Your comments are partially correct, but It's nothing to do with quality, they are both as equal. BaK-4 in is preferable to BK-7 as a prism glass because of the focal ratio. When the focal ratio of objective lens falls below about f/5, binoculars are mostly around f/4 so BaK-4 is needed for their prisms to achieve total internal reflection at the edges of the fast f/4 light cone. Virtually all spotting scopes have focal ratios above f/5 so there's no disadvantage in using BK-7. It achieves total internal reflection just as well as BaK-4. In some telescopes it's actually a slightly better choice because a prism made with BK-7 has a little less spherical overcorrection and chromatic aberration at blue/violet wavelengths than BaK-4.
@@romeomalintad3933 If your asking on how to work out the focal ratio, Focal Length dived by the Objective lens size. EG. A spotting scope with a focal length of say 480mm and objective lens of 80mm. 480 divided 80 = F6
@@romeomalintad3933 BTW. The lower the Focal Ratio number the faster the scope. Which means more light gathering power and brighter and clearer the image. In Astro Telescopes = Better Resolving Power.
I have a pair of binoculars 7x50 using bk7 and the image is amazing, crystal clear and all the way up to the edge these are 20+years old and not an expensive brand (Simmons) . I recently got a spotting scope from Celestron the smallest one 12-36x60 it also uses bk7 and the image is Cristal clear and super bright all the way, from 24x up magnification it looses quality but up to 24 its great. So I'm not so sure about this bak4 thing. Obviously it should be better since expensive manufacturers use it and it's technically superior, but not too much imo. Thanks for the video.
I found a pair of (Jason model 1113F) mercury 10x50. I think its very old, but is this a good binocular and what is that magnification good to see, is it good to look at the stars? I also have the celestron 8x25 that you recommened and I buy it (Im very happy with it). What is the difference with the 8x25 and 10x50
The are some differences: 1. Magnification 10 is more powerful than 8 2. Binoculars with 50mm lenses produce brighter image 3. Magnification 8 has wider field of view than 10 4. 8x25 binocular is lighter than 10x50 5. For astronomical observations, magnification should be at least 16 or 20
@@binocularsguides3582 That's totally wrong. In astronomy we use the lowest magnification binoculars and largest exit pupils for DSOs (deep sky objects). For planets telescopes and tripods are necessary + magnifications of at least 80x is necessary. For planets large exit pupils are not needed. Binoculars are not fit for observing planets. They are only good for observing DSOs if and only if the have lowest magnifications and largest exit pupils. For example, my binos have exit pupils: 4, 6, and 7. For terrestrial observations folks don't need such large exit pupils. Large exit pupils result in what? Well, it results that binoculars are huge and have lenses from 50mm to 100mm. Mine are 7x50, 12x70 and 25x100 with corresponding exit pupils being approx. of 7mm, 6mm, and 4mm, as I already said. Non of this matters for terrestrial observations. All you need is 8x40 or 10x50, i.e. you don't need a lens bigger than 50mm. And you don't need magnification more than 15x because the observation will not be possible. Everything will be shaking madly. I use a tripod even with a 12x70mm, although I can hold binoculars very steady, steadier than other people can! As to BAK 4, yeah, is crisper (offers higher resolution) than BK7. If that matters, you should use BAK-4, otherwise BK7 is fine too. Most important is not to use some very cheap knock-off binos. Those really suck but even they can be used, even they perform their functions. I don't use BK7 as it blurs the image. In astronomy it results in the loss of brightness or stellar magnitude. Not acceptable. I did use BK7 binos though. They were good binos all right but why should I loose stellar magnitude (around 1 mag)/brightness. It's too much to lose that much brightness. It's okay for terrestrial use but not for astronomy!
