[AZ-Observing] Re: Looking for some Opinions...
- From: Tim Jones <tjmac@xxxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Wed, 20 Aug 2014 15:34:43 -0700
David,
Your thinking is sound - you’ll never see visually what the camera picks up -
even in a 60 sec shot - using the same equipment.
However, you shouldn’t assume that because you can’t see the object in a single
1, or even 5 minute frame that it’s not there. I’ve taken a batch of 25 or so
1 minute shots and stacked them in software and the results were amazing.
Things like M57 or the Pelican - among many others, are usually meager sights
in a single frame. however, if you take 20 of those frames and stack them in
an app like Nebulosity or Registax (among others), the results will totally
surprise you.
Also, by reducing the time per frame and then stacking the frames, you really
reduce to probability of smeared images or oval stars. It can also help with
the automatic removal of airplanes, satellites, meteors, and even light
pollution.
The next time you shoot, keep your frames at 5 minutes, but shoot 20 of them on
the same target. Once stacked, I believe that you will be duly impressed with
the difference in your results.
If you’re not sure about stacking, check out this tutorial:
http://www.instructables.com/id/Astrophotography-Star-Photo-Stacking/
Good luck!
Tim
On Aug 20, 2014, at 2:23 PM, David M. Douglass <dmdouglass@xxxxxxxxxxxxxxx>
wrote:
> I am having a personal "wrestling match" with myself on a question, and I
> would like to hear from others on this subject. I am going to post this to
> both the AZ-Observing email thread, as well as the EVAC email thread, as I
> know there are some good "experts" out there would might be able to help me
> out here.
>
> Those that know me, know that "most" of my "observations" are done using a
> camera (SBig ST8300m), and are performed from my back yard observatory in
> beautiful, light polluted Tempe, AZ. I say "most", as I do still do some
> "visual" observations, just to help me remember what it is that I see, both
> visual, and via the camera, and thus why I use the camera mostly.
>
> I have several "standard configuration's that I use when imaging. There are
> the Ha filter images, Double-star images, very bright images, and then the
> "standard" DSO objects. For those (that would be most of them). my
> configuration is to use a Lumicon 2" Deep Sky Filter, AND a Baader UV-IR Cut
> Filter. This has proven to be a very good combination for me. The exposure
> time for these "standard" objects is 5-min per frame, and I usually take
> 4-6 frames per target. And lastly, all exposures are grey-scale (B/W).
>
> Although I can see "most" objects very well in these images, and can resolve
> objects down to 15-16 Mag (stars even dimmer).. Every once in a while, I
> get an object which I think I should be able to detect, and it simply is NOT
> there. So.. The "statement" I sometimes make (to myself) is.. "If I can't
> resolve it, even faintly, in a 5-min exposure, there is NO way that I would
> be able to "see it visually" .", and that is assuming same equipment, same
> viewing location, and same lighting conditions.
>
> Here is the first question: Is that a reasonable statement ?? I am
> thinking so, but am looking for other opinions. If it is not, I would be
> most interested in hearing other opinions.
>
> Now, if the statement is correct, could the "time" be reduced, and still be
> valid? To me, my camera can see far more in 60 seconds, than my 69 year old
> eyes can detect, and I still have reasonably good vision. And maybe
> (probably) that time could even be reduced. Unknown.
>
> Then there is this... If I cannot resolve a dim object in 5-min, is there a
> maximum time that should be considered for the subs ??? To that part of the
> discussion, when I use the Ha filter, my standard exposure length per sub is
> 900 seconds (15-min). For really faint nebulae, I extend to 1200 seconds
> (20-min). My CGEM, guided, has no problem handling that length of exposure.
> Examples of these can be seen at my Astrobin site (
> http://www.astrobin.com/users/dmdouglass/ ). Those would all be Ha images.
>
> Should I consider longer exposures (longer than 5-min) for dim "standard"
> objects. For this discussion, a "standard" objects would be a galaxy,
> cluster (open or tight), some nebulae, and "other" objects.
>
> The two OTA's that are permanently mounted to the CGEM, which is pier
> mounted, are my Celestron Edge(HD) 8" (f/10 - 2000mm fl), and a Mead 80mm
> EDAPO (f/6 - 480mm fl).
>
> Thanks for taking the time to read this. And if you have an opinion on any
> of this, I look forward to hearing from you.
>
> David M. Douglass
> dmdouglass@xxxxxxxxxxxxxxx (secondary)
> david@xxxxxxxxxxxxxxx (main)
> Cell (602) 908-9092
>
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> send personal replies to the author, not the list.
>
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