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)
Vixenâ__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.
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.
- Objective lens design - SD Apochromatic, fully AS coatings, 5 group-5 element design (SD lens x1, ED lens x1
- Effective Aperture - 100mm
- Focal Length - 380mm
- Focal Ratio - f/3.8
- Light gathering power - 204x unaided eye
- Resolving Power - 1.16 arc seconds
- Limiting Magnitude - 11.8
- Image Circle - 70mm, approx. 60% illumination a the edge (covering 645 format)
- Drawtube diameter - 89mm
- Adapter threads dia - M84-pitch 1mm, M60-pitch 0.75mm, M42-pitch 0.75mm
- Push fit - 60.2mm, 31.7mm
- Filter threads dia - 58mm
Size & Weight:
- Optical tube length - 497mm
- Optical tube diameter - 115mm(*SX tube ring 115mm is not compatibel)
- Optical tube weight - 4.5kg
Accessories: Aluminum case, Allen wrench 1.5mm
Optional Accessories: VSD Tube Ring 115mm, Finder Bracket shoe, Camera Mounting adapter for 645D, VSD focal Extender 1.58x, VSD Focal Reducer 0.79x