Telescope Reviews: 127mm f/5.5 binocular

Did you see the binoscope by James Stillburn in pp. 66-67 of the April Sky & Telescope? There, the image is unreversed and erect, with only two mirrors . Each telescope moves as a unit laterally, for interpupillary adjustment. The metalwork shown seems to be of a very high order,and no doubt time-consuming. But the present thread gives hope of an easier approach to an erect, unreversed image, two mirror, binoscope. The wooden box is the key.

In the Matsumoto EMS, the separation of each mirror pair is varied for IPD adjustment. In some or all, the mechanism is a Pentax 67 film camera accessory.

In the present thread, the IPD is via two mirrors, equivalent to the rhomboid prisms which swivel on many of the the 45 degree or 60 degree inclined view WW II Japanese 60, 80, 105, or 120mm binoculars.

The present wooden box structure suggests that metalworking machine tools , such as a lathe and a vertical milling machine, may not be required for a successful binoscope construction.
Mr. Bill used a radial arm saw. A sliding compound miter saw has replaced those for some applications. If applicable, the slider compound miter saw would occupy less shop space. Mine is from Harbor Freight. Adequate slide length seems to be the criterion here.

One can visualize a two mirror erect, unreversed system with a wooden box to house both telescopes:
The mirrors would be arranged as in the beamprint traces illustrated in the drawings of an Amici prism used in the second mode, as found in Mil Handbook 141, which can be found in the bibliography of this forum, or Googled. There, the entire beam passes from one roof face to the other roof face, without being halved or partially divided by the roof edge. Phantom roof edge or virtual roof edge, is a description.

For 90 degree deviation, as chosen by Mr. Stillburn, op. cit., the beamprints are 2:1 major/minor axes ratio. The axial ray has an incidence angle to 60 degrees onto the mirrors.
The Stillburn scope uses 1.414:1 major/minor axes ratio ellipses, the same proportions as the diagonal mirror of a Newtonian telescope, or the mirrors used for the 3-mirror non-compound angle reversed image system of the present thread. So, some of the mirror area is wasted in the Stillburn execution. I do not know what the ratio is in Matsumoto constructions.
One mirror would be in a fixed location inside the wood box. Its mate, which can be smaller, to accept the smaller cone diameter downstream , can be supported by a slide which is supported by a wood or metal lid of the box. The smaller mirror should be large enough to accept the entire cone when moved "upstream" for a large IPD such as 72 or 74mm.

The slide motion direction on or under the box lid,in a plane parallel to the plane of the box lid, for the 90 degree case,can come from a compound angles calculation by the reader,or from your present servant when I retrieve former work on this general topic ,which has been discussed several times in this forum , from Mssrs. Stillburn or Seronik, handbook search, top views of the Matsumoto system, ...? Mr. Stillburn sent to me some fine drawings of his system.
30 deg? 45 deg? 60 deg.?, 54.75 deg. ? I do not recall. I used 3D vectors .

Compound angles are discussed in Machinery's Handbook, finish carpentry books , and probably elsewhere, maybe in trigonometry , certainly in books on solid geometry, which use 3D vectors as the most straightforward approach. My hp48 program is for layout of a general ( not just 90 deg. , but fixed deviation once chosen) two mirror version which uses the WW II Zeiss style IPD change , in which one( and only one) of the eyepieces moves laterally by twice the motion of its roof prism. That system has been considered , but not built, in a 90 deg. overall deviation box form in which the mirrors are supported by the lid of the box.