30x50 Newtonian Binocs?
Posted 12 July 2005 - 10:10 AM
1) What the heck is this binoc and why is it so cheap?
2) I recently heard of binocs using "ED glass", "extra-low dispersion glass" or something similar. What does that mean? Is that similar to APO or something altogether different?
Posted 12 July 2005 - 11:04 AM
First, you would not fully multi coat Lenses and Mirrors. FMC is a light transmission coating (an antireflective coating) applied to a lens to allow more light to pass. Mirrors must be coated with a reflective coating to prevent any light from passing thru and reflect all light that hits the mirror.
Second, unless these are very expensive dielectric mirrors, you will not get as much reflected light from a mirror as will pass through a properly FMC coated prism. The FMC prism will pass 99% of the light hitting it and no light is lost in the internal reflections. Compared to generally a standard mirror diagonal will reflect only 88% of the light hitting it. A dielectric (very expensive) mirror may reflect 96% to 99% of the light hitting it.
Forget about the 30x50 minimal exit pupil. just based on the above two statements, there is no way these binoculars could even come close to matching the performance of a standard porro prism binocular.
And totally unrelated
I recently heard of binocs using "ED glass", "extra-low dispersion glass" or something similar. What does that mean? Is that similar to APO or something altogether different?
ED does not by itself make the outcome similar to APO. ED is simply Extra Low Dispersion glass. In order for it to be APO it still needs to be combined accurately with an appropriate second type of glass element to balance the focal length of the various colors of light.
A binocular using ED glass may be no better than a binocular without ED glass if that element has not been properly mated to correct for color. So ED by itself doesn't mean much.
Apochromatic or APO refers to the criteria by which we measure the difference at what focal lenght all or various of the colors of the spectrum are brought to focus. A standard doublet Achromat can have the blue/red wavelenghts vary by 1/2000 of the focal length. A triplet Apochromat might vary by only 1/5000 to 1/10000 of the focal length, making the difference of the focus point of the colors almost negligable.
Likewise a poorly figured or mated Apochromat that has corrected color focal lenghts to only 1/3000 error may be no better than a well corrected achromat that has also corrected color focal lenths to 1/3000 error. Just by nature of advertising a binocular as a triplet apo or semi apo does not necessarily mean it will always be better than a well figured doublet. Some are and some are not.
Posted 12 July 2005 - 11:28 AM
Forget about the 30x50 minimal exit pupil. just based on the above two statements, there is no way these binoculars could even come close to matching the performance of a standard porro prism binocular. edz
Oh, EdZ, you have no sense of humor! Taken as a whole, that ad should keep you chuckling for a good long time--especially the part about . . . "Newtonian" Binoculars.
And people wonder why I get spun up so much. I can't get a gig doing tech writing for any optical companies because so many are happy as a clam relying on people who are optically clueless. Grumble, Grumble.
Posted 12 July 2005 - 11:34 AM
Oh, EdZ, you have no sense of humor!
you are painfully correct.
Posted 12 July 2005 - 11:45 AM
The next time we are sitting around in a deep philosophical mood concerning the socio-economic ramifications of navel lint, we should try to figure out why "truth in advertising laws" don't apply to the optics world.
Just a thought,
Posted 12 July 2005 - 11:46 AM
Posted 12 July 2005 - 11:50 AM
Posted 12 July 2005 - 12:14 PM
Edmunds Scientifics looks pretty legitimate. They have a nice, big, flashy website, and colorful print catalogs that hit my mailbox every few months. On one page they are selling a pair of image-stabilized Fujinons (respectable) and on the next they are selling "Newtonian Binoculars" of dubious repute. Yes they are sold out, and according to the OpticsPlanet website, they have been discontinued by the manufacturer. Several months ago, before I got my Bachelors in Binoculars from the CNI (Cloudy Nights Institute), I was the typical sap who would have likely ordered a pair of these binocs. Not any longer. My first impression was : if they are so darn good, then why are they so darn cheap? And then the word "newtonian" used in the context of a small (and ostensibly impossible to hand-hold, hand-held binocular) bino also raised a red-flag. So in other words, this bino is to binoculars what the proverbial "department store junk scope" is to telescopes.
Posted 12 July 2005 - 12:15 PM
If they only had ONE to sell - surely it would have been more prudent of them to send it to ME , free of charge , for one of my " mini -reviews " :-)
Posted 12 July 2005 - 04:26 PM
Posted 12 July 2005 - 05:22 PM