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Thread started 08 Oct 2016 (Saturday) 18:29
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My winter project, Orion Molecular Cloud Complex at various focal lengths

 
pdxbenedetti
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Oct 08, 2016 18:29 |  #1

It's been a pretty tough couple weeks, work has been a heavy load and another coworker resigned which means more work onto my plate. On top of that my mom had to go in for open heart surgery 2 weeks ago and has remained in the ICU due to complications so my stress has been off the charts. I haven't done any astrophotography in over a month and missed the last 6 weeks or so of Milky Way season so my stress outlet has been cutoff as well. Luckily my mom's condition has improved enough that I felt comfortable getting away from the city for the night and doing some star shooting.

This is the first part of my big winter project, I'm going to work on imaging the Orion Molecular Cloud Complex at various focal lengths. I recently got a Rokinon 135mm f2 lens so I decided to give it a try on my Nikon D7000 last night. This is roughly 85 minutes worth of exposure, 21 exposures at 3 minutes, 2 exposures at 4.5 minutes, and 16 exposures at 1 minute, all at ISO 800 and f2.8. I'm going to try and get this up to about 4 hours worth of exposure to minimize noise, last night was a learning experience in terms of getting this lens/camera balanced a targeting this region on my Sky Watcher Star Adventurer, I was having real trouble getting decent exposures over 2 minutes without trailing so I wasted about an hour figuring that out. Also having trouble removing chromatic aberration without losing lots of the magenta color in the Horsehead region.

IMAGE: https://c1.staticflickr.com/6/5550/30084497552_b3bbdafb0e_b.jpg
IMAGE LINK: https://flic.kr/p/MQsU​ZE  (external link) The Belt and Sword (external link) by Eric (external link), on Flickr

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Celestron
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Post edited over 3 years ago by Celestron.
     
Oct 08, 2016 21:04 |  #2

Nice capture and edit . Have you considered a CA filter for the lens ?
How To Remove Chromatic Aberration in Photoshop – ProDPI https://prodpi.zendesk​.com …c-Aberration-in-Photoshop (external link)




  
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pdxbenedetti
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Post edited over 3 years ago by pdxbenedetti.
     
Oct 08, 2016 23:29 |  #3

Celestron wrote in post #18151990 (external link)
Nice capture and edit . Have you considered a CA filter for the lens ?
How To Remove Chromatic Aberration in Photoshop – ProDPI https://prodpi.zendesk​.com …c-Aberration-in-Photoshop (external link)

I've never heard of a chromatic aberration filter, are you talking about a physical filter attached to the lens or something for software? I did do some chromatic aberration removal in lightroom, but the more I applied the more artifacts it introduced and color it zapped from the Horsehead Nebula. I'll give the steps in that link a try and see if that works without degrading the overall image, thanks.

Here's another shot from last night, this one shot with my Nikon D600 and Rokinon 85mm f1.4 lens on an iOptron Skytracker mount. I didn't have a lot of time to collect exposures so this is only 11 exposures stacked, 5 minutes per exposure at ISO 800 and f4. This one will get a lot better once I can get more exposures stacked and then mosaic with the upper half of the constellation.

IMAGE: https://c2.staticflickr.com/6/5042/30203904665_7437a2b021_b.jpg
IMAGE LINK: https://flic.kr/p/N21U​yZ  (external link) Orion Constellation bottom half - early edit (external link) by Eric (external link), on Flickr

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pdxbenedetti
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Oct 09, 2016 00:47 |  #4

Here's one more for good measure, decided to take some shots of Pleiades and the California Nebula while I was waiting for Orion to rise. Taken with my Nikon D600 and Rokinon 85mm f1.4 lens. Only 10 exposures, a mix of 3, 4, and 5 minute exposures for about 45 minutes total. I'll probably add some more to this one as well during the winter months.

IMAGE: https://c6.staticflickr.com/9/8713/30119664581_555203d64f_b.jpg
IMAGE LINK: https://flic.kr/p/MTz9​VK  (external link) From Pleiades to California (external link) by Eric (external link), on Flickr

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Celestron
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Oct 09, 2016 07:11 |  #5

That California neb is rare in a wf image , nice capture . Usually most images are bigger of the C.N. . There is a website www.lumicon.com (external link) that sold CA filters for camera lens . Expensive but at one time they were the best . Last I checked the website was down but you might check back and see if they are up . If you can get one that screws in the back of a lens that would be better, if not then one for the front . Orion telescopes use to sell a filter for chromatic telescopes that screwed in the rear if the focuser . Did a good job , I personally looked through a scope that had one . Stars looked just like an APO scope. Don't know if Orion sells one for camera lens thought .




  
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Celestron
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Oct 10, 2016 08:52 |  #6

pdxbenedetti wrote in post #18151926 (external link)
Also having trouble removing chromatic aberration without losing lots of the magenta color in the Horsehead region.


That 85mm Rokinon lens has a 72mm filter size , the filter I'm talking about is a Minus Violet Filter , helps correct CA in refractors and camera lens . Expensive and you might be able to find one cheaper else where but Lumicon has had a reputation in the astronomy section for a very long time as being the best filters but I cannot verify that since I have none of their filters but many do . If the rear of your lens has threads it maybe possible to find a filter that would fit that end if it has threads and there is enough clearance not to interfere with the mirrors and sensor of the camera .

http://www.lumicon.com …-Minus-Violet-Filter.aspx (external link)

http://www.lumicon.com​/ (external link)

https://www.dpreview.c​om …non_85_1p4/spec​ifications (external link)




  
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pdxbenedetti
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Oct 10, 2016 09:48 |  #7

Interesting, I'll have to think about that, quite expensive for a single filter right now but maybe down the line I'll get one. Thanks for the information.


