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Limiting Magnitude in Binoculars
In July 2003, an active discussion took place concerning the topic
"star magnitude and binoculars". This link goes back to the article, which includes links to many sites and formula that relate to this topic. http://groups.google.com/groups?dq=&....astro.amateur A great deal concerning the subject Limiting Magnitude in Binoculars has been published by various noted individuals addressing theoretical LM values that might be reached. Based on previous studies I performed in July 2002 and again in winter 2003 relative to what can be seen in binoculars and the influence of magnification and aperture on various star fields, I questioned some of the results that were being predicted. After many nights of recording field notes testing binocular performance, I was not convinced these limiting magnitude predictive formula were truly representative of results that could be achieved in the field, at least not under all conditions. Based on the questions remaining in my mind after this discussion, I set out to find some answers. But without the proper data and analysis, I could not clearly see where the differences might be. It took a lot longer and a lot more work than I thought before I was convinced I had enough information to answer these questions for myself. After the collection of the field data, it took considerable additional effort to sort it all out and make sense of it. The end result will soon be a published article on CN addressing Limiting Magnitude in Binoculars. Based on testing eight binoculars on many different nights representing a range of conditions, this is some of what I found: Binocular Limiting Magnitudes for a given size aperture are significantly less, nearly one full magnitude lower, than a scope of equal aperture. This is due, among other reasons, to the inability of the aperture in binoculars to reach full potential because of low magnifications in use. Two-eyed viewing vs. one-eyed viewing contributes only a small fractional gain in magnitude. There is no 40% gain realized because you have two apertures of the same size versus a similar sized scope. gain may be more like 15% to 20%. Naked Eye Limiting Magnitude does not act linearly on Binocular Limiting Magnitude. BLM does not increase in step equally as NELM increases. For the tested range with a variance of 1.5+ mag NELM, Binocular Limiting Magnitude varied by less than 0.5 mag. When binocular magnification and binocular aperture are each tested separately, for various sizes and powers of binoculars, magnification produces results about twice what Carlin's formula predicts and aperture produces results about half of what Carlin's formula predicts. When binocular magnification and binocular aperture are each tested separately, by incremental changes in magnification and aperture, it is found for each equal increment that magnification has approximately three to four times the influence as aperture on increases in limiting magnitude. In binoculars much more limiting magnitude gain is realized from increases in magnification than from aperture. This is also related to the fact that aperture is under-utilized in binoculars. Unless optimum magnification is employed, the abilities of the aperture to put an image in the focal plane are never fully delivered to the eye. Based on my results, for commonly used binocular magnifications in mag 6.5+ skies, I approximate the maximum limiting magnitude for a 100mm binocular at mag 12.0, for a 60mm binocular at mag 11.0 and for a 40mm binocular about mag 10.0. For mag 5.0 skies, all limits are about 0.5 mag lower. The ultimate limiting magnitude reached for any given aperture is significantly dependant on the magnification in use. The full article that has been submitted should be available within the next week or two. edz |
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Limiting Magnitude in Binoculars
edz wrote in message . .. snip The full article that has been submitted should be available within the next week or two. Great work ed. Glad that you made and took the time to carry through with collecting some field data. Considering the popularity of binocular observing, it will be an important contribution to amateur observing. Looking forward to seeing what data you collected. - Kurt Naked Eye Limiting Magnitude does not act linearly on Binocular Limiting Magnitude. . . . The ultimate limiting magnitude reached for any given aperture is significantly dependant on the magnification in use. Both consistent with central conclusions of Schaeffer and Clark (ODM). |
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Limiting Magnitude in Binoculars
edz wrote:
