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8SE Imaging (again)

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#51 burb scope

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Posted 09 March 2010 - 03:19 PM

Maybe I missed something, but how did you compensate for field rotation? I thought that long alt-az exposures were all prone to field rotation.

#52 Arctic_Eddie

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Posted 09 March 2010 - 03:22 PM

Use many short exposures so that rotation does not appear. The stacker will shift and rotate each image to fit the group. I've used 15 sec exposures and it works ok.

#53 DaemonGPF

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Posted 09 March 2010 - 06:00 PM

Ok, you've got me convinced to at least TRY to do some DSO imaging with my Nexstar... I was just simply amazed how well mine did with Planetary imaging, but your results above raised the bar big time.

#54 Alex Post

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Posted 09 March 2010 - 06:28 PM

What software do you use to stack your astro pictures?


I don't yet, I've never done any! Although I am equipped with PS CS2 so I imagine I will be able to get plugin for that?

Lots of reading to do!

Chris, I use DSS (DeepSkyStacker), which is free software. Process is very simple. Manuals are available, just do a search on google or here is one link to DSS manual After stacking you will Save File As... let's say TIFF and then open in CS2 for additional processing with Levels and Curves. If at all possible, provide a link to your 16 or 32 bit TIFF so that other people can try to extract details.

#55 Alex Post

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Posted 09 March 2010 - 06:41 PM

What is it about the stacking programs that makes them suitable/unsuitable for DSO's/planetary?

BTW, thanks for your reply about the merits of LiveView.

- Tony

Tony, planetary software analyzes shapes. DSO software analyzes light.

Both kinds of software have some common steps, such as alignment of multiple frames into a single composite. They use different algorithms. An algorithm to align images based on craters on the moon, or Jupiter bands is very different from an algorithm that uses star patterns. In either case multiple frames are aligned, so that motion of the camera relative to the sky (lateral and rotational) is removed.

After that processing is very different. Planetary image processing requires figuring out patterns of shape, or geometry. Wavelets are a powerful method for that and Registax is excellent doing that.

DSO processing is all about SNR - Single to Noise ratio based on photon counting. If a given pixel (after alignment) seems to have a higher probability to appear among multiple frames, then it gets a higher value allocated for computing final image. DSO software also assumes that stars are round and computes shapes of stars based on that assumption. Stars still end up elongated in the final image if there was too much drift.

#56 Alex Post

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Posted 09 March 2010 - 06:45 PM

Maybe I missed something, but how did you compensate for field rotation? I thought that long alt-az exposures were all prone to field rotation.

Yes, as Arctic Eddie explained, short exposures do not show field rotation. Even my 60 second ones show very little rotation, compared to the artifacts caused by AZ mount lateral drift. At 15 seconds or less there is very little rotation, especially if objects are going through "tangential" points, such as meridian.

#57 Alex Post

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Posted 09 March 2010 - 06:54 PM

I have noticed you mention about object
alignment after you located object with eyepiece
it's not the same position once you connected camera.
I got the same issue and I am thinking to get
Celestron radial guider.

The point of LV function built in the camera is that I do not need to swap EP and camera. I have camera attached before I drag the scope out of the house, it stays on during alignment, GoTo, imaging sequence, and then going back to my house. In fact I did three nights in a row without touching the camera (except battery recharging).

Having said that, M42 is a friendly object, since stars in the core are bright enough to be seen on the LV screen. For other objects where there will be no bright enough stars radial guider probably will help a lot. My next project will be Horsehead Nebula, if my skies ever clear up. I am intending to use Alnitak as my "guiding" star by placing it right on the edge of the frame while I am looking at it on the LV screen.

Attached is a simulation from Stellarium. Field of view that I selected here roughly matches the filed of 8SE with f/6.3 FLR and my Canon XSi camera. If I place Alnitak (bright star on top) similar to the arrangement on this simulation (easily visible on LV screen) then I should get Horsehead nebula pretty close to the center.

