Witch Head Nebula NGC1909

[rmuhlack]

My first image for the year, and my first attempt at this target.

Nikkor 200mm f4 AI prime @ f4
20 x 4min guided subs @ ISO800, modded 400D

Ambient temps of 24-28C. Some pretty severe (what I assume to be) amp glow, so this is a cropped image to remove the worst of that gradient.

hi res image available here: http://www.astrobin.com/30061/

Critique welcome :)

[Larryp]

Looks good, Richard! Particularly with a DSLR and warm temp

[swannies1983]

Nice image :thumbsup:


Why do you say amp glow? The 400D doesn't suffer from amp glow. I also have one and can confirm it doesn't. Do you have a picture before you processed it?

[rmuhlack]

Interesting. I have observed that this camera repeatedly exhibits a "build-up" of red towards the bottom right corner of the frame during long exposures, which gets worse as exposure time and/or ISO is increased. (In the case of this image this red 'glow' would be in the top left, as I have rotated the image anti-clockwise by ~90 deg). I had just assumed that this was what people referred to as "amp glow", but I guess i'm mistaken.

Will post a full frame shot when I get back home later today.

[naskies]

Nice work!



Are you sure that it wasn't nebulosity from Barnard's Loop and/or Orion? :lol: See attached screen shot from the Photopic Sky Survey (http://media.skysurvey.org/interactive360/index.html)...

[rmuhlack]

haha - maybe it was! Will have to check the full frame when I get home.

The regular red glow in the bottom right corner is real though (in my mind at least...) - i have noticed it in previous DSLR shots where the subs were longer than about 4mins - and that's throughout the year and in all parts of the sky. But you make a good point - perhaps some of that red was meant to be there and I was just overly zealous with the Pixinsight DBR tool !!

:D

[RickS]

That's a very nice image, Richard!

[rmuhlack]

okay, so now i've compared the full frame shot with naskies 'sky survey' image, and maybe i was a little hasty to call "amp glow":screwy: :rofl::D

here's one example of the red glow i was referring to - with NGC253 as the example. normally i would run DBE hard to get rid of this, so for this example i went back to the unedited stacked image and just applied a stock DBE and histogram stretch only. This was with 4 minute subs in cold weather.

[LewisM]

Yup, that'd be Orion/Barnard glow in the witch...


Nice 253.

[swannies1983]

Agree, nice 253. How many hours of data? The colour might be simply because you have overstretched the data or colour blotch. I also tended to get red colour blotch with my 400d, particularly around the edges. I found Carboni's colour blotch reduction tool do a very good job at removing it.

Do you have an example of a 4min dark file? Does it have this red region in there?

[rmuhlack]

Dan - this is a (highly stretched) single dark from the witch imaging run

btw, NGC253 was ~3.5 hours (4min subs) from last September. (and what I uploaded in the post above was not a finished image, just stretched with a first pass DBR removal only)

[swannies1983]

Nah, I wouldn't say that's amp glow as it should only be on the right edge (I think). I would need to check the darks from my 400D to see what they look like stretched.

I also have a Canon 30D which does suffer amp glow and you can see it on the right edge in an unstretched dark.

[rmuhlack]

Thanks for the clarification Dan :cheers:
Guess I just have to be careful not to overstretch

[swannies1983]

All good :). If you haven't seen it, I highly recommend you (and anyone imaging with a dslr) to have a look at Scott Rosen's website (http://www.astronomersdoitinthedark.com/index.php) to see what can be produced using a dslr camera. Scott has a very helpful video (over 2hrs) showing a workflow where he goes through step-by-step how to process an image. See link here (http://www.astronomersdoitinthedark.com/dslr_llrgb_tutorial.php). One great technique he talks about is the screen mask invert technique (thought up by Jerry Lodriguss). This enables you to bring up the faint details but limits the amount of noise introduced because you actually blur the background.

[rmuhlack]

Thanks for the link - some superb images there! Lots of ideas for some new imaging targets now :)

[naskies]

Could it be light leaking in from the viewfinder (above the LCD screen)? I normally put a piece of duct tape over it while shooting with the DSLR, as I've found that a surprising amount of nearby light (laptop screen, red torch, etc) can leak in.



Thanks for the link - looks like a treasure trove of good info.

[rmuhlack]

good tip - thanks :cheers: