My Astronomy




My Telescopes

My Main Telescope - C14 and Paramount ME

My new Paramount MyT and 8-inch Ritchey-Chretien Telescope

MyT Hand Controller

My Meade 12 inch SCT on a CGEM (Classic) Mount

My 4 inch Meade Refractor with Sky Watcher Guidescope and ZWO camera on a CGEM (Classic) Mount

Skywatcher Star Adventurer Mount with Canon 40D


My Solar setup using a DSLR and Mylar Filter on my ETX90

DSLR attached to ETX90. LiveView image of 2015 partial eclipse on Canon 40D

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About the Site

 I try to log my observing and related activities in a regular blog - sometimes there will be a delay but I usually catch up. An index of all my blogs is on the main menu at the top of the page with daily, weekly or monthly views. My Twitter feed is below. I am also interested in photograping wildlife when I can and there is a menu option above to look at some of my images. I try to keep the news feeds from relevant astronomical sources up to date and you will need to scroll down to find these.

The Celestron 14 is mounted on a Paramount ME that I have been using for about 10 years now - you can see that it is mounted on a tripod so is a portable set up. I still manage to transport it on my own and set it all up even though I have just turned 70! It will run for hours centering galaxies in the 12 minute field even when tripod mounted.


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Day 31 - C14 Telescope with SBIG ST9XE Camera

No Spanish astronomy today - I have taken some remote cluster images from New South Wales that I am working on but thought I would describe my C14 setup with and without a focal reducer. I show an f/6.3 reducer here but have now moved on to a X0.8 reducer.

Camera Setup 1 SBIG ST-9XE with C14 at full focal length


The camera is an SBIG ST-9XE which has a pixel array of 512 X 512 square pixels each of which measures 20 microns on each side.

This gives a CCD side length of 512 X 20 microns which is 10.2 mm. Of course as the CCD is square with square pixels I get a square image.  If the camera is used with my  f/11 Celestron 14 SCT, which has an clear aperture of 355.5mm ,then the focal length is 11 X 355.5 = 3910 mm. The CCD dimensions and focal length can be used to determine the field of view of the CCD with this particular telescope setup .With a knowledge of the field of view of the entire chip the number of arcseconds per pixel can be determined. The FOV is given by 10.2/3910 radians which is 8.96 minutes of arc. The number of arc seconds per pixel will therefore be 8.96X60/512 = 1.05 arcesconds per pixel. This is close to the figure determined by the method below.



 The exact scale can be determined by taking an image then finding a plate solution using The Sky which gives the exact number of arcseconds corresponding to each pixel.

Here is an example. The image below was taken with the set up described above.




The astrometric solution gives the scale of 1.09 arcseconds per pixel.



 So this means with 512 pixels, the exact size of each image is 512 X 1.09 arcseconds = 558.08" = 9.3'

So the Field of View with this set up is 9.3 arc minutes X 9.3 arc minutes.

Note also that the position angle from North is 0.19 degrees which is an acceptable value. It is not essential to have the camera with North at the top but avoids having to rotate the image to give a North up view.


Camera Setup 2 SBIG ST-9XE with C14 with f/6.3 Focal Reducer


  If an f/6.3 focal reducer is used the calculations are as follows.

Pixel size         2.00E-05    
Number of Pixels       512    
Chip Size         1.02E+01 mm  
Focal Length of Telescope     3910 mm  
Diameter of Primary Mirror     355.5 mm  
FocalRatio        11    
Effective Focal Length with f/6.3 reducer   2239.364 mm  
FOV         4.57E-03 radians  
FOV         1.57E+01 minutes of arc
Image scale       1.84E+00 arcseconds
From plate solution the ACTUAL Image Scale is  2.02 arcseconds per pixel
So image size is       17.23733

minutes of arc


minutes of arc



The image above was taken at f/6.3 and solved as below



So the image size is 17.24 minutes of arc