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mismatched star sizes in LRGB sub-frames

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#1 astrojjj

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Posted 04 August 2014 - 06:50 PM

I am new to LRGB imaging, and now get stuck on the mismatched star sizes in different filter frames. When synthesis RGB color, the stars look weird.

 

Any way to match the star sizes?

 

JJ



#2 blueman

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Posted 05 August 2014 - 06:42 PM

I am new to LRGB imaging, and now get stuck on the mismatched star sizes in different filter frames. When synthesis RGB color, the stars look weird.

 

Any way to match the star sizes?

 

JJ

Well the conditions can cause the difference in the star size in the three colors. But of course so can focus.

Yes, you can shrink the stars in the masters that are too big in Photoshop so they match the smaller ones. If you take the smallest size stars as your guide you can use a "Make Stars Smaller" Action via "Annie's Actions" or other action sets available. Or you can use the select color range to pick out the stars in the frame and then the "Minimum" Command can be used too.

This is not something that is not totally easy to explain in a few words.

Not knowing what programs you have to do processing makes it very hard to give advice.

Blueman


Edited by blueman, 05 August 2014 - 06:43 PM.


#3 andysea

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Posted 06 August 2014 - 12:06 AM

Most likely  a focus issue. 

What optics and filters are you using?



#4 astrojjj

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Posted 06 August 2014 - 04:22 PM

Thanks for your advice, blueman.

 

Andy, I use Celestron EdgeHD 800 plus the 0.7x focal reduce, and filters are LRGB.

 

JJ



#5 andysea

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Posted 07 August 2014 - 10:13 AM

Ok

Reason I asked is that with faster optics the critical focus zone gets really tiny. 
I use Astrodon LRGB which are parfocal, perhaps that brand that you use are not perfectly parfocal?



#6 blueman

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Posted 07 August 2014 - 04:26 PM

Do you focus for each filter? If not, then you should. I focus every hour, just so that it stays focused as temps drop. I do this by taking 1 hour of subs of one filter, then change filters and have the autofocus focus on each filter change.

Blueman








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