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TOP >  Ultra Fast Astrograph VSD100F3.8

Ultra Fast Refractor for Astrophotographers featuring a 5 Elements in 5 Group Lens Design. This f/3.8 OTA is Optimized for Digital Imaging

The new Vixen VSD100F3.8 features a surprisingly fast f-ratio of F/3.8 which is the fastest in this class of quality refractors.
The wide and flat imaging field that covers 645 medium format cameras and an innovative 5 elements in 5 group lens design completely eliminates a violet tint in chromatic aberration (blue halo).

It employs a SD lens in the front objective group and an ED lens in the rear objective group to achieve a superb color correction. The blue halos around stars, that are perceptible in astrophotography and that are hard to reduce with a 4 elements in 4 group lens design, are corrected successfully. In addition, astigmatism and coma aberrations are corrected to an extremely high level of image quality.

The Strehl intensity on the lens design of the VSD100F3.8 is better than that on a 4 elements in 4 group lens design by approximately 10%. It does not decrease abruptly on stars away from the center of a photographic field. It is ideally suited to detect faint stars. The image circle is as large as 70mm in diameter (60% illuminated). The star images are as small as 15 microns around the corners, resulting in excellent field flatness.

The VSD100F3.8 have the most up-to-date coatings of extremely high transmission of light. These have been developed to match the characteristics of each lens element in order to avoid the deterioration of image contrast due to the increase of lens elements. It boasts of 99.9% light transmission at the maximum per lens surface and achieves superb images with extremely high contrast with no ghost and no flare images. (Patent pending)

Precision Glass Annealing Process and a Premium Zygo verifire ATZ Laser Interferometer

Vixen has initiated a new project in each stage of their manufacturing proccess to ensure that better quality is realized in the high performance as designed. 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.

In addition, Vixen introduced a premium Zygo verifire ATZ laser interferometer for accurate measurement of optical components. The Zygo verifire ATZ has a 1000 × 1000 pixel digital camera for high resolution metrology that can accurately identify sudden changes of a form on the optical surface of lenses. Any irregularities on the lenses can be inspected individually. This provides an in-depth control of the lens quality which was never realized previously.

The installation of the Zygo verifire ATZ is unique at Vixen. It is placed in a vertical position* together with a vibration isolation table to allow for measuring large aperture lenses like astronomical telescopes without stress.

* Generally the laser interferometers are laid in the horizontal position. Because the large aperture lens can distort due to its weight, the vertical placement is employed to avoid this interference.


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), typically 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 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.

Precision 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.

The grooved large rubber focusing ring can be grasped easily even when wearing gloves.

The thick rubber ring on the top of the dew shield absorbs shock and protects the optics.

The stopper piece inside the helical fine focuser has a slot for smooth focusing movements without slack. This works with the large rubber focus ring allowing the focuser to turn smoothly with a large CCD camera attached.

The length of the dew shield, the positions of the inner baffles and their proportions to the diameter of the optical tube have been designed to eliminate ghost in the lens design process and to successfully prevent stray light and flare images.

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.