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Need some help, please: OIII in pacman / targets with lots of OIII?

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#1 the Elf

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Posted 17 February 2019 - 06:31 AM

Hello all,

 

I'm new to OIII. I'm using my Ha filter on a mono modded T3i almost since I started with AP and all was fine. With OIII several attempts failed. After two nights of Ha under clear but unsteady skies I shot one night of OIII, object is NGC281, the pacman. While Ha is deep an rich there is very little going on in OIII. Here is a screen shot of my PI-screen-stretches Ha and OIII masters:

 

HaOIII.jpg

 

Ha is 27 x 15min, Baader 7nm, OIII is only 14 x 15min, Baader 8nm. OIII is taken through thin fog like clouds, quite some background. All close to full moon. The moon was on it's way to gemini, quite far away from pacman.

I did a quick processing just to see how what it might look like. Used Ha as R, OIII as G and B (HOO) and then made an LRGB combination using a slightly boosted Ha as L.

 

CN.jpg

 

Now my long list of questions:

- Is this what is going on in OIII in the object? Could someone post a "good" OIII master, please?

- Is 3.5h just far to short?

- Is it true that NB works under the full moon with a sky as bright as my flat panel? Or should I shood OIII in moonless nights?

- How far from the moon should the object be for good results? (I learned when the moon light hits the front lens of the refractor I can forget it. I have not tried how the RC responds to it.)

- Are there any objects more suitable for a beginner / DSLR user? I guess dumbbell is very strong in OIII. I read goofi's NB list (https://www.cloudyni...s-for-the-fall/) I do not know if the list contains objects with significant signal in Ha, OIII and SII or if some objects have only one or two of them.

- Is there a book or list with information which object emmits what? Is there a book about NB imaging in general?

- Is SII making a big difference? Can I shoot SII with an uncooled camera at all? So far I did not get that filter. I was expecting SII is even weaker than OIII.

 

The above image is basically an Ha image. OIII just adds signal to the stars and to my very big surprise the stars do have different natural looking colors. In the nebula it is nothing but a bit brightness added in the center. Is this what the pacman really looks like or am I doing something wrong?

Thanks for helping!!


Edited by the Elf, 17 February 2019 - 06:47 AM.

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#2 MikeKy

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Posted 17 February 2019 - 07:30 AM

 Your comparison looks about right. Below are my OIII and Ha stacks with just a PI STF stretch. The full moon will also affect the OIII much more than the Ha.

 

OIII vs Ha.JPG

 

Supernova remnants, planetary nebulae, and some of the brighter emission nebulae will have more OIII. So, Dumbell Nebula, Veil Nebula, Thor's Helmet, or M42 would be good targets for OIII. Even in these targets, though, OIII will be less prominent than Ha. The California Nebula and Horsehead, however, have very little OIII and more SII. The SII in the Pacman is more on the bright edges and helps to provide detail and allows you to have more of a 3-color palette to bring out the blue of the OIII. 

 

Capture.JPG


Edited by MikeKy, 17 February 2019 - 07:42 AM.


#3 ks__observer

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Posted 17 February 2019 - 07:42 AM

Agree with Mike.

My Heart and Cone shots had very little to no Oiii structure, but it does add a nice effect nontheless when combining data.

My M1 shot the Oiii had lots of structure and almost looked like the Ha data.

Oiii, from what I have read, is much more sensitive to moonlight.  I have still gotten decent results but it is not ideal.

Curious what others say about yout other questions.


Edited by ks__observer, 17 February 2019 - 07:44 AM.


#4 terry59

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Posted 17 February 2019 - 07:55 AM

Your data seems ok....how did you blend them?



#5 ChrisWhite

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Posted 17 February 2019 - 07:55 AM

Elf,

How did you process your channels respectively? Did you linearfit the Oiii to the Ha prior to combining? This is important so that you don't totally swamp the weaker oiii signal with the strong Ha.

As for some of your questions, my experience is:
Oiii is often a much weaker signal, so with short integration you just might not have enough. I imaged this object and ended up with 25 hours split between the three channels, so about 8 hours each. I still had to "coax" out the oiii signal when combined as the Ha is so much more dominant.

