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76145 VSD100f3.8


VSD100f3.8 Review

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.

VSD Spot Diagram

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)

Vixen’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.

Lens Performance Comparison

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.




Optional Accessories

Polar Meter
76636 VSD Tube Rings 115mm
High quality, felt lined clam shell style aluminium rings for maximum stability. Supplied with plate for direct attachment to SXP or AXD mount head or to attach an optional Vixen or Losmandy style dovetail plate.
Polarie Polar Axsi Scope
77315 Camera Mounting Adapter for 645D
Push fit adaptor with bayonet mounting for Pentax 645 format DSLR cameras. Delivers a 55mm image circle. Standard 58mm filter thread inside nosepiece.
Ball & Socket Panhead
76637 Focal Reducer 0.79x
Reduces the focal length of the VSD100f3.8 to just f3.0. Features a high quality 3 element, 3 group design using ED glass. 99.9% light transmission at all lens surfaces. Standard 58mm filter thread in nosepiece.
Polarie Cradle
78751 Photo Adapter Canon EOS DX
A superior quality photo adaptor for Canon EOS DSLR cameras. Machined brass is used in the bayonet for a high precision and durable attachment. Six locking bolts with Delrin tips improve locking performance. The interior surfaces of the mount are blackened to reduce stray light.
Weight: 190g (1.94oz)