Rosette Nebula

Lester · #1 21-12-2009, 09:04 AM

Hi all,

I got 1 hour and 20 minutes of 5 and 10 minute exposures with astro 40D at iso 800 using Takahashi Astrograph f3.3 .

Would liked to have got more images of it, but with work today, sleep was needed.

Comments welcome.

http://i638.photobucket.com/albums/u...ckPHSfinal.jpg

CoolhandJo (Paul) · #2 21-12-2009, 09:28 AM

Good shot! I would of thought for 1 hour exposure you would of got more colour (the detai looks like its there though)

Phil Hart · #3 21-12-2009, 09:37 AM

nice shot.

the rosette is fainter than i thought before i imaged it, but i would agree that one hour on modded 40D with Tak at f3.3 (same scope as me by the sounds of it) should have some more red. what processing steps have you used that affect the colour balance?

without any colour changes, the natural colour balance of the astro 40D will be strongly red so you may have gone further with the corrections than you need to?

phil

jjjnettie (Jeanette) · #4 21-12-2009, 10:00 AM

You've got lots of nice detail for the amount of exposure you managed to get.

Lester · #5 22-12-2009, 05:38 PM

Thanks for the comments everyone. All I did in photoshop was balance the histogram with curves to bring the blue and green up to the red, then darkened the image to bring the histogram to the left without clipping it.

I will play around with this a bit more, as cloud looks like it is setting in from the cyclone over W.A. .

All the best.

Phil Hart · #6 22-12-2009, 06:43 PM

you might want to try playing with other ways of adjusting the colour balance in photoshop - if you equalise the R, G and B curves then every object is going to tend to lose its colour somewhat.

for images with my Hutech 40D, I do the colour balancing step in ImagesPlus by multiplying the Green Channel by 1.89 and the Blue Channel by 1.64 (I measured the required values from a grey card). You could do something similar in Photoshop or try playing with some other astro imaging software.

Lester · #7 22-12-2009, 09:26 PM

Thanks for your comments Phil. I have been playing around in Images Plus this afternoon and revealed a heap more nebulosity, but I cannot stop the histogram from getting clipped at the black point. I have been using the Digital Developement process.

Phil Hart · #8 22-12-2009, 09:35 PM

you probably need to decrease the background weight to something around 0.6 or 0.7. compared to the default value of 1.0, that will brighten and broaden the histogram. the auto break point is usually close but agressive, you may like to increase that a bit as well (although that will actually darken an image).

Lester · #9 22-12-2009, 09:56 PM

Thanks again Phil for your guidance. I set the background weight to 0.6, which brightened the image. Although the end result is still clipped. To brighten the image the nebula becomes over exposed.

This image shows a lot more nebula, just need to know how to get the histogram correct.

http://i638.photobucket.com/albums/u...kbackgroun.jpg

Phil Hart · #10 22-12-2009, 10:01 PM

that's looking much better!

if you send or make available the file before DDP i'll have a quick crack and see what i get. it may be that some processing before your stacked composite has clipped the lower levels?

Lester · #11 22-12-2009, 10:22 PM

Hi Phil, the first image on this thread is the image I put into Images Plus. It has been stacked in Deep sky stacker and colour adjustment in photoshop. Histogram is not clipped at this stage.

Thanks.

Phil Hart · #12 22-12-2009, 10:28 PM

did you shoot RAW? your first stacked file should be a 16bit file with very dark levels which requires DDP to bring out the faint subject.

Lester · #13 22-12-2009, 10:34 PM

Hi Phil, yes I always shoot in RAW. I always get a rather faint lifeless image after Deep Sky Stacker, but by lifting the green and blue up to the red with curves, till the histogram shows all three colours at the same strength; this brightens the image similar to the first on this thread. But still way short of what digital developement can do.

Lester · #14 22-12-2009, 11:02 PM

I guess its all easy when one knows how. Got the histogram unclipped. The image doesn't look much different to the last posted on this thread. Would have to be my best effort to date.

Thanks.

http://i638.photobucket.com/albums/u...lippedfina.jpg

AlexN · #15 23-12-2009, 12:06 AM

Wow!

Nice repro mate!

Phil Hart · #16 23-12-2009, 02:49 PM

that's looking great now. nice work.

next step is four hours exposure!

Lester · #17 23-12-2009, 03:46 PM

Thanks Alex and Phil. Yes 4 hours exposure will be good.

How critical is it to track on the same star when exposing an object over many nights? How does one find the same guide star?

Thanks again.

sjastro · #18 23-12-2009, 04:25 PM

Nice shot there Lester.

Should be no problems taking exposures over several nights if you align and stack the images with software like Registar. (I use Registar to align the images but stack in AIP4WIN).

You might have to crop the stacked image in which case make sure the object is roughly in the same position in the FOV for each night. There is nothing stopping you using a different guide star provided there is not much change of the objects position relative to the FOV.

Regards

Steven

Troy · #19 23-12-2009, 04:34 PM

Nice picture

Phil Hart · #20 23-12-2009, 04:38 PM

Quote:

Originally Posted by Lester

How critical is it to track on the same star when exposing an object over many nights? How does one find the same guide star?

I agree with Steve comments.. i don't aim to guide on the same star on separate nights but you do want to get your framing of the image as close to the same as possible.