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First attempt at Imaging - comments welcome...

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Hi Guys,

In the spirit of openness [however embarrassing!], I thought I would share my first imaging attempt.

I thought I would give M42 a try (I know there's a problem balancing out the core etc), on the basis that I could see it clearly when observing. I would appreciate feedback on processing in particular. I've read a few books on the subject/watched a bunch of tutorials, but there is clearly a steep learning curve. My current setup is:

C9.25 XLT

CG5 Mount

Moonlite focuser

Celestron 0.63 reducer

Starlight Xpress SXVR-H694

Xagyl filter wheel with Baader LRGB

The attached thumbnail was taken: RGB 10x 100s unguided (calibrated with 10 Bias/Darks/Flats), using Maxim DL and a bit of PSCS6. I clearly need to progress to guided imaging; which I will do so soon I hope. I have taken 10x 30s LRGB to process out the core and mask in a better looking trapezium. All taken on 2/11/12, relatively low in the sky, with ok seeing in suburban area [Moon was very bright].


10x 100s RGB unguided

My questions are as follows:

1. I've experienced marked vignetting in my setup - very obvious in the flats at 25000 ADU. Am I missing something obvious? It improved when I stuck in the reducer, but it's still there...

2. I tried combining 10x 100s Luminance in Maxim; it seemed to 'wash out' the colours. Is there a good way to combine Luminance and adjust colour balance without faking it [image included below]?

3. I've used fat tail deconvolution, followed by sigma reject to stack the images. I guessed [possibly incorrectly] that each colour channel should be deconvolved prior to stacking. Stars have ended up 'pointy', with a distinctly brighter centre. Is there a better way to do this?

4. I've noticed a periodic error in the CG5 - every six minutes there is a distinct 'stretch' in movement, resulting in eggy stars. I know that the CG5 has no PEC facility; is there any other way [excepting by guiding I guess] to reduce this error?

5. I used linear stretching and curves in PSCS6 to enhance the mid-tones without washing out the trapezium [as suggested in the video tutorials]. Also tried masking and layers to darken the background a bit. I may have been a bit heavy on enhancing the red channel, since the colour looked wrong. Are these the correct processing steps generally?

6. Where can I reference info on how you mix H alpha/UHC/S III/etc filters to replace/update colour mixing. I'd like to experiment with those filters to see what happens...

I appreciate some of these questions may be simplistic, but I guess we all have to start somewhere...

I'm including a link to the stacked, deconvolved images in RGB & LRGB. All images are half real size:


10x 100s RGB unguided


10x 100s LRGB unguided

Feedback appreciated...

Many thanks!


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Hi Sam,

I'm not able to view your images at the moment for some reason though I'm at work and it could be the poor internet connection.

First thing first, your mount. You have over £3000 worth of kit sat on it....with a weight of about 11kg and it's probably at it's max for imaging (some would say over) and that in my opinion wold be with a guiding system.You are wasting what could be achieved with the CCD scope setup you have by not guiding so I'd upgrade the mount as soon as you can (Neq6 minimum).

I think an earth worm burrowing under the mount would be sufficient to give odd shaped stars as at that capacity it's going to be very susceptible to any vibrations/wind.:D

If you are LRGB imaging I wouldn't bother using decon on the colour and although maxim is great for stacking and calibrating images I don't use it for processing stick with Photoshop.

I'd stack and calibrate the images within Maxim, then you can either combine the 3 colour channels in maxim save and stretch in PS or stretch each individual within PS, save them and combine them again within Maxim. Luminosity again stack calibrate within Maxim, export to PS process as you see fit, add as a layer to the RGB image and then set that layer property luminosity and adjust the opacity as you see fit giving you more control over how it is applied. (This is how I would process it though it doesn't mean it's right :D )

Vignetting is due to the chip size and the 1.25" filters though it may help if you increase the ADU of your flats to a min of 26666 up to 33333 (40-50% of you max adu for that CCD) That may help in reducing it in the final image (again I cant see the image to see if any vignetting is present?)

That's all I can suggest for now without having a look at the images I'm afraid?

Clear skies,


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Hi Matt,

Many thanks for taking the time to reply to my questions - I really appreciate it...

Firstly, apologies for the images issue. I followed the instructions on uploading to gallery given in a general post, so I'm stumped with what's happened. :huh:

I'm including a jpeg version of the image as an attachment, so maybe this will work [gallery versions were 16bit tiff (???)].


Secondly, I take your point entirely on the mount and guiding - it sounds like very good advice, and I will do it ASAP. :smiley:

As it happens, I started all this astronomy stuff a month ago (received the basic OTA/mount as a pressy), so assumed I would only be involved in visual observing... Didn't realise what they don't tell you re: what the equipment can't do regardless of what the marketing blurb says...

Thanks for the advice on using Photoshop for combining RGB and Luminance channels; will give that a go as well. I've used Flats at 22,000 ADU for calibration, and the vignetting is unbelievable - big white circle in the middle, and dark all around. I'll try upping them to the figures you suggested. If appropriate, I'll upload a copy of the Master Flats stacked/combined using a Boxcar filter.

Thanks again for your help!

Clear skies...


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Hi again Sam,

I downloaded your JPEG and fired up PS. First thing to jump out is that you've clipped the black point of the image! That is to say you've made it to dark and wiped out loads of data in the process! So get back to the drawing board :D

Have a look at this quick tutorial don't worry that your background is not perfectly black! around the core of M42 is all the gaseous goodness "it's not supposed to be deepest black" :Dhttp://www.corius.net/cont/artic/basimpro.html


Start over from scratch, combine the RGB without decon within maxim, also do the same for the Lum without decon. When you have your lum and rgb go into photoshop, open both files and stretch them using levels only for now (Ctrl L is the shortcut) Pay attention to the black point and noise levels in the histogram. Stretch the rgb to something that gives you the max detail without blowing the core. If at this point you need to colour balance open the histogram and then press Ctrl B to bring up the colour balance tool and set it to highlights and adjust until all three colour channels are equal.

