RE: [ccd-newastro] new user help
- Sounds like you have some light pollution closer to the horizon, and you are
also shooting through thicker atmosphere which tends to scatter the light
more -- and there is also more turbulence near the horizon, further muddying
A flat field would help deal with the "bright center" problem. Focal
reducers almost always cause a central hot spot. The greater the focal
reduction (and f/3.3 is an extreme amount of focal reduction), the greater
the need for a good flat field.
If possible, simply wait until M33 is higher. A light pollution filter may
help, depending on the source of your light pollution. I use the Hutech LPS
(Light Pollution Suppression) filter, and while it doesn't block everything,
it blocks enough to show noticeable improvements for me.
But if you are living in a light polluted area, and especially if you are
using a reducer, learning to take good flat fields will make a huge
difference in not only the quality of your images, but in how effectively
you can process them. You will find yourself able to dig more detail out of
your images if they have a good flat field.
The New CCD Astronomy
From: PlowPlane@... [mailto:PlowPlane@...]
Sent: Sunday, November 04, 2001 10:30 AM
Subject: Re: [ccd-newastro] new user help
Hello all. Last night I began imaging with my new ST-237. I am using an
LX200 8 inch with the e-finder focal reducer at f3.3 or so.....I have taken
the images with 50 second exposures under the track and accumulate mode with
10 images being combined. Dark frames are every 4 images. I do not use
frames and have only the ccdops software for image processing.
My question is this....in using the above method I began to image m31
and came up with an acceptable first image. However when I tried the same
process on M33 which is closer to the horizon the images came out very gray
in color in a large circle with only the outer edges showing a nice dark
background and some stars. The center of the image showed very little
and by reducing the gray color all of the detail was lost.
Are my exposures long enough? Is there a problem with the focal
reducer? Up until last night I had been imaging with a Celestron 255 and
meade 3.3 focal reducer.
I know that the 237 is quite a bit more sensitive but I was not getting
washed out images on my 255.
I am in an extremely light polluted neighborhood and could use some
I would be glad to send the image of M33 to someone to look at if they are
willing to give some suggestions.
Thanks for the time.
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