Vixen Optics SD81S 81mm f/8 ED APO Refractor Telescope (OTA Only)

BH #VISD18S • MFR #ES26146
Vixen Optics
Vixen Optics SD81S 81mm f/8 ED APO Refractor Telescope (OTA Only)
Key Features
  • 81mm Refractor-Style OTA
  • 625mm Focal Length, f/8 Focal Ratio
  • FPL53 Extra-Low Dispersion Glass
  • Apochromatic Lens Configuration
Ideal for visual observation as well as prime focus, eyepiece projection, and afocal imaging astrophotography techniques, the Vixen Optics SD81S 81mm f/8 ED APO Refractor Telescope is an ideal addition to an amateur astronomer or photographer's kit.
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Vixen Optics SD81S Overview

  • 1Description
  • 2Optical Tube
  • 3Mounting
  • 4Included Accessories

Ideal for visual observation as well as prime focus, eyepiece projection, and afocal imaging astrophotography techniques, the Vixen Optics SD81S 81mm f/8 ED APO Refractor Telescope is an ideal addition to an amateur astronomer or photographer's kit.

Optically, Vixen outfitted the SD81S with FPL53 extra-low dispersion (ED) glass, in a fully multi-coated apochromatic lens system that corrects for both spherical and chromatic aberrations, astigmatism, and off-axis comas. This correction creates a wide flat field of view without distortion and removes the blue-tinted "halo" effect for true high-contrast color transmission. Threads on the drawtube allow direct connection of T-rings and other camera mounts.

Included with the the optical tube assembly (OTA) is a flip-mirror diagonal with dual 1.25" holders. The light path can be directed to the upper holder with the mirror in the Up position, and to the rear holder by flipping it down. For visual observation, the mirror can hold two eyepieces to allow easy changes from low to high magnification. When using it for imaging, the camera or imaging system is placed in the back, and an eyepiece can be attached at the top to check alignment and tracking between exposures.

Vixen offers the OTA without a mount and tripod for users who already have a reliable support system, but include a mounting ring assembly and a Vixen-style dovetail plate to make it compatible with a wide variety of mounts. An integrated carry handle makes se tup and break down easier and safer.

Optical Tube

  • Designed to capture the entire field of view of a DSLR camera with a full-frame image sensor
  • 81mm aperture draws in enough light to view the moon, planets, and bright deep sky objects without excessive bulk or weight
  • Fast f/8 focal ratio makes it ideal for long exposure astrophotography and imaging
  • 625mm focal length produces a moderate magnification potential without being too long
  • Refractor-style light path delivers clear and sharp image
  • FPL53 extra-low dispersion glass corrects chromatic aberration across the entire visual spectrum for clearer views and images without halos or fringing
  • Apochromatic lens configuration eliminates spherical aberrations that cause distortion at the edges of the field of view, and further corrects chromatic aberrations
  • Anti-reflection multi-coated optics improve light transmission to produce bright and clear high-contrast images with accurate color fidelity
  • Resolution: 1.43 arcsec
  • 60mm and 42mm adapter threads accept T-ring and camera mounts for astrophotography and imaging


  • Optical tube assembly only — mount head and tripod required for proper use
  • Vixen-style dovetail plate is compatible with a wide variety of mount heads
  • Tube rings enable the OTA orientation to be adjusted for proper balance and to avoid interference with mount and accessories
  • Integrated carry handle for a secure set up and break down
  • Weight: 7.2 lb

Included Accessories

Flip-mirror diagonal:
  • Flip mirror down to direct light straight back or move it up to use upper holder
  • Enables the use of two eyepieces or a guider eyepiece and imaging system
  • 1.25" holders are compatible with a wide variety of eyepieces and accessories
XY Dot Finder:
  • Unmagnified view makes finding alignment stars fast and star-hopping navigation easy
  • Projects a simple red dot into the view, which won't obstruct small stars, planets, or other objects
  • Rheostat controls the variable intensities with 11 levels; allows dot to be seen without affecting night-adjusted vision
  • Runs on one included CR2032 battery

Vixen Optics SD81S Specs

Optical DesignRefractor
Focal Length625mm
Focal Ratiof/7.7
Eyepiece Barrel Diameter1.25"
DiagonalFlip-mirror, dual-eyepiece holder
FinderscopeRed dot
Mount TypeNone
Power SourceNone
Optical Tube Dimensions23.0 x 3.5" / 58.5 x 9.0 cm
Weight7.2 lb / 3.3 kg
Packaging Info
Package Weight10.65 lb
Box Dimensions (LxWxH)24.5 x 11.7 x 8.3"

Vixen Optics SD81S Reviews

All that I hoped for, and More

By Robert
Rated 5 out of 5
Date: 2021-03-29

I upgraded to the SD81S from a 90mm ACO which was a gift, and my first telescope. Although I did as much research as possible before ordering the SD81S, I didn't know exactly what to expect. After my first observing session I knew I made the right choice. The contrast was so good that I was able to view DSOs that I couldn't find before. The stars were just pin pricks of light as they should be. I've been enjoying splitting double and multiple stars. I got the scope too late to do much planet viewing. I've been using my Baader 8mm to 24mm zoom most of the time, and even with less that ideal seeing, I find that I'm using my X2 Barlow (156X) more than I ever did. I've always used a 90 degree finder scope and that's what I put on the SD81S. One night I thought that I'd try the red dot finder, and I was sold on it; much easier to locate targets than with the scope. I am very happy with the SD81 and recommend it for anyone looking for a telescope in its price range.

