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Astrophotography

Posted: 18 Apr 2017 02:35
by pzampella
Bambusman, After some background substraction this is what I got:
► Show Spoiler


I still need a lot of works (and more images to stack).

Astrophotography

Posted: 18 Apr 2017 09:24
by BambusDude
pzampella wrote:
Bambusman, After some background substraction this is what I got:
► Show Spoiler


I still need a lot of works (and more images to stack).

this looks pretty good already!

did you edit a tiff or jpg file, also whats the original resolution of this image?

Astrophotography

Posted: 19 Apr 2017 13:08
by A-L-E-X
Watsisname wrote:
Midtskogen's trick is pretty simple and powerful with a good choice of blur size.  Another technique you could try is to characterize the light pollution and remove it by subtraction or difference modes in an image editor.  Here's a quick summary of how I do it using GIMP: 

1) Open the image

2) Choose the "color picker tool", with the settings "sample average" over a large area (a good portion of the image area), and "set to foreground color".  Then click on the image over an area that is relatively empty of galaxies/nebulae/stars (mostly background noise).  The idea is that you're detecting the average color of just the light pollution in the image, which in a deep sky image should be pretty uniform.

3) Create a new layer filled with this foreground color.  Set the layer mode to "difference", and then slide the opacity until it best cancels out the light pollution.  I find this is usually around 50%.

This is what I get using this method + a bit of curves adjustment on your ISO800 image.  Scaled up 200% to see effects a bit better:

► Show Spoiler


This is a really nice capture by the way.  After the little bit of processing you can even see the star formation regions!


As for the question of ISO vs. exposure time, always go with the lowest ISO / longest exposure time combination that you can manage while obtaining a neutrally exposed image.  Higher ISO can achieve a neutrally exposed image more quickly, but it will be more noisy.

The theory is that you want to maximize the signal to noise ratio (S/N), which represents how much of the light being recorded is actually from the object you want to image, vs. noise from random fluctuations. S/N increases as the square root of the exposure time.  Raising the ISO itself does not do anything for S/N -- it's just acting as an amplifier of both signal and noise by binning pixels together.  But with higher ISO and shorter exposure time, you'll get a noisier image.

Other ways to improve S/N are to stack several images together, which acts to average out the noise.

Indeed.  My experience is that at higher ISO the colors wash out (limited dynamic range at higher ISO?)  Light pollution also seems much more pronounced at higher ISO, regardless of the exposure time.  ISO 1600 is about the limit if you want to be able to see subtle star and nebula colors, but realistically, I've found it's better to push exposure times longer (as long as star streaks aren't apparent) and keep the ISO to 400-800.

Astrophotography

Posted: 19 Apr 2017 16:28
by pzampella
Bambusman wrote:
Source of the post did you edit a tiff or jpg file, also whats the original resolution of this image?

I stacked RAW files into a TIFF file, and that TIFF file was the one that I processed.

A-L-E-X wrote:
Source of the post I've found it's better to push exposure times longer (as long as star streaks aren't apparent) and keep the ISO to 400-800.


Then I'll keep it on ISO 800. Thanks!

Astrophotography

Posted: 19 Apr 2017 16:54
by A-L-E-X
What camera are you using?

Astrophotography

Posted: 20 Apr 2017 15:43
by pzampella
A-L-E-X wrote:
Source of the post What camera are you using?

Canon EOS Rebel T5 (1200D).

Astrophotography

Posted: 22 Apr 2017 06:04
by A-L-E-X
Look up the best settings on sensorgen.org, they have the "sweet spots" for various combo, look for DR > 10 stops to maintain star colors.

Astrophotography

Posted: 02 May 2017 07:20
by pzampella
Well, after 4 hours of multiple sessions with different expositions (51x30s, 39x90s, 62x90s and 20x240s, each one at ISO800), this is the final result:
► Show Spoiler


I don't think it's possible to make any more improvement without a better and darker sky. Any thoughts?

Astrophotography

Posted: 02 May 2017 08:36
by Mosfet
You sacrificed a bit of background data with weaker structures for a darker sky, and by doing so you exalted spiral structures.

I'd wish I could make something like that!

Astrophotography

Posted: 03 May 2017 00:34
by pzampella
Mosfet wrote:
Source of the post I'd wish I could make something like that!

Mosfet, is not that hard! I was just following midtskogen idea of background removal. To achieve that using PixInsight I just had to create a mask to protect brightest stars and galaxies, and then I streched the image with the Histogram Transformation Tool. This could also be done using Photoshop, for example.

Astrophotography

Posted: 03 May 2017 09:21
by HarbingerDawn
Some recent shots of mine

Jupiter on 9 April 2017 - Enlarged by 3x for ease of viewing
Image

Venus 7 hours ago ;) - Enlarged by 2x for ease of viewing
Image

Astrophotography

Posted: 03 May 2017 10:22
by ZackG
Here's my pic. Unfortunately this was taken with a very old DSLR camera. Only 6 MP

Astrophotography

Posted: 03 May 2017 11:25
by DoctorOfSpace
Awesome pictures HarbingerDawn and ZackG

It's not the megapixels in your camera that count, but how you use them.

Astrophotography

Posted: 03 May 2017 15:42
by ZackG
No, I take good care of the camera. the problem is that the CCD I think is old and maybe damaged and also the pictures are saved in a SD drive. but that picture is used with a bulb setting thanks to my intervalometer with 10 second exposure.

Astrophotography

Posted: 03 May 2017 19:01
by Watsisname
That's a nice image of the galactic center -- can clearly see the dust lanes and star clusters. :)

HarbingerDawn wrote:
Source of the post Venus 7 hours ago 

Getting bigger and bigger!