A benefit to imaging narrowband is that you CAN image during brighter moon, but it is certainly not immune to it. Ha and Sii are "okay" in bright moon, but Oiii is not nearly as good. I don't usually image Oiii in anything more than 50% illumination and above 75%, I don't image at all... I always try to stay a ways from the moon... 50 degrees or more... It's really up to you though. You can image in a full moon and still get a nice image but you have to work for it in processing! This was imaged during a FULL moon: https://www.astrobin.../full/272249/0/ This is the same target imaged in darker skies: https://www.astrobin...8094/H/?nc=user

I always like to get some Sii, even if there is no real signal in the target itself. It's good to have a couple of hours of Sii on file in case you want more options for star colors... I like SHO stars better than Bi-Color...

Edited by ChrisWhite, 17 February 2019 - 09:42 AM.

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#6 johnsoda

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Posted 17 February 2019 - 08:07 AM

The Crescent Nebula is a good target for seeing a difference in narrowband, as I explain here:

 

https://www.cloudyni...lter/?p=9082937

 

Of course, you’ll to wait a few months for it.  Same with the Veil Nebula. 

 

I agree that differences in narrowband images are often disappointing, but the OIII and SII can often add interesting “shading” to the Halpha. I’d search Astrobin for “HOO”, “SHO”, and so on for interesting targets. 



#7 schmeah

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Posted 17 February 2019 - 09:00 AM

You just need more OIII if you want that rich blue core. I routinely shoot twice as much OIII than Ha. Here is my result after eight hours of OIII and four hours of Ha:

 

https://pbase.com/ds...image/166196937

 

Derek



#8 the Elf

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Posted 17 February 2019 - 12:31 PM

Thank you for your feedback. I scanned astrobin and found three schools: a) people split the imaging time evenly on all three (H, S, O). b) people using a shorter over all exposure time than a take only little OIII and the results lack the nice blue c) people with integration times I cannot collect in only one season (50h+) shoot more OIII than Ha and the results are stunning. Lots of integration time helps, that's for sure. My situation is like I have to go to work every day, get up early and I can image on friday if a take a nap after work and on saturday. Sunday only in winter, in summer I have to ge to bed before sunset. This is not california, we have clouds and rain most of the time and half the time the moon is there. So I try to figure out what can I do when the moon is at the sky and collect Ha from different objects. Sometimes I can take OSC and L (if required) a few week later, but sometimes there is no clear sky at new moon for 8 or 10 weeks and the object is gone for that year. So my idea was to collect two nights of NB, HSO if possible and have a color image after one weekend. I still don't know if I rather use the time I have for Ha and OIII or split it to Ha, OIII and SII. I just cannot collect 20h of each. I can do that in summer 2038, that is when I'll be retired. Until then I try to make the best out of the weekends.

Last summer I was luck and took Ha at one weekend and OSC at another weekend and got this:

https://www.astrobin.../full/365598/0/

The object is strong enough to look ok with less than 5hours of exposure time. I know that SII is also less sensitive to moonlight, so do you guys think I should get a SII filter even if I have to devide the time to three channels instead of only two?

 

@Chris: this was a 10 minute test processing, totally tired, just HT to both channels until they looked somewhat similar. I hope I can properly process the data this week. I need to be in the right mood for it and work often sends me home in a different mood... I'll post it here when it is done.

 

@terry: as I wrote in the initial post: Ha to red, OIII to green and blue, no inter channel blending. After that Ha as L.

 

@MikeKy: thank you for the screen shots. That helps a lot. Is this the final image from that data? http://www.astrobin.com/full/381024/C/

The result is great for the short exposure time. I guess the clouds and the moonlight killed a lot of my signal in OIII.


Edited by the Elf, 17 February 2019 - 12:40 PM.


#9 MikeKy

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Posted 17 February 2019 - 12:51 PM

Elf,

Yes, that’s the final.

