University of Leicester observatory

PlaneWave CDK20

This is just a little post about the equipment I use at my Uni!

I have access to professional grade observatory equipment at my University’s observatory. They have a CDK20 from PlaneWave instruments. Along with a G3-11000 CCD from Moravian Instruments.

The OTA is a 20 inch, F6.3 Corrected Dall-Kirkham. The CDK is a cassegrain like telescope with correction elements at the end of the optical path, rather than at the aperture. This design improves the overall flatness of your images, and eliminates astigmatism. It makes use of a prolate ellipsoid primary mirror, and a spherical secondary. With a 20 inch diameter mirror, its theoretical resolving power is \(6.88 \times 10^{-7 }°\) or \(2.48\times 10^{-3}”\), at a wavelength of 500nm. However, the real resolving limit comes from the seeing within Leicester! Although the telescope is situated on the outskirts of the city it is still quite bad at times.

What I use the telescope for?

I am currently using the telescope in my research project, where I am observing transiting exoplanets (post coming soon). This is done by detecting faint changes within a stars light output, called its luminosity. The more photons per second the star outputs, the brighter it is. So, when a planet passes in front of a star it reduces the amount of light reaching us. We can detect this change in luminosity and use it to calculate the planets radius!

I can also use it in my own time for either personal research, or just trying to get some nice photos. The CCD is a monochrome sensor, with a set of broadband filters – B, V, I, R and clear. If I do want to get a full colour image then I would need to assign each of the filters to a specific RGB channel. I haven’t had the opportunity to do this yet due to the CCD’s filter wheel being broken for over a year! Turns out the screw holding it in was a bit loose so the motor couldn’t engage with it properly. Then one day it fully came out and wouldn’t home, typically it happened when I was using it. It has only recently been fixed as the issue was unknown for a while, so I have been more focused on using it for my project than anything else.

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