A re-try at shooting the Rosette nebula

Miki G wrote in post #17924726

nice one

that's a really good effort
you can see the huge difference from your previous image, huh

please give all the image info ... camera, f/l, f-stop, exposure time, ISO ... tracking mount etc


Dave

What camera body are you using for this and is it modified for astrophotography?

The Rosette is a tough target if you don't have a modified camera. The Rosette glows primarily in Hydrogen alpha light. The visible light spectrum of runs from roughly 400nm through 700nm. Shorter than 400 is UV. Longer than 700 is IR.

The Hydrogen alpha (Hα) wavelength is at 656.28nm. It's in the visible light spectrum, but human eyes aren't very sensitive to it. It turns out our eyes are most sensitive to the middle of the visible spectrum (around 550nm -- which is green) and taper off as we approach the edges of the spectrum -- especially toward the red side.

Normally you'd want a camera that creates images that look like what your eye can see. But the imaging sensor is equally sensitive to all wavelengths. To correct the image so that it more closely resembles what the eye can see, the camera makers put a filter in front of the sensor to trim increasingly more light as the wavelengths get longer.

This, unfortunately, means that by the time you get to the Hα wavelength the camera is blocking about 75-80% of the light.

Here's a visual:

Much improved image Miki. You're definitely headed in the right direction. Processing data has a pretty steep learning curve and will come with practice. I would suggest you stay focused on collecting quality data and plenty of it. I've been shooting for a lot of years with both a Canon 20D and 5D (classic) right out of the box, absolutely no modification, and have had no problem resolving H-alpha nebula. The key is acquiring individual exposures that are long enough to be data rich. Once I was able to extend exposures to 3 or 4 minutes each and collect between 2 and 5 hours of total time my results improved significantly. It's common for beginners to think that stacking short exposures in the same total times as fewer longer exposures will yield the same results. Your final image is only as good as your individual frames, if the data isn't in each of them it won't be there in the final image. Stacking can't magically create or increase data. Astro specific cameras make the process easier and I'm sure are very rewarding, but at a cost. Early on it's far more important to concentrate on the fundamentals of this challenging endeavor. I find that half the fun is learning how to overcome the difficulties and see my photos improving as a result, just as you've done with your image.

Here are few of my H-alph rich targets taken with my stock DSLRs:
http://i3.photobucket.​com …ellwood2016B.jp​g~original
http://i3.photobucket.​com …sette2012x-1.jpg~original
http://i3.photobucket.​com …_ellwood2015.jp​g~original
http://i3.photobucket.​com …eb_REWORKED2.jp​g~original

Hi Guys.
Sorry for the delay in getting back to you (work commitments).
Great information on filters & required data collection. Very interesting reading.
@ Davenn: 10x90sec exposures @ f/6, ISO 2000 using a Canon 7D (unmodded) on a 80mm refractor (F/L 480mm), mounted on an Astrotrac mount. I also used a Hutech LPS filter. This increased the contrast.
I had been shooting for approx an hour, but the wind was gusting from a recent storm, so the majority of the shots were blurred from vibration. This shot is the result of the 10 sharp shots that survived.
@ Nighthound: Your shots are fantastic.

I have been trying to find some old images I have of the Rosette. These images show what filters can do and what can actually be hiding in an image that you think is no good. I can't find the data for these images but I think they were 45 or 60 seconds long, shooting with white zone light pollution terrible). I was using a SkyWatcher ED80 telescope, and my 1st Canon (a 1000D), and a Astronimik CLS clip in light pollution filter in the camera. I was amazed after I stacked 30 or so images in Deep Sky Stacker and processed it's ouput in PS. It just looked like a bluish-green sky with some stars. I have done better with my newer cameras, different scopes and a darker imaging site, but this shows what you can get from a bad location and images that don't look promising. The CLS filter made all the difference in the world for me.

IMAGE LINK: http://i347.photobucke​t.com …s/p446/mokpt/IM​G_0929.jpg

IMAGE LINK: http://i347.photobucke​t.com …t/12-6-12Rosejpeg2cna.jpg

That second image is a killer ! However the stars center the Rose are slightly leaning towards CYAN .

