Bob's Rock Shop Product Review
GemOro Precision Microscope

Every once in a while you come across a deal you just can't refuse and that's exactly what happened to me during the '97 Tucson Show when I encountered the GemOro binocular microscopes in the Graves tent at the Congress Street Expo. I had stopped by Graves to inspect one of their Mark IV faceting machines, which my faceting instructor told me would be on sale during the show at an attractive price. I had finished my inspection of the Mark IV and was just dazedly browsing around their tent, pondering what was left of my show budget (for the next 3 or 4 years), when I happened upon a display of the GemOro microscopes, regularly $495, on Tucson Show special for just $279!

I had been wanting to get involved in micromounting for some time but the cost of a decent microscope had always put me off. I had hoped to perhaps score an affordable deal on a used scope some day. I had passed on a couple of good deals on more general purpose monocular microscopes - I wanted a micromount optimized binocular. All of that changed for me in a heartbeat or two when I saw one of these microscopes and learned of the gonga deal Graves was offering on them. Needless to say, I finally found my micromount scope and one of these beauties went home with me.

I consider this microscope to represent one of the very best rockhounding related purchases I have ever made in terms of the enjoyment per dollar value it represents. It has truly opened a whole new mineralogical world to me, and it is a beautiful and intriguing world indeed.

This is a full sized microscope, measuring about 14 inches from the table to the top of the eyepieces when fully racked out. As supplied it provides viewing at two different effective magnifications, 10X and 30X. These are right in the ballpark - microminerals typically do not require high magnifications for good viewing. About three quarters of all specimens are best viewed between 10X and 30X. Magnification in the 30X to 60X range covers the remainder of all but a very small percentage, and because depth of field decreases as magnification increases, around 120X is considered to be the upper limit for sustaining a stereo image.

The scope is of primarily metal construction and has a nice, solid heft to it. The overall fit and finish of this instrument is very nice and will please those accustomed to working with precision equipment. The majority of the exterior surfaces are finished in a low gloss black enamel with a very fine pebble like texture, the smooth finished metal surfaces appear to have a black oxide finish applied.

The stage and base are combined into a single unit which houses the transformer that converts 120V line voltage into 12 volts for the stage and sub-stage lamps. At left you can see the transformer peaking out of the back of the base and the fuse-like sub-stage lamp. I think incorporating the transformer in the base is good engineering as it provides weight to keep help the center of gravity low, and I also appreciate a regular plug on the end of the power cord. I don't know about you, but all my power strips are already overloaded with space hogging wall-type transformers. The bottom of the base is covered with a fine expanded metal mesh which provides ventilation to cool the transformer and light. On the bottom of the base are four rubber bumper feet attached by screws at each corner.

Several interchangeable stage elements are provided which simply drop into the 3.75" hole in the top of the base above the sub-stage lamp and rest against a recessed lip. Two pivoting spring steel stage clamps are provided to secure these interchangeable stage parts. One stage element used with ambient light or the topside stage lamp is simply an opaque plastic disk that's black on one side and white on the other. Shown at center is a frosted glass disk supplied for using the sub-stage lamp as a backlight source. Shown at right is the dark field illuminator, a device which reflects light from the sub-stage lamp so that it illuminates objects placed on it from a plane perpendicular to the optical axis.

Most of the time I use the above-stage light only and the opaque plastic insert installed in the stage. I cut a protective overlay for the plastic insert from a piece of black felt after scratching it up a little by sliding rocks around on it.

The above-stage lamp is shown at left, another of those fuse-like 12V bulbs mounted in a rectangular cowling that's readily removed for lamp replacement by undoing a knurled knob. The current from the transformer in the base is fed to this lamp with a durable coil cord that extends and retracts to accommodate the motion as the microscope is racked and adjusted up and down. Note the convenient specimen holder that's supplied, which is basically a glorified alligator type clamp that can be adjusted in three axes of rotation to place a specimen as you like it. This holder slips in and out of convenient receptacles provided on either side of the stage.

A four position rotary switch is provided to control the two lamps, which can be switched on and off independently or together. GemOro has built versatile and proper illumination into this scope, an important feature that is often sadly lacking in entry level and economy priced units.

The entire optical assembly is securely attached to the microscope base via a 14mm (.55") diameter steel shaft. Coarse adjustments to accommodate various size specimens can be made by loosening a thumbwheel knob on the back of the gear drive housing and sliding the optical assembly up and down a 2" range of travel on the shaft. Focusing is done by rotating knobs located on either side of the gear drive housing that drive a rack and pinion. The feel of the rack and pinion drive is smooth and positive and focusing travel is about 1.6". The focus stays where you put it and I have not observed any tendency for things to creep downward over time due to the effect of gravity.

Of course the major design feature that differentiates this microscope from other general types is it's a binocular, or stereoscopic microscope. Because you use both eyes, the image that you see has a fantastic three dimensional quality that's unobtainable with monocular microscopes. Binoculars are definitely where it's at for viewing micromineral specimens. If you've never used a stereoscopic microscope before, the difference is analogous to that between viewing a single transparency with a regular slide viewer and viewing a stereo pair through a Viewmaster (remember those?).

