I'm really glad to find this forum on Nikonians. I've been following the thread over on FM for a while. I'm leaving today to try out my new AstroTrac and wedge in the Mammoth-Mono Lake area. Hopefully I'll have something worth posting when I return.
I'm hoping that someone chimes in with more on post processing. Light frames, dark frames, how many, and where in the process do they go?
Just what I needed: another hobby that takes even more gear and time.
#1. "RE: Ready for astrophotography!!!!" | In response to Reply # 0Tue 07-May-13 02:31 PM | edited Tue 07-May-13 03:38 PM by nrothschild
Thanks for resurrecting this thread. Such a lovely image . I never get tired of Mark's image.
Maybe Mark can weigh in on the processing. However, I have some general advice:
If this is your first attempt at long exposure astrophotography, and especially if this is your first telescope with motorized equatorial mount, take it slow. It is easy to get overwhelmed.
Your main job now is to learn the idiosyncrasies of your mount and scope (yes there are, there have to be ). Learn how to polar align it as best possible because that has a huge effect on your total possible exposure time, and concentrate on refining basic images.
I also suspect that the value of dark frames and all that wizardry has somewhat diminished over the years. Modern cameras have little or no amp noise, especially for exposures on the short end (30s or so). This was not the case 5-8 years ago when the idea became so much in vogue.
The dark frames have the most value when eliminating bad amp noise. For normal Shot Noise it is not really effective since that noise is very random and therefore unpredictable. At least that is my theory.
Just to say it is perhaps a more advanced thing now, and not needed for basic good results. Which is a good thing .
You may find it challenging to get pinpoint stars even with "short" 30s exposures, for a variety of reasons. And that is one reason why many people stack multiple, shorter exposures. That is really job one.
You may want to look into Registax. It is freeware. It stacks multiple images and aggregates dark and light frames. It is freeware and seems to be the reference software of choice, at least in the low or no cost area. There is more expensive paid software but I think a good grounding in Registax is very helpful. Then you can better eval paid software demos, and will have raw images for testing the relative efficiency.
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#2. "RE: Ready for astrophotography!!!!" | In response to Reply # 1winthrop Charter MemberTue 07-May-13 02:46 PM | edited Tue 07-May-13 03:38 PM by nrothschild
The AstroTrac is supposed to give up to two hours of tracking. It seems that getting the polar alignment is critical, and--if it's not raining--I hope to sort that out tonight. I don't have a telescope so I'm taking my 300 f/2.8 and a handful of TCs. I have no great expectations; if I get a decent Milky Way shot I'll be satisfied.
I got the light-frame dark-frame info from the astrophotography thread on Fred Miranda. If I don't have to use it I'll be happy.
Thanks for the Registax tip. I'll give it a try.
#3. "RE: Ready for astrophotography!!!!" | In response to Reply # 2Tue 07-May-13 03:08 PM | edited Tue 07-May-13 03:38 PM by nrothschild
>> It seems that getting the polar alignment is critical,
Yes, and that can entail hours of work for a 5 minute shot . Seriously. If you take it to an extreme.
At a practical level you would invest a certain amount of time to get alignment accurate to a certain point, and then limit your exposures accordingly.
Typically an accurate alignment is done by iterative adjustments while visually observing, at very high magnification, a star move against a cross hair reticle eyepiece.
Viewing a star through even a 600mm lens via the camera viewfinder is not nearly enough. It would be dawn before you saw the star move.
I've had a similar problem where I need to swap a fairly heavy scope in and out to do alignments when I want to shoot with a photo lens. I'm not sure how I would get accurate alignment without that scope.
Your mount might have some sort of polar alignment sight tube (not familiar with it). But those generally only achieve very rough alignment. Might be ok for 300-500mm for 30s, depending how picky you are.
(this is all part of the take it slow thing I mentioned previously )
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#4. "RE: Ready for astrophotography!!!!" | In response to Reply # 3Tue 07-May-13 03:18 PM | edited Tue 07-May-13 03:39 PM by nrothschild
P.S. Take it slow tonight .
Set up your lens without a TC, get your mount aligned as best possible, and then try some 30s exposures at f/2.8 and maybe f/4 to see how you like the stellar images wide open. Don't stop down more than a stop.
When you are satisfied with that, and feel comfortable, then add a 1.4x TC. Get comfy with that, then move on to the next TC.
That is a better approach than diving in at 600mm and getting frustrated and maybe confused. You are learning a lot of new skills at the same time or in rapid succession.
You should use that mount to shoot the crescent new moon, with Earth Shine Exposure, per the May Challenge. It is only up to a 4s exposure or so, relatively simple compared to doing star fields and deep sky objects.
You will get very good results, just eyeballing the alignment, relative to what we get with a fixed tripod. Sometimes when I do short moon exposures I don't even do more than that rough eyeball alignment due to the short exposures. Saves me from from doing the scope/lens swap.
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#5. "RE: Ready for astrophotography!!!!" | In response to Reply # 0
Welcome! Here's hoping you have some fun tonight. We're looking forward to seeing your results.
Just like I previsualized it, more or less...
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