cloudy? want to have a play?

[Tim]

Available for 7 days only, here are my stacked 16 bit Tiffs narrowband data from the Pacman nebula.

the OIII and SII channels are decidedly weak, especially the OIII, but there is enough there to muck about with the HST palette if you so desire.

Post your results under this thread if you like, i'd love to see what others can make of this data.

Cheers

Tim

YouSendIt - Send large files - transfer delivery - FTP Replacement

[narrowbandpaul]

thanks tim....I will see how I do.

i just got some advice from the father of amatuer narrowbandimaging..richard crisp.

btw you should join myself and gordonH over on the NBI yahoo group.

[narrowbandpaul]

i had a quick go...i was pretty bad. result not worthy of uploading. may try again.

thanks for the data though!

[Tim]

btw you should join myself and gordonH over on the NBI yahoo group.

I find I can only concentrate on one forum at a time, dont really get much free time, and hard to take in information from varying sources. I dare say there are quite a few astro sites with great information available, with new ones emerging all the time. However, I like the mix here, people take their imaging and observing seriously, but it doesnt feel like an exclusive club. I'm less than 2 years into the hobby, and still have miles to go and tons to learn, but everything I have picked up to date has pretty much been from here on SGL. I dont buy astro mags or read many websites etc, SGL has provided just nicely for my growing needs. I know that it isn't everybodys cup of tea, that some like a more serious or formally laid out approach, but I'd like to think that we promote a healthy mix of dedication to the hobby, with enough fun & discussion thrown in to encourage newer and beginners to feel free to post and partake.

Thanks for the invite though. Perhaps you would be kind enough to pass on any tips you get here, especially as regards getting the best out of the OIII and SII lines. I might be wrong, but SII especially seems to be very difficult to gather? Or is it target dependent?

Tim

[steve51450]

Your correct tim, SII is like collecting the contents of the original chalice

[GordonH]

Hi Guys

Collecting SII data can seem like hard work but it is worth the effort in the long run, the amount available is very much dependant on the object being imaged and it is not always the case that there is none or virtually none present. There are some emission nebula and supernova remants that have fairly equal quantities of each of the emission lines. If one or two of the channels are weak and it is usually SII and OIII if this is the case then you take more subfames of each of those compared to the Ha data as the weaker channels will need to be pushed more in the processing to get the detail to show through. Emission line imaging does take more patience because the subframes have to be longer (usually in the region of at least 5-10 minutes), which sometimes means several nights imaging to complete one image, a good example of which is my narrow band image of the elephants trunk nebula which took three nights of imaging over a period of two weeks. It really boils down to what you want out of your imaging, if you want to do narrow band which I prefer then you have to accept that the image acquisition will take at least 3 times and possibly more than RGB imaging

Best wishes

Gordon

[Tim]

Here's the best I can get out of the data that is available.

http://stargazerslounge.com/imaging-deep-sky/84353-pacman-2hrs-s2.html#post1259619

Thanks Gordon for the tips

[minimalist]

Tim, I can't get anywhere close to the detail and color you got in that last one, my hat's off to you. I could see no way to pull that extra out, you are truly a wizard at this. I'd be very tempted to put my mosaic up and see what you can do with that one.

Anyhoo, this is my very first attempt at processing anything in narrwoband, so that's my excuse. You're right, I had to do selective color changes to come up with anything near like that pic. I did notice the guy mentioned an Ha overlay, but I tried to add some of the Ha to the red channel and ended up with nothing but muddy colors. So there is more to it than that, I think.

Here it is:

http://tihpkq.bay.livefilestore.com/y1pn_HkGfUF26FF9qfJ3Ab1DBPveh4gNhP3MSk3EtTsrVK7U7gMcKc6djDOYVtXYiZUXPCsXWgSSRsog3x-EKnxHMtjemeFtgHE/TJ%20Pacman.jpg

Daniel

[Aza]

Just goes to show how much more data you need in the weaker channels.

Need a lot more SII and OIII to make the most of this image.

Are you still going to keep getting data?

[Tim]

Thats good Arran. I am going to get a little more OIII tonight if I can and then leave it at that. It was very disheartening to wait 25 mins for a sub to roll in and then see next to no nebulosity in it!

I think I will come back to this one with my SCT, and try and get some closer up detail on that dusty black bit.

[Aza]

This is something that I aim to do.

Use the 8" Newt with the Atik and get a close up.

For these narrowband images, it would be good to get a few people with near enough the same set ups, so we could share in the data collection.

[MartinB]

Well thanks Tim, I'm rushed off my feet with work but couldn't tear myself away from your data. 1st thing I noticed was that they all have a lot of background brightness esp the OIII - 19000ADU. I guess you were using long exposures but with that level of background I think you would be better going for more shorter subs.

The SII signal is always going to be weak. All the lovely data is in Ha which makes it painful to sacrifice Ha time for SII which is never going to be very exciting as a mono image. I combined the images in maxim at a ratio of 4:2:1 SII:OIII:Ha Which is probably an indication of the signal strenghts in the different bands. To avoid a noisy image you have to pull back the Ha stuff and stretch the SII as much as you can.

