View Full Version here: : Colour question? Eta - Keyhole
09-01-2011, 07:54 PM
Thought I would post my first ever Nebula shot. Keyhole in Eta Carina taken Friday night from near the You Yang mountain range in Vic.
I am very new to this so all criticism, comments, guidance etc will more than welcome as I want to learn from you good people out there. :thanx:
I'm looking on a very small screen here, but it looks really good.
Well done and keep at it.
09-01-2011, 10:52 PM
Jeez I wish my first picture looked like that. Well done and welcome.
10-01-2011, 01:12 AM
Good effort what gear camera etc number of exposures
10-01-2011, 07:38 AM
Thanks for the comments. I'vebeen spending every spare minute researching this site and others to prepare for my first imaging trip.
There is a long way to go and set up and alligning took me for ever.
Set up -
Imaging scope - William Optics Zenithstar 105 triplet f7
Guiding - Orion Starshoot Autoguider
Mount - EQ6 Pro
Camera - Canon 5D Mark II
Software - Backyard EOS, EOS Utility
1 x 5 min ISO 800
2 x 3 min ISO 1250
1 x 3min ISO 1600
1 x 3 min ISO 640
This was my first time setting up in field and the subs were pretty much all experimental.
Stacked in Lynkeos (Mac)
Processed in CS5
Location: You Yangs Victoria
Please be critical - Any tips on imaging, use of subs and ISO, processing etc would be really appreciated
10-01-2011, 11:54 AM
Good stuff. I like the blue colors around the keyhole. :thumbsup:
10-01-2011, 12:16 PM
Changing exposure time or ISO etc means you need to take corresponding darks so no benefit is gained from this on most targets.
Varying the exposure times is good for those objects which have a large dynamic range eg: Orion with the bright core or globulars where you wish to be able to show detail in the core.
Remember the more subs you catch the better, when I was shooting with a DSLR I used Jim Solomon's Cookbook as a guide, it's a good introductory tutorial to imaging with a DSLR
ps: look at the ETA C image I posted here 10 x 330s frames at ISO800 with a modified Canon 350d
10-01-2011, 01:46 PM
I will certainly look this book up. Your ETA C image shows great detail. I need to read up on taking darks as it doesn't quite make sense why they need to mirror the image sub? I thought a dark was a dark but obviously not.
10-01-2011, 01:49 PM
Yeah the blue was a bit of a surprise! It gives some contrast to the keyhole. Not sure if it's a true reflection of the object though?
15-01-2011, 01:09 PM
This is one sub from the same picture in unedited RAW data form
1 frame un-cropped
The blue around the keyhole is evident in this frame. Would this be natural light colour emission or would it be the effect of the camera filtering?
15-01-2011, 01:18 PM
It looks fabulous especially for a first time image. Nice colours.
Its a bit hard to comment further as the thumbnail doesn't show any detail.
Can you post a link to a larger version?
One comment it may be that focus was slightly off as the star sizes seem a little large for the image scale.
If it was correct then there are techniques to reduce them slightly and make them less prominent.
15-01-2011, 02:00 PM
Try this link. It is in Flickr so not sure if you will be able to see it more clearly file is about 15meg. http://www.flickr.com/photos/58381941@N08/5356202516/lightbox/
I think the focus may have been a little out.
15-01-2011, 03:09 PM
A couple of points that may help.
Firstly a 5D is a full frame sensor and a very large chip. Virtually no scope except an RC or corrected Dall Kirkham scope can handle that size without a field flattener. You have some evidence of star issues in the top right corner which comes from coma. A field flattener with your scope will help.
Secondly because it is such a large chip you are getting bad vignetting in the corners. This is normal with a large chip camera and you need to take flats to help with this. I use a white Tshirt put over the end of the scope and take a very short exposure like 3 seconds at dusk. Take 3-5 of these and combine them using median combine.
Similarly use a dark which is an exposure with no light for the length of the exposures you will be using. Take at least 6 and sigma reject combine to form a master dark. It has to be the same expoure time and ISO. So decide on a standard exposure time and ISO. Many use about 5 minutes and ISO800 or 1600 for DSLR imaging. I wouldn't use less than ISO800 as you would be wasting time in extra exposure time.
When you use darks with a DSLR you use adaptive darks. Images Plus has that facility and it scales the darks to match the exposure it is being used with.
Thirdly, you have done a total of about 16 minutes of exposure time.
This is good for starting up and getting used to your gear but really to make any image it takes more like 1-12 hours total combined exposure time to get a decent enough image. The brighter the object the less you will need, also the darker the skies you are imaging from the less also.
So in summary you need;
1. A flattener for you scope.
2. Standardise your exposure lengths and ISO and use them.
3. Create darks for that exposure/ISO
4. Make flats for your imaging setup using a white T shirt and taken at dusk. You want 1/3rd of a histogram exposure so check the histogram until you get that (usually the light is starting to get quite dim).
5. Take longer exposures and lots of them.
6. Use Images Plus as this is the best DSLR image processing software.
I hope this helps.
15-01-2011, 03:28 PM
Thank you very much Greg,
You have explained it all very simply. Your quality of your work is exceptional and your guidance is greatly appreciated.
Thank you again
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