I'm wanting to get in to EAA and I am researching various options including either night-vision or near real-time images with a camera/computer setup. I've mainly researched the camera approach so far but now I am getting into researching the night-vision approach.
There seems to be 2 NV approaches:
- Afocal with using eyepiece where effective system focal length & speed can be changed by the choice of eyepiece to use. Either a PVS14 or Mod3b could be used
- prime focal-point. Effective focal length/speed can be changed by adding focal reducers/barlows to telescope. Mod3b with C-mount can be used.
I've read that the Afocal approach has more glass involved but may allow for focus to be more easily achieved.
Tele Vue likes the AFocal approach since they can sell you more eye-pieces.
The prime focal-point approach may save a bit of money since no eye-pieces involved.
I played around with the on-line field-of-view calculator with the Afocal approach with using the following scope as an example:
FL: 812 mm
eyepieces: 55mm (red) , 27mm (yellow) , 17mm (green)
In each case, I used the eyepiece FofV calculator with using an "eyepiece" FL of 26 mm and FOV of 40 degrees for the NV device.
I then calculated a telescope "Effective FL" for the system with the following simple equation:
Effective FL = FL(telescope) * ( FL(nightVision) / FL(eyepiece used) )
Effective FL using 55 mm eyepiece = 812 * 26/55 = 384 mm (red)
Effective FL using 27 mm eyepiece = 812 * 26/27 = 782 mm (yellow)
Effective FL using 17 mm eyepiece = 812 * 26/17 = 1242 mm (green)
I would enter this Effective FL into the FOV calculator along with the true telescope aperture.
Am I doing these FOV calculations right?
I included below one large target and one medium target.
Edited by jprideaux, 20 January 2019 - 05:42 PM.