Product Review: The Bresser Makro Stand for converting compact binoculars into a stereo microscope
by David Walker, UK
Commercial devices for converting binoculars into a stereo microscope are well established and homemade designs have also been presented; the Fun Science Gallery for example has some very neat looking designs with either fixed or even zoom magnification.
Although I have a competent stereo microscope, a secondhand Meiji EMZ1, it's intrigued me how well these type of devices work as they have some appeal—in particular for field use or if travelling. So the author shares his experiences of a current commercial model below for the popular compact roof prism binoculars. I tried the 'Bresser Makro-Stand Microscope Base' which sells new in UK from typically £25 upwards; a 'Waltex Stereo Adapter' is also sold for typically £48 with a similar external design. Bresser Optik are a German based company selling various consumer optical items.
Zeiss also made a similar design for their compact binoculars but not sure if still available (a mint, boxed used example sold on eBay at time of writing for £103).
Note added Aug. 20th 2009: Thank you to Manuel del Cerro who tells me there was a Bushnell Portascope. Manuel writes: The Bushnell PortaScope, a B&L, pseudo-stereo stand, was designed to accommodate a pair of Bushnell 7 x 35 binoculars. Moderately acceptable optics, now at a very moderate price on eBay.
Bresser Makro Stand, shown here at its working distance of ca. 11.5 cm when used with a pair of compact 8x21 roof prism binoculars.
The working height to the binocular eyepieces was ca. 24 cm. Weight was ca. 440g / 680g with and without typical binoculars.
For transmitted light studies, it works well as shown with a slimline 35 mm slide viewer, (this example by Jessops UK, battery / mains operated).
Its open plan allows ambient light to be used for incident light studies, but could be supplemented with a suitable portable or mains lamp.
A standard 9 cm Petri dish sits between base limbs e.g. for pond life studies.
To minimise distortion when viewing flat subjects, a simple support as shown at ca. 15° can be made to present the subject at right angles to the optical axis.
The maker's state the unit is guaranteed for ten years.
Design: The Bresser has a sturdy metal base and flat limb at ca. 15º to the vertical. The limb screws onto the base, so for the most compact packing the base and limb could be split. The back of the limb has a cross-hatched etching in the metal surface. A stiff rubber collar on the focus knob bar acts on this to give a friction focus.
The binoculars sit in a recess in a plastic mount above two ports; they are held on by a sturdy rubber belt looping over the binoculars. There's a common main objective (CMO) in the base of unit (glass; a plano-convex doublet?) and via two glass trapezoidal prisms presents an image through each side of the binocular. In the author's example the CMO was poorly secured and rattled (its exact alignment didn't seem to noticeably affect collimation), I reset this but could do with a more robust mount.
In use: It has sufficient weight for reasonable stability while still being portable. The magnification is stated to be twice that of the binoculars, i.e. 16x with 8x 'binos'. This is a useful magnification for many subjects beyond that of a typical 10X hand lens. The field of view was ca. 13 mm. The focus point is held well but the visual field does wobble somewhat during focus and also has a focus take-up jump. This wasn't unduly bothersome for flat subjects when unit focussed once, but for 3D subjects where the focus will be continually adjusted, it did make its use rather clunky, although can't be too critical in this price bracket! The author tried it with two brands of 8x21 roof prism binoculars used in the family, and both worked equally well. It may work best with 6x binos to give a 12X mag for greater depth of field and unit stability.
The short instructions supplied state the binoculars should be focussed off the unit first (at infinity?). By trial and error, the exact alignment of the binoculars over the ports didn't seem that critical for use.
Normal subjects I had no trouble merging L-R to form an image, but a 0.1 mm micrometer slide I could not merge at all, and had occasional problems with 1 mm graph paper, although my brother had no problems (I'm very shortsighted he's long sighted), comments welcomed! This may be because the collimation is only fair on this design / example, but as the binoculars optics are parallel and are used with a CMO I'm not certain if the eyestrain associated with Greenough stereos if not highly collimated also applies to this design. (See footnote on internal construction). Certainly for a reasonable length of use both my brother and I didn't notice any undue eye strain but don't think this would be a unit of choice for long term studies. I estimate horizontal image misalignment L-R to be 1 mm on this example. From past experience, collimation can be variable for budget stereos even by big names; two paired objectives I had with a Meiji entry level SKCT stereo (not my current EMZ1) were poorly collimated.