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Oct 10, 2016 12:39 |  #8

The minus-violet filters are intended for use on achromatic refractors. These are shot using camera lenses which are already somewhat corrected for CA and as I inspect the corners I don't see evidence of color fringing.

One way to deal with CA (real CA) is to split the image into it's constituent RGB & L channels, then use software that can "register" the images (do a star alignment) with the ability to scale images (PixInsight can do this), then bring the registered channels back together into a combined RGB and the CA problem would be gone. (But again, I really am not noticing a CA problem in these images... they look great to my eyes.)

In the shot of the Pleiades and California nebula I do notice some coma in the corners. Often you can improve that just by stopping down a bit.

The pictures are fantastic!

Sorry to hear your mom is in the hospital. I do hope she recovers soon.




  
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Celestron
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Oct 10, 2016 18:14 |  #9

TCampbell wrote in post #18153236 (external link)
The minus-violet filters are intended for use on achromatic refractors. These are shot using camera lenses which are already somewhat corrected for CA and as I inspect the corners I don't see evidence of color fringing.

If you been in the hobby as long as you project then you should already know about Lumicon filters . If they were strictly for Achromatic scopes Lumicon would not make a 72mm filter to fit camera lens . If you would check out the link I provided one is strictly for camera lens with a 72mm filter for a "Camera Lens" . http://www.lumicon.com …-Minus-Violet-Filter.aspx (external link) , as I explained to him they are expensive and that he might find one elsewhere cheaper .




  
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Oct 10, 2016 18:59 |  #10

Really nice captures! I dig wide field.

Very best,


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TCampbell
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Oct 11, 2016 00:32 |  #11

Celestron wrote in post #18153520 (external link)
If you been in the hobby as long as you project then you should already know about Lumicon filters . If they were strictly for Achromatic scopes Lumicon would not make a 72mm filter to fit camera lens . If you would check out the link I provided one is strictly for camera lens with a 72mm filter for a "Camera Lens" . http://www.lumicon.com …-Minus-Violet-Filter.aspx (external link) , as I explained to him they are expensive and that he might find one elsewhere cheaper .

Yes, I know who Lumicon is (I own several of them). Baader Planetarium makes a filter called the "fringe killer" (it's their minus-violet filter). Their marketing literature begins "Achromat owners rejoice..." (and they go on). This is because achromats (or anything using an arrangement of the achromatic doublet) only moderately correct for CA (that's the point of the doublet configuration) but it isn't very effective and you can see CA (color fringing... red on one side, blue on the other) usually near the edges or corners. You might also see CA in a budget-grade photographic lens. Reflectors and apochromatic scopes either don't have the issue or they correct for it so well that you wouldn't see a CA problem in the images (although you might see atmospheric dispersion... but that's caused by the atmosphere and not the telescope optics, but it can resemble CA.)

But again... Eric's shots look fantastic. I'm inspecting the corners and I'm just not seeing the color fringing so I don't think it will be very helpful in this case.




  
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Celestron
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Oct 11, 2016 06:28 as a reply to  @ TCampbell's post |  #12

His shot looks good cause he already worked out the CA , as he mentioned it was hard for him to work out . I'm merely suggesting a filter to help if he wanted something that would help stop it from the beginning . At least that's the way I took it when I read his statement . Maybe I read it wrong , how about you ?




  
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Oct 11, 2016 09:17 as a reply to  @ Celestron's post |  #13

Both CA and atmospheric dispersion (AD) spread the light from any given source based on wavelength of the light. It will, in effect, smear a white pinpoint source into a very tiny rainbow. You would see a red fringe on one edge and a blue fringe on the other edge.

A minus-violet filter tries to make the rainbow less noticeable by blocking the blues (but it doesn't fix red fringing).

A better way to correct for CA after it's already happened is to split the color image into RGB channels, then use star-alignment to register the frames to a master. This requires not just shifting the position of each image (a typical registration) but also re-scaling the images to fit (I'm not sure if Deep Sky Stacker supports re-scaling when it registers images... PixInsight definitely supports it.) Once the images have been "registered" (shifted and/or re-scaled to make sure that all stars in each image precisely match up to the stars in the master registration frame) you can re-combine the R, G, & B channels into a color RGB image and it will eliminate the CA.

There are a few advantages to that approach... (1) you can fix images after they are captured (whereas using a filter would have required knowing you were going to have an issue and putting the filter in to try to stop it during capture, and (2) you get to keep the full spectrum so you don't have color balance issues, also (3) you get a better result because it aligns the red, green, and blue color channels instead of just eliminating the blue to make the blue fringing less noticeable.




  
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Oct 11, 2016 12:22 |  #14

Do you have a tutorial on splitting the individual channels and restacking? I'm using PixInsight, I've gotten somewhat comfortable with the calibration, registration, and integration process (including debayering and drizzle), but I've not read about that kind of process.

The CA removal is ok for most of the image, but it definitely creates weird artifacts in the Horsehead region (colorless rings around stars) mostly due to the fact that the color in that region is the same as the CA being removed. What I ended up doing was removing the CA in one version of the image, then layering another version of the image without any CA removal and masking in the Horsehead region. This is with the 135mm lens, btw, the 85mm lens appears to have a bit less CA and so removal didn't really create any artifacts or problems. I also had the 85mm lens stopped down quite a bit to f4 to reduce coma and taking 5 minute exposures whereas with the 135mm I was shooting f2.8 to capture more light with 2 minute exposures.


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Oct 13, 2016 06:11 |  #15

Really nice shots. I really like the detail pulled out in the dark dust clouds. Makes me want to try some more shots with lenses. Maybe 1 rig with a scope and one with lenses.




  
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My winter project, Orion Molecular Cloud Complex at various focal lengths
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