Attached Thumbnails

  • 3670678-horsehead.jpg


#58 GizmoDave

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Posted 09 March 2010 - 09:55 PM

I am thinking to get
Celestron radial guider. I thought in this case
I will be able to have camera connected to the
telescope and I will be able to align object /sync
the same time using eyepiece connected.
Do you think it might help?


I attempted the radial guider and gave up on it. No mater how I adjusted I could not see the subject in the guider view. I ended up attempting Alex's horse head targeting technique but failed. Too narrow a field of view and no LV to assist in focusing.

Awesome work Alex!

#59 a_savvin

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Posted 09 March 2010 - 10:44 PM

Thank you for your feedback.
I decided dont buy radial guider.
Ive ordered Celestron f/6.3 FLR.

#60 Skip

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Posted 10 March 2010 - 10:37 AM

Skip,

If you and I could agree on these items, maybe we could get discounts by ordering two of each!

- Tony


Tony,

I'd be willing to give that a try. However, due to my personal situation, I won't be able to do it before summer. It's killing me to wait - I'm not much of a delayed gratification guy! :grin: If you are willing to wait until then, we should give it a try. If not, no hard feelings, I understand. :)

FYI, the camera I want to get is the Canon EOS Rebel XSi (which I believe is also called the 450D) here . I think this is the one Alex uses. It gets very good reviews over on the DSLR Imaging Forum, even from guys like Jerry Lodriguss, who wrote the book on DSLR AP. I have seen better prices for it, but the link has all the specs and features. And, of course, if all you want it for is AP, I think you can buy just the body w/o the lens. I would probably get the kit (with the 18-55 mm lens)so I could use it for other purposes as well. Also, because I'll be waiting until summer, I'm sure I may reconsider and go for the slightly more expensive T1i or T2i.

All the best,

#61 TonyDralle

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Posted 10 March 2010 - 02:46 PM

Skip,

If you and I could agree on these items, maybe we could get discounts by ordering two of each!
- Tony


Hi, Skip,

I must admit, I was joking about that, because when you said that now all you need is a DSLR and a computer, you were echoing my exact thoughts. (Of course, you didn't know that -- I should have been more clear.)

I'll just be browsing around for both -- don't know when I'll buy anything. (It definitely won't be while there are still 6" of frozen snow on my patio.) But I do appreciate your recommendations.

- Tony

#62 Skip

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Posted 10 March 2010 - 05:56 PM

Hi Tony,

Okie dokie, no problem. I wasn't sure if you were kidding or not. :grin:

Still have 6" of snow? Good grief! It was almost 80 here in San Antone today. :cool:

BTW, I'm not sure I'm ready for summer and DST!!! Won't be able to start viewing until after 9:30 or so. GAAAK! :p

#63 TonyDralle

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Posted 10 March 2010 - 11:06 PM

Still have 6" of snow?


We have had warmer temps. and some sunshine the last few days. Where the sun shines most of the day, the snow is gone and we can actually see grass (which I remember from last fall).

Where there is a lot of shade, as on my patio where I usually set up my 8SE, the snow has partially melted and now is mostly snowy ice (or icey snow). Can't wait to take my scope out, but I'll need to clear an area for it and for me. It'll be easier to wait for it all to melt.

In DST, you can observe later in the morning!

Happy viewing,
- Tony

#64 Arthur Dent

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Posted 11 March 2010 - 02:43 PM

Alex

Just one word:

AWESOME

Yup, I think that covers it! Thanks for sharing. Excellent tutorial, one that will be transferred to WORD and stored on my laptops.

I haven't installed the EOS utilities form my 400D (aka Digital Rebel XTi) but you've encouraged me to give it a go.

You camera (the Rebel XSi) is the equivalent of the 450D (the first Canon camera that came with "Live View"). I'm wondering how the 1000D (The Rebel XS)- which is cheaper here in the UK than the 450D - would fare.

Art :bow:

#65 a_savvin

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Posted 11 March 2010 - 03:56 PM

Hi Alex
Did you get any lack with horse nebula?
I tried last night. I used camera LV for alignment
and focusing. Looks like I was able to get Alnitak
on my camera LV. I used 30 sec and exp 3200.
I got just star I didn't get nebula. But for M42
it worked well.

