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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 26 Feb 2012 (Sunday) 14:12
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Rosette and Orion widefied

 
huangyu84
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Feb 26, 2012 14:12 |  #1

I managed to get H-alpha imaging done by Astrotrac tracking mount. Canon T3 self modified plus a nikon 180 ED lens.

Orion widefiled

IMAGE: http://farm8.staticflickr.com/7193/6786321784_92166718f5_b.jpg

Rosette
IMAGE: http://farm8.staticflickr.com/7037/6932495221_d63f34a766_b.jpg



  
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butcherman
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Feb 26, 2012 14:16 |  #2

Nice shots! I need to get a tracking mount.


Canon 7D, Canon 50mm F1.8 STM, Canon EF-S 55-250mm f/4-5.6 IS STM, Sigma 17-50mm f/2.8 OS HSM , Yongnuo YN560 IV

  
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troypiggo
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Feb 26, 2012 15:27 |  #3

Both are fantastic. Great fields of view.


"Interesting. You're afraid of insects and women. Ladybugs must render you catatonic." - Sheldon
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Toxic ­ Coolaid
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Feb 26, 2012 15:50 |  #4

Very nice! Can you put up some info on your exposure settings? I've had little success trying widefields due to the LP here. Yours are wonderful.




  
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huangyu84
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Feb 26, 2012 16:33 |  #5

thanks for the comments.

I was imaging from a red zone (light pollution). That's why I went to the narrowband imaging route. I usually take 2min subs but I change the ISO setting to adjust the histogram such that it is located below 1/3. For Orion wide filed, I put 1 hour for H-alpha (12nm astronomik H-alpha clip in filter) and 3 hours for RGB (astronomik CLS-CCD clip in filter). The final image is a composition of HaGB. For Rosette, only two hours of integration of H-alpha was attempted.

IMHO, the key to battle light pollution is significantly longer integration time to improve S/N ratio.I have been struggling with light pollution before, and found using a faster optics and light pollution filter can save you much of integration time.




  
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troypiggo
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Feb 26, 2012 18:57 |  #6

I've often wondered about S/N ratio and light pollution. I have a friend that reckons he got better results with his 10" reflector than ED80 from the suburbs.

Personally, I can't understand how it can be better. The 10" of course has a bigger aperture than ED80, so I understand that it has better light gathering capability, better resolution etc. But that must just mean it's sucking in more light pollution as well as deep sky stuff. If the LP pollution is at a level that it drowns out, say, a faint galaxy, it's going to do that no matter what aperture. If the brightness of the object is above the LP threshold (for want of a better term), then the 10" will be better. But as the brightness approaches the brightness of the LP, and if it falls below the LP brightness, it'll just get drowned out.

I know more subs gives better S/N. But LP isn't random noise per se. It will become part of the signal. So it just hangs around in all subs.

Can anyone convince me otherwise?


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huangyu84
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Feb 26, 2012 19:22 |  #7

troypiggo wrote in post #13971820 (external link)
I've often wondered about S/N ratio and light pollution. I have a friend that reckons he got better results with his 10" reflector than ED80 from the suburbs.

Personally, I can't understand how it can be better. The 10" of course has a bigger aperture than ED80, so I understand that it has better light gathering capability, better resolution etc. But that must just mean it's sucking in more light pollution as well as deep sky stuff. If the LP pollution is at a level that it drowns out, say, a faint galaxy, it's going to do that no matter what aperture. If the brightness of the object is above the LP threshold (for want of a better term), then the 10" will be better. But as the brightness approaches the brightness of the LP, and if it falls below the LP brightness, it'll just get drowned out.

I know more subs gives better S/N. But LP isn't random noise per se. It will become part of the signal. So it just hangs around in all subs.

Can anyone convince me otherwise?

You are right, LP is part of the signal that we do not need. However, there is also a shot noise introduced by LP. Actually, we stack because we want to minimize the noise introduced by LP. If the LP is ideal without shot noise. We can easily remove it by adjusting curves in post-processing, then the DSO will pop up nicely. Believe or not, theoretically you can image any DSO during daytime given sufficient long integration time.




  
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troypiggo
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Feb 26, 2012 20:39 |  #8

I suspect what you're talking about is if the DSO brightness is just above the background LP. If it's just a teeny tiny bit brighter, then when we stretch the histogram to separate the signal we want (DSO) and the signal we don't want (LP), we may also be working around the same signal strength as any residual random noise, so the image will look noisier. More subs, stronger S/N ratio, might get rid of that residual random noise.

I can explain that. Still can't see how a DSO that is less bright than the LP can come through no matter how many subs.

Re your comment about daytime astronomy - coincidentally read this morning an observing report on the Stellarvue group about viewing Jupiter and even Ganymede in the daytime. Bands visible and everything. Just really hard to locate. But that's a very bright, point light source, much brighter than the background light. We're talking about very faint objects (galaxies, nebulae) that aren't as bright as the background light.

Anyway, sorry to get OT.


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huangyu84
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Feb 26, 2012 21:07 |  #9

troypiggo wrote in post #13972527 (external link)
I suspect what you're talking about is if the DSO brightness is just above the background LP. If it's just a teeny tiny bit brighter, then when we stretch the histogram to separate the signal we want (DSO) and the signal we don't want (LP), we may also be working around the same signal strength as any residual random noise, so the image will look noisier. More subs, stronger S/N ratio, might get rid of that residual random noise.

I can explain that. Still can't see how a DSO that is less bright than the LP can come through no matter how many subs.

Re your comment about daytime astronomy - coincidentally read this morning an observing report on the Stellarvue group about viewing Jupiter and even Ganymede in the daytime. Bands visible and everything. Just really hard to locate. But that's a very bright, point light source, much brighter than the background light. We're talking about very faint objects (galaxies, nebulae) that aren't as bright as the background light.

Anyway, sorry to get OT.

I understand what you said. I think the signal of the final image is the sum of DSO plus LP. For example, we receive 1000 photons/sec from LP and 1 photon/sec from DSO at one pixel in our camera chip. Both light source are noise free. And another pixel only receive 1000 photos/sec from LP. Even though the difference is only 0.1% between two pixel, after clipping out the LP part in post-processing, the DSO will come out nicely. The DSO will no get drown by the LP, the signal coming from DSO is counted by the camera chip once the photo hits it. And this part of signal is always there and will not get washed out.

No matter how heavy the LP is, should the signal of DSO always add on to the LP part? Once the shot noise is minimized, the base part of LP can be clipped out (assuming no other types of noise such as dark noise, read-out nosie).




  
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ady.space
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Feb 27, 2012 07:09 |  #10

very nice images, i own a astrotrac as well great piece of kit. keep them coming ;)


canon d6,canon d1000(modded) canon 200mm f/2.8,canon 20mm f/2.8, canon 50mm f/1.8 samyang 14mm f/2.8, carl ziess 35mm f/2.4

  
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Harm
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Feb 28, 2012 12:54 |  #11

bw!


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victorelessar
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Feb 28, 2012 19:03 |  #12

wonderful shots


Canon EOS 1100D | Canon EF-S 18-55mm | Helios 50mm 1:2 | sigma DL 70-300mm

  
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ramv
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Mar 03, 2012 01:43 |  #13

Beautiful!




  
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Rosette and Orion widefied
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