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Field curvature and eyepieces.
Hi all,
This weekend finally saw me understand the term "field curvature" and its manifestation in eyepieces.
In a nutshell, it means the ability of an eyepieces to deal with the steepness of the cone of light towards the edge of its FOV. This in turn can become more obvious as the f/ratio gets faster, or the FOV exceeds the EP's design capabilities.
It has nothing to do with coma as such, as you can have a 100deg EP show terrible field curvature in an f/15 scope, yet in a 45 deg EP, the entire field can be pin sharp in an f/4 scope.
Coma correctors may or may not help.
I've been trying to find some reference where I can look up the suitablity of different EPs in a range of different f/ratios. What may work just fine in an f/15 scope can be totally useless in an f/4 scope (I saw this on the weekend). Most eyepieces "lists" I've seen don't mention field curvature capability, and their "design description", plossl, kellner, nagler, etc, can be meaningless.
Is there a reference somewhere to do with field curvature & f/ratio with respects to eyepieces, like a list noting brand vs. properties? A tool like this can be invaluble in determining EP suitability, and not have to go through heart ache to find that your $400 EP isn't much chop in your f/3.3 scope.
Cheers,
Mental.
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