Describing Lens Performance with MTF Characteristics
Vixen’s goal was to develop a process to outperform the views from a premium
photo lens. The result is the introduction of MTF (Abbreviation of Modulation
Transfer Function), previously used for evaluating the optical performance of
camera lenses. The diagram clearly describes the optical performance of the
VSD100F3.8 as compared to a 4 element 4 group design. Thus, it allows for a more
precise evaluation of the photographic performance as compared to conventional
spot diagrams. This is a new direction in the choice of an astrograph.
Precison Over-sized focuser and Large Rubber Focus Ring
The VSD100F3.8 has an oversized focuser that can be attached to the 645
medium format cameras without difficulty. Highly accurate focusing is possible
with the non-rotational helical fine focuser, where the distance of drawing in
and out the focuser can be read as small as 20 microns with the provided vernier
scale. All the graduations are engraved. 
Optional Focal Reducer and Optional Tele-Extender
A focal reducer (0.79x) with the optical design of 3 elements in 3 groups and
a tele-extender (1.58x) with the optical design of 4 elements in 3 groups will
be available as optional parts. With the use of these optional accessories, the
VSD100F3.8 can be transformed to an even faster astrograph with 300mm in focal
length at F3.0, or can be converted to a more multi use optical tube with 600mm
in focal length at F6.0 for observing planets and other celestial objects.
Precision Glass Annealing Process and a Premium Zygo Verifier ATZ Laser
Interferometer. In the process of manufacturing optical glass, all the
five lens elements are annealed with a precision annealing process (The
annealing can straighten molecular arrangements of lens elements and thus unify
the characteristic of optical glass.) The homogeneity of refractivity in optical
glass is enhanced to the highest degree.
Back focus: 116mm
Back focus with focal reducer: 63.5mm
Deal shield outside diameter: 140mm
