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# Relationship LP and Telescope magnitude limit

6 replies to this topic

### #1 WRAK

WRAK

Apollo

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Posted 25 November 2012 - 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

### #2 csa/montana

csa/montana

Den Mama

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Posted 26 November 2012 - 09:57 AM

Here's one that might be of interest:

Naked eye limiting magnitude

### #3 WRAK

WRAK

Apollo

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Posted 27 November 2012 - 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

### #4 derangedhermit

derangedhermit

Apollo

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Posted 27 November 2012 - 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.

### #5 Tony Flanders

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Posted 27 November 2012 - 09:10 PM

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.

### #6 WRAK

WRAK

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Posted 28 November 2012 - 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

### #7 GeneT

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Posted 03 December 2012 - 10:08 PM

Here's one that might be of interest:

Naked eye limiting magnitude

Nice chart!

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