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