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Trying to get to grips with DSLR photography on my scope. Managed to locate M31 and took 3x10s shots at ISO 1600 (20s at 800 showed drift). Stacked in Registax, producing a lacklustre bluish image, so exported as FITS and colourised in PS, resulting in a better, but very monochrome image. I can only just make out that it's a galaxy! Should I be trying for a much longer exposure (which will surely blow out the centre)? How the devil do I get those beautiful colours I see in other photos?? Aaargh - willing to work at it, but knowledge is power!!

David

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I read m31 is quite challenging and you need like one hour of combined exposure and some slick processing skills to get the best out of it. Then again I got no experience on imaging and would be very happy with that as my 1st try on M31.

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The beautiful colours come with a) practice and :) data.

3 lots of 10 seconds is barely enough to pick up any colour at all and stretching this small amount of data will introduce more noise than signal - especially at ISO 1600.

So, I would forget the scope, and mount the camera + lens on your HEQ5. This will be more forgiving with the trailing. Then learn how to align the mount a bit more accurately to cut down the trailing.

Then take the images in RAW mode, not JPG and start reading up on darks and flats and image processing.

Welcome to the dark, slippery slope!!

:)

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Well, the only thing I can't put my hand up to is not using RAW, and I seem to be on overload on the reading :)

I'm off to re-check the alignment on the scope - it's clearly off because it's way off M31 now. Got a 2x ep magnifier for the Nikon coming tomorrow - at least then I may be able to focus without doing 20 trial exposures...

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Hi DLP

I'm in the same boat as you, (a bit further down the stream) although I don't have the guts to post any of my attempts at the moment :).

Daz's comments are spot on & there is a lot of reading to do to short cut some of the learning curve.

But so far I've found that its a case of practise, practise, practise & a lot of patience :).

Good luck & clear skies

Paul

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Daz is bang on. With my mono CCD I would use something like 15 x 5 minute exposures of Red, Green and Blue channels (that's 225 minutes) for the outer limbs and probably overlay 15 x 2 minute exposures (in RG&:) for the center. Then I would carefully combine the data so that the core is not too blown out but you have detail in the outer areas. Total imaging time in excess of 5 hours and probably 3 times that to process it.

If you want an example look at MartinB's recent M31. He put 2 hours and 40 minutes of exposures into this colour CCD version: http://stargazerslounge.com/imaging-deep-sky/116240-m31-again-happier-now.html

Take it slowly and experiment with exposure length. Try to get as many exposures of the longest duration that you can without trailing. Then combine them.

Imaging is a hard task master but well worth it. :)

Mark

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The M31 I have recently posted on the Deep Sky Imaging board was shot using a super sensitive CCD camera in a screamingly fast f3.9 scope and about five hours' worth of data did not blow out the core. (Or at least, no more than in most other images of this tricky customer!) Subs were five minutes. I did try some short exposures of 20 and 60 seconds but they did not really get me any deeper into the core than the 5 min subs. I have used ten second subs only once, to get the Trapezium supergiants resolved in an image of M42. Most of the image used 60 and 300 second subs.

So the way forward is polar alignment and autoguiding and longer subs. Have a look at Frans Kroon for DSLR imaging. He generally goes for 8 minute subs in a modded and latterly cooled DSLR.

www.franskroon.nl

I'm trying to give you a frame of reference for exposure times. 10 seconds is miniscule in deep sky terms but you already have a hint of the dust lanes.

Olly

PS, apologies to Mark and Paul (though we agree!) but we crossed in the post as it were. When you look at Martin's excellent image remember that it, too, was shot in an extremely fast scope. Exposure goes up as the square of the f ratio. Scarey! Regarding short exposures on areas of high dynamic range, I think the problem is this; you want to avoid blowing out the bright part but you also want to catch the faint, darker detail. Too short and you don't blow the bright part but nor do you catch anything faint. Catch 22. What I often do is prepare two stretches of the same set of data, one for the overall image with a few burnt out parts and another in which I look only at the bright parts and try to get those right. Then I blend the two in Photoshop. There are all sorts of ways of dealing with this and I certainly make no special claim for mine.

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Thanks for all the information - clearly I'm being too impatient (sure you've seen it all before!). Re-aligned the scope (must set down some level concrete in the lawn) and I now have about 10 contrails criss-crossing Andromeda, hey ho, just like fishing.

Another question though - is Registax that clever that if I'd say taken another 'n' images it would have found more colour?

David

PS Incidentally, thought I'd 'have a go' with my QC3000(Philips chip) before I got out the DSLR. It saw nothing but blackness, gain up to full up.

PPS Registax doesn't seem to like Nikon RAW (.nef) files as they come out almost black, had to convert to tiff first.

