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oldannie

First attempt at collecting Ha not gone to plan!

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Am trying to image the Crescent Nebula as my first image with a CCD camera having just moved from DSLR imaging and  realise I am quite ignorant about some of the basics.  Having collected some RGB subs, stacked and aligned in DSS using  a red channel sub as reference image I have managed to generate a color image in photoshop.   Last night I took some Ha - 25x600sec using Atik capture software, Artemis.  When I lightened the first sub in Artemis it looked great with lots of detail - a wow moment!  This morning I stacked  and aligned in DSS using the same red channel sub as reference image   together with darks, flats and bias frames and as is often the case the result was a quite dark image.  Opened it in photoshop expecting to reproduce the same detail I saw on my computor screen last night but it still  showed very little detail and soon showed signs of over - processing when I tried to use levels.  As is oft the case with this hobby have gone from euphoria to disappointment in the space of 12 hours!!  Have I missed something obvious - it wouldn't be the first time!! 

Using Takahashi 106ed, Atik 460ex on neq6 with lacerta mgen stand alone guider.

Annie

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Begin by eliminating all the things that can go wrong by integrating just the per-filter light frames and no calibration frames. Make no changes to the image in DSS after integration and just export it to Photoshop, then try levels and curves again. Is the image now good enough to support further processing, if yes, examine your calibration frames for problems, if no, look at all the light subs individually to see if they pass muster, any that aren't up to scratch should be eliminated from integration and then try just integrating the good frames.

Bad calibration frames will easily degrade good lights so when troubleshooting always look at the source data sets individually and make sure it is good before chucking it all into DSS.

Edited by Oddsocks
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I think that's very good advice and in fact I thought maybe I'd posted a little prematurely (ie. before I'd thought  it through properly!!)  I have already tried it without any calibration files and it's quite  a bit better so am going to go through my calibration files as you suggest and also my light subs. 

Much appreciated.

Annie

 

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taking darks in itesl is more than just a case of putting a lens cap over the scope, light still gets in, i take my camera off, put the camera cap on and put it inside something dark, properly covered, flat frames are another tricky one to get write, you need an adu reading around 24000 ish

 

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Yes you're right.  Am def going to check my calibration files.  The Ha flats were taken at around 24000 adu's  so that part should be ok but I do take your point about stray light and think I might need to be a bit more careful about that aspect.

Thanks

Annie

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On 29/09/2018 at 17:09, oldannie said:

Yes you're right.  Am def going to check my calibration files.  The Ha flats were taken at around 24000 adu's  so that part should be ok but I do take your point about stray light and think I might need to be a bit more careful about that aspect.

Thanks

Annie

Hi Annie. Did you get anywhere with this?

A good idea when looking for an issue like this is to post the raw stack or single frames and calibration frames, along with the settings you used in stacking, plenty of helpful people here. I was chasing a flats issue by my stubborn self for days until i posted in the help with processing section and had a solution within about an hour.

Richard.

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Thanks for your reply Richard.  My broadband speed is low (2/3mps) so I have difficulty posting anything other than  jpegs and have tried using Dropbox but again the low broadband speed makes that difficult.  I did check all my calibration files and couldn't see anything obvious so sent a jpeg copy of my stacked Ha to Carol (a regular in SGL) and much to my embarrassment it has turned out to be lack of skill in processing that has been the problem!!!  Still I've learnt a lot in the process of finding that out! In the past I've tended to ask before I've allowed myself sufficient time to think through the issue but I take your point about advice being readily forthcoming and have already experienced that.

 Here is a copy of the stacked and processed Ha data - 25x600 secs using Takahashi 106ed: Atik 460es mono: stand alone mgen Lacerta guider on neq6.  Hope the 8bit jpeg image appears ok - just under  500kb!  Do you think the stars look a bit odd or am I being pedantic?

Thanks again Richard

Annie

Cresc_Ha_stack_-process_SGL.jpg

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Looks pretty good to me Annie given the jpeg compression you have to use...  maybe some halos around the brighter stars, difficult to tell. Not unusual with narrowband imaging. Maybe post a crop of the stars you think are odd.

Dave

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Thanks Dave.  Some of the stars look as though they have a 'pimple' on the end but perhaps what I'm seeing is just smaller less bright stars very close to brighter ones - if that makes sense!  In other words I'm seeing stars!

Annie

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I can see them now on my laptop...  (phone previously) they shouldn't be there, I'd check your individual subs and guide graph (if your kit gives one) to see what's happening

Dave

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Thanks Dave - I didn't think they were right.  I'll check my individual subs.  I think the Lacerta  guider does enable you to record the guiding and presumably produce a graph but in order to keep things simple I have avoided it.  Something else to learn how to do next time - it seems pretty important to be able to look at the guiding.

