m51 image

Okay, another astro photo. This one was a little longer exposure, taken Saturday night/Sunday morning of the spiral galaxy M51 from my little property in Wonder Valley California:


[img]/resized-image.ashx/__size/800x0/__key/CommunityServer-Discussions-Components-Files/15/5314.m51-800-centered.JPG[/img]


5DII with AP130GT (819mm f/6.3) with field flattener on Mach 1 GTO mount, autoguided (with orion short tube 80 + Starshoot autoguider)


I used 20 exposures, 10 minutes each. stacked with deep sky stacker and processed with DPP and Gimp Notice the smaller galaxy in the upper left. There are actually several others (including a very dim one close to the galaxy which I haven't been able to image before).


This picture pales compared to what the serious types are doing these days, but I think it is pretty cool what modern CCD technology makes possible for a goof-off like me who barely knows how to point the scope and press the shutter button [:)]

WOW, mega impressed,


funny, i was watching a program about the universe on sunday and thought i should have a go at that, i thought of hiring a big lens and going to one of the

Thanks :)


If you're interested in astrophotography, you are likely to need a good photographic mount in addition to a telescope or lens (in fact, most astrophotographers feel that the mount is actually more important than the lens/telescope, and it is not unusual for them to spend 2x as much on the mount as on the optics).


You might consider a telescope instead of a camera lens. An 8" SCT with a nice mount costs far less than a canon 800mm f/5.6 L but gathers about 2 times as much light (so exposures take half as long). But then, I'm not sure where one can rent a telescope.


I think it is great that you have dark sky parks in Scotland. We don't really have anything like that in the US. I drove 2 hours each way to my dark site :)

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Originally Posted by Ade

anyone fancy a trip to give this a go, could split the cost of hiring a HUGE lens

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Sorry Ade, I don't see any HUGE lenses on that link. I would want one of these, plus a rock solid tripod and an autoguider to keep the camera pointed at the right part of the sky for 3 hours. Oh, and a clear sky. When did you last see one of those in Scotland?

Also, we would need to do it before 26th April or after 18th August, otherwise the sky wouldn't be dark enough for long enough due to the astronomical twilight which occurs when the sun is less than 18° below the horizon in southern Scotland.

If you think you can overcome those obstacles, let me know and we can maybe sort something out. Failing that, we could lower our expectations and go for some star trails like those by Tim or Chris in this thread.

Excellent capture, Jon, and thanks for the tips on optics. There might be a cheaper way after all.

Wow John, that

Thanks, Rich!

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Originally Posted by Richard Lane

Can you shoot birds with it?

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It's manual focus and is no doubt optimized for imaging at infinity, but other than that it should be okay for birds. [:)]

Flip, a bit more involved than i first thought, I think i may downgrade my aspirations to star trails, but they were pretty cool too.......I bet if i tried hard i could get a picture of the moon!


Andy, I

Beautiful Jon!

Thanks, Mark :)


Ade, for the price of the 1200mm, you could get a really nice telescope for astrophotography, like a big RC.

Sweet, can you hire them?


LOL, I get it guys, taking pictures of far away galaxys is SLIGHTLY more involved than i first thought, but hey, i've been on google images and a chap called Hubble took some nice pics and that must have been about 70 years ago, i guess he used a box brownie or something, how hard can it be........[8-|]

Very Nice, The only thing I would recommend is to be careful when adjusting the Curves or levels so you don

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Originally Posted by tkerr

The only thing I would recommend is to be careful when adjusting the Curves or levels so you don't over clip the dark points(shadows), or blow out the highlights.

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Yeah, you are right. I have to fix the blown highlights. As for the blacks, I just like them that way. I know some people don't, but don't like seeing a greyish background.

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Originally Posted by tkerr

Don't know why you used DPP when you're using gimp

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Don't I need DPP to convert the .cr2 to .tiff? DSS won't work with .cr2 files, will it? And I like to do some 16 bit processing before going to gimp. Gimp only handles 8 bit files.

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Originally Posted by tkerr

Did you shoot and use and Darks, Flats or Bias for the image data calibration and stacking?

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Ahem. No. Not this time. The AP really doesn't require flats. This weekend I'm going out again, and I'll take some shots with the Edge HD, and I'll try doing it right (or at least, a little more right) [:)]

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Originally Posted by Jon Ruyle

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Quote:

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Originally Posted by tkerr

The only thing I
would recommend is to be careful when adjusting the Curves or levels so
you don't over clip the dark points(shadows), or blow out the
highlights.

---

Yeah, you are right. I have to fix the blown highlights. As for the blacks, I just like them that way. I know some people don't, but don't like seeing a greyish background.

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You can adjust the shadows so the sky is still dark without over clipping. And provided you got enough image data in the first place you will leave faint subtle details intact.