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Gotta say, I have to agree... I did an image of M31 with my 450d last year... I shot 76 x 6 minute exposures at ISO800... I for some nice colour coming out, but it took an age to process it. You have to shoot raw, and use deep sky stacker instead of registax. deep sky stacker produces a significantly different result to registax.

As for the contrails... if you shoot enough frames, deep sky stacker will remove them in the stacking process (use kappa sigma stacking).

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I use PixInsight (As I'm sure someone else will mention shortly :) ) but any "stacking" procedure should be able to "sum" the signal from multiple exposures and improve "colour" or "Signal to noise" ratio.

The fundamental problem is that summing many short exposures will not show the same detail as summing a few long exposures (e.g. 300 x 10s is not the same as 10 x 300s). The difference at higher exposure lengths will be less but the principle is sound.

Mark

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have to agree DSS for deep space from a dslr every time for me and registax for planetary work from a web cam.

two key points to work on and get right alignment and focus so your set up routine needs to be the same every time to ensure the same results all the time. Iron out one fault at a time. the first you have in hand, a solid base to work from. mark the ground so you set up in the same position every time. then get the polar scope aligned preciusly. you could look a the dark art of drift alignment method I used it to set my mount up way back ( permenantly set up until recently). practice practice practice and it will come. even when you got it sussed setting up takes time and dont rush. my first attempt was short exposures but i ended up around two mins exposures but it took time to get the set up to that stage.

i took 10 90 second exposures and 5 30 second along with 5 and 3 dark frames respectively. I should have done flats and bias as well but did not know about them a that time.

looking at your frame above my 30 seconds were not much diffrent. but i added much more and tried and tried again by the end of the month i had nailed it 1st attempt from early july 07 and one from the end of the month.

this is to show you what can be attained with time and more data

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lol!!

I did say it was a slippery slope! :)

Paulus - please post up your images. They would be good to see and of course, you'll get lots of advice :)

One thing to remember is that the people you see posting up the lovely colour images all started from the same position. At the beginning! They went through the same issues and had the same questions and are now happy to share that knowledge!

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lol!!

I did say it was a slippery slope! :)

Paulus - please post up your images. They would be good to see and of course, you'll get lots of advice :)

One thing to remember is that the people you see posting up the lovely colour images all started from the same position. At the beginning! They went through the same issues and had the same questions and are now happy to share that knowledge!

Daz (and Grahame) are right, just take a step at a time. You already have a picture. You just want a slightly better one... and so on and on. We are all in exactly the same situation.

Olly

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Inspired by all the comments and will try harder tonight. Thanks BJGC for your images; worth a thousand words and proof that I'm certainly not alone! If I can get to the stage of your second image within a month I'll be well pleased.

This forum is brilliant - if it was an open software project it'd probably knock Apple off its pedestal.

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and took 3x10s shots at ISO 1600 (20s at 800 showed drift).

Be aware that changing ISO does not make your camera any more sensitive - what matters to how faint you go is the total exposure time in seconds. ISO has a role to play in how saturated the core gets, but that is all.

NigelM

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Not quite sure I am understanding you there Nigel. ISO on digital cameras is effectively GAIN, and follows the same square law as aperture. It has nothing to do with saturation except in terms of more exposure=more saturation. Higher ISO obviously equates to more noise though. On my test, 10s @ 1600 is the same exposure as 20s @ 800.

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I think you should be pleased with your attempt above. I can clearly begin to make out where the dust lanes are.

I am in the same position as you with my latest imaging attempts, Im pleased with them, but aspire to improve having looked at the standard of work here :)

As advised by Olly (and others in this thread) take baby steps. Learn what needs to be done to improve your shots and improve each item in turn - i.e. alignment, framing, focussing etc etc

All the advice above is excellent and if followed Im sure you will improve in no time at all, this is whats great about this forum.

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I've just downloaded the deepskystacker & Manual, OMG :(

I knew there was some processing to do, once you get a set of subs. I assumed that it was Photoshop processing that took time then the stacker stacked them for you once you pointed out a few reference points! :)

A lot more reading to do!!!

And yes Daz, I will post my attempts, once I've worked out how to get them from huge RAW picture format to a size that will fit here, without loosing what little data I have. More reading :)

Paul

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  • 2 weeks later...

Had another crack at this last Monday - 18x20s images @3200ISO, 10 darks, 10 flats. Some improvement but at least I can see it!

I shot in (Nikon) raw, but Maxim doesn't seem to like those files so I converted to TIF. Maxim then ran out of memory (4Gb on my machine), so I ended up resizing down to 1200 px wide which probably helped lose some noise, and detail.

Below is a JPG which has lost more detail, but hope you can see some improvement.

post-21430-133877497878_thumb.jpg

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