Mark V Binocular Viewer from Baader Planetarium (BPMARKV)

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, high transmission coatings and diopter adjustment to individually focus each eye.

For information regarding the previous Giant Binocular Viewer model, 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 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. 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 - 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.

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

Removable 1.25x Compensating Optical Element - which 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 Glaspath 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) Glaspath Compensators. The 2.6x Glaspath Compensator is not available at this time.


Clear Aperture: 1.1" at the prism entrance w/o the compensator and 0.96" with the compensator.
Weight: 2 lbs 4 oz with Prism Diagonal and 2" Nospiece

Tips for Using Your Mark V Binocular Viewer

The Mark V Binocular Viewer includes the viewer itself with built-in (but removable) 1.25x compensating element (BP4A), Prism Diagonal (BP1), and the 2" Nosepiece (AP16T) as shown on the assembly diagram. Optional items include: 1.25" eyepieces, the Convertible Barlow (BARCON), items from the FFC System and filters. We also offer several adapters with brass locking rings for various scopes. These adapters can be used to securely hold the Mark V Binocular Viewer and other valuable accessories in place.

While the binocular viewer works extremely well for showing subtle features on the lunar surface and for bringing out planetary detail, we recommend that you thread in part of our Convertible Barlow (BARCON), with an effective magnification 2.4x, to the front of the viewer for critical high-power observing (such as double star observations). This optional accessory lens narrows the incoming beam and results in the sharpest possible images at the eyepiece end of the binocular viewer. Another excellent option is the Fluorite Flatfield Converter Barlow (FFC) manufactured by Baader Planetarium. We suggest that you review the entire range of options in the FFC System (PDF document).

Assembly Diagram

This assembly diagram shows how the the Mark V Binocular Viewer is used in various configurations.Click on it to enlarge.

Recommended Accessories

Convertible Barlow (BARCON)
1.75x Glaspath Compensator (BP4B)
48mm Moon & Skyglowfilter (BPMS2)
Accessories from the Baader Planetarium FFC System

1.25" eyepieces. We typically use a set of Plossls in a medium power range. A set of 19mm or 22mm Panoptics eyepieces are particular favorites of our binocular viewer customers. Note that the 22mm Panoptics may not be suitable for viewers with wider noses. TeleVue Radians are also favored by many. Please call us for your TeleVue eyepiece purchases.

48mm Color Filters will be available from Baader Planetarium in late 2003. These will be optically polished as are the Moon & Skyglowfilters and 1.25" Colored Glass Filters (BPCF125). Please contact us if you are interested. Note, we do not recommend using 1.25" eyepiece filters since they will add additional length to your barrel and require additional backfocus. As a result, they may not work with some eyepieces. We recommend 48mm filters.

Other 48mm filters that you typically use in your observing sessions.

Backfocus (In-travel) Requirements

Backfocus (also refered to as in-travel) is the difference between where the light focuses and the back of the focuser needs to be. The back focus requirements will vary depending upon your configuration. Please note that this viewer 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.

Binoviewer with 1.25x Compensator, 2" Barrel and Convertible Barlow - needs 0.6" in-travel
Binoviewer with 1.25x Compensator, Prism and Convertible Barlow - needs 1.8" in-travel
Binoviewer with 1.25x Compensator and 2" Adapter - needs 3.5" in-travel
Binoviewer with 1.25x Compensator and Prism - needs 4.5" in-travel

Binoviewer with 1.75x Compensator, 2" Barrel and Convertible Barlow - needs 0.7" out-travel
Binoviewer with 1.75x Compensator, Prism and Convertible Barlow - needs 0.55 " in-travel
Binoviewer with 1.75x Compensator and 2" Adapter - needs 2.25" in-travel
Binoviewer with 1.75x Compensator and Prism - needs 3.25" in-travel

If you do not use the 1.25x compensator, the backfocus is increased by 1.25x in all configurations
Binoviewer with 2" Barrel and Convertible Barlow - needs 0.9" in-travel
Binoviewer with Prism and Convertible Barlow - needs 2.25" in-travel
Binoviewer with 2" Adapter - needs 4.4" in-travel
Binoviewer with Prism - needs 5.6" in-travel.

Prices and availability

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This page was last modified: July 23, 2003

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