Author Topic: HDR composition  (Read 249 times)

Offline polare70

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HDR composition
« on: 2019 May 11 14:18:09 »
Hello everyone !
I have two masters with the same optical tube and the same CCD ... a 180 '' other 300 'master master' to easily combine HDR composition (as with photo settings well)!?
Thanks for your answers!

clear skies at all;)
https://www.flickr.com/photos/126536798@N07/

-Gemini G53F
-Ritchey-Chrétien Astrograph 10'' Apo triplet T.Sky 130/900-EDT 80/480
-Starlight Lodestar
- Moravian G2-4000,Atik 414EX

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Re: HDR composition
« Reply #1 on: 2019 May 11 17:31:36 »
HDRComposition is not likely to be necessary for this type of image, unless some of the stars are saturated in the 300" master...

if there's no saturation you can probably just combine all the subs with ImageIntegration.

rob

Offline polare70

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Re: HDR composition
« Reply #2 on: 2019 May 12 06:13:50 »
Thanks for the reply!
Then I can also use Master 60 '' and 120 '' or 180''  together with 300 'all with ImageIntegration
clear skies at all;)
https://www.flickr.com/photos/126536798@N07/

-Gemini G53F
-Ritchey-Chrétien Astrograph 10'' Apo triplet T.Sky 130/900-EDT 80/480
-Starlight Lodestar
- Moravian G2-4000,Atik 414EX

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Re: HDR composition
« Reply #3 on: 2019 May 12 20:55:03 »
there's no reason why you can't do that... but i think you should analyze the masters first to see if there are saturated stars in the 300" master. if not, integrating everything together is fine. if there are saturated stars in the 300" master, then the HDRComposition tool would be useful. you need to pay attention to the masks it outputs to see if any data has actually been substituted from the shorter exposures into the final product.

rob

Offline ngc1535

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Re: HDR composition
« Reply #4 on: 2019 May 12 22:25:57 »
HI Polare70,

As you might be aware this is both the technique I employed *and* the object I worked on recently.
(See the M5 APOD https://apod.nasa.gov/apod/ap190509.html by me from a few days ago)
Another good (I think even better example) of M15 is shown below.

Typically as stars near saturation they tend to lose their nice PSFs (this is especially true for ABG cameras where they become non-linear near the top end).
This becomes an issue when (perhaps) later applying HDRMT on the final combined image after HDRComposition.

So even if stars are not entirely saturated, HDRComposition can still be nice. Just specify a threshold considerably beneath the actual saturation value.
One of the keys is to have really short exposures, for the short data set, since you are just taking care of the absolute brightest offenders in the image- especially in the core of the cluster.
The 60 second exposure is OK...but I suspect even half of that might even be good- but it depends on what values you are getting for the stars (which depends on the camera, filter, telescope...etc etc).

One quick tip if you go down this road is to deconvolve the two images (the combined long and combined short) *before* doing HDRComposition. Trying to do deconvolution on an HDRComposition result is really asking for problems.

-adam




Offline polare70

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Re: HDR composition
« Reply #5 on: 2019 May 15 04:49:12 »
Beautiful photo of M5-congratulations! I thank you again for your intervention on my question.
We hope for clear nights to proceed with new files to integrate and try the procedure :)

  ...Zlatko
clear skies at all;)
https://www.flickr.com/photos/126536798@N07/

-Gemini G53F
-Ritchey-Chrétien Astrograph 10'' Apo triplet T.Sky 130/900-EDT 80/480
-Starlight Lodestar
- Moravian G2-4000,Atik 414EX