The Ideal Birding Binocular - from BVD

[etc]

An old article (13 years old) but interesting.


....
the design of most roof prism binoculars requires that one surface of the prism be an aluminized mirror to work properly. This means that roof prism binoculars typically will not be as bright as similar-aperture/similarly coated porro prism models, due to the 12% light loss typical of an ordinary aluminized mirror (or the 4-6% light loss of an enhanced aluminum mirror). During daylight observing, however, this light loss is rarely visible. Roof prism binoculars that use high-reflectivity silver (98% reflective) or dielectric-coated mirrors (greater than 99% reflective), on the other hand, can be virtually as bright as similar-aperture BaK-4 porro prism models.
......


http://www.betterviewdesired.com/The-Ideal-Birding-Binocular.php

[trashbird]

At the bottom of the article it says it was updated in 2007.

I don't think they had dielectric coatings 13 years ago.

I think the article is pretty good. I probably read it at some point in the past 13 years.

A few comments:

Depth of field: This is simply a function of magnification. The higher the magnification, the shallower the depth of field. Photographers understand this. Given the same aperture, the depth of field will be shallower with a more powerful telephoto lens, and deeper with a less powerful one. Want lots of depth of field? Get a 6x binocular. The actual binocular effect may give you the idea that you are getting more depth of field -- but it's not true depth of field.

IPD: Interpupillary Distance. This is crucial. People come with eyes set apart farther and closer. When you get glasses the optical technician checks your IPD. They want the optical center of the lens to be right where your eyes are. If you can't get the eyepieces of your bino close enough together or far enough apart, two things will happen. First, you won't get a binocular view -- you won't be able to fuse the two images together into one image. Second, your image will be full of extraneous aberrations like color fringing. Some people here have talked about this effect when you don't get your IPD right. Most binoculars will have an IPD range down to 58mm, but personally I need more, like down to 56mm at least. Also, I have noticed that I need to get my eyepieces closer for close up views and farther for distant views. The Pentax Pupilio solved this problem by making their oculars move closer together as you focus closer.

Finally, you need to actually take the bino out birding and see how it feels. A bino with the perfect specifications may still not be comfortable for you. There are many subjective qualities about what makes a bino feel right for a given person. So buy your binos form a place where you can send it or take it back for an exchange of refund.

[Tero]

The roofs are as brighter now, some 97% or better transmission of light.

[trashbird]

"The Pentax Pupilio solved this problem by making their oculars move closer together as you focus closer."

Oops, I meant "objective" instead of "ocular".