The end result will soon be a published article on CN addressing Limiting Magnitude in Binoculars. Pardon me, but "CN" has no meaning to me. Is it a journal, a website or a magazine? Based on my results, for commonly used binocular magnifications in mag 6.5+ skies, I approximate the maximum limiting magnitude for a 100mm binocular at mag 12.0, for a 60mm binocular at mag 11.0 and for a 40mm binocular about mag 10.0. Am I correct to assume that 50mm binoculars were not included in your study? If they were, were their performance closer to the 60mm or to the 40mm instruments? Halfway? Maybe I should just upgrade from a 50mm to a 60mm and save the money I would have spent on a 100mm for something else, like a decent focusser for my Dob! The mag 1 improvement from a 60mm to a 100mm instrument makes one feel the extra weight and money is not worth it. The full article that has been submitted should be available within the next week or two. I do look forward to your findings! |
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Limiting Magnitude in Binoculars
Pardon me, but "CN" has no meaning to me. Is it a journal, a website or a magazine? CN= www.cloudlynights.com The mag 1 improvement from a 60mm to a 100mm instrument makes one feel the extra weight and money is not worth it. 1 magnitude improvement, a factor of 2.5, is about what one would expect when moving from a 6 inch to a 10 inch telescope, proportionally the same change, obviously a significant increase in capability. In my experience certainly worth the effort and expense. Note that going from 40mm binos to 50mm binos is a only a 1/2 magintude improvement mathamatically but again, the difference is obvious. jon isaacs |
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Limiting Magnitude in Binoculars
CN= www.cloudlynights.com
Oh yes of course! It should be compulsory reading for everyone on this newsgroup. The mag 1 improvement from a 60mm to a 100mm instrument makes one feel the extra weight and money is not worth it. 1 magnitude improvement, a factor of 2.5, is about what one would expect when moving from a 6 inch to a 10 inch telescope, proportionally the same change, obviously a significant increase in capability. In my experience certainly worth the effort and expense. Yes, I see what you mean. The difference from a 6" to a 10" puts it all in perspective. The 100mm is back on my to-buy list and a 60mm Pentax PCF WP is tempting, but I must be strong! ;-) |
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Limiting Magnitude in Binoculars
Victor wrote in message ...
Pardon me, but "CN" has no meaning to me. Is it a journal, a website or a magazine? Am I correct to assume that 50mm binoculars were not included in your study? If they were, were their performance closer to the 60mm or to the 40mm instruments? Halfway? CN is CloudyNights.com, an astronomy website for publishing articles and equipment reviews. Hundreds of excellent articles there. I included 10x50s and 12x50s in these tests. I used eight binoculars from 8x42 up to 20x80. I tested all my binoculars above 50mm also masked down to 50mm. So, in effect, I've included results for six differnt 50mm binoculars. My 60mm binocular was a 16x60. The 10x50 is closer to 8x42. The 12x50 is closer to 16x60. The 12x50 is more difficult to hand hold than the 10x. A 10x50 sees 50% more stars than a 8x42. A 16x60 sees nearly twice as many stars as a 10x50. Each jump in magnification from 8x to 10x or from 10x to 12x or from 12x to 16x produces far more significant increases in limiting magnitude than the jumps from 42mm to 50mm or from 50mm to 60mm. edz |
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Limiting Magnitude in Binoculars
1 magnitude improvement, a factor of 2.5, is about what one would expect The 100mm is back on my to-buy list and a 60mm Pentax PCF WP is tempting, but I must be strong! ;-) The jump from 60mm to 100mm aperture will provide only about 0.3 to 0.4 LM gain. The jump from 10x to 16x and likewise the jump from 16x to 25x will provide 0.4 to 0.6 LM gain each. You will gain more from the magnification than you will from the aperture. You don't need 100mm lenses in the binoculars to get the gain. edz |
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Limiting Magnitude in Binoculars
So if that is true, what would be the difference for me when switching
from a 20x60 oberwerk to a 20x100 miyauchi fluo? Nearly none???? Hard to believe! TK (edz) wrote in message . com... 1 magnitude improvement, a factor of 2.5, is about what one would expect The 100mm is back on my to-buy list and a 60mm Pentax PCF WP is tempting, but I must be strong! ;-) The jump from 60mm to 100mm aperture will provide only about 0.3 to 0.4 LM gain. The jump from 10x to 16x and likewise the jump from 16x to 25x will provide 0.4 to 0.6 LM gain each. You will gain more from the magnification than you will from the aperture. You don't need 100mm lenses in the binoculars to get the gain. edz |
#9
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Limiting Magnitude in Binoculars
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