What Focal Length Should I Use?
The North America Nebula (NGC 7000) is used in this example.
Calculated field of view is based on sensor size for Canon 400D (XTi).
Calculations made using Howard Edin's Field of View calculator found here.The focal length given is the actual setting on the lens used. The focal lengths given below should be multiplied by 1.6 to account for the crop factor of the Canon 400D sensor. Your camera may have a different sensor size and field of view.
Note these images are not processed to their full potential, but just enough to show you the size of the target within the frame.
Though it's not obvious in these examples, higher focal lengths tend to reduce light pollution.
28mm.
F.O.V. = 43.25 x 29.6 degreesThe North America nebula is buried in the red glow at lower left.
F.O.V. = 25 x 16.8 degrees
F.O.V. = 18 x 12 degrees
F.O.V. = 10 x 6.8 degrees
F.O.V. = 7.2 x 4.8 degrees
F.O.V. = 6.35 x 4.24 degrees
F.O.V. = 5.57 x 3.72 degrees
F.O.V. = 4.24 x 2.83 degrees
F.O.V. = 2.54 x 1.69 degrees
