Dumbbell stacking or processing problems? Help needed.

[tich]

Hi everyone.

I've been dabbling with some DSO imaging using a Canon 1000D with some success & after reading some tutorials here & online I've been managing to stack & process my images better although I do still have a way to go. However I got myself a modded 1000D recently & I managed to try it out for the first time last night & I noticed straight away that it was showing up more reds. I stacked the images in DSS leaving the settings alone as I found in the past that changing them tended to make the end result worse. All seemed ok so far so then I'd go into the processing part. After adjusting the levels & curves I began to see some red blue & green streaks appearing on the image which I hope that they are visible.

Does anyone know what is causing this? I tried stacking the images with my existing DSLR data which made it up to 4½ hours worth of data but still these streaks were showing.

The image posted was set at ISO 800 for 90 seconds, 40 lights & 20 darks unguided using a 200P, NEQ6 & modded 1000D, no light pollution filter was used.

I just had a thought, the darks were taken with my unmodded 1000D so maybe I need to take some with the modded one? Unless it's something else of course, any help would be appreciated.

[tich]

I've cropped a part of the image to show the strange artefact I'm talking about in case it's not sowing up to well.

[Chris]

I get a lot of these streaks with DSLR imaging, generally the older the sensor the more hot pixels that appear during a long exposure, then when you stack a load of these long exposures they form a streak due to even a small amount of tracking error which adds up over the imaging run. I've seen much worse examples than this from my previous images and I get round it by using the eraser tool in post processing which if you rub over the streak will replace that area with an un-effected area close by. I usually zoom right in on the image so I can be quite accurate. Olly P mentioned a much less labour intensive way around this issue a while ago but I can't remember what it was. Even fairly new cameras have a few hot pixels so its not uncommon, but they do get more over time which is annoying.

I'll sign up for this thread, it will be interesting to see how other people deal with this problem

Chris

[rfdesigner]

You can remove these in IRIS (usually) with the COSME command (you make a map of the hot pixels from your darks).. you can also use the OPT command which does a correlation between the dark and the light frames to establish just how much dark to remove (takes some account of sensor temperature changes)

Neither is an out an out magic bullet but they do help.. other programs may well have similar capabilities

SD

[Helen]

There's a hot and cold pixel removal bit in DSS, under cosmetics. Don't know if that will help! Your darks do need to come from the same camera as the lights though.

Otherwise, its a very nice Dumbell :-)

Helen

[ollypenrice]

Yes, darks are specific to one camera at one temperature. You can't swap darks from one camera to another, they record the defects of a particular chip. That's their point.

In Photoshop you can always use the Colour Select tool to pick particular colours. Then use the Median filter to reset the pixels of that colour to the value of their neighbours. If you do this to a copy layer you can erase the copy layer everywhere except where the process has worked perfectly, so if it has messed up the Dumbbell you would erase the messed up part.

Olly

[Superdavo]

Couldn't you use Photoshop's healing brush to get rid of it? I'm not sure why it's there though

[tich]

Thanks for the replies & your help everyone, I'm not very proficient at using photoshop as yet but slowly learning & getting there. I was out again last night so I fired off some darks using the modded DSLR & some more lights on the dumbbell & ring nebula so I'm in the process of stacking them as I type, I will post results when I've finished processing them.

[tich]

Using the darks from the same DSLR has done the trick so lesson learnt. I fired off some more lights & darks when I was out last night & added them to my previous subs making this image which is up to 3hrs 9 mins of data. I'm using a newt to image plus it's unguided so its not perfect but I'm getting there slowly.

Again thanks for your help everyone.

[Aenima]

Happy to see you got rid of those streaks. Also pleased that my first guess ended up being right 0.0 (Doesnt happen too often, but great stuff all round)

Aenima

[russellhq]

Did you still get the streaks when you stacked with no darks? Might have been something in the darks from the other camera that caused it.

[SnakeyJ]

Great result on that second attempt - viva la cure. Good post and very interesting read

[tich]

Did you still get the streaks when you stacked with no darks? Might have been something in the darks from the other camera that caused it.

I never tried stacking without any darks, but I know when I stacked the lights & darks using the unmodded DSLR & it turned out fine.

[Stargazer33]

Very nice capture tich!

I hope to be trying this one any night now, if I can cure my mount tracking problems!

[jaspalchadha]

30min capture