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General Astronomy >> Light Pollution

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WRAK
Pooh-Bah

Reged: 02/18/12

Loc: Vienna, Austria, Europe
Relationship LP and Telescope magnitude limit
#5538310 - 11/25/12 06:17 AM

There are established algorithms for calculating the theoretical magnitude limit of a telescope depending on aperture. Do you know of a similar proven formula for light polluted skies based not only on aperture but also on the naked eye magnitude limit?
Wilfried

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csa/montana
Den Mama

Reged: 05/14/05

Loc: montana
Re: Relationship LP and Telescope magnitude limit [Re: WRAK]
#5540008 - 11/26/12 09:57 AM

Here's one that might be of interest:

Naked eye limiting magnitude

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WRAK
Pooh-Bah

Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Relationship LP and Telescope magnitude limit [Re: csa/montana]
#5541508 - 11/27/12 04:20 AM

Thanks, certainly of interest - but what I am looking for exactly would be an extension to the formula for calculating the Telescope Limiting Magnitude like for example "TLM=2,7+5*LOG10(D_mm)-f(NELM)".
Wilfried

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derangedhermit
Pooh-Bah

Reged: 10/07/09

Loc: USA
Re: Relationship LP and Telescope magnitude limit [Re: WRAK]
#5542455 - 11/27/12 04:41 PM

NELM is not a useful measurement of light pollution for use in such a formula. It is too dependent on the observer.

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Tony Flanders
Postmaster

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: Relationship LP and Telescope magnitude limit [Re: WRAK]
#5542827 - 11/27/12 09:10 PM

Quote:

Thanks, certainly of interest - but what I am looking for exactly would be an extension to the formula for calculating the Telescope Limiting Magnitude like for example "TLM=2,7+5*LOG10(D_mm)-f(NELM)".
Wilfried

I'd say that a fair approximation for binoculars is:

BLM = NELM + 2.5*LOG10(mm/7 * mag)

However, this isn't really linear with magnification; it's faster than linear for low magnifications, and magnification becomes almost irrelevant at exit pupils smaller than 1 mm.

Binocular vision is worth about 1/4 magnitude. So subtract 1/4 mag for monocular telescopes.

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WRAK
Pooh-Bah

Reged: 02/18/12

Loc: Vienna, Austria, Europe
Re: Relationship LP and Telescope magnitude limit [Re: Tony Flanders]
#5543691 - 11/28/12 11:39 AM

Tony, thanks - I have checked this and found good values with strong light pollution with NELM around 3 but not these good with less light pollution giving values above the standard TLM formula. But this should be resolvable with some adaptions.
Wilfried

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GeneT
Ely Kid

Reged: 11/07/08

Loc: South Texas
Re: Relationship LP and Telescope magnitude limit [Re: csa/montana]
#5552959 - 12/03/12 10:08 PM

Quote:

Here's one that might be of interest:

Naked eye limiting magnitude

Nice chart!

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