table shows all the club eyepieces available with both the 10 and 12 inch
However, you can clear that data and enter in your own telescope and
eyepiece details to see what they give you.
barlow value below represents the barlowed binoviewer that goes with the
10" scope, you can put your own barlow value in there, common values
would be 1.5, 2, 3, no barlow would be a value of 1.
focal length should be in the instructions of your scope, the focal length
of the eyepiece is usually on a sticker or engraved onto the eyepiece.
apparent field of view (aFOV) is as particular to an eyepeice as its focal
length, if its not printed on the eyepiece then it can usually be found on
the web, at the bottom of this page is a list of aFOV's for some of the
most popular eyepieces. The aFOV is
the width in degrees of the field as seen through just the eyepiece alone.
If you have two eyepieces with the same focal length, the one with the
larger apparent field of view will show more of the sky if inserted into
the same telescope. This parameter is determined by the design of the
lenses inside an eyepiece.
pupil is the size of the light cone leaving the eyepiece, if it's above
7mm then you're effectively stepping down the aperture of your scope, if
its very low (<1mm) then the eyepiece can be difficult to see into. The
lenses in an eyepiece form an image that floats in midair just outside the
lens closest to your eye. When you observe you place your eye so that it
can see this exit pupil image. If all is going as planned, the image size
will fit with room to spare within your eye. The size of this image is the
Field of View (FOV) is measured in degrees, the bigger it is, then the
wider the image will be. A small true FOV would look like youre
looking through a long narrow tube, a very wide FOV can give you an almost
spacewalk experience. The true FOV is
the field of view of the entire telescope system, including the eyepiece
The maximum magnification given below
is the absolute maximum the optics can do, the practical maximum is
often alot less then this because of atmospheric seeing,
miscollimation and warm optics. Going below the minimum
magnification will effectively reduce the aperture of your