Mark V Binocular Viewer from Baader Planetarium (BPMARKVS)

The Mark V Binocular Viewer is the culmination of years of research and development, originally by Carl Zeiss Jena and further advanced by Baader Planetarium. It combines all the best features to provide a superb viewing experience: optical quality, critical colimation, high transmission coatings and diopter adjustment to individually focus each eye.

If you own the previous Giant Binocular Viewer (BPBINOV) model and need information, please click here.


ClickLock Eyepiece Clamps - The ClickLock mechanism grips your eyepiece firmly using a 3-point contact that accurately centers each eyepiece. Insert the eyepiece and lock it in place with a gentle twist of the outer locking ring (just two tenths of a full turn). The clamp applies gentle, even pressure to lock the eyepiece in place and centered. Please refer to additional information from Baader Planetarium regarding the new ClickLock feature.

Diopter Adjustment - You can now achieve perfect focus for each eye with the silky smooth microfocusing collar, which allows 8mm of focus travel. Please refer to additional information from Baader Planetarium regarding this new ClickLock feature.

Dielectric Coating of Prisms - The dielectric coating increases throughput by 8.9% from previous models. The coatings were carefully matched to the index of the glass used for the prisms. They allow maximum transmission at 510nm - exactly where the dark accommodated eye has its maximum sensitivity. This is especially important for night vision.

Mirror Diagonal - The Baader T-2 Mirror Diagonal features durable, 99% reflective Maxbright dielectric coatings. Its compact size allows the shortest possible light path. It is also part of the T-2 system, allowing a variety of configurations. The mirror diagonal offers the same optical performance as the prism diagonal that was offered prior to December 2011.

Interocular Separation Adjustment - Adjusting the eyepiece spacing does not affect focus. The interocular distance can be adjusted from 55mm to 75mm.

Removable 1.25x Compensating Optical Element - This optical element eliminates the slight color error and spherical aberration that a prism beam splitter naturally introduces into the light path of all binocular viewers. It allows you to enjoy wide-field, low-power views of deep-sky objects, as well as high powers. This element (also known as a Glasspath Compensator) was designed by Roland Christen of Astro-Physics and is essential for telescopes with fast focal ratios. Baader Planetarium was the first to introduce this feature for the binocular viewer. We also offer the 1.7x (BP4B) and the 2.6x (BP4C) Glasspath Compensators and the 2" 1.8x Glasspath Corrector for Refractors and SCTs (BPRSGC18) to provide higher magnifications. A 2" 1.7x Glasspath and Coma Corrector for Newtonians (BPNGCC17) is also available. [See this link for Glasspath Compensator Placement.] One of these optics should always be part of the optical path of telescopes with fast focal ratios unless a BARADV or BPFFC is used.

Quality custom case - Your investment is well protected in a high-quality custom foam-lined case.   The case is included with Mark V Binoviwers shipping since September 2014.


Clear Aperture: 1.1" at the prism entrance w/o the compensator and 0.96" with the compensator.
Weight: 2.25 lbs with Mirror or Prism Diagonal and 2" Nosepiece


IMPORTANT: If you are using the thin 2" adapter (ADA2013) or the 92mm f5 or f7 Stowaway, you should not use the AP16T nosepiece since the brass ring of these parts do not grab onto the AP16T securely. You can upgrade to the new thin 2" adapter (ADA20132), or alternately, you can use the 2" nosepiece from Baader Planetarium (part # BP16), which must be purchased separately.

Magnification Alternatives with Your Mark V Binocular Viewer

The Mark V Binocular Viewer is well suited for lunar, planetary and double star viewing. When you wish to push the magnification higher in order to bring out more detail, we recommend that you thread the optical section of our Convertible Barlow (BARADV) into the front of the diagonal. This optional accessory lens narrows the incoming beam and results in the sharpest possible images at the eyepiece end of the binocular viewer. It may be used with or without the Glasspath Compensator, depending on the magnification desired. Another excellent option is to use the Fluorite Flatfield Converter Barlow (BPFFC) manufactured by Baader Planetarium to achieve even higher magnification. We suggest that you review the entire range of options in the FFC System (PDF document).

To achieve the definitive image it is better to do your magnification using a barlow in front of the Mark V than to increase magnification with short focal length eyepieces. A narrower light cone passing through the binocular viewer is what provides the sharpest images.

Examples of Approximate Magnifications:

  • 1.25x using standard configuration with 2" Nosepiece and 1.25x Compensator
  • 1.70x using standard configuration with 2" Nosepiece and 1.70x Compensator
  • 2.40x BARADV threaded directly into the Mirror or Prism Diagonal - no Compensator
  • 2.60x using standard configuration with 2" Nosepiece and 2.60x Compensator
  • 3.00x BARADV threaded directly into the Mirror or Prism Diagonal and 1.25x Compensator
  • 4.70x BPFFC threaded directly into the Mirror or Prism Diagonal - no Compensator
2" 1.8x Glasspath Corrector for Refractors & SCTs (BPRSGC18)

Mark V User Manual

Please clink on this link to open a PDF of the Mark V User Manual.

Assembly Diagram

The assembly diagram linked below shows how the Mark V Binocular Viewer is used in various configurations. It also shows several adapters with brass locking rings that we offer for various scopes. These adapters can be used to securely hold the Mark V Binocular Viewer and other valuable accessories in place. Please see the assemby diagram for details.

Click diagram to open a PDF file.

Recommended Accessories

Advanced Barlow (BARADV)
1.70x Glasspath Compensator (BP4B)
2.6x Glasspath Compensator (BP4C)
2" 1.8x Glasspath Corrector for Refractors and SCTs (BPRSGC18)
2" 1.7x Glasspath and Coma Corrector for Newtonians (BPNGCC17)
48mm Moon & Skyglow filter (BPMS2)
Accessories from the Baader Planetarium FFC System
Heavy-Duty T-2 Quick Changer (BP6A)


NEW! Heavy-DutyT-2 Quick Changer (BP6A)

1.25" eyepieces.
We typically use a set of Plossls in a medium power range. A set of 19mm or 24mm Panoptics and 11mm or 16mm Naglers are particular favorites of our binocular viewer customers. TeleVue Radians are also favored by many. Note that while the thin 13mm and shorter Ethos eyepieces work, they have a large offset weight and it must be remembered to securely tighten the Mark V and telescope locking thumbscrews.

Note: we do not recommend using 1.25" eyepiece filters since they will add additional length to your barrel and may strke the prism of the binocular viewer. We recommend using 48mm filters at the nosepiece.

Backfocus (In-travel) Requirements

It is important to consider the optical spacing distance of the Mark V Binoviewer (with diagonal) to ensure that it can be used with your scope. Backfocus (also referred to as in-travel) is the difference between where the light focuses and the back of the focuser needs to be. The backfocus requirements will vary depending upon your configuration. Please note that this binoviewer may not reach focus with some instruments, including some earlier models of our refractors. Determine the back focus of your instrument by measuring the distance from the 2" opening of your scope to the focus point.

Approximate spacing:
Binoviewer with 1.25x Compensator and T-2 Diagonal - needs 5.3" (135 mm) in-travel
Binoviewer with 1.70x Compensator and T-2 Diagonal - needs 4.7" (120 mm) in-travel
Binoviewer with 2.60x Compensator and T-2 Diagonal - needs 3.4" (87 mm) in-travel

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This page was last modified: March 1, 2018

Astro-Physics, Inc.
11250 Forest Hills Road, Rockford, IL  61115, U.S.A.
Phone: 815-282-1513   Fax: 815-282-9847