Where mags is the cellname that contains the mag/arcsec2 reading.
Convert cd/m² to visual mags/arcsecond²
Using the formula:
[value in mag/arcsec2]
=
Log10([value in cd/m2]/108000)/-0.4
OpenOffice formula:
=(LOG(cdm2/108000))/-0.4))
Where cdm2 is the cellname that contains the cd/m2 reading.
This formula was derived from conversations on the Yahoo-groups darksky-list
Topic: [DSLF] Conversion from mg/arcsec^2 to cd/m^2
Date range: Fri, 1 Jul 2005 17:36:41 +0900 to Fri, 15 Jul 2005 08:17:52 -0400
PDF summary of conversation.
Percentages to mpsas to percentages
The direction of darkening/lightening is included the calculation. For example:
an increase of 0.5mpsas is 36.90% darker.
a decrease of 0.5mpsas is 58% brighter.
You can use the following formulas:
Percent to mpsas:
mpsas =-2.5*LOG(1 + pct)
Ex. for darkening of 36.9%:
mpsas = -2.5*log(1 - 0.369)
= .5 mpsas
mpsas to percent:
10^(mpsas/-2.5)-1
(Open office formula) POWER(10,(mpsas/-2.5))-1
Ex. for darkening of 0.5mpsas:
pct = 10^(0.5/-2.5)-1
= 10^(-0.2)-1
= 0.631 -1
= -36.9%
