View Full Version here: : Southern Cross
25-03-2012, 12:17 AM
I have always wanted to get an astrophoto of the Southern Cross and of course the 50mm Canon Lens lets you do that.
This has about 90 minutes RGB (ST8300), with synthetic luminance. Came out really nice I think.
http://www.martinpughastrophotography.id.a u/images/Southern-Cross-RGB-v1.jpg (6MB)
Hope you like it.
25-03-2012, 01:52 AM
Bloody marvellous, what F did u use ?
25-03-2012, 07:32 AM
Great photo. These wide FOV shots help me to learn the sky. I enjoyed finding some DSO's in your image:
Galaxy NGC 4945 is easy to see in the bottom left of the frame,
The Jewel Box is on fire, and
I think the Blue Planetary, NGC 3918 is visible above the crux.
Thanks for posting. :thumbsup:
25-03-2012, 09:20 AM
You've got that lens firing now.
25-03-2012, 09:46 AM
Thanks very much for the posts.
I have found this lens/camera combination to work optimally at f4.5.
I am going to take it to one more level now and get those stop-down covers - anyone know where I can source one from that would fit the 50mm Canon lens?
Mike - you asked an earlier question about how much cropping was had on the image (of Eta). Other than minor alignment artefacts, the cropping was miniscule. However, on this image, I reframed the target halfway through, so there was some cropping, but again, really small.
25-03-2012, 10:56 AM
I really like this Martin! The cross stars aren't artificially bloated, the colour is exquisite and it's beauty is very natural looking.
25-03-2012, 11:05 AM
a pearler of a shot with a hint of chicken spices.....
25-03-2012, 11:12 AM
Very nice Martin - nice and sharp and comments as below.
25-03-2012, 12:32 PM
don't expect a huge improvement with external stop-down aperture.
In my experience they work only on certain, highly asymmetrical lens designs ( telephoto, 200mm and up).
They are not effective at short FL (Gaussian ) designs, see here:http://www.iceinspace.com.au/forum/showthread.php?t=58629&highlight=Canon+100mm. On that lens, the external aperture was actually detrimental - I wanted to get rid of CA and all I've got was un-correctable coma
The spikes that you are probably annoyed with are OK for most people (including myself) and if you really want to get rid of them, there are software tools available for this job.
25-03-2012, 12:38 PM
Thanks for the comments and the tip there. I was actually on the understanding that those stop-down covers did eliminate the diffraction spikes created by the lens diaphragm....obviously not!
25-03-2012, 12:41 PM
Fantastic view Martin, thanks.
25-03-2012, 12:47 PM
Martin, perhaps I didn't express myself clear enough - external apertures do not create spikes, but they may introduce other problems to your 50mm lens (which is designed to have iris where it is at the moment).
However, don't feel like I am attempting to stop you from trying - the simple, carefully cut hole in the black paper over your lens will indicate if the external diaphragm is worth the effort or not.
Of course, with external diaphragm you will have to open the internal iris of your lens to the max (F1.2) otherwise you will still have spikes. However you may have additional problems with vignetting and possibly CA and/or coma (both of them are nicely gone at F4.5 from you photo - BTW, I am using my modified Canon FD F1.4 at the same aperture (F4.5) and the behaviour is similar to yours).
25-03-2012, 01:45 PM
Wow, really nice Martin. I see you got NGC 4945 in there too, and a bit of Lambda Cen Neb.
How did you construct the synthetic luminance?
Agreed, a top shot indeed Martin, so many Stars in there, well done,
25-03-2012, 04:36 PM
well that Martin, is how superb wide-field imaging is done! next time it'll be us asking you for advice! your next challenge is a mosaic ;)
i don't mind the diffraction spikes either, but i'd try looking on ebay for your aperture masks.. i've got lots of step-up/down rings etc and other things like that for peanuts in the past.
if you do that though, you'll probably find the bright stars get lost and so you will start looking for a blur filter to make them big again (in separate exposures to be added later) and then you'll be unhappy with how un-natural they look and start a lifelong search for the perfect blur filter and you will never be satisfied.. how do i know this you ask?..:rolleyes:
25-03-2012, 06:10 PM
Thanks again everyone.
Phil - I view your comments in high regard given your accomplishments in DSLR astrophotography. Thanks.
If I can get those stepdown rings for peanuts, it will be worth a go to see what happens.
Cam - luminance is everything. I rarely create an image these days without luminance data (lots of it) whether it be synthetic or real.
In this case, I DDP'd the rgb frames individually so that their histograms were similar. I then combined them using different permutations of pixel math to get the brightest result, with the most detail. The added benefit is that it has the same result of stacking lots of frames - you gain signal to process (less noise).
The key then of course is to process that lum to the best of your ability, because it will be that layer which will make the final image look great.
25-03-2012, 07:18 PM
50mm is perfect for this region isn't it. :D
A lovely field of view.
25-03-2012, 08:25 PM
Looks better than the real thing ;) well done Martin!
25-03-2012, 09:22 PM
I am starting to really like these wide field camera shots.
In some ways they have more appeal than telescope photos.
A very nice job.
26-03-2012, 06:31 PM
Wonderfully natural looking image. I love it the way it is, diffraction spikes and all.
27-03-2012, 08:05 AM
At $1.90 - might be worth a punt!!
27-03-2012, 07:39 PM
Thanks very much, particulary for the ebay link. For $1.90 its worth trying.
28-03-2012, 10:19 AM
A great photo Martin.
The lens is working well.
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