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txairman
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Reged: 04/18/11

Comet PANSTARRS imaging - learn from my mistakes
      #5732446 - 03/14/13 03:42 PM

Here's my attempt to catch this elusive comet.

Good things:
- Went far away from the air and light pollution to the dry desert area with good transparency (11 hours drive)
- Climbed higher from the low atmospheric level (4000 ft)
- Found a place with pretty looking western horizon line

Now the bad thing:
The camera was setup for night long exposure imaging:
High ISO NR: OFF
Long Exposure NR: OFF
ISO: 1600 (!)

Is there any way to get rid of that noise in post processing? Thanks!



Edited by txairman (03/14/13 05:13 PM)


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Jared
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Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: txairman]
      #5732460 - 03/14/13 03:51 PM

Yes--if you can figure out what the temperature was at the time you took the image, get the camera to the same temperature, then take a dark frame and subtract it out.

Alternately, you could try putting the camera in the refrigerator, taking it out every couple of minutes and taking a dark frame, then using trial-and-error to see which dark frame matches the image best (noise reduction without creating "black spots" in your image--an indication of over-subtraction).

You can do the dark subtraction in Photoshop--don't need special astro-imaging software.


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txairman
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Reged: 04/18/11

Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: Jared]
      #5732536 - 03/14/13 04:37 PM

Jared,

Thank you for the great advice. I took darks later that night during deep sky imaging but the temperature changed so I'll have to try the trick with fridge.

I simply could have used lowest ISO since it was on tracking mount anyways.

Generally, what is the best settings for such kind of images? Long Exposure Noise reduction ON or OFF? The exposure was 1/4 s. Is dark frame subtraction equivalent to in camera NR? Which one is better or they are complementary?


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Kokatha man
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Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: txairman]
      #5732832 - 03/14/13 07:48 PM

Very nice with the crescent Moon "sitting" on those rocky outcrops..!

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Dave440
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Reged: 11/19/05

Loc: So. FL
Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: txairman]
      #5735134 - 03/15/13 10:23 PM Attachment (18 downloads)

It was definitely worth the drive. Great shot!

Cleaned it up a bit for you with Neat Image.
Loses a bit of detail whenever you remove noise but not much. It wasn't that bad to begin with. Have you seen my comet pics at ISO 200 using a superzoom digtal camera? Looks like its being viewed with a rabbit ears antenna from back in the day...LOL!!!


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txairman
member


Reged: 04/18/11

Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: Dave440]
      #5735455 - 03/16/13 02:18 AM

Thanks, Dave! It really looks clean now. I tried to subtract dark that was taken at close temperature (within 5 degrees) but it did not have any effect. I may not doing it right, but being a noob in AP I need to read up on that.

I looked at your image, it's great, especially considering P&S camera. I like the "rabbit ears" analogy.


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AstroTripper
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Reged: 01/16/13

Loc: Central Europe
Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: txairman]
      #5735704 - 03/16/13 09:05 AM

Quote:


Generally, what is the best settings for such kind of images? Long Exposure Noise reduction ON or OFF? The exposure was 1/4 s. Is dark frame subtraction equivalent to in camera NR? Which one is better or they are complementary?




I think that normally, long exposure NR would only kick in for long exposures (what is considered "long" might differ from camera to camera I guess). So it would do nothing for your shot. From what I gather, long exposure NR = dark frame subtraction. I would leave it OFF on all occasions, and shoot my own darks just before or after shooting the subject. And I would shoot darks even for short exposures, just in case they would be needed.

Don't know what software you use for processing RAW images, but it should have an option for subtracting a dark frame, so you don't have to do it manually in Photoshop (or whatever you use). I use RawTherapee and used such functionality to eliminate hot pixels.

Anyway, I don't think dark frame subtraction would help much with your shot, as I suspect most of the noise comes from the use of high ISO.

As for what High ISO NR does, it probably depends on the camera. But I'm betting that in most cases, it will be doing software denoising. You can pretty much do the same with your RAW processing software (again, RawTherapee does have noise reduction functions, haven't used them thought). Or you can use any other denoising software you find. The results should be similar to what your camera would output.


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bilgebayModerator
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Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: AstroTripper]
      #5736794 - 03/16/13 06:10 PM

The temperature of the frame can be read with the help of EXIF Tools. I hope you were using a Canon. All Canons, starting from 450D record the sensor temperature into the EXIF Header. I have no idea if Nikon cameras do the same or not.

Nevertheless, this is a lovely frame!


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lakeorion
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Reged: 08/03/10

Loc: Lake Orion MI
Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: bilgebay]
      #5737798 - 03/17/13 12:32 AM

It's not a mistake. It's still a pretty picture.

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txairman
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Reged: 04/18/11

Re: Comet PANSTARRS imaging - learn from my mistakes new [Re: bilgebay]
      #5737867 - 03/17/13 01:16 AM

Yes, this was new Canon T3i I just bought specifically for this trip (now if I could buy the ability to proper use it as package ). You guys rock, so much good advice. Thank you!
Quote:

The temperature of the frame can be read with the help of EXIF Tools. I hope you were using a Canon. All Canons, starting from 450D record the sensor temperature into the EXIF Header. I have no idea if Nikon cameras do the same or not.

Nevertheless, this is a lovely frame!




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