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Originally Posted by Jon Ruyle

Quote:

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Originally Posted by tkerr

Don't know why you used DPP when you're using gimp

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Don't I need DPP to convert the .cr2 to .tiff? DSS won't work with .cr2 files, will it? And I like to do some 16 bit processing before going to gimp. Gimp only handles 8 bit files.

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DSS works fine with CR2 files. It did have some problems with RAW Files from the T1i and T2i cameras, but last I heard that has since been fixed.
I haven't used gimp in a while, but I thought that it did allow you to load 16 bit tif files and do some editing at 16 bits now. Might be wrong.

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Originally Posted by Jon Ruyle

Quote:

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Originally Posted by tkerr

Did you shoot and use and Darks, Flats or Bias for the image data calibration and stacking?

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Ahem. No. Not this time. The AP really doesn't require flats. This weekend I'm going out again, and I'll take some shots with the Edge HD, and I'll try doing it right (or at least, a little more right) [img]/emoticons/emotion-1.gif[/img]

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Flat field calibration isn't only to correct optical errors/artifacts or uneven filed illumination that might be caused by a telescope or lens system. What About your camera? Flats are also used to correct for variations in the sensors pixel to pixel response, or artifacts on the sensor such as dust motes.
http://www.cyanogen.com/help/maximdl...alibration.htm

http://en.wikipedia.org/wiki/Flat-field_correction


When stacking with DSS or any astroimage stacking software you really should use Darks, Bias, Flats and Dark Flats for a properly calibrated and stacked image. The quantity of each depends greatly on the SNR of all your Light Frames. But it is often otherwise recommended to use a 1:1 ratio for each.

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Originally Posted by tkerr

DSS works fine with CR2 files.

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Didn't know or expect that. Thanks! Srue simplifies things :)

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Originally Posted by tkerr

I haven't used gimp in a while, but I thought that it did allow you to load 16 bit tif files and do some editing at 16 bits now.

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Well, the one installed on my computer does not allow 16 bits, but it has been a while since I updated. I'll get a new version and see. Here's hoping...

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Originally Posted by tkerr

When stacking with DSS or any astroimage stacking software you really should use Darks, Bias, Flats and Dark Flats for a properly calibrated and stacked image.

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To be honest, whenever I've tried to get DSS to do anything other than light frames, it has not worked for me. I get funny streaks in the image when I use darks, and I get strange radial patterns when I try flats. Perhaps my flats are uneven, perhaps I am using the program wrong, or perhaps DSS isn't working properly. In any case, I get better results when I use in-camera noise reduction and no flats.


As I said, though, I try again this weekend. I won't do any in-camera noise reduction and will take some darks during my session.


I appreciate your suggestiions.

Make sure you shoot your darks at the same exposure that you shoot your light frames. I usually shot some just prior to my image run and some immediately after.


The problem with using in camera High ISO or Long Exposure Noise reduction is that it might also remove some stuff that you want to keep. Such as small smudges that are galaxies or nebulae in the background, and more often small stars that belong in there.

I was pretty careful when I used to shoot darks: I

Well, close but not exactly the same, nevertheless, there are advantages to shooting Darks vs using LENR. Time!


Using LENR doubles your time for each exposure, and that is time you could be using to gather more Image data(Light Frames) instead.


When shooting Flats I hang a white sheet in front of the telescope and light it up with a couple white lights. That way I am assured that I get even illumination rather than changing illumination like you get when shooting the predawn sky for them. One of these days I'll get around to making a light-box to fit over the end of my telescope.


Additionally, if you don't make sure you are get the exposure right on your flats they can do more harm than good. (35%-50% of full saturation) Also shoot Dark Flats!


The Work Flow for DSS when you use all the files necessary for image calibration and stacking. Lights, Bias, Darks, Flats and Dark-Flats


The Master Bias/Offset is created from all your Bias frames.


Next the Master Bias/Offset is subtracted from your Darks and a Master Dark file is created.


Then the Master Bias/Offset is subtracted from your Dark-Flats and a Master Dark-Flat is created.


Then the Master Bias/Offset and Master Dark-Flat is subtracted from all your Flats when creating the Master Flat.


Finally the Master Bias/Offset and Master Dark are subtracted from each light frame and the results are divided by the Master Flat then stacked into your final image stack which you will save for post-processing.


When you use The cameras LENR it's essentially creating and then subtracting a Dark Frame from your light frame. But that doesn't remove all unwanted noise or artifacts that using bias darks and flats will.


When you provide DSS with everything it will work and put out a good quality stacked image.

Ade, I hope you're still following all this and taking lots of notes. I'm completely baffled. Do you think"shooting darks" means "leaving the lens cap on"?


I think I'll leave the experts to get on with it...

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Originally Posted by Andy Stringer

Do you think"shooting darks" means "leaving the lens cap on"?

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That's exactly what it means [:)]