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Stretched sub

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#1 Jack160219

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Posted 28 July 2021 - 04:18 PM

I was out and imaged m101 with my asi 1600 mc pro. At 180 secs . My stretched subs barely showed the arms of the spiral. So ,not going by the histogram,shouldn’t you be able to see the galaxy arms clearly on the subs? Do color cams require a lot more exposure? I’m wondering if it’s even worthwhile during the fires out west. Jack



#2 TelescopeGreg

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Posted 28 July 2021 - 04:34 PM

If you were using the f/10 SCT, 3 minutes may not be not long enough.  What was the ADU of the background, and what sort of Bortle zone were you in?

 

I imaged M101 at f/7 using 5 minute exposures with my ASI2600MC, and the arms were clearly visible.  That said, I also imaged the Fireworks Galaxy for this month's Challenge, and the entire galaxy was pretty much invisible in the individual subs.  But stacking 3+ hours of them resulted in a surprisingly good image.

 

Have you stacked a bunch of them to see what our miraculous software can do with it?


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#3 EasyQuest

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Posted 28 July 2021 - 04:35 PM

Given what you have provided, I am assume you are going no filter or at least simple light pollution filter and you are using your SCT at native focal length or reduced 6.3?

 

Either or, it is going to be difficult for 180 sec subs at f/10 or f/6.3 as the camera is 1/4 Red 1/2 Green and 1/4 Blue. You can try 300s, your mount is more than enough for that scope. I do not know how many subs you are stacking before stretching. I think the moon is rising as well but you are facing the other way.

 

On top of that fire to the west in the same general direction of the object makes this project a tall order to complete.



#4 idclimber

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Posted 28 July 2021 - 04:56 PM

I did some imaging on M101 last year with my 12" SCT at f/6.3 with my ASI1600mm. My RGB filters exposures were at 120" at a gain of 76. I concur with the others the if you are shooting f/10 you will need more time. 

 

Better though would be to install a reducer. This will also flatten and correct the field so your stars also look nice. 

 

I revisited this target this spring with much better success. This with a better f/7 reducer from Starizona and the 2600mm camera. The results are over in my Astobin account in my sig. There I shot 5 minute exposures and I also can see the arms clearly in my individual subs. 




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