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Is it worth combining subs from two very different focal lengths?

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#1 DaveB

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Posted 18 September 2020 - 09:28 PM

I started imaging M33 with my 80mm refractor (FL=480mm) but later realized that it could fit into the FOV of my longer scope (FL=1333). The camera is the same in both cases, and it is a mono camera with LRGB subs in both cases.

 

Does it make any sense to combine both sets of subs? Perhaps just the color filters from the short refractor? I'd like to get some sense before processing the image.

 

Thanks

 



#2 terry59

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Posted 19 September 2020 - 07:24 AM

You will need to rescale the image from the smaller scope. The only way to know what that will make the data look like is to try it

 

shrug.gif

 

Off your topic a bit...right now I am struggling with combining CCD and CMOS data



#3 RJF-Astro

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Posted 19 September 2020 - 07:27 AM

Hi Dave, yes this can be done and I think it is worthwhile when you use RGB made by the 480 and L made by the 1333. Color data does not need to be very high res. I even blur the color channels somethimes in Photoshop before applying the luminance layer. Works great.


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#4 DaveB

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Posted 19 September 2020 - 09:07 AM

Thanks, I'll give it a whirl. I have 6 hours of L data and 2 hours each of R/G/B on both scopes, so for starters, I'll be creating two separate images. I can't imagine the L data from the small refractor being useful on the longer scope, but I'll use the R/G/B data. Should I create stacked frames from each and then combine the stacked frames, or does it make more sense to combine the subs from both scopes together?



#5 RJF-Astro

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Posted 19 September 2020 - 01:00 PM

Ah, you have RGB from both scopes. I do not know if you can combine those subs. Stacking requires specific calibration frames, and I do not know if stacking software will combine different scales.

Maybe there is someone with experience who can chime in. If not, I would stack both and pick the one that looks best in terms of noise, star color and color quality.

#6 Lead_Weight

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Posted 19 September 2020 - 03:31 PM

Astro Pixel Processor will do this out of the box, but one of your images will get resampled larger, or smaller as someone mentioned above. I’ve actually done this. I wasn’t super impressed with the results, as color in one image wasn’t that great, and it did show.

 

get.jpg?insecure

 

If you look through my other images, you’ll find the originals. One was shot mono at 514mm focal length, the other was at 1980mm with an OSC.



#7 Lead_Weight

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Posted 19 September 2020 - 03:43 PM

I forgot to mention, unless you crop the image to the smaller of the two, there will be an obvious change in the noise pattern.

#8 vnc1218

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Posted 20 September 2020 - 09:32 AM

You can use the GradientMergeMosaic process in Pixinsight, after registering the images to each other (with thin plate splines/distortion correction).


Edited by vnc1218, 20 September 2020 - 09:33 AM.



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