This Astro-Tech 10mm Titan is a very wide 70° field medium to
medium-high power 1.25" eyepiece at a very economical price. Its 10mm
focal length makes it a good choice for high power lunar/planetary
observing and binary star splitting with a long focal length telescope.
For
instance, with an 8" f/10 catadioptric, it provides 200x with a 1mm
exit pupil, the optimum exit pupil generally recommended to best match
the resolution of your telescope to the resolution of your eye. The
field of view with such an 8" f/10 scope is a surprising 0.35° at 200x,
nearly three-quarters the lunar diameter.
With short focal length
refractors and fast focal ratio reflectors, it makes globular clusters
and compact nebulas vivid and nearly three-dimensional. An f/4 Meade 8"
Schmidt-Newtonian reflector, for example, yields a 2.5mm exit pupil,
81x, and a generous 0.86° field of view that’s perfect for globular
clusters like M9, M13, and M22. All fit nicely into the eyepiece field
of view, with a framework of black velvet sky around them to set off
their subtleties.
The 66mm f/6 Astro-Tech AT-66 refractor, on the
other hand, has a magnification of 40x with this eyepiece, with a
1.66mm exit pupil and a generous 1.75° field (three and a half times as
wide as the full Moon). That wide field is good for observing open
clusters such as the Pleiades and the Double Cluster in Perseus; large
nebulas such as the Lagoon, Veil, and Orion; and large globulars such as
M-13 and Omega Centauri. All will fit nicely into the field of view,
with a framework of black velvet sky around them to set off their
subtleties.
The 7mm eye relief is somewhat short for those who
must wear eyeglasses while observing due to astigmatism, and will
somewhat vignette the field. This is of minor concern, as even those who
don’t have to wear glasses while observing will find they have to move
their head from side to side while observing to see the entire huge
field of view.
