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VIXEN VSD 100mm f/3.8 Astrographic Apo Telescope:

Item #26145- Vixen VSD 100mm f/3.8 Astrograph (185,876 bytes)

Above: VIXEN VSD 100mm f/3.8 Astrographic Apo Telescope, introduced in 2014 (108,422 bytes).
Click on image to see enlarged view (185,876 bytes).

Click on thumbnails below to see images taken by the VSD100F3.8,
click on the image to see enlarged view:


The Vixen VSD 100mm f3.8 astrograph is the world's most compact high performance 10cm (4 inch) class refracting telescope. It, with a suitable camera or imaging system, is capable of recording stunningly wide angle fields of view or it can be driven well into those higher magnifications required to reveal changing features on the major planets.

The back focus (distance between the rear of the telescope and the focal plane) is comparatively limited; this is not a concern for most users who would be imaging but it can be an obstacle to accept the accessories necessary for visual observing. As it is delivered (shown at top of this page) there is a pyramidal 1-¼-inch diameter accessory holder so an optional 1-¼-inch eyepiece could be attached and, depending on eyepiece design, it will reach focus and show up to just over a four (4) degree actual field of view. However, this would be observing in a straight-through orientation, in this configuration will may not be comfortable when trying to observe objects overhead. Furthermore, as with all refracting telescopes the image will appear upside down and reversed left to right, so this may not be a best choice for terrestrial observing. Company Seven can configure the telescope to accept slip-fit 2-inch accessories; with either a 1-¼-inch or 2 inch mirror diagonal so that with some suitable eyepieces the observing position would be more comfortable, the image would be erect but still reversed left to right.

One solution to add back focus would be to incorporate a negative lens, commonly termed a Barlow. This would allow the visual use of the telescope with a wider range of eyepieces, but at an focal length that is increased by the factor of the Barlow lens. This counters part of the wide field benefits of the telescope of course - but it you no other premium 4 inch Apo will pack down into so small a space as can the VSD. Because the basic focal length of the telescope is so low, in order to reach those higher magnifications needed to observe features on the major planets you will likely need to employ a good quality negative lens system.

The optics are optimized with the astrophotographer and professional astronomer in mind. It features an innovative wide and flat imaging field, one that can cover up to a 645 medium format camera. The five (5) lens elements are arranged individually, in five (5) groups, so this is a fully air-spaced design with nothing to go wrong over decades (or centuries?) of use. The optical design completely eliminates chromatic aberration, the secondary violet tint or blue halo that will be detected in lesser telescopes. With an SD lens in the front objective group and an ED lens in the rear objective group, this scope achieves superb color correction. The blue halos around stars, that are visible in astrophotography and are hard to reduce with a four elements in four 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 their prior 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, appearing excellent in terms of field flatness.

The air-spaced lenses of the VSD100F3.8 have the most up-to-date, customized antireflection coatings. These have been developed to match the characteristics of each lens element curve and materials in order to avoid the deterioration of image contrast due to the increased number of lens elements. These result in 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).

Company Seven hosts images taken by Tony Hallas, one of more accomplished astrophotographers who also helped to popularize the highly regarded Astro-Physics Apo telescopes. Tony commented:

"To have this level of performance from an f/3.8 is remarkable. All in all..a very impressive little telescope! The telescope is essentially sensational. It accomplishes the impossible. Mechanically superb as well, supporting the heavy 16803 camera without any complaint and the enormous helical focuser is tight and accurate. With extremely fast optics, flat field, and superb color correction it is a unique product not just a rehash of the same."

The telescope is provided with a lightweight aluminum clad storage case, so it is 'carry-on luggage' portable; although Company Seven does offer custom ATA Approved shipping cases. The telescope is so lightweight, just under ten (10) pounds that it can be managed by a broad selection of optional lightweight tripod and head sets however, for deep space imaging it will be best and most versatile for astronomy on a German Equatorial Mount. The VSD 100 is so compact and handy that some, those who can afford to pay the premium this innovative design commands, to buy this for use as a large finderscope or for panoramic observing or for backpacking and travel.


Precision Glass Annealing Process and a Premium Zygo Verifier ATZ Laser Interferometer: during the process of manufacturing optical glass, all the raw elements used to make each of the five lens elements are annealed with a precision process. This annealing can straighten and align the molecular arrangements within the lens element, and thus unify the characteristic of optical glass. The homogeneity, the purity and efficiency, of refractivity in optical glass is enhanced to the highest degree.

