Quote:
Originally Posted by Varangian
Keep in mind that a 2X barlow will effectively cut your FOV in half, so a 52 degree plossl will be cut to 26 degrees.
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This is not correct (Sorry John). The APPARENT FOV of the ep will still be whatever it was before. So a 52deg plossl will still show the same apparent field however the TRUE FIELD will be halved. So a Televue Plossl in an 8" f6 will yield a TFOV of 1 deg and if you bang it into a 2x barlow it will cut this to 0.5deg.
Just t explain the diff. The TFOV is the area of sky that you can see in the eyepiece, so in this case a 25mm ep barlowed yielding a TFOV would just about be filled by the full moon (which averages around 0.5deg in angular size. The AFOV is the width of the field as it appears to your eye. So if you managed to create an optical system that had zero magnification with a 50deg AFOV and lookat at the full moon, the moon would take of 1% of its width.
It is fairly important to avoid confusion when talking about FOV to be clear as to whether we are talking TFOV or AFOV.
Cheers
Malcolm