The 10X eyepieces supplied are the 31.5 mm diameter, wide field type. 20X eyepieces are not supplied but are available. The eyepieces, or oculars, can be removed from the eyepiece tubes by undoing a small Phillips screw that engages a recessed ring on the eyepiece. When 20X eyepieces are installed the scope provides effective magnifications of 20X and 60X. Included are rubber eye cups that simply slip over the eyepieces. The eyepiece and prism assemblies are eccentrically mounted and are pivoted to provide interpupillary adjustment to match the center to center dimension between your eyes. Shown at left are these assemblies adjusted all the way together (51 mm) and at center they are shown all the way apart (75 mm).

The left ocular tube also provides a 5mm dioptive adjustment via a knurled ring. This adjustment is used to independently adjust the focus of the left eyepiece relative to the right in case you have one eye that focuses differently than the other, like me (20-20 and 20-320 or so).

The objectives are housed in a rotatable, cowled nosepiece with a knurled grip. It is rotated 90 degrees to switch between pairs of 1X and 3X objectives. I never noticed it until working on this review, as it was not until I inspected the knurled cowl to try to identify the finish on it that I realized it was plastic. It blends so well with the other metal parts I had just assumed it was black anodized aluminum. This does not affect the functionality of the cowl - it's quite sturdy - and molding rather than machining this part no doubt helps keep the price down. Should I ever win the lottery I'll commission a machinist friend of mine custom to turn one from a solid billet with diamond knurling to suit my aesthetic sensitivities...

At center you can see the two pairs of objectives. The general design of this stereo microscope would be classified as a Greenough type binocular, which is essentially two compound microscopes placed side by side forming an angle between them. This angle is evident in the picture at right of the objective turret with the cowl removed. The 3X objectives are the longer pair. The objectives and turret are assembled with miniature Phillips head and set screws but this is as far as I'm taking my baby apart.

Another general type of stereo microscope is the wide-field type, which is characterized by a single, larger lensed objective, with the stereo effect generated by optically splitting and adjusting the light path to the oculars after the entering light has passed through the objective lens. The wide-field type is commonly employed with binocular microscopes which provide zoom magnification. There are performance tradeoffs between these two general types. Because the Greenough type binocular employs paraxial geometry, it is capable of truer color and better resolution than the wide-field type at expense of softer edge focus at higher magnifications. The wide-field type binocular is capable of better edge focus and is "faster" than the Greenough type at the expense of inherent chromatic aberrations caused by off-axis rays entering the single objective lens, which are inevitably further compounded if a zoom element is also incorporated.

The matched objectives of the Greenough type must be placed close together which limits their maximum size and therefore the amount of light they pass. You need more light to produce a bright image with a Greenough type, but the light sources provided with the GemOro are well matched to the design. To my way of thinking, the better color and resolution of the Greenough type has a lot going for it balanced against potential soft edge focus. The depth of field is sufficient at lower magnifications where most specimens are best viewed that edge focus is not a practical issue.

The GemOro microscope came packed in a nice molded foam box. I live in an apartment and have found this case to be very handy for properly storing the scope when I need to clear my work bench for larger projects. No doubt it will be handy if I ever need to send the microscope in for service too. GemOro provides a 5 year mechanical warranty and a 2 year electrical warranty on this scope. Normally the GemOro sits out on my bench, protected from dust, cockatiels, flying rock chips and whatnot by this handy cover that's included.

As you have no doubt surmized, I am one satisfied customer of Graves and GemOro regarding this microscope, especially considering the gonga deal at $279 I got on it at the Tucson Show! If you're looking for an affordable scope that will provide an excellent entry into micromounting, the GemOro is definitely worthy of your consideration.

11-7-98 Update: A new model GemOro microscope, the 1030 Elite, has succeeded the unit I purchased from Graves at the '97 Tucson Show. The 1030 is substantially the same scope as reviewed above, with the additional feature of a mechanical, iris type diaphragm to adjust the amount of light passed from the substage lamp. While I haven't used a 1030 and it's not that relevant for viewing microminerals, I suspect the diaphragm would prove especially useful for viewing gemstones with the dark field illuminator, or other subjects requiring backlit illumination. Graves has also lowered their regular catalog price on the GemOro since I purchased mine, from $495 to $349.95. :)

Graves offers a free equipment catalog you can order from their web site. You can also contact Graves for further information on purchasing the GemOro scope by email to gemcut@compuserve.com.


The Complete Book of Micromounting

If you're interested in micromounting and collecting micromineral specimens and looking for a good book on the subject, The Complete Book of Micromounting by Quintin Wight is the most definitive and comprehensive text on the subject I've found to date. This informative 283-page book elaborates on many facets of collecting, identifying, preparing, viewing, photographing and trading micromineral specimens.

Published by The Mineralogical Record, this book is profusely illustrated with photographs and illustrations, including a color album of 165 beautiful micromineral photographs. You can order it directly from the MR web site.

At $65 this book will not be a casual acquisition for some, but you'll get what you pay for. There is plenty of how-to in it, and with this book, a microscope (a good quality 10X hand loupe will suffice to start with), and a very modest assortment of hand tools and materials, the novice micromounter can be collecting, preparing, trading, and enjoying micromounts in short order! This is a classic that belongs in any rockhound's library.

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Bob Keller