The F/3.8 optics set consists of four (4) elements in Four (4) groups (design for reference):

Vixen VSD Telescope cutaway

Spot Diagram: Center of frame, Edge of full frame 35mm, Edge of a digital 645 format, Edge of full frame 645 format.

Vixen VSD Telescope spot diagram
Above: Spot Diagrams, left to right: center of frame, edge of full frame 35mmm, edge of a digital 645 format, edge of full frame 645 format.
For comparison, the lower set of images show spot diagrams for a four element, four group f3.8 optical system.

Spatial frequency, Sagittal and Meridional:

Vixen VSD Telescope Spatial Frequency
Above: the graph at left shows performance of the VSD100F3.8 at 10 lines / mm; 30 lines /mm;
For comparison, the graph at right diagrams performance of a four element, four group f3.8 optical system.

Vixen VSD Telescope Focuser (140,921 bytes) Precision Over-sized Focuser with Rubber Grip Focus Ring: the VSD100F3.8 telescope optical tube assembly incorporates a versatile oversized focuser that can accommodate visual or imaging accessories by means of optimized series of optional attachment hardware; you need purchase only that which you intend to employ with the VSD100F3.8 telescope. While the conventional remote control focusing sets designed for rack and pinion focuser are not compatible with this arrangement, there are third party belt drive focus systems made specifically for these focusers.

Right: Micrometer Scale of the VSD 100mm telescope focuser (108,422 bytes).
Click on image to see enlarged view (140,921 bytes).

The optical arrangement is designed so that this can support film or digital imaging cameras with formats as large as the 645 medium format without difficulty. With the more popular DSLR 35mm full frame sensors field of view of up to 5.3 x 3.6 degrees, with nearly 6-½ degrees across the diagonal, are practical. Options for this focuser include an optional matched 0.79x Focal Reducer that can support a film or digital imaging camera with format of up to a full 35mm (24mm x 36mm).

The precision focus mechanism is is a highly accurate, non-shifting, and non-rotational helical fine focuser. The distance of drawing in and out the focuser draw tube can be read as small as 20 microns with the provided vernier scale; all the graduations are precisely engraved. With such wide field coverage the telescope relies on the focuser and hardware being adjusted just right to assure the image plane is perfectly parallel to the sensor plane; we at Company Seven do check this as part of our routine quality control testing. There are provisions (with instructions) so that the owner could adjust this if it ever became necessary.


  Optical specifications   Lens design   SD Apochromatic, fully AS coatings, 5 element in 5 groups design (SD lens x1, ED lens x1
  Effective Aperture   100mm (3.94 inches)
  Focal Length   380mm
  Focal Ratio   f/3.8
  Light gathering power   Approx. 185x that of the unaided eye
  Resolving Power   1.16 arc seconds
  Limiting Magnitude, V   12.3
  Image Circle   70mm, Approx. 60% illumination a the edge (covering 645 format)
  Focuser   Drawtube diameter   89mm
  Adapter thread diameter   M84-pitch 1mm, M60-pitch 0.75mm, M42-pitch 0.75mm
  Push fit   60.2mm, 31.7mm
  Push Fit adapter Filter thread   58mm diameter (internally threaded adaptor that couples to focuser drawtube)
  Dew/Lens Shield   Arrangment   Fixed, thread-on
  Front diameter   139.9mm
  Size & Weight   Optical tube length   497mm (19.57 inches), or 451mm (17-¾ inches) with 2" Back
  Optical tube diameter   115mm (4.53 inches), note: *the SX 115mm tube ring is not compatible
  Optical tube weight   4.5kg (9.9 lbs.)
  Provided accessories   1-¼ inch eyepiece/accessory holder, Aluminum-clad case (553 x 17.8 x 17.8mm / 21-¾ x 7 x 7 inches), Allen wrench 1.5mm


PN 37315 - Camera Mount adapter for 645D PN 26636 - VSD100 Tube Ring with Plate PN 26637 - VSD100F3.8 0.79x Focal Reducer PN 5971 - 50.8 x 10mm Reducer
Vixen Camera Mount adapter for 645D Vixen VSD Tube Ring with Plate Vixen 0.79x Reducer for VDS100 Vixen 50.8 x 10mm Reducer