Vixen VSD100 f3.8 Astrograph Telescope & Flight Case

An ultra-fast refractor designed for discerning astrophotographers featuring a 5 element optical design. This f3.8 OTA is optimised for digital imaging.

The innovative wide and flat imaging field that covers 645 medium format cameras and 5 element, 5 group lens design completely eliminates the violet tint that can be caused by chromatic aberration. With an Super ED (SD) lens in the front objective group and an ED lens in the rear objective group, this scope achieves superb colour correction. The blue halos around stars, that can be visible in astrophotography and are hard to reduce with a 4 element, 4 group design, are well-corrected. In addition, astigmatism and coma aberrations are corrected to an extremely high level.

The Strehl ratio of the lens design of the VSD100F3.8 is better than that of a 4 element, 4 group design by approximately 10%. In addition it does not decrease significantly on stars away from the centre of the photographic field. The image circle is as large as 70mm in diameter (60% illuminated). Star images are as small as 15 microns around the corners, resulting in excellent field flatness.

Spot diagram images from left to right:
Centre of frame
Edge of full frame 35mm
Edge of a digital 645 format 
Edge of full frame 645 format

The lower set of images shows the comparable spot diagrams for a 4 element, 4 group f3.8 optical system as a reference.

Measuring Lens Performance Using MTF (Modulation Transfer Function)

Vixenƒ__s goal was to develop an instrument that outperforms a premium photo lens. To measure this performance Vixen uses MTF (Modulation Transfer Function) which is typically used for evaluating the optical performance of camera lenses. The diagram below clearly shows the optical performance of the VSD100F3.8 as compared to a 4 element, 4 group design. This allows a more precise evaluation of the photographic performance as compared to conventional spot diagrams.

Precision Over-sized Focuser and Large Rubber Focus Ring

The VSD100F3.8 has an oversized focuser that can be attached to 645 medium format cameras. Highly accurate focusing is possible with the helical focuser where the amount of inward and outward focus travel can be measured down to 20 micron steps using the engraved Vernier scale.