the less well polished area in the middle. Looking at the Ronchi test the overall shape of the mirror is roughly spherical as it should.
Our Ronchi tester consists of a wooden mirror stand made from plywood with three long M6 bolts to hold the mirror. We're using an LED as a light source, and the 100 lines per inch grating is printed on an overhead-slide with a laser printer.
The radius of curvature is roughly 288 cm indicating a focal length of 144 cm which would make for a focal ratio of F/6.
Fine-grinding of the mirror has progressed without problems. Around 1.5 hours of work per grit-size was enough to achieve a uniform surface roughness. After the finest grit, 15 micron Aluminium oxide in our case, it's time to polish the mirror using a Pitch lap and cerium oxide.
We heated around 500g of pitch on an electric plate. Note the tube that sucks away the fumes (normally used when soldering). Pitch is an interesting material to play around with, hard and brittle when cold, almost as runny as water when hot, and all kinds of viscosities and 'feel' in between. The mirror and glass tool were heated in an oven to around 65 C and a dam of paper masking tape was added to the tool. After pouring the pitch we waited for it to cool a bit and then made some channels using a steel ruler. Then the lap was pressed, mirror on top, with water and soap covering the surfaces to avoid sticking. Finally when the lap had cooled using a sharp knife the edges were bevelled and the channels re-opened.
About 10 hours of polishing now follows...
