Telescope Reviews: These Look The Same, are they?

How many times have we seen this question come up? We have a long list already tagged in our "Best Of" links to help answer this question, but let me highlight some points. I am not making any claim that one particular brand or another does or does not conform to a higher standard, but some of these differences have been noticed between various brands of look-alike binoculars.

Aside from the differences in introductory pricing to secure some market share, 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) the degree to which all the optical surfaces have been figured, polished and coated. There are many other things that make a difference in the quality and most of them are not visible on the outside.

I have seen it posted on so many boards around the internet that there is no difference between a $149 model and the $79 look-alike. I would submit that type of statement is being made by someone who has not tested a variety of binoculars side-by side with the intentions of providing a detailed report on the measured performance of the brands in question.

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. 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. 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.

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 muster.

There are anywhere from 14 to 18 glass surfaces in a binocular, 2-3 lenses for the objective, 2 prisms and 3-4 lenses in the eyepieces. I could multi coat ONE lens and call the binocular multi -coated. I could then provide this same binocular with uncoated lenses in the eyepiece or uncoated prisms, but it would still be a multi-coated binocular.

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.

Even with that being siad, it was discovered several years ago that it is necessary for the importer to clearly define the criteria for fully multi-coated to insure you get what you ask for. It was found 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.

The objective could be a doublet or a triplet.

I could be choosing lenses that have passed a specific selection criteria for the objectives that are used in one binocular. For another brand binocular, I could be selecting lenses that have not been tested at all, so I take my chances. For a third brand, I may be using the lenses that did not pass the inspection criteria used to get the lenses in the first brand 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 doesn't mean they can't be used for brand C.

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.

A telltale sign that not all binoculars that look alike have the same eyepieces is the fact that they do not all have the same eye relief.

Sometimes we have binoculars that apear 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 white or bright exposed surfaces on inside of barrels will diminish contrast.

No retainer clips holding prisms in place. If the prism glue comes loose you have a loose prism shaking around that requires a shop to repair. Probably more expensive than the binocs.

If a lens has several layers of MgF, then it is multicoated. But if so, it may likely not have the characteristic blue color of an 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 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 thickness will reflect more light than it should. However, a properly multi-coated lens can give off a faint green color or a faint purple/pink color.

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. So you could be buying a fully multi-coated binocular that has lenses that don't meet stringent coating thickness criteria.

BaK4 (Barium crown) has no advantage over BK7 (Borosilicate) when used in in a situation where the incoming light beam angle is very narrow. However in wide field applications such as low power binoculars there are advantages - increasing the brightness of the edge of field while having no effect on the on-axis image. There are two things which make Bk7 perform poorly in a binocular. It's not that Bk7 glass is inherintly bad, it's actually pretty good for several optical applications such as an objective lens since it allows the light to pass through it, but in a binocular which uses this glass as a prism depending on the angle at which the light enters the glass, some of it doesn't bounce out the other end so we end up loosing something like 8-12% of the light.

The disadvantages of BaK4 is that it introduces more spherical aberration into the optical path than BK7. BaK4 also introduces more chromatic aberration than BK7. However, what BaK4 adds to the aberrations, for several reasons might not be so noticable, especially in low power binoculars. And in this case low power would include all commercial fixed power binoculars.

A recent question came up.
referring to the 25x65 binos mentioned.... They are made by Burgess with FPL53 glass... Compared to a Takahasi FL binocular.
The question: If Tak can't afford to produce the FLs because of the high cost of FL glass, then HOW could Burgess be offering a similar model for only $295?

It is similar, but is it the same?

Ohara FPL53 ED glass is not quite the same thing as Fluorite. It is fluorite glass re-melted with other ingredients to make a more homogeneous glass that is easier to polish and is easier to multi-coat. Fluorite has a crystalline structure that makes the glass soft, harder to polish and it more difficult to hold multicoatings. FPL53 is cheaper to manufacture, easier to polish, and holds hard multicoatings without any crystalline interference from the glass. FPL53 is also on the order of 2 to 3 times cheaper than Fluorite glass. But that is not the end of the cost difference story.

We need to assume the reason for the use of the ED glass is color correction. The use of ED glass can aid in achieving better color correction, but not without the proper mating element. Even if you use fluorite or in this case FPL53 ED glass, that in itself does not provide better color correction. These materials by themselves cannot correct color. The real key to color correction is the mating element that is used with the ED element.

Various mating elements can be selected that might result in poor, good, excellent or perfect color correction. It gets more expensive to pair a higher performance lens combination. At some point between poor and perfect, each manufacturer decides where the image produced by the doublet ( or sometimes triplet) is good enough. It is more difficult to discern any differences of performance in smaller lenses, therefore a smaller lens can be made just good enough and need not be perfect. Hence you can get an inexpensive binocular with an FPL53 ED lens component by selecting a less expensive mating element for the finished doublet.

None of this even addresses the degree of figuring of the ED lens. My guess is a Tak FL binocular might have the upper hand because 1, the lens elements may be figured to a finer degree and 2, the selected mating element could be higher up the performance curve, both resulting in a more costly manufacturing process but also resulting in a much better performing product.

edz

more to come.

edz

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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
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Edited by EdZ (11/14/05 09:05 PM)

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