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Jellyfish, Monkeyhead and M35!


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Hi

Earlier in the month I took about 50 x 360s subs of the above with the cooled Mono 550d and Takumar 200mm f4 with a Baader Ha 7nm on the front. Unfortunately the 550d has since died so won't be getting any more subs with it :( (unless I can get it fixed). Anyway, I centered on the star 6Gem which I decided gave me a nice composition. Stacked 42 of the subs in DSS using Kappa Sigma algorithm. Seems to have come out ok. There is some horizontal noise in the lower background and it appears the noise was a sign of the camera failing... Hopefully, it's not too apparent. I've since been taking subs of the same target using an unmodified 550d. I've not stacked them yet but if they come out ok I might try to combine them with the Ha :) 

Image is resized to 50% of the original:

6GemJellyM36_Ha_42x360s_ps50pc.png

 

There seems to be a dark area in the middle - not sure why that is. Flats problem? Any ideas? I'll investigate when I get a minute.

Louise

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Just now, graemlourens said:

Hi Louise.

A great catch! I totally forgot about the monkey head nebula! great target.

Concerning the dark area in the middle, could be a doughnut from 'bad' flats (or no flats), but its not uniformely round, and that surprises me...

Kind regards Graem

Thanks! Maybe the dark patch is really there!? My eyes go funny when I stare at it!

Louise

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4 minutes ago, Thalestris24 said:

Thanks! Maybe the dark patch is really there!? My eyes go funny when I stare at it!

Louise

Could be, and i didnt image the area with that fov. I'd compare uncalibrated vs calibrated to see if you can see the reverse effect in the uncalibrated image (brighter in the center).

did your flats always work and you didnt change anything to your OTA setup?

Looking at other images though in the net, i can not find that kind of dark patch.

Kind regards, Graem

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1 minute ago, graemlourens said:

Could be, and i didnt image the area with that fov. I'd compare uncalibrated vs calibrated to see if you can see the reverse effect in the uncalibrated image (brighter in the center).

did your flats always work and you didnt change anything to your OTA setup?

I'll have a closer look when I get the chance. I'm pretty sure the master flat was ok with other images but I'll double check. Unfortunately, I can't take any more flats cos the camera died so I'll have to make do. Nothing changed in the setup - just camera and lens. I have some other Ha and luminance images I've yet to stack and process.

Louise

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It's great to see this in a single frame capture. Tom, guests and I did it in a multi panel mosaic early in the year. It was not, as in not, easy! I very rarely post links to other images in another person's thread but this has a direct bearing on the dark patch in the middle. I believe it's false but am standing by to be shot down!

IC443%20M35%20Monkeyhead%20HaOIIILRGB%20

Your image is great for many reasons but one of those reasons is that it shows the relative brightness of the Monkey Head and the Jellyfish. In making mosaics I thnk we are guilty of inventing those relative brightnesses!

Olly

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1 hour ago, ollypenrice said:

It's great to see this in a single frame capture. Tom, guests and I did it in a multi panel mosaic early in the year. It was not, as in not, easy! I very rarely post links to other images in another person's thread but this has a direct bearing on the dark patch in the middle. I believe it's false but am standing by to be shot down!

IC443%20M35%20Monkeyhead%20HaOIIILRGB%20

Your image is great for many reasons but one of those reasons is that it shows the relative brightness of the Monkey Head and the Jellyfish. In making mosaics I thnk we are guilty of inventing those relative brightnesses!

Olly

Thanks for the comments, Olly. Yeah, you're right! As a sanity check, I looked at similar examples from the net earlier. I think it might be a flats issue. I'll try stacking again but without the flats. Even though the lights were 360s the individual Ha raws were rather dark, especially compared to the jpegs - not sure if that has any bearing. I'll see if I can fiddle about and maybe improve on my initial attempt.

Louise

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Just now, morimarty said:

Thats a very impressive widefield image louise. you have certainly smoothed out them gradients!

Thanks! They weren't gradients as such - just a problem with the flats! There is still a problem with the second version. It needs some patient tinkering and adjustment. I'm hoping the colour version comes out ok. I'll try and stack all the subs this week. The jpegs show red haloes around the bright stars...

Louise

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1 hour ago, Thalestris24 said:

Thanks! They weren't gradients as such - just a problem with the flats! There is still a problem with the second version. It needs some patient tinkering and adjustment. I'm hoping the colour version comes out ok. I'll try and stack all the subs this week. The jpegs show red haloes around the bright stars...

Louise

Do you use photoshop? You can use a black and white adjustment layer with the red saturation dialled right down and the set the layer opacity to about 50%. That will take care of lots of colour defects like star halos. You then simply mask out the stuff you don't want affected. 

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4 hours ago, Tiny Small said:

Do you use photoshop? You can use a black and white adjustment layer with the red saturation dialled right down and the set the layer opacity to about 50%. That will take care of lots of colour defects like star halos. You then simply mask out the stuff you don't want affected. 

Hiya

I only have CS2 but do have PI :) I'll have to have a play. I'll see how the raws stack first - they may come out better than the unwhite-balanced individual jpegs indicate. Thanks for the tips :)

Louise

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Do you dark subtract your flats? I just use a master bias on all of them, but it removes the bias pedestal and stops them from over correcting.

Your reflattended version is great. To be honest I'd probably just run the Dodge tool set to a couple of % and Shadows over that left had edge with a big feathered brush.

This trio of objects are rarely captured together, which strikes me as odd because they hang together so sweetly.

Olly

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2 hours ago, ollypenrice said:

Do you dark subtract your flats? I just use a master bias on all of them, but it removes the bias pedestal and stops them from over correcting.

Your reflattended version is great. To be honest I'd probably just run the Dodge tool set to a couple of % and Shadows over that left had edge with a big feathered brush.

This trio of objects are rarely captured together, which strikes me as odd because they hang together so sweetly.

Olly

It's just flats and biases in dss, Olly. Negligible processing - levels and curves.

Louise

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6 hours ago, Thalestris24 said:

It's just flats and biases in dss, Olly. Negligible processing - levels and curves.

Louise

But does DSS know to subtract the bias from the flats? You have to put the bias in a box called Flat Dark, I think, if you want it to do so.

Olly

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2 hours ago, ollypenrice said:

But does DSS know to subtract the bias from the flats? You have to put the bias in a box called Flat Dark, I think, if you want it to do so.

Olly

Hi Olly

Hmm... DSS actually only gives 3 calibration possibilities which it considers legitimate  - all calibration frames combined (bias, dark, dark flat, flat), bias, dark and flat, or dark, dark flat and flat. So all versions appear to involve darks! Fortunately I have a set of darks as well as some dark flats so I might try re-stacking to see if I get a noticeably better result :)

Louise

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