Russian BMT-110 20x110 "Marine Binocular Telescope"

Mfr: KOMZ (Kazan Optical Mechanical Plant), Russia.  See web site.

Serial Number: 049* (* represents a Cyrillic character)

Date: 1994

AFOV: ~100 degrees

TFOV: ~5 degrees

Eye Relief: 17mm (measured ~16mm)

Prisms: 45deg and 105 deg

Total weight with pier: 74 kg (~163 pounds)

Diagrams from the owner's manual:

The Russian BMT-110 is an ultra wide angle military binocular telescope made for naval use.  I  believe the manufacturer is KOMZ.  There are air purging ports and a desiccant cartridge on the top of the body.  There is also a knob to select three filters, neutral (dark), polarizing, and orange.  The right eyepiece has a cross hair reticle.   My particular sample has no manufacturer markings although it has English markings on the filter knob and desiccant cartridge.  In addition, the accompanying manuals are in English.  This unit was likely an export model.

The design of the BMT-110 dates back to at least the 1950's (I have seen a manual dated 1957).  It has many noticeable influences from German military optics of WWII.  Some of these are listed below:

    1. Cradle appears to be copied from the 10x80 20 degree

    2. Interocular adjustment from blc 12x60 and 25x100

    3. Objective shade and flaps similar to blc 12x60 and 25x100

    4. Eyepiece design influenced by blc 25x100

It is very ruggedly constructed and comes with a heavy duty cradle and elevating pier.  Obviously it was originally intended to be permanently mounted.  For amateur use it is very awkward to set up as a portable instrument.  I attach a flat wooden base as a platform for the pedestal.  I have successfully set up this binocular in the field on my own but its weight makes it quite difficult.  Once set up the mechanics are a pleasure to use.

The BMT-110 has a very complicated optical design (see the diagram above).  Each side has a 45 degree prism and a 110 degree prism.  In addition, there is a three element lens between the prisms which "serves to compensate the eyepiece aberrations".  The eyepieces are said to be at 60 degrees to the optical axis.  The eyepieces (not counting the relay lens) have a 3-2-1 configuration.  The eye lens has an inner surface with a very steep curvature, possibly aspheric like in the blc 25x100.  This surface is so steep that one can see a ring of total internal reflection when the eyepiece is in a bright environment (this can be seen in the close up picture above).  The optics appear to have multi layer coatings of reasonably good quality.

The major feature of the 20x110 is its ultra wide viewing angle.  I am not aware of any binocular produced with such a wide apparent field.  Even with twenty power the field of view is an amazingly wide five degrees.  I have had a lot of enjoyment scanning the Milky Way and nebulas with this instrument.  This binocular does have some quirks.  The eyepieces are a bit sensitive to eye placement, perhaps due to some spherical aberration of the exit pupil.  The eye relief is fine when viewing without glasses but not enough to see the entire field with glasses on.   Like most Russian optics, the image has a somewhat unnatural tint, in this case greenish yellow.  This may be due to the characteristics of the glass used.  The optics are fairly well corrected for rectilinear distortion.  However, with such a wide field, strange distortion effects are visible when panning.  Also, there is quite of bit of astigmatism and some field curvature toward the edge of the field.  This edge softness is mainly noticeable when viewing stars.  Finally, there are some chromatic aberrations visible, including lateral color.   Despite these drawbacks  I am still glad to have this unique binocular.