What are the field stop diameters of Meade's Ultra Wide and Super Wide eyepieces?

Answer 1

It varies greatly depending upon the size and focal length of the respective lens. I cite a reference table below which has a table of a variety of Super wide and Ultra wide eyepieces and their respective field stop diameters:


These by the way are for the older series 4000 eyepieces, I imagine the 5000's are different.

Astrobuf

Answer 2

Unlike Tele Vue, Meade doesn't publish a detailed table of their eyepieces' specifications. It's possible to measure the field stops on the Super Wides yourself, because these are external to the eyepieces. The Ultra Wides have internal field stops, so cannot be measured directly. You can use Tele Vue's specifications as a rough guide, since Meade's Super Wides are clones of TV's Panoptics and Meade's Ultra Wides are clones of TV's Naglers.

Answer 3

There are various formulae for calculating field stop diameters, none of which are completely accurate. The reason for this is the unavoidable distortion present in a wide-field eyepiece. If the eyepiece is designed for zero angular magnification distortion (circles stay circular), the calculation is

field stop = eyepiece focal length * AFOV * π / 180

For zero rectilinear magnification distortion (straight lines stay straight) it's
field stop = eyepiece focal length * 2 tan(AFOV/2)

Astronomical eyepieces usually come out closer to the first formula, which for the 30mm Ultrawide, is 30*82*π/180 = 42.9mm. You often can't just measure with eyepieces like this because the actual field stop may be internal, and differing from the effective field stop diameter by some optical magnification factor.

Added: If you measure the true field of view, (TFOV) eyepiece distortion is irrelevant and
field stop = TFOV * telescope focal length * π/180

Answer 4

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Answer 5

Most manufacturers don't supply this measurement, but you can compute it quite easily:

fsd = 2 * L * tan[1/2(fov)]

... where fsd is field stop diameter, fov is field of view, and L is the focal length of the eyepiece.

Example: the Meade SuperWide 18mm has a fov of 67°. Field stop diameter is then
2 * 18 * tan(33.5) = 36 * .6619 = 23.8 mm