Oh yeah, it has some problems. Like I said, I've done better since, and I could probably improve it with processing. I just wanted to let Miki know that good data can be in images that don't look like much.

I had the same problem shooting from my light polluted backyard till I tried the CLS filter from Astronomik. Quite a difference. Toxic Coolaid, aka Mo, you do some fine work. Don't listen to Celestron...every star in my images lean toward cyan too! Just joking there Ron....

Greg

I guess I forgot to mention that the 1st pic there is how all of Lights looked in the stack. The 2nd pic is what I got after stacking and processing. The CLS was a game changer for me when shooting from home. I would often shoot new targets from home to get an idea of what to expect and make sure I would use up that rare time shooting from my dark location. Greg, I know we have similar LP and some of the same equipment. It help me appreciate your work even more. We all know Ron will tell you like it is. He even keeps the Hubble guys in line

Mo

I see Celestron's point. It's a gorgeous image ... but the stars do have a slight blue color cast to them.

I have the Lumicon Deep Sky and the Lumicon CLS. They are similar... but the CLS is a bit more aggressive than the Deep Sky. So if I don't need the CLS, I prefer the Deep Sky.

But both filters cut out chunks of the spectrum that provide color balance to the stars. Stars are basically "black body" radiation in the light spectrum meaning that the pump out full-spectrum light (not just specific wavelengths based on the gases involved). The filters tend to chop out the bits of the visible spectrum mostly associated with Mercury and Sodium lighting (traditionally these contribute the highest amount of light to light pollution -- I'm not sure how the new movement to LED lighting changes that).

The result is that it chops off much of the green part of the spectrum and leaves us with a disproportionately higher amount of blue spectrum and also a bit of red. "Red giant" stars aren't really "red"... they're yellow to yellow-orange (only carbon stars tend to appear "red"). Most stars should be "white" or close to white, with a few tending toward yellows or maybe a bit on the orange side (but very few) and also a few tending to a bit of a bluish hue -- but again... just a few should have that bluish hue, most stars should be very close to white.

Ideally I suppose you could shoot some full-spectrum images and layer those on top of the CLS images with a high opacity so that the stars with a CLS filter color cast issues don't show through.

BUT... When I did their problem when I shot the Dumbbell nebula through the Lumicon Deep Sky, I just masked the stars, and de-saturated the blues and reds (so the blues look less-blue and the reds looked less-red and more yellow-orange.).

You can always shoot more data and add to the image later if you want. Even if you don't... it's still a beautiful image.

Thanks Toxic Coolaid.
The differences between the 1st & 2nd images are amazing. I definitely need to gather more data if I'm to produce anything worthwhile. Also, I need to practice processing a lot more. In the shot I posted, I was happy to have captured a hint of nebulosity which was totally invisible to my eyes while shooting. I was unsure of which way to expose the shots i.e. shorter exposures to avoid blowing out detail or longer exposures to bring out feint detail or a mix of both. Also, I'm not too familiar with stacking images. I had Deep sky stacker installed on my computer, but was constantly getting memory errors while using it, so I uninstalled it. Is aligning and blending images and converting the result to Tiff the same as stacking images, or am I losing data doing this ( I'm using Paintshop pro x5 to process my shots)?

That's what I was trying to do, just show you what can be in there. I wasn't worried about the little finial details. As for length of images, See what you can get with your equipment without star tracking. See what length your light pollution will allow. Your histogram should have its biggest hump about 1/3 over from the left. When starting out you'll usually come out better with 30x 30sec images than 15x 60sec. You be much better off with DSS. Make sure 2x or 3x drizzel are NOT checked. Here are a few links that may help.

Here are links I refer to:
http://flintstonestarg​azing.com/?s=deepskyst​acker
step by step for DSS

http://www.myastronomy​journal.com …AIP/C002-M31-Walkthrough/
excellent walkthrough in PS

http://www.youtube.com …er_embedded&v=e​0JSTF8SGi4!
Step by step using both DSS and PS

https://photography-on-the.net …/showthread.php​?t=1241460
a right up by TC_Fenua from this forum

http://mophopix.smugmu​g.com …p#!i=2369399143​&k=BcwQ5b4
processing videos I have found and put up on my site.