M31 - Struggling with processing or bad data?

[Digz]

Hi Guys,

Been looking at some great images here lately which is really inspiring me to keep up with this imaging lark, so here is my latest attempt at M31:

21 x 120s (approx) subs totalling approximately 44min of exposure, darks and flats. Combined in DSS, stretched in DSS and finished in CS4.

Taken with my Nikon D200 and 400mm sigma prime. The sigma lens isn't the sharpest lens I have but its adequate.

Now I don't seem to be able to get much detail out of this image and would like to ask the forum for any help. It takes me a cuple of hours to play about with it in DSS trying various settings some yield more detail than others but then the wider star field is blown and grainy.

Issues flying around in my head are as follows:

1. Is 44min of exposure enough for this object?

2. The sky is fairly light polluted which I imagine will affect the quality the of the data - unfortunately I cant benefit from a CLS LP filter ;

3. I know Nikons aren't ideal for AP but I have seen some great images taken with Nikon so I want to perservere with it;

4. I think there may be an issue with stray light entering the back of the camera through the viewfinder - do people block theirs off on their DSLRs when imaging?

Anyway enough rambling, I would be grateful for any input and how I can improve. Also, if anyone feels like it, I would like to see what others can come up with therefore I can upload the original tiff from DSS - any takers?

TIA

[gary1968]

Hi Digz,

I had a wee play with the jpg and I could see a bit more. Now, I am no processing expert but in the absence of my own new data, if you dont mind, I would like a go with the tff. But straight after the stacking, dont adjust anything in DSS, if thats possible m8.

Cheers,

Gary

[Digz]

Hi Gary appreciate the feedback. I can upload the tiff straight out of DSS. Can you recommend a file sharing site as the tiff is nearly 100mb in size!

[Beyond_Vision]

Thats a very reasonable result for short sub length and short overall time. It's far better than my first attempts. I would try to increase the number of exposure so that you get atleast a couple of hours worth. If you can lengthen the individual exposure time that would help too. You may also have some frames with thin cloud in them. It would be worth going through each frame and rejecting any with a lower quality score in DSS. Light pollution filter would certainly help. Although you may not be able to use a CLS filter with the Nikon a front mounted filter would be possible but expensive. A fellow poster Brian B suggested in another thread about using a relatively cheap daytime photgraphy filter which happens to block sodium street lighting by accident rather than design. I will try to find the post if I can

Regards

Kevin

[gary1968]

100Mb............

Not sure where you could upload that for sharing....... Will have a wee think/google and see if I can come up with owt.

Gary

[Roger B]

you can send via www.yousendit.com or co.uk not to sure.

I'd say you need longer subs but for that you will need a filter. But yours is good for the exposure.

Roger

[Beyond_Vision]

Link as promised

http://stargazerslounge.com/imaging-discussion/115808-annoying-imaging-problem.html#post1547328

[glennbech]

I think you have pulled out the detail possible for the image. If you overdo it, you magnify the noise as well. It is better not to overdo processing.

Get more subs and longer -)

[Digz]

Hi all, thanks for the feedback

If anyone is interested in showing me what they can do I would be more than grateful.

Here is a link to the autosave straight from DSS, thanks to RogerB :

https://www.yousendit.com/download/ZGJlU2VveDM5eFUwTVE9PQ

Kevin, thanks for the input, Ill be sure to capture and add more detail to see what I get. At the moment I can only manage a 3min sub (on a good night) - would that make much difference? Thanks for the link as well, Ill look those filters up, might be useful. Ill also have a look at ditching any low grade subs.

Glennbech, appreciate the comments. I guess M31 will be one that I will end up collecting data for a while to get something reasonable.

[James]

Ill also have a look at ditching any low grade subs.

Looking good so far Lee. As everyone has said the usual recommendation is more subs, longer subs and as you've put above I've found it helpful to ditch subs that aren't as good as the rest

James

[Digz]

Hi James, thanks for the input.

I have had a go at reprocessing and removing some of the duff frames. I also noticed DSS was set to stack 100% of the frames which I have revised to 75%.

The image below is now 16 frames.

I think I have picked out more detail in the dust lanes, but the core is blown. I also definitely think there is stray light coming in through the viewfinder. Ill have to dig out by cap.

There is a purple fringe at the edges as now flats were applied only lights and darks. I am trying to work out a way where I can tell DSS to edit the incoming RAW files i.e. brightness and WB etc but not affect the flats - if that makes sense?

Anyway, I think I am heading in the right directions. Thanks all for you help, its much appreciated.

[glennbech]

Hi Digz,

I opened your TIF file in photoshop. It seems like the image is a tad out of focus. You will also have more fun processing your images if you take flats :-)

Keep up the good work!

[Digz]

Hi Glenbech, thanks for the input

I take it you couldnt extract much more out of the data then? I did take flats but here is where I am struggling:

I load my subs as RAW files and adjust some settings in DSS, for example increase the brightness to get squeeze some extra detail from the RAWs;

Then when I load in my darks and flats (again as RAW files) these obviously get altered by the same settings as above.

Will it make a big difference in the output? Should my darks and flats not be 'edited' as such and used 'as is'?

My darks dont seem to be removing the ampglow visible around the corners as well which is annoying.

I've got some more images from the other night which I will post soon. Although the images are perfect I do feel like I am learning a lot from them and hopefully soon it will all come to fruition.

[glennbech]

I load my subs as RAW files and adjust some settings in DSS, for example increase the brightness to get squeeze some extra detail from the RAWs;

Then when I load in my darks and flats (again as RAW files) these obviously get altered by the same settings as above.

Hi, do you manipulate the light frames before stacking? I would not recommend that. You are better off adjusting the final image, after stacking.

[Digz]

Hi glennbech,

I have tried adjusting the settings in DSS to increase the brightness of the light frames which then obviously affects the flats and darks if they are also loaded in as RAW files. I was just seeing if I could squeeze the extra data that is containing within the RAW files as wouldnt this be lost once the stack is complete?

Ill be sure to try again without altering the settings in DSS thus not altering the light frames as well to see what that does.

[ollypenrice]

M31 can look monochromatic straight from the can. I have had monochromatic greens and monochromatic reds so how do you tease out the colour? First you need longer and deeper data as has been said. Then you need to get the top left of the histogram in the same place for each colour channel. You can do this by careful clipping back of the black point in Ps, channel by channel, but don't clip back into the real data in the main peak.

Then comes the jiggery pokery! I have a basic 'galaxy curve' routine in which I put opposite S shaped curves into red and blue. Red gets to come down near the bottom and up near the top and Blue the reverse. The adjustments are slight and Green holds tha balance of power...

I had a real fight with the M31 I have just posted. I don't know who won!

Olly

[Digz]

Hi Olly, thanks for the reply. Ill be sure to make note of what you have said when I next try processing some data.

I think I saw your M31 and reckon you may have just begun to win! Seriously I wish I could get that sort of image!