The mirror for our 240 mm Newtonian has now been coated.

Act 0 (anecdotal): In which the Builders catch the Aperture Fever and start to dream of mirrors large. Act 1 (2008 July 22): In which the Builders acquire the Glass and first smell the Carborundum. Act 2 (2008 July 30): In which the Glass is bevelled. Act 3 (2008 August 1): In which the Builders [...]

After 11 months in the making, July 2nd 2009 will be the historical date to remember when our 240 mm Newtonian saw First Light! July is not dark at all in Finland, but that didn’t prevent us from setting up in the back-yard to have a look at the moon. Predictably the clouds soon rolled [...]

When epoxy cures it releases heat in an exothermic reaction. I was adding some glass-fibre reinforcement to the telescope tube and mixed 140 g of L285 epoxy into an ordinary plastic cup. I got about half-way through the job when I noticed the cup heating up. I tried putting it in a cold water-bath, but [...]

The mirror has been figured and ready for some time now, but we’ve been so busy with other things that the telescope hasn’t been finished. Now the plan is to assemble the mirror-cell, mount the 2ndary, and install the focuser so we can do some initial star-testing before aluminizing the mirror. Nice images of the [...]

The mirror is now parabolized to better than 1/18-wave RMS, so we are assembling the telescope to star-test it prior aluminizing the mirror. If and when everything looks OK through the scope we will send the mirror to be aluminized. We came up with this mirror holder out of ca 20mm thick oak board. There [...]

A few pictures and some notes on the polishing tools which we’ve used for the 240mm F/6 mirror for the Newtonian telescope we are making. This is the full-size pitch-lap on top of the mirror. It’s important to have good contact between the tool and the mirror at all times, so the pitch is pressed [...]

After a few (2-3) more hours of polishing with the full-size lap the mirror was fully polished. No holes or marks can be seen in the mirror surface with an upside-down 25mm eyepiece. Final polishing progressed rapidly when we used a weight (4-6 kg) on top of the mirror/tool. The following task is called figuring, [...]

Started out this evening with a 1 mm sagitta on the 240 mm mirror. Started with no60 carborundum and ca. 20 + 30 min of grinding, which got us down to a 1.9-2.0 mm sagitta. The picture shows a 2.0mm drill bit under a steel ruler used for measuring the sagitta. The surface of the [...]