[APML] limiting magnitude (was asteroid photography)

[William Mattil <wrmattil@ix.netcom.com>]

Anthony Ayiomamitis wrote:
>
>       With an aperture of 8", you have a limiting visual magnitude of
> about 14.2 under excellent skies and if you have good optics.
> Similarly, with a focal lengh of 1000 mm and also with good optics and
> excellent skies, you have a limiting photographic magnitude of about
> 17.
> 

Group,

I am a newbie at this so this may be stupid question but given that the
data given above is correct (and I wouldn't doubt that it is) a 10" f/6
would have a limiting visual magnitude of ~14.5. From a dark sky
location Friday night I imaged NGC 2024 (Flame Nebula) using Royal Gold
ASA 400. Exposures of 10 min and 20 min. Wind gusts made guiding
*interesting* and photographically these pictures are unremarkable so I
thought I would do some comparisons with some sky charts to try and
determine what my photographic magnitude is/was. It appears that the
best I could do was mag 13. I realise that I lost some because of the
guiding errors (wind) but does this seem accurate ? How much time is
required to reach limiting photographic magnitude ? Sheesh that one *is*
probably a dumb question because film types and speeds could screw it
up. What would be appropriate for this aperature 10" f/6 and RG 400
(unhypered) ? Thanks to any persons who can shed some light on this for
me.


Best Regards

Bill

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