Due to work schedule, weather, etc. I also have limited imaging time with most NB images getting only 7 or 8 hours total.



#10 the Elf

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Posted 17 February 2019 - 01:04 PM

Looks like I should get the SII and image OIII without moon. I'll check the price....

 

I found this in the triad filter discussion:

 

https://www.cloudyni...lter/?p=9080650

 

 

We get it. You have great skies. Not all or us do. I have horrible skies, all narrowband and LRGB filters and I can personally see the attractiveness of the filter, just not at that price. Easy narrowband with a color camera. It's clear this filter isn't for you. Sometimes I wish I could shoot all of the narrowband filters at once so I can get a color image in one night in my light polluted skies. The snr of each image will be lower, yes. But, 4 hours of data could get an image where normal filters, that would be 1 filter or maybe 2. Then clouds come along and prevent me from getting the rest of the data. With this filter, I would be able to get them all in a night. Then in 3 weeks when the weather aligns with my schedule I could do another target. The filter makes sense. Just not for you, and at that price not for most people. Your advertisement of monochrome imaging would be just as misleading as theirs because in order to get images like that you have to be fortunate enough to live within driving distance of great skies. Most people who aren't retired can't drive several hours and have time to image before work the next day and be lucky enough to have good weather on the weekend. Maybe the bad weather is an east coast thing.

This is exactly my situation. I can add that the east coast weather goes on over the atlantik all over Europe and ends at the ural mountains in Russia. I guess New England is called so because the weather is like "old" England.



#11 terry59

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Posted 17 February 2019 - 01:11 PM

Thank you for your feedback. I scanned astrobin and found three schools: a) people split the imaging time evenly on all three (H, S, O). b) people using a shorter over all exposure time than a take only little OIII and the results lack the nice blue c) people with integration times I cannot collect in only one season (50h+) shoot more OIII than Ha and the results are stunning. Lots of integration time helps, that's for sure. My situation is like I have to go to work every day, get up early and I can image on friday if a take a nap after work and on saturday. Sunday only in winter, in summer I have to ge to bed before sunset. This is not california, we have clouds and rain most of the time and half the time the moon is there. So I try to figure out what can I do when the moon is at the sky and collect Ha from different objects. Sometimes I can take OSC and L (if required) a few week later, but sometimes there is no clear sky at new moon for 8 or 10 weeks and the object is gone for that year. So my idea was to collect two nights of NB, HSO if possible and have a color image after one weekend. I still don't know if I rather use the time I have for Ha and OIII or split it to Ha, OIII and SII. I just cannot collect 20h of each. I can do that in summer 2038, that is when I'll be retired. Until then I try to make the best out of the weekends.

Last summer I was luck and took Ha at one weekend and OSC at another weekend and got this:

https://www.astrobin.../full/365598/0/

The object is strong enough to look ok with less than 5hours of exposure time. I know that SII is also less sensitive to moonlight, so do you guys think I should get a SII filter even if I have to devide the time to three channels instead of only two?

 

@Chris: this was a 10 minute test processing, totally tired, just HT to both channels until they looked somewhat similar. I hope I can properly process the data this week. I need to be in the right mood for it and work often sends me home in a different mood... I'll post it here when it is done.

 

@terry: as I wrote in the initial post: Ha to red, OIII to green and blue, no inter channel blending. After that Ha as L.

 

@MikeKy: thank you for the screen shots. That helps a lot. Is this the final image from that data? http://www.astrobin.com/full/381024/C/

The result is great for the short exposure time. I guess the clouds and the moonlight killed a lot of my signal in OIII.

Sorry....what method did you use for blending? PI or PS?



#12 the Elf

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Posted 17 February 2019 - 01:16 PM

I used PI. Sorry, I did not post that.



#13 RJF-Astro

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Posted 17 February 2019 - 04:42 PM

Last week I had a few good nights on IC 410 (tadpoles). There was a 60-70% moon not too far away, but to my suprise the O3 data came out quite ok. I have 2 hours on S2, 2.5 hours on O3 and 3 hours on Ha (ASI1600MMC, F7.5). This is a quick processed version and I need to refine it, but there is a nice blue color coming up. It did take a lot of color tweaking to get it out though.

