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seventyf

Staring mono CCD help

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After a few semi successful attempts with my 60D I recently got a 314L+ from Ebay. The first night under the stars I could manage due to work and other commitments was 30/11/17. Just trying to get everything working with SGPro tried to capture some images of M1. I have a 200P on an EQ6. I was taking 60 second subs with no filters unguided. The results were less than great. My subs seemed ok, nothing amazing but ok. When I stacked 30 of them I started to see something faint and fuzzy. I wasn't expecting a lot for my first attempt with a mono CCD but I've a few questions about how I deal with the issues I have. I am imaging from the my back garden in a suburban area, I have a few street lights that shine into my garden.

I seem to have a pretty bad gradient in the stacked image, I assume this is from street lights. Will a light pollution filter help? If so any recommendations, are there any other tricks to help?

1 x 60 Sec

Untitled.thumb.jpg.0f3f5dae75b72c7fb318742df942823c.jpg

30 x 60 Sec
stacked.thumb.jpg.e5184a525fdd1dcb52ca1d08a8f3ebd1.jpg

The other issue I have is when stacked and aligned the image has a large area of lines at the side. I'm pretty sure this because I wasn't very diligent with my polar alignment. I know guiding would help this but better polar alignment would be needed anyway. I have a DFK 21AU04, can this be used as a guide camera, its probably not ideal as its a colour. I have got it connected to PHD but I haven't had time to use it under the stars. I don't have a guide scope and was planning to convert a finder, is this a good idea or is it better to save up and get a OAG and different camera?

Misaligned.png.454f4167172fd83eb1128bd68346e471.png

 

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It would be hlpful if you could upload a raw sub to dropbox or wherever and link to it. I'm wondering if your subs are underexposed

The dark areas at the sides are stacking artefacts from the view shifting from one sub to another. You should crop them before any other processing.

You can also see some dark horizontal lines which are called "walking noise". These could be something like cold pixels - they "walk" because of the shifting between subs.

Most likely cause of shifting between subs is differential flexure so an OAG would help there. Field rotation is another possibility and polar alignment would help there. Your guide camera should be ok but you don't say what your guide scope is. It would be helpful to list your gear in your sig.

There's a diagonal elongation that could be due any number of things.  If you could post your guide log that would provide some clues. 

 

Edited by kens
Just reread and saw you aren't guiding

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Thanks for the speedy reply. Sorry I probabaly should have said I used an unregistered version of nebulousity so the horizontal lines are an artefact that it puts in to degrade the image.

I’ll upload a raw sub tomorrow for you to look at.

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Those dark lines were a bit of a head scratcher :)

Guiding is definitely the way to go. Starting with a finder and the DFK would work fine but down the track you might want to move to an OAG to avoid differential flxure but they are rather fiddly to set up and you would probably want a smaller/lighter guide camera, possibl with higher sensitivity. But before you go to OAG you may be better served looking at filters and a filter wheel. Personally I'm not a fan of LP filters for AP. If funds are limited you could try just a Ha filter which, with the right targets, gives amazing results. Later on you could move to LRGB AP.

If you get yours subs right and have enough integration time, gradients can be removed in post processing without too much trouble.

By th way, its helpful for analysis to know how your images are oriented as the direction of the trails helps identify the cause. If you are not sure you can find out by platesolving at nova.astrometry.net 

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8 hours ago, seventyf said:

 

I seem to have a pretty bad gradient in the stacked image, I assume this is from street lights. Will a light pollution filter help? If so any recommendations, are there any other tricks to help?

 

Narrowband filters certainly help with LP .

This is what it's like here and you can see my Ha images here.

lp001.thumb.jpg.d43385fcfb985aae60b12b727f166d07.jpg

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I'm not yet convinced that the vertical lines are edge artefacts created by the stacking of frames which have moved relative to each other due to polar misalignment. To check this, could you:

1) Look at every sub in the stack to see if any of them has a set of these lines.

2) Stack just the first and last sub together to see if the movement agrees with the scale of the line pattern in the original stack.

The lines just don't look quite right to me as 'stacking of misaligned frame' artefacts. I could be wrong because, though I've worked with data showing mild misalignment, I've not stacked any badly misaligned frames so far as I can remember.

