[AZ-Observing] Re: How deep can you see? was: Re: Lunar observing tonight
- From: "Joe Macke" <joe01@xxxxxxxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>
- Date: Fri, 13 Dec 2002 02:25:07 -0700
(This is a repost (twice) because I violated the quoted lines limit)
Bigger pupils appear to lead to a reduced mag limit because the equation is
adjusting an individual's unaided eye limiting magnitude to that same
individual's aided limit. So someone with a larger dark adapted pupil size
would, presumably, have a higher (dimmer) unaided eye limiting mag.
Similarly, two observers with the same unaided limiting mag, but differing
pupil sizes would have the same aided limit, because the assistance provided
by the telescope would apply equally to both.
This might be more easily seen (if you speak math) if you change the
equation to:
10^m = 10^Alpha x (d/Delta)
Here it is more obvious that the assisted limiting magnitude is simply the
unaided limit adjusted by the ratio of the telescope's aperture to the
observer's eye's aperture. Then converted to the logarithmic magnitude
scale.
Joe
(P.S. RE the dancing mirages....but can you hear the music?)
From: Matt Luttinen <mluttinen@xxxxxxxxx>
To: az-observing@xxxxxxxxxxxxx <az-observing@xxxxxxxxxxxxx>
Date: Friday, December 13, 2002 12:26 AM
Subject: [AZ-Observing] How deep can you see? was: Re: Lunar observing
tonight
>Jack,
>
>I *know* I didn't see the G component, as it is about mag 15 or 16, I
think, and thus way below the limit of my scope. I learned that night that
averted vision can fool you. I know it fooled me. I have since used stars in
M45 to estimate my limiting mag with the 120mm to be right at 12.4, which is
exactly the theoretical limit (~12.4 for my 6.3 mm dilated pupil and a
limiting naked-eye mag of ~6) for a 120mm objective.
>
>BTW, the formula I found for limiting visual mag is:
>
>m = Alpha - 5 log Delta + 5 log D
>
>(assuming transparent dark-sky conditions and magnification > = 1D , D in
mm)
>
>where:
>m is the approximate limiting visual magnitude
>Alpha is the estimated naked-eye mag limit
>Delta is the dilated pupil diameter in mm
>D is the diameter of the objective in mm
>
>Got this from Company Seven's site, with minor modifications by me.
>
>I wonder about this formula due to the fact that Alpha and Delta are almost
always estimated. Company Seven inputs Delta = 7.5 (!) This seems arbitrary,
maybe to make the equation work.
>
>It seems to me that finding the true limiting mag of your scope is more
dependent on your naked-eye limit than anything else, and that is always
subjective to each observer. It is safe to say, though, that very few people
have better than mag 7 eyes. So, if this equation is right, anyone who has
seen a mag 15 object through a 120mm scope with dark-adapted eyes (Delta >5,
Alpha = 7, to be generous) is seeing a mirage.
>
>Notice how increasing pupil size reduces the mag limit. This seems
counter-intuitive to me. Comments anyone?
>
>Matt
>
>PS: I have seen many mirages in my life, and it's funny, they are always
dancing . . .
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