Stacking Images from a Nikon D800

[gnomus]

I would be grateful for any assistance.  

I recently had a go at imaging M33.  This was my first attempt at any sort of deep sky imaging.  I used my Nikon D800E camera through my "focally reduced" Celestron 8 inch scope (so that it was operating at f/7).  I decided to take 2 minute exposures with the camera set at 800 ISO.  (I suspect that the resulting image was underexposed, but I wasn't guiding, and I had only used the Nexstar "polar alignment" routine.

I shot 25 Lights; 25 Darks; 25 Bias; and 25 Flat frames.  On checking through I had to discard 13 of the lights due to trailing stars.

It may be relevant to note that the D800 is full-frame and 36MP (this slows down processing quite considerably).

I loaded all my images into DSS.  The first issue that I had was that all of my images were displayed as being "Greyscale".  I didn't understand this since the NEF (RAW) files were all in Adobe RGB.  I did get an image out of DSS.  Photoshop showed this as being a 32 bit TIFF.  I processed it as best I could, but it looks to me as if it is in monochrome, albeit with a blue tint to it.

I downloaded Nebulosity and ran that as a trial.  The image that this produced was quite definitely greyscale.  

I'm not sure what to make of this.

I tried converting my NEFs to TIFFs.  These files are, of course, considerably larger than the NEF filles - and both DSS and Nebulosity gave up the ghost.  I have a reasonably fast machine - it's a quad core with 12MB of RAM.

Has anyone any experience of using a Nikon D800 for astrophotography?  If so would you have any idea what is happening with my images in these software packages?

[WaveSoarer]

My images also tend to end up looking rather grey. Once stacking has been done, and you've both adjusted the RGB levels and stretched the curve as best you can, try increasing the saturation to see if that makes a difference.

[idigitize]

In nebulosity you need to convert the files to colour, using the batch demosaic tool. There are some great tutorials on YouTube if you google nebulosity tutorials. (I'm not sure if imy allowed to link to it)

Remember raw files don't have a colour space, so the fact it's set to Adobe rgb is totally irrelevant, unless you use capture nx or shoot jpeg.

[gnomus]

OK - I did try the debayering.  I am not sure which settings to use in the dialogue box that came up.  I stuck with the defaults.  This did have an effect but it seemed to turn most of the stars in the image a sort of green colour.  Further processing was a bit fraught - I am getting very frequent crashes with Nebulosity.  Sometimes the program tells me it cannot allocate enough memory.  At other times I get various "exceptions" and the program closes down.  Quite frustrating really.  

Would anyone have any other sugestions - either for Nebulosity (which this guy seemed to like a great deal: https://www.youtube.com/watch?v=OMhLYg-xPuc - or for an alternative?

Thanks in anticipation.

[Shelster1973]

With Nebulosity debayering, you have to adjust the RGB settings so that they match the matrix within your camera.  Not sure what the ones are for yours, but some Google-Fu should reveal teh correct settings for you.

As for the crashes, I get those too with Nebulosity.  They mostly occur after doing the pre-processing prior to stacking.  If i try and stack then it throws a wobbler on me.  I just restart the program and carry on and all goes ok.  Is weird as have 32GB of RAM in my computer so there should be no issues with memory.  I have a feeling it is to do with the way that it has been coded and handles memory.

I mainly use Neb for my stacking and occasionally use DSS.  I did download the demo of PixInsight but found that to be a very complex program to get to grips with.  There are plenty of tutorials out and about for that one too.  That seems to be th eone that most of the very experienced users on here have and use too.

[gnomus]

Thanks for your advice.  

I have been unable to find the correct settings for my Nikon.  I have, however, at least been able to produce an image (quite possibly the worst picture of M33 ever taken).  I know its not ideal, but I converted my NEF files to JPEGs (the TIFFs were just too large).  Using JPEGs in DSS seemed to at least produce a result.  

I think I may try setting the D800 into "DX" mode next session.  I am sure that half the problem is the size of the NEF files (some 72.5 MB each).  It's a bit disappointing that I can't get Nebulosity to produce anything other than a very green image.  I really liked the program, but I am not going to shell out $80 if I can't get it to work with my gear.

Thanks again. 

[Shelster1973]

The settings for my D7100 are 0, 0, 2, 0, 1, 0, 2, 0, 0 (read from top left) these may help you with a starter for ten.

There are whoppers of files there.  I thought mine were bad at 30 MB for NEF files.

Have you tried just stacking a couple of images to start with...then build up from there?

Have to admit is do use my D7100 in cropped DX mode too.  Seems to increase the size of the target I am going for..well I say that. As it has been nearly 2 months since I actually attempted any imaging I am not sure if I can still remember which end of the scope to point to where any more

[gnomus]

The settings for my D7100 are 0, 0, 2, 0, 1, 0, 2, 0, 0 (read from top left) these may help you with a starter for ten.

There are whoppers of files there.  I thought mine were bad at 30 MB for NEF files.

Have you tried just stacking a couple of images to start with...then build up from there?

Have to admit is do use my D7100 in cropped DX mode too.  Seems to increase the size of the target I am going for..well I say that. As it has been nearly 2 months since I actually attempted any imaging I am not sure if I can still remember which end of the scope to point to where any more

Thank you again.  I will try these numbers and see how I get on.  May need to try the cropped DX mode too.

[astromartian]

On checking through I had to discard 13 of the lights due to trailing stars.

