Quote:
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Originally Posted by ausastronomer
Stu/Dobman,
You need to understand the difference between Apparent Field of View (AFOV) and True or Actual Field of View (TFOV).
CS-John B
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Sorry to back track a bit but I haven't learnt how to use the "subscribe to thread" thing yet so I miss some replies...
John, I am very aware of the difference between AFOV and TFOV (which I just call FOV) and spend much of the night during the calculations in my head...
But what I was trying to say is that if I get (for example) a Nagler and a Panoptic with the same FL side by side (in my scope...one after the other), if I can see the field stop in the Nagler it gets me a bit
because I feel ripped off.
If I struggle to see the field stop in a panoptic and can see it in a Nagler then I don't know how the Nagler could ever win my heart
because the panoptic has other very slight benifits. Also I have found that some Naglers I can see the field stop and others I can't.
I think that Geoff solved the problem. Some of the longer focal length Naglers I am getting to close to (the lens). The field stop becomes much easier to see at that point and the image is not as good. I have to learn to step back a bit and then I might appreciate the disappearing field stop...