9 Lens type Achromat
Apochromat Focuser size See note (5) 1 1/4 inches Carrying case Included Optional Tripod mounting block Included Optional (8) Minimum tube length 10 1/4 inches 15 3/4 inches Weight 1 lb (0.
For decades observers working with achromats
have used color filters (usually yellows like Wratten 4, 8, 12, and 15 or greens like Wratten 11, 56, and 58) to block the secondary spectrum's defocused red, blue, and violet light.
By the way, achromat
means "without color," while apochromat means "without color--but, we're serious this time.
The Nighthawk is more expensive than other imported short-tube achromats
, but it also outperforms them to a degree that even novice observers will quickly appreciate.
Far from overwhelming, this is generally quite unobtrusive and significantly better than in a number of other budget achromats
Fortunately, we are using two identical achromats
with a focal length of 100 mm each, which when combined provide an effective focal length of 50 mm.
This home-built telescope squeezes all the performance advantages of the classic achromat
into a wooden box half the length of a typical refractor.
From personal experience, I have found that achromats
in the f/2 to f/3 range work the best.
On the downside, refractors, especially conventional achromats
, create problems for CCD cameras that "see" wavelengths (colors) well outside the range brought to a common focus by the objective.
For the first four years optics from old photocopying machines served as objective lenses, but in 1990 Tyler found a source of inexpensive, high-quality air-spaced achromats
Since we wanted our spectrograph to be capable of operating at this extreme without wasting light or resolution, we selected high-quality f/2 achromats
of 80-millimeter focal length for the collimating and focusing lenses.
My first trials involved contact achromats
, with either the flint or crown element in front.