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Veil Nebula help?


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Hi! 

I'm new, and I've taken this image of the veil nebula, which, even in this photo is undeniably beautiful, but I'm not too satisfied with my capture. First of all, it has some vicious signeting. I was unsure as to how exactly I should get really good flat frames, so I've lately just been taking care of that in photoshop. All of my images are taken for 30 second exposures at ISO 800, so if anybody has a good recipe for flats at these settings, please let me know! I also was a little disappointed by the sheer graininess of this image! If you look closely, it has small pixels of weird colors, and the image is also a bit fuzzy :( I have been told that taking longer exposures would create crisper images. I would like to do this, but I do not yet have an auto guider, and I am not in any rush to spend the extra money on it for at least a couple months... I am using an Orion Atlas mount with PEC, so if I take my time getting the PEC, do you think I'd be able to produce nice 2 min subs? I should also say that most of the frames here were taken in last night's full moon (smart, I know).

This image was made on deep sky stacker from 424 frames at 30 seconds, ISO800 with 80 dark frames, & 80 bias frames.

I am using a nikon D3200 on an 8" Orion Newtonian Astrograph with a Baader MPCC Mark III and an Astronomik LPR filter. This is on an Orion Atlas mount with a SynScan goto computer.

Thanks so much for your help! :)

Veil Nebula copy.jpg

Edited by Costas Soler
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You can get rid of the funny pixels by using sigma-clipping and by moving the camera a bit between frames. Some mounts can do this for you. 

You've got 3.5 hours of light there, that seems like a pretty grainy image for such a long exposure time. I might advise against dark frames, since the temperature of the sensor is always changing. Also, I have that same camera and can honestly say that running it for more than a few minutes produces horrific results (See the image below, 10 minute exposure in a room I could hardly see in. It might look fine, but download it and zoom in...)

13116317_1031047403645167_44213942338321

And then there's the 30 minute image I took with the lens cap on... I didn't even edit it.

13131641_1031047406978500_45300356796218

The solution here isn't necessarily to replace the camera, but replace your expectations of what a £200 standard-use camera body can do :)

I get the problem you have in the top of your image all the time... It's infuriating and I can never figure out how to fix it.

 

    ~pip

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That's a nice veil you caught on camera; very nicely framed and with round stars.

As for imaging/processing;

You do need to take flats, but they don't have to be at 30 seconds or even ISO 800. The easiest (not necessarily best) way is to point your scope /lens at an evenly lit, neutral colour surface. Take exposures such that the histogram peak in the camera is somewhat left of the middle. As the flats are much brighter than your bias and darks, you won't have to take so many of them.

The best way to get rid of noise is to use longer exposure times. If you have a stronger signal, you don't need to stretch the image as hard. This will help keep the noise down.

As Pip already mentioned, dithering (= moving the camera between exposures, some 12 pixels) will break up the pattern left by hot pixels. For the images already taken, you can play around with cosmetic correction (hot pixel filter) settings in your stacking program.

With your setup, balanced and polar aligned, you should be able to do 2 minute exposures unguided. You may lose a few subs, but the longer exposure time will make up for that.

Good luck,

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From my attempt on the Veil, I found 30secs @ ISO1600 (450D) wasn't really long enough exposure and needed a mighty stretch, although I only had 15mins total exposure.

I plan a serious second assault using 60 seconds at ISO1600

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Yeh green speckles is why I bought a CCD, you can do a lot to process them out but it is a real pain and requires a lot of data.

Flats will help, darks not so much.

 

I take it the camera isn't modded?  The Ha isn't coming through so well but the OIII areas look good.

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Hi. I found that the speckling can be removed by dithering and losing the dark frames. That was with a modified Canon but It may be worth a go on your Nikon too as I think the sensors are similar. I think that if you took the red curve up a little, you'd have a great shot. 

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Here's my routine for taking subs.

 

1. Get the scope setup, pointed, focus, guiding etc.

2. Take the set of light frames. You appear to have this part down pat :)

3. put the lens cap on, and then cover the scope with a bag.  Now take a set of dark frames.  These will be the same exposure time as for your light frames.  1 dark frame for every so many light frames (I normally do 1 dark for 5 light frames).

4. Next, point the scope at a target that is evenly illuminated.  The cheapest way of doing this is get a white t-shirt, and drape it over the end of the scope.  Then shine a powerful torch at the T-shirt, you should see an even white surface though the camera view finder.   On your camera settings, put it into Ap mode, let the camera work out the exposure time and take a set of frames - those will be your lights.

5. Change your camera to manual and put the shutter speed to the fastest exposure that you can.  Take a set of those frames.   These are your flat bias frames.

 

When you download your images from your camera, you'll have easily identifiable sets of images - lights, darks, flat, flat bias   in that order. you'll be able to tell easily where one group stops and the next starts, so there's no mistaking them ;-)

you don't need to worry about dark bias frames, as they're already built into the dark frames.

 

When you process, subtract the bias frames from the flats first, you'll ended up with "corrected flats" (not an official name, I'm using that to help keep things clear)

Next, process your lights using DSS, or whatever program you use.   At this point you only need to supply the lights, darks and corrected flats.

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8 hours ago, cjdawson said:

3. put the lens cap on, and then cover the scope with a bag.  Now take a set of dark frames.  These will be the same exposure time as for your light frames.  1 dark frame for every so many light frames (I normally do 1 dark for 5 light frames).

Hi. An excellent plain English description of what took me yonks to get to grips with when I started. I've a little more experience and would now not recommend this step. I find it introduces more noise; especially brighter coloured pixels. I'd recommend using the time to take more light frames instead. The theory includes stuff about the impossibility of matching the sensor temperature, the mysterioysly named dark current and a myriad of other reasons which are as hotly disputed by some as the pixels themselves. Summary from this newbie: take more snaps under the stars. Add flat and bias frames. Repeat with even more snaps. Just my 0.02 Euros. Clear skies.

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10 hours ago, Astrosurf said:

Nice image. Ditto the above. Have you thought about drift alignment? I've not done it but I hear that it can be done quite quickly once you've got used to it. It'll increase your exposure times. See here:

http://www.cloudynights.com/page/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760

Alexxx

I actually find drift alignment easier that using the polar scope as I live at a high latitude viewing the polar scope requires you to be a contortionist.

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Thank you very much, I have kind of devised my own method of dithering. What I'll do is rotate the camera in the focuser every 10-20 images, and continue to do this. First, it reduces-eliminates hot pixels. Second, it eliminates that weird bright portion caused by my dslr. Also, I am very glad you enjoyed the image. Thanks! 

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