I'd also measure your power supply with a multimeter. CCD cameras act up if even slightly low on voltage.

Olly

 

 

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I'm not yet convinced that the vertical lines are edge artefacts created by the stacking of frames which have moved relative to each other due to polar misalignment. 

I am positive this is the result of not guiding and probable slightly inaccurate PA, I used to get this effect before I started guiding.

Guiding is definitely the way forward, that's a cracking little camera you have bought and capable of some very good results, just need longer subs, calibration and you'll be happy.

Carole 

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On 1/20/2018 at 10:57, carastro said:

I am positive this is the result of not guiding and probable slightly inaccurate PA, I used to get this effect before I started guiding.

Guiding is definitely the way forward, that's a cracking little camera you have bought and capable of some very good results, just need longer subs, calibration and you'll be happy.

Carole 

But why has the effect only appeared on the vertical axis? It strikes me as improbable that the movement of the frame over time wouldn't see movement (I should say 'drift') in the horizontal axis as well...

Olly

Edited by ollypenrice
Clarification

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But why has the effect only appeared on the vertical axis? It strikes me as improbable that the movement of the frame over time wouldn't see movement (I should say 'drift') in the horizontal axis as well...

Olly

I think it has Olly, it's just not obvious on the image posted.  

If you look at this image, there is dark space below the image, but some stars in it as well.

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30 x 60 Sec
stacked.thumb.jpg.e5184a525fdd1dcb52ca1d08a8f3ebd1.jpg

 

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6 hours ago, carastro said:

I think it has Olly, it's just not obvious on the image posted.  

If you look at this image, there is dark space below the image, but some stars in it as well.

 

But the horizontal bottom edge has some stars showing 'off image' against black. The vertical edge has a series of vertical lines 'on image.' These are quite different artefacts. Why would the edges be different if the cause were simply the drift of the frames due to polar misalignment? You might be perfectly correct but there's something here I'm not grasping.

Olly

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The stacking edges I usually get don't have these well defined thin (single pixel?) black lines. (I mean the vertical ones, not the short horizontal dashes. Those were explained earlier.) Rather, the image shows a darkening, and very noisy band at the edge of the reference frame. Something like this (extreme crop)

ngc7023_l_Preview01.jpg.355d07d64c1cff3762462c9b8870d93a.jpg

But if the sensor has an edge that is not illuminated (effective pixels vs active pixels), I suppose these black lines could show.

The dark band at the bottom of the OP's image could have a simple explanation:

If a test frame was kept in the stack, and inadvertently used as the reference frame for stacking, an edge like this can be the result. The test frame can be a shorter exposure than the "real" frames, and show as black with only very few stars. (Been there, done that, don't want to wear the t-shirt.) Removing the culprit and restacking will resolve this.

As for the stacking edges, you'd crop these anyway.

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But the horizontal bottom edge has some stars showing 'off image' against black. The vertical edge has a series of vertical lines 'on image.' These are quite different artefacts. Why would the edges be different if the cause were simply the drift of the frames due to polar misalignment? You might be perfectly correct but there's something here I'm not grasping.

I am going to duck out of this one and bow to your superior knowledge.  It just looks how my images used to look before I started guiding, though I must admit I probably did have lines underneath as well. 

Carole 

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9 hours ago, wimvb said:

The stacking edges I usually get don't have these well defined thin (single pixel?) black lines. (I mean the vertical ones, not the short horizontal dashes. Those were explained earlier.) Rather, the image shows a darkening, and very noisy band at the edge of the reference frame. Something like this (extreme crop)

ngc7023_l_Preview01.jpg.355d07d64c1cff3762462c9b8870d93a.jpg

But if the sensor has an edge that is not illuminated (effective pixels vs active pixels), I suppose these black lines could show.

The dark band at the bottom of the OP's image could have a simple explanation:

If a test frame was kept in the stack, and inadvertently used as the reference frame for stacking, an edge like this can be the result. The test frame can be a shorter exposure than the "real" frames, and show as black with only very few stars. (Been there, done that, don't want to wear the t-shirt.) Removing the culprit and restacking will resolve this.

As for the stacking edges, you'd crop these anyway.

This is exactly what I think. Those lines look electronic in origin to me.

Olly

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