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Wednesday, November 16, 2011

How to capture a dancing planet

When Jupiter dances, you may need GRGB !
Since two years I capture the planets by using a powerful one shot color webcam, the TIS DBK21USB. It produces regular avi video files. After stacking the avi files with the software Registax, I produce FITS files, need sharpening. The sharpening step is done by using the wavelets function in Registax. Finally, I split the best FITS image in its three separate channels R,G, and B in order to use one of them as luminance, since my seeing conditions from my roof observatory are usually bad.

I need a luminance! But which one?
Depending on what kind of details you want to visualize on a specific planet (i.e. cloud or surface details), a suitable channel should be used as luminance. See below:

Jupiter and Saturn
I extract the G (green) channel in order to set it as a luminance.  It has a higher resolution than red or blue because of the RGGB mask placed on the camera sensor. Two of the four pixels in the RGGB matrix are green.

Examples on other planets:

Mars
I extract the R (red) channel in order to set it as luminance to bring out more albedo details under my poor seeing conditions.  The red channel does not suffer from seeing so much as the green and blue channel. It has a low resolution, since only one of the four pixels in the RGGB matrix is red.
If you want to visualize the orographic cloud structures on Mars you will want to use the B (blue) channel as luminance. You need very good seeing to get a sharp blue channel. These are very rare especially from roof observatories, where the local seeing also plays a role. Perhaps once a year? I think so.

Venus
I extract the B (blue) channel in order to set it as luminance as the cloud structures on Venus are visible in the blue/UV channel. As I said before, the blue channel suffers more from the seeing than the red or the green channel. Its resolution is also low.

NOTE: If your seeing conditions are excellent, the most accurate method for planet photography is simply RGB. You prevent sacrifying details both in the cloud structures and on the surface of the planets using the classic RGB method. See my latest results on Jupiter at http://dark.astrodigital.net.
If you are interested on how to process a RGB planet photos with the software GIOTTO and MaximDL please visit my homepage at: http://www.astrodigital.net

Photo shooting with IC Capture.AS
This is the software package I use with my DBK21 webcam. One of the advantages it provides is the live display of the RGB values. I pay special attention during the image acquisition, not to exceed the max. values of 255 in each RGB diagram. The screenshot above shows the settings, I always use. When the values tends to exceed the limits (255) during the session, I reduce immediately both the gain and the exposure time.

Jupiter rocks :-)
Jupiter rotates fast! Its rotation is easily noticeable at 3850mm focal length I use. I keep the time window for each avi video file short enough to prevent smearing due to its fast rotation. I developed an application to calculate the allowed time window to capture a given planet, taking into account your telescope/camera system! You can download it here for free. See also a screenshot of it:
Figure: My telescope, eyepiece and CCD calculator
/Panagiotis

Wednesday, November 09, 2011

I wonder (a poem)


I wonder

I wonder how come the angels fly high
while we are forced to walk

I wonder how come the stars always shine
but we see them only by night

I wonder how come six senses we've got
but we use only the eye

I wonder how come people don't ask
what's beyond the deep blue sky


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Email: Maria.Kafritsas(@)gmail.com
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