Telescope Reviews: If They Look the Same, What Could be Different?

We see this question all the time. "They look exactly the same on the outside. Why would anyone pay more if you can get the same thing for less"? Usually, it's because they are much different on the inside.

One of the things we've been trying to teach people for years is there are a list of some of the differences you CAN'T see. Some are highlighted here:

Contrary to what you might read elsewhere, any shortcuts that can be allowed in the manufacturing process will result in a less expensive product that can be distrubuted for lower cost. Considerable savings in time and process results in a less expensive product, a much bigger savings than a few $$, but one that will not perform as well.

Probably the most important differences in any two binoculars that look the same but sell for much different prices is (A)the mechanical construction, workings and range of adjustment, and (B)(likely more important) the degree to which all the optical surfaces have been figured, polished and coated. There are other things that make a difference in the quality and most of them are not visible on the outside.

If one dealer orders all his binoculars without coated prisms, the manufacturer can simply take the prisms off the shelf and install them directly without putting the prisms through the 3 hour process of the coating machine and then inspection.

It is not the cost of the automated polishing machine that adds to your cost, it is the cost of an individual testing and inspecting each piece of glass before it passes the level of QC demanded by the distributor.

Uncoated or single coated lenses or prisms will considerably increase the amount of light that gets reflected around the inside of the binocular, causing ghost images and reducing image contrast. A fully multi coated binocular requires multi-coating on ALL surfaces. It was discovered several years ago that that the factory claim of fully multicoated was being applied to binoculars that had some multi-coated components and some single coated components. This type of factory claim is still passed on by some importers.

You could be getting lenses that have passed a specific selection criteria for the objectives in one binocular. For another brand binocular, you could get lenses that have not passed the test for brand A, so you take your chances. For a third brand, you may be getting the lenses that did not pass any inspection criteria used to get the lenses in the first two brands noted above. You don't honestly think they throw away all the lenses that do not meet a specified test criteria, do you? Just because they don't meet the criteria for brand A or B doesn't mean they can't be used for brand C. More on this below.

The same binocular body could be fitted out with very different eyepieces and still look exactly the same. I once tested 3 different 20mm plossl eyepieces. They ranged in price from $29 to $89. With minor modifications they could all be fit into the same eyepiece housing. The difference in performance between the three was like night and day. The lowest cost 20mm eyepiece had severe distortion in the outer 40-50% of the field of view and beyond 60% out from center lost a full magnitude to the best eyepiece. The best 20mm eyepiece could still see not only the faintest stars but also very fine resolution at the extreme edge of the field stop.

Sometimes we have binoculars that appear exactly the same, but one model has a much wider field of view than the other. This can be accomplished by simply eliminating the field stop from the eyepiece housing. Of course, what you end up with is a wider fov, but it is not a sharply defined field stop and is generally mush towards the outer edges. Also, this may allow undesirable stray light to enter the fov. Neither the removal of the field stop for the wider soft field nor the stray light improves the image, but it is cheaper to make the eyepieces without the field stop.

The eyepiece lens edges could be blackened or not.
The objective lens edges could be blackened or not.

Shiny or bright metal exposed surfaces on inside of barrels will diminish contrast. Not all binoculars are fully blackened at all internal surfaces.

If a lens has several layers of MgF, then it is multicoated. If so, it may likely not have the characteristic blue color of a single MgF coated lens. A properly multicoated lens surface may reflect only 0.2% to 0.5% of the entering light. A properly single-coated lens surface may reflect only 1.5% of the light. An uncoated lens surface may reflect 4% of the light. Considering a binocular might have 12 to 18 surfaces, the importance of multicoating soon becomes evident.

Probably just as important is simply having multicaotings is the precise control of the thickness of the coating process. An improperly controlled multi-coating process can produce a lens coating that reflects more light than a single coating. Although you can't truely determine anything about the precision of the coating application by the color of the coating, in general, poorly coated lenses tend to look bright green. The bright green color could result from coatings being applied too thick. Improper coating thickness will reflect more light than it should, reduce the light transmission of the optics and if bad enough may cause internal reflections.

Lenses that fail the extremely tight tollerances required in the coating process should not be categorized as premium multicoated lenses. But they are still multi-coated lenses and will be used in the manufacture of some brand of binocular (same as objectives mentioned above that don't pass QC criteria). So you could be buying a fully multi-coated binocular that has lenses that don't meet stringent coating thickness criteria.

Here is a quote from a highly respected individual that has been associated with the optics industry. His comments below pertain also to my comments above re: QC of lenses and coatings.