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Author Topic: Low contrast images - suggestions  (Read 1753 times)

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Offline jmbillings

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Low contrast images - suggestions
« on: 09:53:12, 20 January, 2014 »
Hi folks.
I went out last night for my second attempt at guiding with PHD. I thought I'd try grabbing some frames of the rosette neb, and although my guiding appears to have worked ok (at least for a second attempt!) I'm struggling to get anything useful out of the images due to light pollution (I do have a basic light pollution filter in place)

I thought I'd post them here to see what people cleverer than me can do, to know if it's worth me persevering or if I need to look at a more agressive filter. By way of example, here's a small JPG of one frame here:



You can download the TIF files here: https://dl.dropboxusercontent.com/u/3646168/DSC00566.zip

I tried stacking in DSS and got a very bright washed out image with all three colours in a very narrow band. With some very agressive editing of the curves, I could pull out a hint of the nebula but it wasn't a nice picture. Any tips (including don't bother!) appreciated. I know I don't have flats/darks here, but I don't want to spend time on those until I know I will have some useful data to begin with...

I have access to DSS, Lightroom and GIMP, no Photoshop.

Offline chris.bailey

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Re: Low contrast images - suggestions
« Reply #1 on: 10:28:43, 20 January, 2014 »
James

Could you give us some details of what exposures those are and any details of that light pollution filter.

If you could also put the raw files straight out of the camera into a dropbox folder it would give one of us a bit more of a chance, those tiffs already seem to be stretched.

Chris

ps guiding looks good so that is one battle won.
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Offline ChrisLX200

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Re: Low contrast images - suggestions
« Reply #2 on: 10:35:32, 20 January, 2014 »
I used a UHC on this to get a reasonable result, though it's not really a photo filter it was effective at cutting the LP and retained the colour balance.

ChrisH
Chris Heapy - current: 10-Micron GM2000HPS-II U/P, G11/Gemini, TV NP127is, Altair 8" RC, TV Genesis SDF, TV Pronto, SW Equinox 80ED, 10" LX200, 12" f/5.4 Newt, Vixen 90mm.
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Offline jmbillings

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Re: Low contrast images - suggestions
« Reply #3 on: 10:56:44, 20 January, 2014 »
The original RAW files are here - all I did to make the TIF's was to export in Lightroom but resized down to ~1080P (DSS always seems to crash for me with the RAW files :( )

These are 8m at ISO 800

Offline Einari

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Re: Low contrast images - suggestions
« Reply #4 on: 10:59:10, 20 January, 2014 »
Rosette is pretty faint and large so it needs long exposure (+5 min subs) and short focal length (say 500mm with DSLR).

As for DSS, get the newest beta of it.
Tapio

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Offline jmbillings

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Re: Low contrast images - suggestions
« Reply #5 on: 11:11:09, 20 January, 2014 »
OK- I've spotted DSS is OK with my RAWs if I turn off drizzle... So that's one to try later. Off to work now!

Offline chris.bailey

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Re: Low contrast images - suggestions
« Reply #6 on: 12:28:35, 20 January, 2014 »
James

This is what I get (taking a bit of a guess at the colour matrix in your Sony Camera) so you have some recognisable Rosette features coming out but they are at a level barely above the background skyglow. A good light pollution filter will help and you really do need to use Flats (and Bias) to get rid of the vignetting and dust motes. I would not bother with darks personally at this stage. After that its taking a lot more frames than that, I would start at a run of 16 and see where that gets you.

In conclusion it is most definately not a "dont bother", more a "keep going".

Chris

ps using lightroom to create .tiffs to input into DSS is not such a good idea as it applies some processing to them. DSS likes RAW images best.
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Offline jmbillings

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Re: Low contrast images - suggestions
« Reply #7 on: 12:37:59, 20 January, 2014 »
Thanks Chris- I guess I'm partly pleased that you've not been able to get much out of it either! My current filter is just one the generic skyglow ones, not a nebula specific one or anything; it get's rid of the complete orange washout I'd get otherwise but at these length exposures it's obviously not cutting quite enough.

Offline ChrisLX200

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Re: Low contrast images - suggestions
« Reply #8 on: 12:52:08, 20 January, 2014 »
This is a 10min ISO800 exposure through my 70D DSLR with the aforementioned UHC filter, un-processed (albeit a jpg not the RAW file) so it shows the resultant colour balance under my light-polluted skies. It would be an orange wash-out without the filter at this exposure length.



ChrisH
Chris Heapy - current: 10-Micron GM2000HPS-II U/P, G11/Gemini, TV NP127is, Altair 8" RC, TV Genesis SDF, TV Pronto, SW Equinox 80ED, 10" LX200, 12" f/5.4 Newt, Vixen 90mm.
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Offline jmbillings

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Re: Low contrast images - suggestions
« Reply #9 on: 13:01:35, 20 January, 2014 »
Yeah, that's quite a noticeable difference, a much better starting point!

Offline jmbillings

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Re: Low contrast images - suggestions
« Reply #10 on: 13:52:57, 20 January, 2014 »
Hm, FLO seem to do a couple of different variations. Any opinion on differences between the skywatcher and the baader?
Currently I'm just using the generic Skywatcher LPF

Offline chris.bailey

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Re: Low contrast images - suggestions
« Reply #11 on: 14:48:42, 20 January, 2014 »
James

I have only ever used the Astronomik CLS filter http://www.modernastronomy.com/filtersAstronomik.htm#aCls both with CCD and DSLR. For An unmodded DSLR you want the non IR block one.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
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Offline Nomis Elfactem

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Re: Low contrast images - suggestions
« Reply #12 on: 22:06:04, 21 January, 2014 »
James - I use the SkyWatcher LPF which is (actually was as I don't use one at all now since moving house) fine for me but it is at the bottom end of the scale (hence its price comparison). 

I saw recently someone who'd done a review between the difference types (I'll try and find it a link) and the difference was quite stark.  If you're in a high LP area I too would recommend getting a good filter... it will make a huge difference.

S.
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Offline jmbillings

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Re: Low contrast images - suggestions
« Reply #13 on: 08:51:20, 22 January, 2014 »
Yeah, definitely looks like I need a better filter for some of the fainter objects. Something to invest in when I have a little more spare cash. I'll stick to slightly brighter objects in the meantime; I got an unguided M81/M82 with short exposures last year and I'm keen to revisit that.

The CLS looks good, I'm just reading up on people having problems getting the colour cast out. Seems possible if you know the right tricks though... :)

Offline chris.bailey

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Re: Low contrast images - suggestions
« Reply #14 on: 09:07:41, 22 January, 2014 »
James

All colour astro images will need colour balancing, the colour cast from the CLS filter is pretty strong but there will tend to be less LP gradient. An overall colour balance is easier to correct that a complex gradient such as you may get over a reasonable period of integration time where the skyglow in each successive frame occupies a slightly different portion of the image. When this is mixed in with some bright nebulosity is can be very tricky to extract.

Chris
LX200|ZS70|FSQ85|FLT110|Altair DF250RC|EQ6 Pro(Rowan Belt Mod)|ParamountMX
ATIK383L+/EFW2/OAG|Lodestar|Baader 36mm LRGBHaSIIOIII
Starlight Express SXVRH16/ONAG/FW|Lodestar X2|Baader 2" Filters
Starlight Express SXVRH814/ONAG/FW|LodestarX2|Baader 2" Filters
Lunt LS60PTBF1200|DMK41|Quark Chromo
Samyang 135mm f1.8

 

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