Next the Lum. Stretch it using levels until again you have max detail without burning out the core. To copy this to you RGB as a layer click on the lum..press Ctrl A to select the image, then Ctrl C to copy.The select your RGB image and press Ctrl V this copies the Lum to the RGB as another layer. To align this layer to the RGB select the Lum layer and in the drop box above select "Difference" this will show you any misalignment between the RGB and Lum.If both layers are aligned the image will look uniform if not it will look something like this.


Use the transform tool and arrow keys to move it about until it aligns.Then whilst still on the LUM layer from the same drop box as "Difference" choose "Luminosity" This now sets that layer as, you've guessed it luminosity :D like this.


Sorry if you already know all this?

The beauty of doing it this way is that you can adjust the sharpness etc of the luminosity and see the results instantly also if it's "Washing out the image" you can then reduce the opacity of the layer to suit. I think a lot of the washing out may be due to your clipping of the black point in the original RGB.

It's a steep learning curve I know, I've been at this a couple of years now and I'm just starting to get images I'm really liking (but know with a few more thousand pounds spent I could do better :D :D ).

Personally with your setup I'd be hitting some galaxies! M42 is going to be done to death over the next months...every next post will be an M42..dare to be different lol! But as a starting point to hone your skills you are onto a cracking start matey!

Have another go mate and see what you can come up with.

If you like you can post an unstretched stack here as a jpeg and I can have a go myself!

Cheers matey,

Clear skies,


Edited by SlipperySquid

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Hi Matt,

Thanks for your advice, I'll definitely have a go the way you suggested... :smiley:

As it happens, I did actually do it pretty much that way the first time round, except that I also used decon on each channel prior to combining RGB.

I followed the instructions in the pegged post video tutorial at


My first big problem is really stupid but I'm struggling to get over it; i.e. how to upload full tiff files with all the data preserved.

The reason the jpeg looks like rubbish is that I had to strip out almost all the data from the tiff in order to reduce a 35Mb file to under 1Mb [used Maxim]. I would appreciate if you would advise how to upload 'big' files to gallery, and what format is best [i currently used 16bit tiffs].

Please don't worry about teaching me to suck eggs - I appreciate how little I know at this point!

The process I used was:

1. Calibrated, Registered, Stacked and Deconned each channel in Maxim

2. Combined RGB only in Maxim in one version, and LRGB in another

I have FITs versions of these

Then converted to 16 bit tiffs and:

3. Used linear Levels in Ps to stretch each channel separately, as per tutorial 1 & 2.

4. Used Curves in Ps to stretch nebulosity, but pegged background and stars, as per tutorial 2

I have a version to this point...

and the following bit which I probably got wrong

5. Used layers and masks to mask out the nebula, select background, darken it up and adjust opacity to bleed thru to base image, as per tutorial 2 &3

6. Increased red saturation using Levels, to get the colour richer

The jpeg I posted yesterday is a heavily stripped & reduced version of this, and lost a lot of detail in the nebula and trapezium when I look at the original

If you could advise how to upload these files without screwing them up, we could look at the real data which I think has the black point preserved - I read about image backgrounds/interstellar dust/background radiation etc, so I uderstand why it should be gray etc...

I will also follow process and tutorial you suggested and post results ASAP.

Cheers Matt, thanks for taking the time to help out a complete nubie! :grin:

Clear skies...


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Hi again Matt,

Scratch previous comment re uploading; would you mind trying to access the latest gallery I just created - lets see if this works...

I have included RGB and LRGB from Maxim,

RGB processed using Levels & Curves in PS,

RGB processed using Levels, Curves, Masking & Layering in PS

Individual LRGB channels

Individual LRGB decon channels

Master Bias, Darks, & Flats

Please let me know if you get any joy with this...



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Hi again Sam,

Can't do anything with them images I'm afraid mate as the jpeg conversion has fluffed up the data :( but never mind.You're on the right track! Only problem I see at the moment is the stars. Small pinpoints of light with the fuzzy halo, I remember this happening to some of my images and I couldn't find out why some earlier processing work had better stars with the same setup.

I found my answer was the stacking method, try using an alternative to sigma clip, maybe just "Median" or Sdmask to see if the stars improve?

Other than that Sam it's just hours and hours of subs now :D I would say the most important thing about imaging is patience! Don't try and get 10 images in the first month (I know it's really hard not to just take a few shots and hit the next target).Stick to one image until you feel it's complete (though they never are :D). I don't get really deep into processing, well not as far as some other people go, I just learn the bits I need as I go along and I'm still learning. As long as your image is in good focus and you have plenty of time on the target you will get a decent image, by plenty of time I mean a few hours on each channel!!!

You will find after a couple of months that processing becomes a lot easier and you will produce a workflow that works best for you become comfortable with stretching and combining then move onto the harder things like masks etc, sometimes less really is more.

Guiding really is a must for you with that setup. Try a finder guider setup as a cheap option to start (that's what I use) and I'm banging out 15 minute subs, though guiding itself introduces even more problems lol.

You've chosen a nightmare of a hobby mate you really have. If you need any help with specifics just drop me a PM and I'll help you as much as I can.

As to uploading tiffs, the only way I'd know is by using a free drop box site online to upload files to?

Let me know how you get on,

Clear skies,

and may the force be with you (You're gunna need it)


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Thanks Matt, good advice again...

Will keep at it as you suggest - 'If it's easy, it's not worth doing'!

Will post images in future once I feel I'm getting better results.

Cheers, and thanks again for your help.

Clear skies,


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