Quote:
Originally Posted by Startrek
JA
I was referring to Image Scale or Pixel Scale as the angular resolution of your image train ( telescope and camera ) expressed in arc sec per pixel
IS or PS = camera pixel size in microns x 206.3 / telescope focal length
General rule of thumb, < 1.0 arc sec per pixel means your oversampling and > 2 arc sec per pixel means your undersampling
Are you referring to FOV of your image train ( telescope and camera ) expressed in arc minutes
FOV = width of camera sensor in mm x 3460 / telescope focal length in mm
Eg: M8 lagoon nebula 90 arc minutes horizontal by 40 arc minutes vertical
Sorry but I don’t quite get what your referring to , excuse my ignorance
ST
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Hi ST,
I'm referring to the angle subtended by each pixel in the recorded image, (the image scale, some call it the pixel scale), it's just that I find it more intuitive to use a first principles approach, i.e: for the image as a whole in either dimension horizontally or vertically, what angle of view is seen by the imaging sensor at the focal plane, expressed in arcseconds DIVIDED by the number of pixels that represent that.
I'm a DSLR guy and compute the image scale for all my lenses / telescopes /sensor combinations and tabulate these for comparison/reference (see excerpt attached, incomplete in some cells, hopefully not too many typos. there is a Nikon D600 Image scale column and a
Nikon D800 Image scale column in RED).
As an example:
Take a Nikon D800 coupled to a Nikkor 400mm f2.8
The Nikon D800 has a Full Frame ~36 (35.9)mm Horizontal x ~24mm Vertical sized sensor with 7360 pixels Horizontally and 4912 pixels vertically in landscape orientation.
When used as intended on Full-frame cameras the Nikkor 400mm f2.8 has a 5.2 degree Horizontal angle of view and a 3.4 degree Vertical angle of view. If you need to you can get /compute these angles from manufacturer's data, although they unhelpfully use diagonal angle, but you can work back to the Horizontal & Vertical angles using the sensor 3:2 ratio in a right angle triangle OR use the Scantips FOV calculator ( I will link later).
OK now use these data to calculate the Image scale for the example:
Horizontal FOV = 5.2 degrees = 18720 arcseconds (5.2x3600)
Horizontal pixels = 7360 pixels,
therefore
Image scale = 18720 / 7360 = 2.54 arcseconds/pixel
Now try the same calculation your way (using The Nikon D800 with 4.88* µm pixels,) coupled to a 400mm Focal length and see what you get..........
Best
JA
* Based on 35.9mm (35900 µm) wide sensor of 7360 pixels = 4.88 µm sized pixels