This is the result of four contiguous areas taken with the Canon 5DH and 300mm F2.8L. Gradients are a major problem with widefields but with my new methods managed to almost eliminate them without compromising the real image data too much.
I have mentioned it before Doug. This is a fuller explanation. GradientXterminator is fine if you have a galaxy or nebula in the center of your frame. You are in deep trouble with faint nebulae all over a widefield. Sure you get rid of gradients but you also lose faint nebula detail as it looks like gradients to the program.
What I do is split the colour image into RGB fits and then make R,G & B tifs of each. PS has not got a clue about fits images. I then treat each monocolour tiff with GradientXterminator in the usual way.
The advantage now is you can isolate real faint nebulosity from gradients and GX does not fart around with the other colours. I do not know what his algorithms or protocols are but this eliminates unwanted suppression of real faint nebulous data. Each image has its own method that you must work out by trial and error. It pays to be consistent with the RGB for the same image for Detail and Aggressiveness and only vary the areas with the Lasso tool.
I have metioned it before Doug. This is a fuller explanation. GradientXterminator is fine if you have a galaxy or nebula in the center of your frame. You are in deep trouble with faint nebulae all over a widefield. Sure you get rid of gradients but you also lose faint nebula detail as it looks like gradients to the program.
What I do is split the colour image into RGB fits and then make R,G & B tifs of each. PS has not got a clue about fits images. I then treat each monocolour tiff with GradientXterminator in the usual way.
The advantage now is you can isolate real faint nebulosity from gradients and GX does not fart around with the other colours. I do not know what his algorithms or protocols are but this eliminates unwanted suppression of real faint nebulous data. Each image has its own method that you must work out by trial and error. It pays to be consistent with the RGB for the same image for Detail and Aggressiveness and only vary the areas with the Lasso tool.
Hope this helps. Any futher questions?
Bert
Thanks Bert,
I have GradXterminator so I may give this a go.
Do you need a plug in to split the RGB image into fits files?
I'm using PS CS2.
Doug
Thanks all for the comments. Yes the stars look square if anyone wants it, I will put up the 43MB jpg where they don't (the original tiiff is 235MB). The problem is that the sampling diagonally is at root two the sampling vertically and horizontally. I have never seen this minor criticism with low resolution crappy jpg's that don't do the original image justice. So why start now on a high res image. The Canon 300mm F2.8L has more resolution than even the Canon 5D sensor.It should be interesting what it can do with the Canon 5D mark II. Thanks Greg and Mike as I value both of your opinions.
Omaroo I only shoot 'em I don't make 'em. If you want to see dim nebs you get lots of stars.
I do all my imaging from a light polluted site (home 16k from Melbourne) so gradients are a real pain. I think setting up at a dark sky site would be even more painful.
Stars look very square - ... just saw your post below - an artifact of processing .
I'd love to see the full image - too big to email as an attachment , even compressed by WinZip I expect. Got a link to it ?
Those 300mm F/2.8 Ls are good gear , too pricey for me right now , but I still lust for one or maybe a 200mm F/2 L . I can't justify that kind of expense on one telephoto for the 40D.
Wonder how those Sigma 300mm F/2.8 APOs compare - still outside my bracket though.
Wish it was possible to lease these lenses for a week, fortnight or month (like you can in the states) at reasonable (CHEAP) rates.
Last edited by Ian Robinson; 09-12-2008 at 03:41 AM.
Omaroo I only shoot 'em I don't make 'em. If you want to see dim nebs you get lots of stars.
Thanks for advising me of that. I wasn't aware.
After re-visiting the higher resolution versions I think it is, indeed, the squareness of the stars that throw me. They probably look more prominent on my screen, to me, at full scale because of this. If I had an incredibly large monitor that let me stand right back a few feet to view the image at full size and 72dpi, I'm sure it'd look utterly fantastic. Seeing small segments and panning around on a desktop screen doesn't do your supply of a full resolution image justice.
I've also not seen many super-wide field renditions of the Eta Carinae area - most images I've seen to date are of the central core - and the Homunculus/Keyhole in particular. Around these features the starfield has always appeared less dense in the shots I remember, that's all. Is this because of the long focal lengths and highr f/ratios used to capture this local area full frame are not letting a rich star field develop?
I can see now after looking at several other images I've Googled this morning that the starfield is in fact incredibly dense in several widefield presentations. It never clicked with me that the Eta Carinae region in widefield was so dim. So with that go my apologies.
Mike - thanks for making me appear a goose. Go eat bananas.
I have never seen this minor criticism with low resolution crappy jpg's that don't do the original image justice. So why start now on a high res image.
Wasn't a criticism at all Bert. I don't understand how downsampling a high resolution image would make these kind of star shapes. I compress large frames to JPEG format in Photoshop all the time prior to uploading but I never had a problem with the resampling of the pictures. Do you use Photoshop to resize?
Bert, when did you take the central part of your image?
Just in case, I marked the area where Nova Carinae appeared.. there is something very faint there on your image (sorry, I had no patience to wait for less compressed image, even with this 5MB I had more than 10 download interruptions before it came through).
Have a look.
Regards,
Bojan
Chris, Chris, Chris...that's what's in the sky ma man! 
Carl Sagan would have you for heresy.
I don't understand how downsampling a high resolution image would make these kind of star shapes. I compress large frames to JPEG format in Photoshop all the time prior to uploading but I never had a problem with the resampling of the pictures. Do you use Photoshop to resize?