 

20190216 IC410 eerste poging.jpg

 

Without the moon it probably would have been better, but it's not undoable.


Edited by RJF-Astro, 17 February 2019 - 04:44 PM.

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#14 the Elf

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Posted 17 February 2019 - 11:15 PM

RJF-Astro: That image from the Netherlands in 7.5h at F7.5? Wow. There is hope. My camera is less sensitive but all other conditions are quite similar. Thank you for posting! ... and I like your Rosette image. Very nice.


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#15 APshooter

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Posted 18 February 2019 - 12:43 AM

Oiii is concentrated mostly in planetary nebulas and in certain emission nebulas.  It was really dense in M27 butvery faint in the Wizard nebula I imaged which was 30 hrs!

 

Sii is really prevalent in the Eagle nebula and a few other regions I've done, but hardly any in others.  Even shooting deeply, 8 hrs or more, can't bring out what element isn't there or exists only in trace amounts.  I wonder if searching images in Astrobin might give clues as to how much might be there visually, and then cross reference that with hr shot.

 

Like you, I seem to have far fewer hrs to image due to weather.  I'm hoping my Rasa will give me more photons per hour to try and gather data in only 2 nights instead of shooting for a week to gather 30 hrs of data (which I haven't done in years).

 

By the way, here's the amount of Sii in M16, five hours worth...its almost as much as the Ha signal.

 

get.jpg?insecure


Edited by APshooter, 18 February 2019 - 12:45 AM.

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#16 the Elf

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Posted 18 February 2019 - 02:07 AM

APshooter, thank you! I tried the wizard myself (see my astrobin) but I did not get much OIII and was thinking it is my fault. Now that you say it is that faint I understand that it was not the ideal object for the first try. I got a decent amount of signal from M1 but my seeing was poor. I hope I get some Ha soon under better seeing to combine it. 

I tried to make a table for myself, could you perhaps fill the gaps, correct what is wrong and add some? I guess there must be a list like that somewhere in the endless internet, but I could not find it.

 

Object              / Ha / OIII / SII

========================

Wizard                ++ / -- / ?

Crab M1             ++ / +  / ?

Eagle M16         ++ / ? / ++

Orion                +++ / + / ?

Dumbbell M27   ++ / ++ / ?

Rosette             ++ / ?  / ?

....



#17 cyber

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Posted 18 February 2019 - 06:19 AM

Hi Elf, I live in Belgium and I guess that my weather conditions are very similar to yours. We just shoot data whenever there's clear sky. Most of these nights have a full Moon for some reason. undecided.gif

Here are a couple more examples of my own Ha/OIII data, all captured with an 80mm refractor reduced to f/4.8, ASI1600MM-C and 7 nm ZWO filters.

 

Pacman (NGC 281): this data was captured on two moonless nights, under ~19.4 mag/arcsec^2 skies.

3h Ha/ 1h OIII

 

pacman.jpg

 

Final result after a lot of massaging in PixInsight:

 

get.jpg?insecure

 

With 3.5 hours of integration and a f/5.3 reduced RC, I would also expect to see more OIII signal in your stack. As said above, the OIII contrast is strongly affected by your background sky. Moonless nights, darker skies and narrower filter passbands are all very beneficial for your SNR here.

 

Dumbell (M27): this one is really bright, should look great with an RC!

From home, background SQM ~ 17.5

2h Ha / 2h OIII

 

dumbell.jpg

 

Final result:

 

get.jpg?insecure

 

Orion Nebula: also a good amount of OIII here.