The end result is red stars, the blight of NB imaging. You can mix in a better balanced star layer but this is quite time consuming and I haven't had time to do this. For me with narrow band images I throw away the idea of a natural image and try to hightlight the detail that the NBs are good at showing such as ionisation fronts.

I've faded the stars out way more than I ever would with a broad band image, accepted some red stars as the price of pushing the SII. I haven't selectively picked out areas for extra colouration but did use masks to keep adjustments either to the background or the nebula.

The trouble with processing this stuff is that it is very subjective. You can work your rocks off getting things just so and someone comes up and says "prefer RGB meself". The fact is that nothing shows up nebular detail like narrowband.

Here's todays waste of time!

[Tim]

I like that one Martin. The OIII layer was blighted by clouds, I only had 8 subs and normally would have scrapped 4 of them due to background, but with the overall lack of data decided to throw them in. Hopefully get another couple of hours tonight.

I notice that OIII isn't as good at stopping a LP gradient either

[Aza]

I think to get the best out of narrowband, you need the best filters.

I am saving up for a set of Astrodons (very expensive!)

Ha and SII (5nm)

OIII (3nm)

OIII is more effected by light pollution and moonlight, hence the narrower band.

Martin did mention to me before that these are too narrow for f5 scopes, however I had this reply from Don Goldman: (Have you seen this before Martin?)

There will be no significant effect for 5 nm and even 3 nm filters at f/5.

Please see slides 25-28 for supporting data from my talk at the Advanced Imaging

Conference (AIC) in 2007 at:

http://www.aicccd.com/archive/aic2007/Goldman-AIC2007Talk2.pdf

Hope this helps.

Don Goldman

[Whippy]

I think to get the best out of narrowband, you need the best filters.

I don't think that's quite the case Arran. The problem with having such narrow passes is that your exposure times will go up by loads but obviously the upside is that what data you'll have is much 'purer'. If that's where you want to go, then go for it but the attraction of narrowband for most people (including me) is that you can image when the Moon is about, so why spend hours and hours with super narrow filters when you could achieve the same result in much less time using wider filters?

Interesting about the OIII filter though, I was planning on getting one but if it's that badly affected by LP and the Moon I might just stick to Ha.

Tony..

[Aza]

Yeah you dont need to go that narrow.

But if you are on a mission to get the BEST out of your system, then I think these filters are nessessary.

If I ever get a set, I will do some direct comparisons compared to my current filters

[MartinB]

Thanks for that Arran. I hadn't seen it before and what little I understood was very interesting. I couldn't grasp whether these band shift findings apply to other makes of filter or whether he was implying that you had to go with Astrodon. There are some serious filter wars out there! Worth knowing since I am planning a fair bit of F5 and faster imaging.

It would only be the band shift that would worry me (quite apart from the cost of course). If the filter lets through all the Ha, exposure times to achieve a given s/n shouldn't be affected. Desirable exposure time will increase because of reduced undesirable light transmission

[Tim]

Martin warned me about the filters shifting things a bit on fast scopes. I checked up a bit on this and found the consensus to be that f3.8 and faster is what they consider 'fast'.

Baader claim that their new range of filters have all the characteristics of the Astrodon ones, without the premium. Although they are more expensive than the astronomik ones.

There is definetly a distinct lack of halo with the 7nm baader filter, a big improvement on their old one.

[Whippy]

Just for grins really, first crack at false colour processing and all that...

Tony..

[Tim]

Thats the thing Tony, with false colour, the colour cant be wrong!

Actually I have an RGB version of this somewhere taken with a dslr, and the colours came through not too disimilar to what you have there.

My ultimate goal is to put together a method which will enable the detail available in narrowband, to shine through in an image with 'normal' RGB colours, ie, those you get from a OSC camera. Dunno if it can be done, but i'll have fun trying

It's been quite a useful exercise, making the data available, i think i'll do the same again for my next project, thanks to all those who have had a go so far.

[RobH]

Hello Tim,

I just followed your link but it says no files are there.

Wouldn't mind a crack at some HST pallette stuff while the weather is like this

Cheers

Rob

[Whippy]

Cheers Tim, I liked having a play with it (even though I basically made it up as I went along!). As it goes, I'm thinking about something you may be interested in. I shall let thee know ..

Tony..

[Tim]

Rob, thanks for sending that info, got it yesterday. Very interesting. Will give that a go.

I got another 5 x 20 mins OIII last night, and they have come through very nicely, 4 of them being very good quality, so i'll re-jig the mix and send you the new data. Hoping to grab a bit more S2 tonight and then that will be it. Maybe.

[roundycat]

interesting to hear different people's opinions about the relative merits of narrowband filters versus even narrower band filters.

Surely if the emission from a nebula has a very narrow bandwidth, along the lines of Fraunhofer (!), then provided the filter is wider than that there will be no discernable difference. If the different bandpass filters have a similar transmission, say 95%, then narrower filters do not need longer exposures. They are merely cutting out more of the background noise which is why we use them in the first place.

The only problem I can see is if the light in, say, Ha is being frequency or phase shifted as it travels to us. In that case narrower filters will need longer exposures because some of the signal is being lost and will only be captured by a wider filter.

True or Rubbish?

Dennis

[narrowbandpaul]

what evidence do you have that astrodon make the best filters....how can you know this?

paul