Re: [APML] E200 exposure times for f2.8, f4, f6, f8

["Steve Walters" <swalters@att.net>]

Joe,

No one can really quite answer your question. Here's why.

The goal for most deep sky objects (there are exceptions) is to expose to a
point that fogging due to light pollution just begins to show up in the
image. Exposing beyond this point is not worthwhile because the light
pollution will begin to intrude on detail that you have captured. The amount
of time that this takes depends on the site. Your first time at a site, you
should shoot a series of exposures ranging from 10 minutes to 45 or 60
minutes.

At a nearby light polluted site here in New Jersey, I can only expose E200
for 20 minutes at f/5 before sky fog starts to show up. At a site in north
central PA which is very very dark, I can go for 60 minutes and just barely
see fogging. I've learned this by experimenting at each site.

After some time, you begin to get some rough feel for this based on your
experiences.

The exceptions I mentioned above is that many objects such as M13, M31, M42
and others which are very bright will saturate the film during really long
exposures. Many of these can be captured adequately in 5 or 10 minute shots.
That is the bright core detail can be captured. So many people take a long
exposure of an object like M13 to capture surrounding details and the
"fringe" of the object and then combine this with a shorter exposure of 5 or
10 minutes. You may not want to start with this somewhat complex step so I
would advise short exposures for bright objects, maybe 10 minutes or 15
minutes at f/5, less at f/2.8.

The best advice is to just get out there and start shooting at different
exposures say 10, 20 and 30 minutes and then you'll learn what works best.
There are other limitations for the longer exposures such as having really
excellent polar alignment to avoid field rotation, preventing mechanical
flexure in the optics and mounting and having an autoguider to get excellent
tracking. These items become more and more stringent as exposure duration
increases. And some, like getting a good drift alignment, show up even in
shorter exposures.

Good luck and Clear Skies!

Steve...

swalters@att.net
http://astrophoto.home.att.net

> > I need some exposure times for Kodak E200 for f2.8, f4, f6,
> > f8 f-ratios
> > (refractor


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