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What should I expect from a single narrow-band frame?

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#1 Fukinagashi

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Posted 25 May 2018 - 07:39 AM

I've just started to play with a new brand Chroma 3nm Ha filter and a QHY163M camera.

Waiting for gases to come up, yesterday night I got the Iris nebula rising at NNE just to see what I can get from this setup.

This is a single (unstacked, uncalibrated) stretched (non-linear) frame with Exp=1200s, Gain=180, Offset=60 taken with an old Celestron 8 (orange tube).

Now to my surprise I see nothing but a small nebulosity around the HD20775 star and a lot of noise!

I know I have to take a lot of images to get enough signal but I was expecting something more...

What I'm doing wrong?

 

Attached Thumbnails

  • NGC7023-1-1200s-6-CFW0.jpg


#2 RMannix57

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Posted 25 May 2018 - 07:56 AM

This is a reflection nebula, just a huge dust cloud. Not a good target for Ha. NGC 281 or NGC 7380 are nearby and a better test for Ha


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#3 Jeff2011

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Posted 25 May 2018 - 08:30 AM

This is a reflection nebula, just a huge dust cloud. Not a good target for Ha. NGC 281 or NGC 7380 are nearby and a better test for Ha

+1

 

Also you don't have to expose that long for a CMOS camera.   You just need to take more exposures.  You may have to bump up of the gain for narrowband but you will need to find the optimum settings for your imaging system.  An Ha rich target will show a lot of detail even with a much shorter exposure.  Not sure how M8 fits in your field of view but that is a good one to start with.


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#4 bobzeq25

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Posted 25 May 2018 - 09:06 AM

As others have said, wrong target.  But, if you look at others work, be sure to remember you're using a very slow F10.  Mostly Ha involves faster telescopes.  Bumping the gain will compensate, at least to some degree.  While you may be able to shoot shorter subframes, you'll need more total imaging time.

 

Most people doing Ha would use a reducer on that scope.


Edited by bobzeq25, 25 May 2018 - 09:07 AM.

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#5 Fukinagashi

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Posted 25 May 2018 - 09:17 AM

As others have said, wrong target.  But, if you look at others work, be sure to remember you're using a very slow F10.  Mostly Ha involves faster telescopes.  Bumping the gain will compensate, at least to some degree.  While you may be able to shoot shorter subframes, you'll need more total imaging time.

 

Most people doing Ha would use a reducer on that scope.

Sorry I forgot to say that I worked at F6.3


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#6 spokeshave

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Posted 25 May 2018 - 11:15 AM

While it is true that there isn't a lot of Ha in the Iris, there is some, and you captured it. If you do go after this target seriously, added Ha really makes it pop.

 

Tim


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#7 Goofi

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Posted 25 May 2018 - 06:59 PM

As others have said - wrong target. Fortunately, you've got some decent choices available.

 

M97 (Owl Nebula) and NGC 6543 (Cats Eye Nebula) both have Ha lines, are decently positioned and reasonably bright. Plus, they'll work with your field of view. M97 will be in the north past the meridian, setting .. so maybe the Cats Eye is a better choice.


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#8 Fukinagashi

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Posted 25 May 2018 - 07:08 PM

First of all thanks for suggestions. I tried the wizard (NGC7380) and here is the result of a single (non calibrated) frame Exp=600s, Gain=180, Offset=60.

Seems to me very nice! Can't wait for some more integration... waytogo.gif

 

 

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  • NGC7380-1-600s-1-CFW0.jpg


#9 Fukinagashi

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Posted 25 May 2018 - 07:16 PM

...more in general: is there any catalog around showing the average HII, OIII and SII content of each object?



#10 Goofi

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Posted 25 May 2018 - 09:26 PM

On narrowband catalog's ... yes and no.

 

No, there are no user-friendly catalog's for amateur's that I know of. But - here's the "yes" part - www.astrobin.com is an amazing resource. Browse what's being posted there and you can see how each of the filters comes through on a target.

 

 

My two cents is start with Ha ... lots and lots of Ha targets out there. Do Oiii on those targets with decent Oiii. I'd view Sii (and Nii if you go that way) as optional; Sii rarely adds much interest to targets since where there's Sii there is usually also Ha, and the Ha is much stronger.


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