The angled limb gives a pleasing working angle and height for many subjects. It is less suited for flat objects like coins, stamps, microscope slides which should ideally be perpendicular to the optical axis for an undistorted flat view and to be in focus over field of view. A simple workaround for these sort of subjects is to make a simple support at ca. 15º (shown above).
Images: The images were competent, bright and contrasty with the good quality binoculars tried and comparable with those from the author's Meiji EMZ1 stereo 'scope at same mag. When taking the photos below using identical illuminated base, the Bresser needed half to one stop less exposure suggesting they're as bright or slightly brighter. An estimate of the numerical aperture NA (from working distance and entrance port, assuming this method is valid for this design) gave an NA ca. 0.05 - 0.06 for the Bresser; a lab stereo workhorse like the Meiji EMZ1 has NA ca. 0.075.
The entry level stereos on the market (ca. £75+) typically have much lower NAs (the author's old budget Meiji stereo NA was ca. 0.022 and give markedly lower image quality than EMZ1 from author's tests (see this stereo microscope review).
Photography The Bresser is inevitably not as sturdy as a conventional lab stereo but with care and good lighting, the typical consumer digicam with small diameter lens can be held quite steadily on the binocular eyepiece. This permitted more objective image comparisons to be made, as shown below.
Meiji EMZ-1 zoom stereo microscope cf Bresser Makro stand with Leica 8x21 binoculars.
Same lighting base used, Meiji set to 1.6x with 10x eyepieces to match 16x Bresser. Sony P200 digicam handheld over eyepieces.
No zoom in. Auto white balance, autofocus. No image editing other than resize.
Note, sharpness cannot be compared due to handheld camera variations, shutter ca 1/15th - 1/60th.
Distortion check: 1 mm graph paper. Left Meiji, right Bresser. Slightly more pin cushion on Bresser but both competent.
Water beetle, Victorian mount: upper image - Meiji, lower image - Bresser. Tonality interpretation may be camera related to some extent, Meiji slightly more contrasty.
Worn pound coin detail: Upper image - Meiji, lower image - Bresser. Lighting source same but not same angle.
Rough collimation check with 1 mm graph paper. Image should not shift between left and right eyepiece if perfect.
Comments Overall the Bresser Makro Stand or similar design seems potentially useful, assuming a good pair of suitable binoculars are available, especially where lowest cost and/or portability was important e.g on field trips for sorting freshwater life, studying insects or small plants like mosses, lichens etc. A wide variety of hand held loupes and pocket microscopes are also available in this price bracket or less for greater portability. The most appealing features of the Bresser design are most likely to be the hands free binocular 3D views and the high quality image.
There's inevitably compromises with the Bresser design and the price bracket (the basic focussing and uncertainties in long term strain free viewing if collimation only fair) and probably best suited for short term use as a supplementary portable stand rather than for more intensive work. At its lower price bracket of £25 it seems good value but for the models at twice this price other options aren't far off in price (e.g used stereos). Although as remarked, entry level new stereos in this price bracket may struggle to match its image quality and I was surprised when tried with high quality binoculars how close the imagery was to that of the mid price level Meiji EMZ1 stereo.
Comments to the author David Walker are welcomed.
Footnote on internal construction.
The base plate on which the binoculars sit shown upside down.
Two trapezoidal prisms in grooved mount direct the L-R images from the CMO to each port of the binoculars.
Base of unit showing the common main objective (CMO). This lens had no securing mount and was just lightly glued to the base so had to be reset in this example. The base plate is lightly glued into this unit. Two blunt pegs inserted in holes seen far left and right push the plate out.
Because the Bresser optical construction was simple, I did try to improve the collimation after marking original prism positions by trying lateral and angled displacement of prisms, but didn't really discover the source of the slight misalignment so reset to factory condition, perhaps inherent in the design; comments welcomed. (Such dismantling does of course invalidate the guarantee and would be better to return it if unhappy with the unit, but I'm a curious soul!)
Published in the August 2009 edition of Micscape.
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