Same location as above, SQM ~17.5

1.5h Ha / 6h OIII

 

orion.jpg

 

Final result:

 

get.jpg?insecure



#18 calypsob

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Posted 18 February 2019 - 11:09 AM

Hello all,

 

I'm new to OIII. I'm using my Ha filter on a mono modded T3i almost since I started with AP and all was fine. With OIII several attempts failed. After two nights of Ha under clear but unsteady skies I shot one night of OIII, object is NGC281, the pacman. While Ha is deep an rich there is very little going on in OIII. Here is a screen shot of my PI-screen-stretches Ha and OIII masters:

 

attachicon.gif HaOIII.jpg

 

Ha is 27 x 15min, Baader 7nm, OIII is only 14 x 15min, Baader 8nm. OIII is taken through thin fog like clouds, quite some background. All close to full moon. The moon was on it's way to gemini, quite far away from pacman.

I did a quick processing just to see how what it might look like. Used Ha as R, OIII as G and B (HOO) and then made an LRGB combination using a slightly boosted Ha as L.

 

attachicon.gif CN.jpg

 

Now my long list of questions:

- Is this what is going on in OIII in the object? Could someone post a "good" OIII master, please?

- Is 3.5h just far to short?

- Is it true that NB works under the full moon with a sky as bright as my flat panel? Or should I shood OIII in moonless nights?

- How far from the moon should the object be for good results? (I learned when the moon light hits the front lens of the refractor I can forget it. I have not tried how the RC responds to it.)

- Are there any objects more suitable for a beginner / DSLR user? I guess dumbbell is very strong in OIII. I read goofi's NB list (https://www.cloudyni...s-for-the-fall/) I do not know if the list contains objects with significant signal in Ha, OIII and SII or if some objects have only one or two of them.

- Is there a book or list with information which object emmits what? Is there a book about NB imaging in general?

- Is SII making a big difference? Can I shoot SII with an uncooled camera at all? So far I did not get that filter. I was expecting SII is even weaker than OIII.

 

The above image is basically an Ha image. OIII just adds signal to the stars and to my very big surprise the stars do have different natural looking colors. In the nebula it is nothing but a bit brightness added in the center. Is this what the pacman really looks like or am I doing something wrong?

Thanks for helping!!

Oiii is pretty faint, I own the 12nm astronomik oiii filter and it does not do well in light polluted skies. I tested the dumbell with my RC8 before I sold it and I was saturating the histogram at 120 seconds in the suburbs and 1,200 seconds at the darksite. I can definitely understand why a full moon would make it harder to get a good signal. I should mention that back when I did this test I did not yet own a monochrome dslr. I am curious to try again with my Newtonian from my yard now that I have a visible sky. Im curious to see your results when the moon is gone.



#19 lucam

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Posted 18 February 2019 - 11:58 AM

Elf, bandwidth of the filter obviously matters. Compare these two images, both 15 minute subs taken with Astrodon 3nm OIII fiilters and SX Trius 814 CCD:

 

2 days after new moon:

Screen Shot 2019-02-18 at 11.38.54 AM.jpg

 

3 days after full moon:

Screen Shot 2019-02-18 at 11.38.45 AM.jpg

 

Quick integration of 3.25 hours of OIII (45 minutes close to new moon, rest close to full moon) (calibration with bias frames, crop, DBE, MSLT, Histrogram transformation):

Screen Shot 2019-02-18 at 11.39.08 AM.jpg

 

Something to keep in mind in the decision of ratio of imaging time between Ha and OIII is the amount of high-resolution detail in the channel. With SII there is almost always very little high resolution detail and the master can take aggressive denoising to allow enough stretching to bring out the signal. OIII depends on the object. Some objects have a lot of high resolution detail complementary to Ha (for example the Veil nebula). In that case, you need to integrate and will choose to image for at least as much time Ha and OIII. Other objects are pretty diffuse in OIII and can take more aggressive denoising without degrading the image. In that case, your image will look better with excellent detail in Ha, for given total integration time and more imaging devoted to Ha vs OIII will pay off. 



