LP Filter for comet ISON

[multiweb]

Tonight might be clear and I'm setting up with the C11/hyperstar to do some deep shots see if I can pick up comet ISON. My problem is light pollution. I'll be shooting with the QHY9 mono. Is there any kind of dense filter that I can use to minimise that? I have Baader Nebulae filters, RGB set, UV/IR block, etc...

Ha is out of the question I suppose. Would it turn up in Oiii? Just thinking aloud here. What would work for that comet. What is it made out of? Anything that will stop me from taking flat frames. It's pretty bad LP.

TIA for any pointer. :thumbsup:

[Merlin66]

Marc,
If you check out Rob K spectra of the comets you'll see the pronounced SWAN bands of C2.
Any filter that doesn't pass these bands will rob the light away from the comet image.....
Lumicon used to sell a "Swan Comet filter" which had a band pass to pick up all these bands.
http://www.iceinspace.com.au/forum/showthread.php?t=104028&highlight=rob

[multiweb]

Cool - thanks. So to make sure I'm reading this right. Ideally I'm looking at the range between 450nm to 650nm right?

So the Baader Lum filter ranging from 400nm to 700nm would cover the range and hopefuly be narrow enough to clip out a lot of unwanted glow?

Or can I be more specific and use the Blue or Green only to narrow the range further? Is ISON more green than blue?

[Merlin66]

http://www.astroshop.eu/comet-filters/lumicon-swan-band-comet-filter-1-25--/p,6750#tab_bar_1_select

If you look at the transmission curve it has a bandwidth to cover the brightest Swan band around 520nm.
(An "L" filter doesn't filter any visible wavelengths.....)

[multiweb]

:confuse3: Ok I get it now. It's much narrower than what I thought and it's in between blue and green so I can't combine any of the filters I have to get me that range. It's in the overlap zone. I wish you could arrange filters some how and do an exclusion rather than an union. :P

There's always another filter to buy.... Might try my luck in Oiii tonight. I know it's narrow but it's within that area and it's better than letting all the spot lights in.

[mithrandir]

Stacked filters should subtract. eg, Astrodon Gen 2 Blue+Green (both E and I series) should only allow about 490 to 510nm There is no overlap in the bandpass with their Green and Red filters.

[Merlin66]

Yeah, but...
The final transmission efficiency is the multiplier of each transmission at the over lap wavelengths.......

[mithrandir]

True, but given the specs for those filters you should a reasonable amount of light in a narrow band centered on 500nm. Both are supposed to pass close to 100% at 500nm.

[multiweb]

Of course and that's what I want. So if I stack the Green + Blue I will get the area common to both in the transmission chart. I don't know what I was thinking. Cool. I'll do that next time. Oiii turned out to be way too narrow after all.

[Suzy]

Hi Marc,

Damian Peach imaged ISON recently.
Just look at that gorgeous little tail already, and it's still over 700 million kms away. :)
Looking forward to seeing more Ison pics. :D

134572

[multiweb]

I can see a faint tail in mine too but the Oiii filter I used is too narrow. John Glossop (JohnG) did some gorgeous shots of it with his FSQ106. You can see the tail structure even.