Lots of things have gone slightly wrong with my first attempt at CCD imaging but other bits have gone better than anticipated and have learnt a lot.  I'm not very technically minded so it's all a big challenge but an enjoyable one -

well most of the time ?

Annie

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The stars look like you had a guiding problem.  If just one sub is affected then you should get a better result by excluding the bad sub.

 

You have captured the background stuff very nicely. 

You could also try some different noise rejection methods in your stacking software.

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Thanks to 'Oddsocks' for recommending Avis Fits viewer I've been able to look at all my Ha subs.  The files are numbered sequentially ....595 to ....614.  The first two are fine; 599 shows bad trailing and nos 601-606 show trailing also. Have not experienced this before with my guider though only recently started using it with a CCD .  What might have caused this?  I can record and download a guiding file from my guider but need to download the PC application first.

Annie

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Just seen your reply - I agree it's definitely a guiding problem - not one I've had before!  Happy with the background - thanks for that.

Annie

 

 

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Given that its a new camera maybe something loose in your imaging train, so check everything's tight, plus the usual stuff cable drag etc..  Awaiting trail free restack with interest :) , I'm sure it'll be great.

Dave

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Hi Annie

Just looked and your guider allows you to save a guide log by opening a new file at the start.  Suggest you do that net time...  Looks a neat bit of kit.

Dave

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Glad you are making some progress Annie, that image looks much better than the one you sent me.  

I agree about the "pimple" being a guiding issue as all the star have a pimple.  You will initially just have to eliminate any bad subs from your stack.  Then the difficult task of finding the cause.  It could be something quite simple like a snagging cable.  Was there any wind that night?  

You did mention about tying back your cables, is there anything pulling?

Carole 

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yes Dave - I've had the guider for a number of years now and it's been great - I do wonder if it's something simple like cables pulling as I'm not used to lots of cables!  I think recording a guide log on the mgen is easy it will be working out which driver to download and how to download it but am sure I'll get there.

 

Carol - I don't think it was particularly windy that night but I do think cables pulling would be a logical reason.  I was so busy checking my guide star was there that I forgot to check how the cables were doing!!  Don't think there will be that much detail left when I eliminate all the bad subs.  Learning a lot though.

 

Thanks folks

 

Annie

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59 minutes ago, oldannie said:

I do think cables pulling would be a logical reason.

I've just fixed (I hope!) a very similar problem.  I posted a guide log here:

and there's a 'fixed' one in the following post.

It was, apparently, a power cable dragging the tiniest of amounts, but big enough to put huge spikes into the guiding, leading to similarly bad stars.  It seems that nothing should hang in big loops and certainly anything that's meant to move should touch anything that isn't.  Anyway, guide log should be very diagnostic.  It was for me.

Tony

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Thanks Tony - am hoping it is the most obvious cause - snagging cables.  

Annie

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Still trying to sort out  the reasons for the star trailing with Ha subs . On the first occasion I took 24x600 sec subs in Ha and around half suffered from star trailing.  At the next imaging session I took  some 600sec RGB subs with no signs of trailing. Next session I took 12x600 Ha subs (nothing else) and 8 out of 12 showed trailing stars.  The first two subs were ok and the last two almost ok!  Last night I took solely RGB subs and no trailing.  Have checked for signs of anything obvious in my cabling/connections and will download the PC application for my guide camera so I can record a guide log  next time but in the meantime is there anything else I need to consider - is it just coincidence that the trailing has only occurred when I take Ha.  Star trailing is not something I have encountered until I moved from DSLR imaging to CCD imaging.

Annie

 

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Hi Annie... Not what you want to hear but it might just be that the trailing is more obvious with the Ha Subs as the stars are so much smaller.. Maybe you could post some subs with/without trailing Ha/ RGB up for others to have a look at.   Best bet would be to look at your guiding logs though, does the setup you are using allow you to see the guiding in real time?

 

Dave

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No Dave my set up doesn't enable me to to view my guiding in real time so will def have to download the PC application for my MGEN so I can at least generate a guide graph.  It's an interesting point about the stars being smaller with Ha subs - didn't appreciate that!  Will try and post some subs as you suggest.

Mant thanks

Annie

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Here are two Ha subs - one looks ok , the other has stars trailing.  Viewed via Avis Fits viewer the trails are obviously much more pronounced.  Hope they post ok.

cresc_Ha_second batch_622Ha.jpg

cresc_Ha_second batch_624Ha.jpg

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I'd go through all of your subs and bin all the ones with trailing. You'll have less subs so your fi Al image will be a bit noisier but you'll have a better quality image. 

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