Resolving power of Bins.

[MAN or ASTROMAN]

Can anyone give me a rough and ready approximation of the resolving power of Bins according to their Objective size and magnifying power? I know that the 'Dawes limit' comes into this as regards objective size,but what about magnification?? I'm looking at this re the ability to split double stars of equal brightness. Nothing too technical please!

[Charic]

Try dividing 116 by your aperture?

20x80 gives  @ 1.5 secs of arc! 

If I'm right, the practical limit on resolving power for a telescope, known as the Dawes limit is 4.56 seconds of arc, divided by the telescopes aperture in inches. You can multiply the Dawes limit by 25.4 to convert to the metric system (in mm), which gets you to 115.8 ( hence the 116 ) you could even round up to 120 and still get 1.5 seconds of arc?

[MAN or ASTROMAN]

TA!

[Charic]

Theres a chart here, and looks like a good book too?

http://books.google.co.uk/books?id=8mQmvT4wpWQC&pg=PA14&lpg=PA14&dq=binocular+Dawes+Limit&source=bl&ots=xEAzpxic8c&sig=Z8yLG7NSXDrjHJ9YmaOSHH0pTgU&hl=en&sa=X&ei=NHd7VNaAHoXJPYqUgKgF&ved=0CCgQ6AEwAQ#v=onepage&q=binocular%20Dawes%20Limit&f=false

Having  just read some of the text my own views have  now changed regarding the ability of binoculars?  The recommended  Table 1.4 may be of interest, which refers to  magnification  and resolution thresholds?

[Peter Drew]

I think it would be a very rare binocular that would resolve double stars down to 1.5 arc seconds at the magnification normally applied. 

[Charic]

......the text goes on to say that binoculars don't come even close, so I would agree, but sometime ago, I wanted to know the same information.  Were learning all the time, but I do like the book the information  came from, so maybe another purchase for my library?

[Stu]

I agree with Peter, my Canon 15x50 binos just about split Mizar on a good night at 14.3" separation. A mounted pair of 20 or 25 x 80 or 100mm would obviously manage better but not down to 1.5"

Stu

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[MAN or ASTROMAN]

Thanks for the heads up on the book,Charic.Phil Harrington's writing is always a good read imho.

I think it would be a very rare binocular that would resolve double stars down to 1.5 arc seconds at the magnification normally applied. 

 My thoughts as well,Peter.Thats why I asked about the capacity of the somewhat limited magnifying power of bins,in conjunction with  various Bino apertures. Please keep the info coming!

[MAN or ASTROMAN]

Cheers BigMak.

[BinocularSky]

You might be interested in what Ed Zarenski has done on this:

Theoretical: http://www.cloudynights.com/documents/performance.pdf

In Practice: http://www.cloudynights.com/page/articles/cat/cn-reports/binocular-reports/binocular-resolution-handheld-vs-mounted-r1369

[michael.h.f.wilkinson]

You might be interested in what Ed Zarenski has done on this:

Theoretical: http://www.cloudynights.com/documents/performance.pdf

In Practice: http://www.cloudynights.com/page/articles/cat/cn-reports/binocular-reports/binocular-resolution-handheld-vs-mounted-r1369

Very interesting read. I do suspect there are huge interindividual differences between the results for different people. I appear to have very steady hands (granted: depending on fatigue), and have hand-held 20x80 bins successfully. Having said that, there is a huge difference between p-mounted and hand-held use

[MAN or ASTROMAN]

Thank you very much Steve,that is just the sort of information that I wanted-and more!  Both articles are extremely interesting,and will r epay repeat reading for me.( Says the man who got a 'D' in O Level Physics!  )

[mdstuart]

Try splitting 61 Cygni in a 7 or 10 times set of binoculars..

http://en.wikipedia.org/wiki/61_Cygni

They are around 20 secs of arc and are a good test for standard binoculars

I can split down to 10 secs in my 25 x 100 for two equal brightness stars...

Mark

[cathalferris]

I can split albireo and mizar in my 10x50 when tripod mounted., and carefully focused.

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[chiltonstar]

I tried a few and was surprised at how poor the resolution was with my (Celestron) 15x70s;

Albireo (35") easy handheld or supported (elbows on car roof).

Mizar (14") supported - easy, but not handheld.

Gamma And (10", unequal), only possible supported, with left eyecap in place, and eyepiece rubber cup offset from eye to prevent defocusing. Blue secondary clearly visible.

Chris