#20 2ghouls

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Posted 18 February 2019 - 12:34 PM

I agree with much of what has already been said.  One thing missing from the conversation so far is that many narrowband images you see online use a post-processing technique called tone mapping. It was popularized for amateur astrophotographers by a great Finnish astrophotographer named J.P. Metsavainio, and it is a way to stretch very dim OIII and SII signal equal in intensity to Ha without bloating the stars. The way that is accomplished is by first removing the stars. This could be considered controversial because when you first practice it, you may find that you are introducing processing artifacts to the image through the star removal process. With enough practice, I think it works REALLY well. Most of my narrowband images on astrobin are tone mapped. Some are better examples than others. I think my recent mosaic is pretty decent. It helps to have RGB data as well because then the colorful star halos will cover any leftover "smudges" that the star removal may have left.

 

Anyways, here are some resources on tone mapping if you want to go down that road:

 

J. P. Metsavainio's original blog post in 2009: https://astroanarchy...ne-mapping.html

 

J.P. Metsavainio's powepoint on tone mapping (Photoshop workflow): http://www.skypixels...one_Mapping.pdf

 

pbkoden's PixInsight Tone Mapping workflow: https://www.cloudyni...ing-melotte-15/

 

And even though you already have some good answers. I will give my 2 cents on your questions below.

 

Now my long list of questions:

- Is this what is going on in OIII in the object? Could someone post a "good" OIII master, please?

Some people already have. And I agree that equipment can make a difference here. Narrower filters will have better contrast, etc. BUT your result looks quite good for 3.5 hours IMO.

- Is 3.5h just far to short?

Subjective of course, but for me, YES. I personally would go 6-10 hours for run of the mill OIII objects, and more for challenging ones.

- Is it true that NB works under the full moon with a sky as bright as my flat panel? Or should I shood OIII in moonless nights?

I do not shoot OIII with full moon or in my backyard due to LED street lamps. It is much easier for me to get longer Ha and Sii integrations because they seem less susceptible to moonlight.

- How far from the moon should the object be for good results? (I learned when the moon light hits the front lens of the refractor I can forget it. I have not tried how the RC responds to it.)

As far away as possible. I look at where the moon will be when I am planning out my imaging sessions for the season. I would say at least 30 degrees away, and preferable not full. If it's full, I only shoot Ha.

- Are there any objects more suitable for a beginner / DSLR user? I guess dumbbell is very strong in OIII. I read goofi's NB list (https://www.cloudyni...s-for-the-fall/) I do not know if the list contains objects with significant signal in Ha, OIII and SII or if some objects have only one or two of them.

M27, Heart and Soul, North America and Pelican (summer)

- Is there a book or list with information which object emmits what? Is there a book about NB imaging in general?

Charles Bracken's Astrophotography Sky Atlas has a nice list with notes that include comments on OIII and SII strength. A few astrophotographers will post their channels as well as their finished image. Bill Snyder's site (http://billsnyderastrophotography.com/) is quite good for this, and he even often posts what a single subframe look like for each narrowband channel. I hope to get more up on my site too, as it does really help in object planning. 

- Is SII making a big difference? Can I shoot SII with an uncooled camera at all? So far I did not get that filter. I was expecting SII is even weaker than OIII.

For most objects, SII is weak or non-existent. Of course, there are some objects where it really adds interest/depth. Some of these are showpiece objects like N. America / Pelican, etc. I was recently shooting the Seagull, and it looked OK there. Usually it follows the Ha more closely than the OIII does. Personally, I would NOT make getting a SII filter a priority at all. But I really like the HaOII bi-color (with RGB stars) look, while others prefer straight SHO.

 

The above image is basically an Ha image. OIII just adds signal to the stars and to my very big surprise the stars do have different natural looking colors. In the nebula it is nothing but a bit brightness added in the center. Is this what the pacman really looks like or am I doing something wrong?

No, you aren't doing anything wrong. Your result looks very natural and pleasing to me, and I do think the OIII added dimension to the nebula that wouldn't be there if you had just shot HaRGB for example. If you want it to look blue like in some people's photos, you would need to do something different in processing. Tone mapping is one option, but there are others (some already mentioned I believe).

Thanks for helping!!

