Whats a good light pollution filter for imaging?

[gregbradley]

I am interested to hear what the consensus is on the best light pollution filter for imaging?

Also do you think focal length or F ratio of scopes is relevant when imaging in light polluted areas?

Do you need to take shorter exposures with CCD cams? I know you need to limit exposures with DSLRs otherwise you get the sky glow easily.

Greg.

[Marke]

Greg
I went thru this recently and from what I learnt the Hutech was the way to go http://www.sciencecenter.net/hutech/idas/lps.htm
I ended up getting the LPS-P2-48 and very happy with it short of
going narrow band.

[gregbradley]

Thanks for that Mark.

I remember a thread about this sometime ago and IDAS also rated well.
Hutech supplied them as well.

Are you using this with a DSLR or CCD camera?

What scope do you use and how are you finding it in light polluted areas?

Cheers,

Greg.

[Marke]

Greg I used it with a D700 and just recently with a qhy10 on a C9.25
Havent tried with the new RC10 yet.
I had a Lumicon before and found it introduced colour cast which the
Hutech doesnt , and I was supprised how good it looked from the prelim
images at 5min exp at least.

[cventer]

Greg

I have used an idas lps from suburbs of Melbourne With great success. I typically used it on my fs-102 (your old one I bought from you) at f9 and f6

I found with sbig-ST-2000xm I had to keep my subs to about 6 min before skyglow became and issue. Green channel was always most troublesome and even with idas needs a fair bit of cleanup in photoshop.

But definitely needed from suburbia.

Cheer
Chris

[DavidTrap]

I had limited success with the Hutech one with a DSLR. Rather than persevere, I decided I'd shoot narrowband from the city and use the excuse of needing to shoot LRGB as a reason to go away to the country! Also used this as justification to buy a CCD camera.

DT

[dugnsuz]

For DSLR I've used the IDAS LPS-2 and the Astronomik CLS-CCD.
Hutech/IDAS filter is better in colour correction IMO.
I keep returning to that filter - just bought the MFA clip in version from Peter Tan in Honkers!
http://www.tan14.com/Dwg/mfa.pdf

I've found the LPS-2 cope with sky glow very nicely too - allows me 15min RGB images when required.
Good Luck
Doug

[leon]

Yep everything that Doug said.

Leon

[Paul Haese]

Although I have only used an IDAS filter for DSLR I did find it restrictive to sub lengths. I don't think I could go back to that again. Just my opinion but I think you need to go with narrow band.

[RobF]

I always use an IDAS LPS when doing CCD LRGB from the 'burbs Greg and have been very happy with colour recovery. It just requires different colour cal at the processing stage. Then every time I go "dark sky" I think I'm nuts, then some new success from the city renews my enthusiasm. In reality I think its going to depend heavily on the brightness of the neb, brightness of the pollution, moon, etc. A slightly dimmer object might give a LOT less signal to noise from the city.

I've read a bit about optimal sub times lately and would be interested to hear more about people's thoughts there too. It would appear to be a very subtle thing depending on nature of pollution, CCD response, filter bandpass and brightness of the object. I found this article excellent:
http://www.cloudynights.com/item.php?item_id=1622

It also discusses in detail another topic I don't think is given enough discussion - the optimal number of subs (as well as their length) to start to tackle typical noise signals effectively. For example, if you know you really need at least 5 goods subs per filter and you're shooting LRGB and the L data will be collected at least twice as long as the RGB then that starts to give you an idea just how much data you'll need, especially for those of us without the luxury of an observatory setup.

Oops, anyway, back to LPS. +1 for the Hutech :)

[cventer]

Interesting article in that link. Although i need someone with many more brain cells than i have to summarise it up in terms of the question Greg asked.

Be nice to turn that into some rules of thumb for various types of objects at varying degrees of suburban locations.

[gregbradley]

Good to hear the FS102 is being put to good use.





Hehe sounds as good as any.



Thanks Doug. I should try one out even though my skies are reasonably dark to the west I still get some glow I have to process out.



Thanks Leon.

[White Rabbit]

I use a 5dmkii unmodded, 2x power mate on a 102 f7 refractor and the cls 2" filter. The cls clip does give you an extended blue channel but if you set dss to align the rgb channels and set the black point to 0 after it stacks it's a non issue.

I live in the inner west 9 km from syd cbd so my sky glow is significant. The longest subs I can do is about 10 min but only past zenith facing west otherwise I stick to 5 min subs.

[CoolhandJo]

I use hutech lps2 for all my city based imaging both for Dslr and ccd. I have not yet reached sky glow at 10 min subs. The best way to judge is to look to the spectral graph. If you look at the lps2 you note that it is very narrow in it's blocking of the worst types of light pollution whereas other filters overlap into the wavelength you want to preserve.
Here is a link to the graph http://www.sciencecenter.net/hutech/idas/filtdata.htm

[gregbradley]

Thanks for the replies. Very informative.

Cheers,

Greg.