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Ultra Short-Focus Refractor for Astrophotographers featuring a 5 Elements in 5 Group Lens Design
The Vixen VSD100 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 elliminates a violet tint in chromatic aberration (blue halo).
It employs an 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 4 elements in 4 group lens design, are corrected successfully. In addition, astigmatismus and coma aberrations are corrected to an extremely high level of image quality.
The Strehl intensity on the lens design of the VSD100 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 VSD 100 has the most up-to-date coatings of extremely high reflectivity. 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.
Precision Over-sized Focuser and Large Rubber Focus Ring: The VSD 100 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 camera attached.
The length of the dew shield, the positions ot 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.