#66 Pete GLA

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Posted 11 March 2010 - 04:12 PM

I am thinking to get
Celestron radial guider. I thought in this case
I will be able to have camera connected to the
telescope and I will be able to align object /sync
the same time using eyepiece connected.
Do you think it might help?


I attempted the radial guider and gave up on it. No mater how I adjusted I could not see the subject in the guider view. I ended up attempting Alex's horse head targeting technique but failed. Too narrow a field of view and no LV to assist in focusing.

Awesome work Alex!


If you place the intended DSO, etc, in the extreme lower right FOV of your DSLR, then the DSO will be near center of the EP's FOV that is housed in the Radial Guider.
Since you do not want to view the DSO thru the EP, you'd select a star nearby.

So before you set out to image DSOs, take a peek at the DSO in Stellarium or any other software, and pick a suitable star that is ~ 0.5dgs SW of the DSO. This should help you.
Note you must orient (or turn )the DSLR to immitate Earth's rotation, to view the selected nearby star thru the EP's FOV.

As stated in another post, Celestron suggests that you use the 6.3 Focal Reducer with the Radial Guider. I also purchased a Micro Guider that has etched parallel lines with evenly spaced hash marks (among other things). This helps greatly in trying to keep the star stationary (especially for exp times over a few seconds). Also I've stated that an equatorial mount is a must, if you do not have the patience (this applies strictly to manually guided long exposures). No computers, no autoguiders. Just me, my Angela (Art knows), CG-5 and DSLR...

I'm sure that there are more experienced APers that can help you, as well as I on this subject. (I'm just inserting my Big Toe in the shallowest part of the Ocean) that being attempting serious AP.

FOV of my DSLR (Nikon D60) at Prime Focus is ~ 64'x43'arc.

Good Luck,
Pete

#67 Alex Post

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Posted 12 March 2010 - 09:41 AM

Excellent tutorial, one that will be transferred to WORD and stored on my laptops.

Art, I am working on the paper this week. I hope to complete it by end of next weekend. I will post it here.

Andrey, no I did not have a chance to try Horsehead yet, cloudy nights :(

#68 Alex Post

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Posted 14 March 2010 - 12:44 AM

I have compiled my notes in a PDF: M42 with 8SE and DSLR. I hope it will be of use to someone.

#69 tvader

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Posted 14 March 2010 - 03:10 AM

Excellent guide Alex. Thank you!

#70 Half-Life

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Posted 14 March 2010 - 05:55 AM

Alex,
Fantastic work! Thanks for posting your guide. I've saved it to my PC for future reference as I've only just begun a renewed interest in watching the sky.

Phil

#71 Tel

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Posted 14 March 2010 - 06:27 AM

Hi Alex,

I absolutely agree with Phil ! I too have comitted your paper to my files.

As you know it's long since that I gave up trying to get any decent DSO images with my N8i from its existing Alt.Az. base and switched to the use of a GEM for the purpose, but your tenacity, perserverance and skill has proved exemplary in demonstrating against the odds, that such imaging can be done and done well !

Terrific stuff!

Best regards,
Tel

BTW. Much appreciation for the acknowledgement but the credit is all yours ! :bow:

#72 a_savvin

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Posted 14 March 2010 - 09:11 AM

Hi Alex,

WOW! I am going to use this doc.

Thank you

#73 Peter9

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Posted 14 March 2010 - 09:21 AM

Hi Alex,

Thank you on behalf of all Nexstar owners for taking the time and trouble to present your work in the way you have for the benefit of all.
You are one top person.

Best Regards. Peter.

#74 Alex Post

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Posted 14 March 2010 - 10:09 AM

This is my 500th message on this forum. I thought it would be appropriate for me to "graduate" with something concrete and useful to the community that gave me so much in the past 18 months, since I started this hobby. Thanks guys.

#75 Midnight Dan

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Posted 14 March 2010 - 11:14 AM

Thanks Alex! Very nice work and very useful! :waytogo:

-Dan


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