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It's equivalent to about a 140mm scope for light-gathering. Resolution - which depends on the objective size - will be no better than a 100mm scope.

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Last thing, first. Rusty is correct that resolution depends on objective size. However, it also depends on magnification (focal length). In addition, while resolution may not be increased mathematically, the additional optical system will enhance resolution somewhat via perceptions of the “human experience” that the computer has yet to master.

Then onto increased light-grasp.

Last week, I learned from this forum that at least ONE star—the name of which was derived from what you would get if you ran over Paul McCartney with a steam roller—can be seen as having a measurable disk. I don’t know if I am ready to believe that quite yet. However, I accept the possibility and look forward to having my mind changed on any subject wherein I have been mistaken.

With that in mind, I would ask that someone give me the source material which states that combining the light grasp of two objectives renders a substantial increase in image brightness. I would like to share that knowledge with some of my friends from the Optical Sciences Center in Tucson, especially bino buff Dan Vukobratovich, Ph.D., now with Raytheon.

It has always been my understanding that while contrast MAY be increased by AS MUCH AS 40%, overall image brightness is not increased by any appreciable amount, which 10%, 20%, 40%, or 41% would certainly be.

Again, I would appreciate being corrected. But, this is how this old country boy sees it from an empirical standpoint:

1) The difference here is sensory and not optical. Whether one is using a 35mm, 50mm, 70mm, 100mm bino, or naked eyes it should not matter because we are not speaking of quality, but rather, quantity.

2) If, while looking out your window, with either your naked eyes or a 100mm bino, you place a piece of black cardboard in front of one of the objectives or one eye, does the image brightness decrease by even as much as the stated 10%? The answer, of course, is “no.” Conversely, does removing the paper cause the image to brighten by 10%, or 20%, etc.? Once again the answer is “no.” Until, I am corrected by someone who has been published by SPIE, I will be reticent about believing that the increase in perceived brightness is greater than about 1.5%.

Just as with BeatleJuice, I anxiously await correction.

Cheers,

Bill

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William J. Cook, Chief Opticalman, USNR-Ret.
Founding Editor, Amateur Telescope Making Journal
20-year vet. of Captain's Nautical Supplies, Optics Dept. Mgr.
Optics Machanic, WG11-3306, Ft. Lewis, Tacoma,WA
Yata, Yata, Yata . . .


Edited by billcook (03/02/05 02:52 PM)

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