 

Cheers, Nico


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#21 calypsob

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Posted 18 February 2019 - 01:13 PM

I agree with much of what has already been said.  One thing missing from the conversation so far is that many narrowband images you see online use a post-processing technique called tone mapping. It was popularized for amateur astrophotographers by a great Finnish astrophotographer named J.P. Metsavainio, and it is a way to stretch very dim OIII and SII signal equal in intensity to Ha without bloating the stars. The way that is accomplished is by first removing the stars. This could be considered controversial because when you first practice it, you may find that you are introducing processing artifacts to the image through the star removal process. With enough practice, I think it works REALLY well. Most of my narrowband images on astrobin are tone mapped. Some are better examples than others. I think my recent mosaic is pretty decent. It helps to have RGB data as well because then the colorful star halos will cover any leftover "smudges" that the star removal may have left.

 

Anyways, here are some resources on tone mapping if you want to go down that road:

 

J. P. Metsavainio's original blog post in 2009: https://astroanarchy...ne-mapping.html

 

J.P. Metsavainio's powepoint on tone mapping (Photoshop workflow): http://www.skypixels...one_Mapping.pdf

 

pbkoden's PixInsight Tone Mapping workflow: https://www.cloudyni...ing-melotte-15/

 

And even though you already have some good answers. I will give my 2 cents on your questions below.

Sometimes I will go so long without imaging or processing that my memory and skills completely fall apart, but I have found on several occasions that destructively shrinking your stars

before doing a star removal will allow you to reduce the size of the artifacts which can occur around the stars.  When you re introduce the original stars they are much larger than the artifacts and hide the issues created by removal. It does not always work, but is certainly a powerful technique. 


Edited by calypsob, 18 February 2019 - 01:13 PM.

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#22 the Elf

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Posted 19 February 2019 - 03:02 PM

Again thank you all for the feedback. There is still one thing I cannot get in my head: as soon as a newbee posts "starting AP, need advice, live in downtown <any big city>" almost automatically everyone posts the same answer: "you could image planets or go NB". I was always thinking I don't believe the second and it seems like it is just not true. Many OIII filters are 8nm wide in order to collect the two neighboring lines. At least in that case moon and light pollution matters. It rather seems like the correct answer is "you can shoot planets and Ha and SII but for OIII drive to a not so bright place".

Right now I'm not sure if I get an SII by Baader or if I sell my OIII and get both SII and OIII astrodon filters with a smaller bandwith. I think I will try some objects suggested above with the 8nm Baader when the moon is under the horizon and find out if I like the results.

In my test image I stretched OIII far more than Ha but the stars did not bloat. For my skill level I'm happy with the star color. A pro might have higher expectations. I'm just trying to do a propper processing but I am too tired to make it. It is the same work that allows you to pay the equipment that also absorbs your time and energy and keeps you from imaging and processing. That's life, I guess.



#23 miwitte

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Posted 19 February 2019 - 08:07 PM

One thing you should look into is tone mapping starless images which allow you to really stretch the data more. I've had some good results in increasing the Oiii signal doing that. Jon has advised my to do 2-3 times the Oiii and SII data than Ha that's what I'll be doing next.

#24 cyber

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Posted 20 February 2019 - 02:27 AM

Elf I saw in some of your other posts that you're using a 'monomod' T3i. Removing the CFA also removes the microlenses, which can significantly lower sensor QE, especially with those tiny CMOS pixels.

Here's some experimental evidence from a Dutch astrophotographer: http://www.astrojac....t een DSLR.pptx

#25 the Elf

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Posted 20 February 2019 - 04:00 PM

cyber, I know. For typical daylight the removal of the filters evens out the missing microlenses and sensitivity is pretty much the same for the visual spectrum. IR is a different story. There is no alternative to me. I have to deal with computer problmes at work 8 hours a day and been doing so since 21 years now. I DO NOT WANT TO BOTHER WITH COMPUTERS AT NIGHT. That is why I use the DSLR. A personal decision. I would not do AP if it was not possible to do it with a DSLR. I accept the downsides of my approach.

Just processing my data. I added more subs that I had taken in november with the refractor. I'm at 15 hours total exposure now. Wait and see....




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