Good Scope

By Richard
Rated 4 out of 5
Date: 2020-02-16

After 20 years using an Orion Short Tube 80 and a SkyQuest 8 inch dob, I finally spent 1k to get the best APO refractor I could afford. My Short Tube 80 had a GSO Crayford focuser added 3 years ago giving it a much better star test and removed image shift. My SkyQuest Dob has a Parks 8 inch mirror I installed 15 years ago. Making the scope deliver much better resolution. Now for my new Vixen SD81s. First impression the scope looks like a nicer Synta type scope. Cast rack and pinion focuser gives it the Synta look. A little disappointed but the scope grew on me by the end of the day. All set up with it’s handle, tube rings and dove plate gives the scope an “all business “ look. Definitely made better than a Chinese scope. First impression with 25mm eyepiece was similar to my Short tube 80. Orion Nebula did have more definition and contrast in the Vixen. But not much more. Went to a 10mm eyepiece. Now the Vixen pulled way ahead. Stars were sharp. Nebula had noticeably better contrast and definition. Trapezium felt like you could drive a truck through it. Probably due to F7.7. As well as the better glass doublet. I saw glimpses of the “E” Star. Used a 2x Barlow. Stars still sharp. Trapezium still had good contrast but image was dimmer. Went to 7mm eyepiece. Sharp and contrasty. Barlow the 7 mm and I reached the limit. Stars still sharp but image was too dim to be satisfying. Swung scope to Rigel. Using 10mm eyepiece the B Star was easily visible. My Orion Short tube would rarely see Rigel as a double star. The Vixen SD81s quickly shows it’s a good star splitter. It’s actually very good. This scope can take power. Using a 4.5mm I could drive a bus between Rigel A and B. Rigel star test was very good outside of focus. Inside was not quite as good. Vixen shows color on both sides of focus only on the brightest of stars. Otherwise no color. Focuser works very well. Don’t need a fine focus. Slight image shift at very high powers. Excellent scope!

Very Good Telescope

By Richard
Rated 5 out of 5
Date: 2020-05-25

Couldn't resist writing a 3rd review. I have owned the scope 3 months now and the experience gets better and better. Very good optics. This scope can split double stars very well. Izar clean split at first diffraction ring using a 5mm eyepiece. Epsilon Lyra double double clean split on most nights. Dim globular clusters start to resolve using averted vision. M-3 and M-13 start to resolve with direct vision. Globular clusters are right at the edge of this scopes limitation. This scope does see them though. Very little color inside and outside of focus on bright stars only. Otherwise no color. I could not see any color on the edge of 3rd quarter moon. Airy disc prominently seen at 5mm eyepiece. I can 2x barlow a 4.8 mm to 2.4 mm and split Izar airy disk even farther apart. That's 240x. Very good for a 81mm scope. Focuser could be better. It works but comes with image shift. You have to find the sweet spot using the screw tensioner. Like turning a 16th of a turn at a time. When you feel the knob start to lightly tension, that's when to stop turning it. It doesn't take much. Then the focuser works well. To tight and you will get way too much image shift. I cant recommend upgrading focuser because it defeats the good price of the scope. Star Test is excellent with this focuser so why risk it. I used the B&H credit card 0% rate to get this purchase past my wife. She said OK. Now I can sneak some accessories by her later using the card again ;). If I was to brag, I would say this SD81s is one of the best 80mm scopes for the money optically. If you like nice focusers, look somewhere else. I was looking for good optics. I found them. Overserving highlight so far, seeing a crescent moon in front of the Pleiades. Wow. Dark side of moon looked like you could reach out and touch it. Watched stars disappear behind the moons edge.... Thought I was in a space ship.... Ground control to Major Rich.... Can you hear me?...……….

Updated Review. Great Scope

By Richard
Rated 4 out of 5
Date: 2020-02-26

Very nice telescope. Good for double stars. Especially for its compact scope size. Resolves a very dim M-15 and M-13. Not to their core but enough to make out some individual stars. Not bad for an 80 mm scope. Can take up to 7mm eyepiece. After that, image is an airy disk. Maybe a little more (5mm eyepiece) would work for some. Focuser does have image shift. However it gets the job done. From what I’ve read it’s not worth upgrading focuser. To difficult to swap out a Vixen focuser. I would add it’s not worth taking the chance because this scope has a very good star test and I wouldn’t want to lose that. It’s a budget APO. Start adding stuff to it defeats the good original price. M-81 and M-82 were visible with some definition. Really nice views. Stars are crisp. Scope does show color on both sides of focus only on bright stars. Otherwise no color. I would say this is a very good 80 mm scope. It’s not a high end triplet APO but it’s also not priced like one either. I would recommend this for visual observers and beginner Astrophotography.

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