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The next eshine telescope

Design ideas and tests for a new generation of automatic earthshine telescope

What did we learn from the first try?

More on testing DSLR RGB halos

CCD Posted on Sat, October 19, 2013 12:22:24

We test Hans’ 450D optics by imaging the Full Moon (t_exp = 0.02 s, f=5.6, focal length=300 mm (i.e. tele-lens)). Using IRIS to extract the R G and B fields we align, normalize and average these and plot the profile from Moon disc centre and out into the halo. We get:

The red, green and blue curves represent the halo in R G and B, respectively. The black line is a 1/r³ curve. R, G and B images normalized by their total flux before plotting.

It would seem that, as in the case of the image found on the internet, the profiles of R G and B are very similar, and also of ‘high quality’ – i.e. they are almost at the limit of what is possible in terms of dropoff slope.

This has bearing on choice of future cameras – CMOS or filtered CCD. I think the similarity of the profiles is due to the light having traversed the same optics – which is not the case with the filter-wheel.

I am not sure why the profiles are so close to 1/r³. It seems our optics in the MLO telescope cannot match this.

It should be said that the DSLR optics show ghosting – this can interfere with the DS photometry if unluckily placed – but apparently does not gives us shallow halo profiles.

The ghost image (same size as Moon, positioned at 11 o’clock) is due to internal reflections in the compact tele-lens used. Perhaps an image of the Moon is reflected from the CMOS surface, reflects off the back of the optics and is recorded. The above ghost would be very intense compared to the DS. Similar ghosts are seen in the wide-angle lens image taken with the Sigma camera, but as magnification is less the ghost is easily placed away from the Moon.

One thing to notice is the 2-orders of magnitude of drop in intensity from the disc brightness to the start of the halo – is this what we get with our MLO telescope? Perhaps the 1/r³ drop is an artifact of a high starting level? Need to check that.

Testing CR2 and X3F files

CCD Posted on Sat, October 19, 2013 09:31:05

IRIS is a piece of Windows software that will readily convert CR2 files into FITS files. It can be done via pull-down menus or via ‘scripts’

A typical script is:

loadcam IMG_7536
save IMG_7536
loadcam IMG_7537
save IMG_7537
loadcam IMG_7538
save IMG_7538
loadcam IMG_7539
save IMG_7539
loadcam IMG_7540
save IMG_7540

Image files named IMG_XXXX.CR2 are here being loaded and saved as 16-bit FITS named

It is necessary to first, via pull-down menus, set up IRIS to expect a Canon EOS camera (hence it understands to look for CR2 files in the script). You must also set the paths (in Settings…) to where the data are and where the scripts are. When you want to process .X3F images you must pick the SIGMA SD10 camera from the ‘camera’ menu in IRIS.

The script is a text file with extention ‘.pgm’ and is run from the ‘console’ in IRIS – this is the 11th icon along the toolbar. Simply write

RUN nameofscript (omit the .pgm, apparently)

and it will run, saving files for you.

X3F files are not yet understood – IRIS will open a file and save a FITS but there is only one ‘colour-plane’ in the FITS file – in the CR2 files converted above we get 3.

IRIS can be run from ‘wine’ in Ubuntu.