Not an expert by any stretch but how can you have trailing starts in lights?

[gnomus]

Not an expert by any stretch but how can you have trailing starts in lights?

I'm not sure I understand the question.  'Lights' = subs = the images themselves (not flats).  The stars trail because of tracking inaccuracies that were no doubt due to my inexpert setup.    

[gnomus]

The settings for my D7100 are 0, 0, 2, 0, 1, 0, 2, 0, 0 (read from top left) these may help you with a starter for ten.

There are whoppers of files there.  I thought mine were bad at 30 MB for NEF files.

Have you tried just stacking a couple of images to start with...then build up from there?

Have to admit is do use my D7100 in cropped DX mode too.  Seems to increase the size of the target I am going for..well I say that. As it has been nearly 2 months since I actually attempted any imaging I am not sure if I can still remember which end of the scope to point to where any more

Those settings made my image pink!!

Here are the settings I have.  Do these look OK?

[idigitize]

Hi, yes those are the correct way to enter the settings.

And yes it does make it go a bit pink. but this is corrected with adjusting the image background offset.. Also, have you unchecked the Auto box on the display histogram?

I had some D800 images from early this year… not very great ones, but those settings worked Ok. (actually very poor )  This is one short D800 sub, was through an st80. But you can make out the colour in M82.

I find nebulosity very good, albeit slightly long winded in the processes, but logical also.

Jpeg preview of raw file

mono on import of nebulosity, and applied settings as above in debayer menu

Pinkish tone

background colour offset

And final 'ish' corrected image.

[idigitize]

"actually very poor' is referring to the images, not the settings… sorry I can't edit the post!

[gnomus]

"actually very poor' is referring to the images, not the settings… sorry I can't edit the post!

Thanks idiitize

I'll post up some examples too:

First image is the best I could do in DSS (probably overprocessed):

Second is the pink (in fact nearer magenta) image I get in DSS (I didn't do much processing on that one since I just wanted to show the colour cast - NB: there are artefacts from me using the demo version of Nebulosity):

Lastly a 100% crop from the first image showing noise levels:

[astromartian]

I'm not sure I understand the question.  'Lights' = subs = the images themselves (not flats).  The stars trail because of tracking inaccuracies that were no doubt due to my inexpert setup.

Yeah I misunderstood, having done some reading I realised that lights refers to the actual pictures.

[gnomus]

I downloaded the Maxim DL trial version.  I'm getting magenta with that too!

It seems a very "deep" cast - wwhat I mean is that I can play around in photoshop and get different colours to the cast but I don't seem able to remove it and get anything like a "natural" result.  Any thoughts would be much appreciated

[glowingturnip]

I found Maxim DL would give a strong magenta colour cast to my D80 NEFs too, no matter what settings I had in the debayer dialogue, and the downstream colour balancing tools I found weren't really good enough to get rid of it.

You should be able to roughly get rid of a colour cast in photoshop by adjusting the black point sliders in each of the R, G and B channels separately so that they all start on the left in roughly the same place (be careful not to clip any of the histograms).

Pixinsight will handle a colour cast masterfully with the DBE, Background Neutralisation and Colour Calibration tools.  Does a better job of stacking than DSS too.

[gnomus]

I found Maxim DL would give a strong magenta colour cast to my D80 NEFs too, no matter what settings I had in the debayer dialogue, and the downstream colour balancing tools I found weren't really good enough to get rid of it.

You should be able to roughly get rid of a colour cast in photoshop by adjusting the black point sliders in each of the R, G and B channels separately so that they all start on the left in roughly the same place (be careful not to clip any of the histograms).

Pixinsight will handle a colour cast masterfully with the DBE, Background Neutralisation and Colour Calibration tools.  Does a better job of stacking than DSS too.

OK - I downloaded and tried Pixinsight.  A very steep learning curve!!!  Nevertheless, I think this has given the best result of all the software I have tried.  I'm not entirely sure whether to thank you or not Stuart, given the cost of the package 

I suspect that I am still not using the package entriely correctly - it doesn't seem to work at all like other image processing software.  I've watched the two video tutorials on the site - they were a little difficult to follow.  Are there any "Idiot's Guide" to PixInsight tutorials that folks who have had experience of this software would recommend?  I attach the PixInsight version of my first attempt at astrophotography.  I suspect that I still need longer exposures.  If the clouds ever lift, I may give it another go.  I've seen images with more colour variation in the centre of M33.  

[glowingturnip]

 I'm not entirely sure whether to thank you or not Stuart, given the cost of the package 

Haha, well the way I view it is that though I have distinctly sub-optimal equipment, at least I have state-of-the-art processing software  .  Besides, it does give you a lifetime any-PC licence, and they're constantly bringing out new features etc, so I reckon it's worth it.

Harry Page's video tutorials are the best to go through, in fact I'd consider them essential, and he hangs around on this site sometimes too.  http://harrysastroshed.com/pixinsight/pixinsight%20video%20html/Pixinsighthome.html

Still looking a little green there.  The SNCR tool would fix that right away, but if you go through the tutorials and try again with DBE, Background Neutralisiation and Colour Calibration, you should get a good result.

Edit:  this was your first DSO astophotograph ?  Wow, I'm impressed !

[gnomus]

Thanks again.  Did some more tweaking in PixInsight after having watched the videos you suggested.  It's still not quite there but I think this is as good as I am going to get with the data I had:

[gnomus]

Image didn't attach... second attempt: