Re: [APML] Exposure Question

["Brian Larmay" <astrobri@ameritech.net>]

Hi Stuart...yes ..as others are amazed also.
This is at one of my darker locations using a 10 min exposure @ f/4  of
cygnus.
It seems to me that for some reason I do capture alot of what is out there
with these exposure times
Heres cyg @ 10 mins: http://www.astrobri.com/cygnus.htm and Cassiopeia @ 12
at yet a darker location: http://www.astrobri.com/cassiopeia.htm

Skyfog does not let me go any longer then this.

I do not comprehend how others can or need to go longer then this unless
they stop down incredibly.

Brian




My Photography
Homepage: www.astrobri.com

Geographic Longitude= 88W
Geographic Latitude= 43N
Corrected Magnetic Latitude= 53

----- Original Message ----- 
From: "Stuart Heggie" <stuart.j.heggie@sympatico.ca>
To: "Discussion of Film Astrophotography" <astro-photo@seds.org>
Sent: Saturday, September 20, 2003 4:53 PM
Subject: Re: [APML] Exposure Question


> Brian, I am amazed you can shoot at f/4 on E200 for only 7 minutes and
> see anything on the film/slide. I shoot 40 min on Supra 400 at f/4 and
> my math says you should go 80 min on E200. That said, for every full
> stop you go down, you double the exposure time and for every factor of 2
> you change film speed you change the exposure by the same factor (in the
> opposite direction e.g. half the film speed requires double the exposure
> time to be even).
>
> All this of course ignores reciprocity failure which is a function of
> the specific film (each layer in the film having its own curve), the
> outside temp, the sky fog limit and probably the optics of the
> lens/scope. Some folks subscribe to the argument that a 16mm at 2.8 is
> different than say a 50mm at 2.8 but I think this is suspicious (mind
> you the source of this view is pretty expert so I am "agnostic" in this
> matter).
>
> Short answer: if you shoot 7 min now on E200 at f/4 you should shoot 14
> min on E200 at f/5.6 but that is ignoring the paragraphs above. I cannot
> imagine that exposures that short are going to get you much.
>
> Stuart
>
> Brian Larmay wrote:
>
> >Hi all,
> >
> >Ive been slipping on everything concerning astrophoto since spring and
will
> >finally be getting out tonight for some long overdue practice.
> >My question is concerning exposure time...I always stop my lens to f/4
with
> >exposure times of 7 mins, but this time I want to stop down to f/5.6 ...
> >what would the correct exposure time be then?
> >Whats the formula?
> >Will this sharpen my images noticably vs @ f/4?
> >Will this reduce Vignette and help me to create mosaics alot easier?
> >
> >All exposures are made using Kodak E200 tonight.
> >
> >Ty,
> >Brin
> >
> >My Photography
> >Homepage: www.astrobri.com
> >
> >Geographic Longitude= 88W
> >Geographic Latitude= 43N
> >Corrected Magnetic Latitude= 53
> >
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> >http://seds.org/mailman/listinfo/astro-photo
> >
> >
> >
>
>
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