Microscope eyepieces are generally designated by a magnification factor
such as 10X. Telescope eyepieces are designated only with focal length.
Magnification in a telescope is determined by dividing the focal
length of the objective lens by the focal length of the eyepiece. eg: a
135mm lens used with a 12mm eyepiece would yield 11.25X. Field of view
for the combination is the field of view of the eyepiece (usually in the
range 35-70 degrees) divided by the magnification. 50 degrees is about
average for eyepieces these days so 50/11.25 would give a 4.4 degree
field of view or a bit less then a 500mm lens on a 35mm frame.
Chuck Norcutt
Darin wrote:
> One of the shops in my area had one the last time I was in there a few weeks
> ago, made by Rokinon in OM mount, of probably the same vintage as the
> Spiritone version. It's only about the size of a 25mm extension tube with an
> eye cup on the back, if I recall correctly it is a 10X eyepiece, and the
> image is inverted to the correct orientation. I mounted it on a Zuiko 135mm
> to see how well it worked and was surprised by the image quality. I think
> they where asking $45, a little more than I wanted to spend at the time for
> a novelty item, but the more I think about it, the more I want it. Maybe
> I'll get it if they still have it next time I make it in there.
>
> Darin
>
> Chuck wrote:
>> I haven't seen any of these things offered for many, many years.
>> Spiratone was the only seller of same that I can recall so we're
>> basically talking maybe through the 70's and early 80's at latest. I
>> don't recall exactly when Spiratone bit the dust.
>>
>
>
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