ATM Camera lenses as eyepieces

[Clint Bach <clintbach@earthlink.net>]

Hi all,

I do use camera lenses as eyepieces and SOME of them work quite well.  I use
the old Canon 55mm f/1.2 on my 12.5" f/4.8 and the stars are crisp and round
all the way to the edge and the true field of view is 100 arc minutes.  At
about a 10 mm exit pupil a lot of aperature is wasted but the view is still
great.  A higher f/ ratio on the primary would help waste less aperature.
The eye relief is luxurious with this lense, about 1.5 inches or so.  I have
never seen better edge of field correction on any eyepiece.  It works on my
camera too!

Update on camera lenses as eyepieces!  I found an old video camera lense at
a yard sale for $.25, yes, just one quarter!  This lense is an 8mm f/1.3.
True to form for camera lenses, this lense gives excellent images edge to
edge.  It has about a 40 degree apparent field of view and good eye relief
to boot.  It is very nice for lunar and planetary viewing.  The only
disadvantage is that it takes more in travel of the focuser than any other
eyepiece I use.

I have tried dozens of camera lenses as eyepieces...  Most are quite sharp,
most also have quite narrow apparent fields of view.  The f/ ratio seems to
be directly related to the apparent field of view.  Closing down the lens
narrows the field of view.  Lenses of f/1.2 to f/1.4 seem to be very usable,
f/ 1.8 is marginal f/2.5 and up don't seem to be worth the trouble.  BTW, in
use, the "front" of the lense is toward the telescope and the "back" of the
lense is toward your eye.

Go ahead!  Drag out those old camera lenses.  You may just be surprised.

Clear skies!

Clint Bach