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Less common filters to use in 8th slot?

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#1 medderx

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Posted 28 July 2021 - 04:10 AM

Im looking at swapping out my current set of baaders for their new “cmos optimized” line, still not sure if I want to go with 3.5/4nm or 6.5nm. Anyways my 8th slot has just been filled by a clear filter that sees no use, what are some less than common filters that would be interesting to use (36mm needed). The few that I have come up with are sloan i’, H-βeta, “dark”, or an ir like 685nm for times when I want to look past the seeing but the i’ could do that too somewhat.

 

The camera is a stt-8300 so there is no use for a planetary specific filter like CH4.

 

Thanks for any and all suggestions.



#2 happylimpet

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Posted 28 July 2021 - 04:24 AM

ZWO 850nm longpass is fun for highly obscured galaxies, or for just getting a different take. M42 for example shows much less nebulosity and many more stars. That would be my suggestion, or the 685 as you suggest.

 

Im surprised you dont find a use for the clear filter. I find one very useful for imaging faint targets like obscure comets and KBOs.


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#3 pyrasanth

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Posted 28 July 2021 - 05:20 AM

A Hydrogen beta filter is good for the Horse Head nebula.



#4 Narrowbandpaul

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Posted 28 July 2021 - 05:38 AM

Nice to have a spare slot!

I wouldn’t go with Hbeta. It will have the same spatial distribution as Halpha (since it’s all hydrogen), it will just be weaker. I believe the quantum mechanics shows that it would be 2.9x weaker for a fully ionised gas. However deviations from the theoretical ratio would indicate dust.

I would go for IR. I have the Sloan filters including I’ and whilst I don’t have a lot of experience it’s quite cool. It’s a subtle effect…less gas and very red or reddened stars are much more prominent. Maybe not an exciting filter on its own but as part of RGB it could have a good effect. M81 is just the core you get, the arms are dim in IR, reflecting the kinds of stars found there.

UV is interesting too but maybe not from sea level…too much extinction though I think cameras like the IMX455 do have a decent NUV response.

Other exotic narrowband would most likely be NII which necessitates a 3nm Ha or the HeII which is very faint but shows up in planetary neb and WR neb

Good luck
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#5 happylimpet

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Posted 28 July 2021 - 08:30 AM

A Hydrogen beta filter is good for the Horse Head nebula.

Only for visual, because the eye is insensitive to H alpha.



#6 OldManSky

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Posted 28 July 2021 - 08:44 AM

I have a "dark" filter in my 8th slot.

What's "dark" filter, you ask?

It's an old, cheap Orion moon filter, spray-painted flat black on both sides.

 

It allows me to do dark frames automated and unattended, just by having NINA select the "dark" filter and then running darks as part of a sequence.

As long as I do them before twilight.  The dark filter works great, but there are small light leaks in other parts of the system -- tiny ones, but ones that mean I can't do darks in my backyard observatory with the roof open if it's beyond the beginning of twilight.

 

But for 30 minutes before starting an imaging run at night, or 30 minutes after one during early morning pre-twilight -- it works great :)


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#7 TopherTheME

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Posted 28 July 2021 - 12:56 PM

I have a free slot as well and would really like something for monochrome images of galaxies but don’t know what. I thought about using a generic light pollution filter but from what I’ve read you’re usually better off not using one. The IR filter is an interesting idea but I worry how well it blocks light pollution.

#8 Dan Crowson

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Posted 28 July 2021 - 05:14 PM

I have a "dark" filter in my 8th slot.

What's "dark" filter, you ask?

It's an old, cheap Orion moon filter, spray-painted flat black on both sides.

 

It allows me to do dark frames automated and unattended, just by having NINA select the "dark" filter and then running darks as part of a sequence.

As long as I do them before twilight.  The dark filter works great, but there are small light leaks in other parts of the system -- tiny ones, but ones that mean I can't do darks in my backyard observatory with the roof open if it's beyond the beginning of twilight.

 

But for 30 minutes before starting an imaging run at night, or 30 minutes after one during early morning pre-twilight -- it works great smile.gif

The STT has a real shutter. There's little need for a dark filter.



#9 Dan Crowson

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Posted 28 July 2021 - 05:16 PM

If you ever think about scientific work (say variable stars), a V filter is what I use in my 8th slot. You can get away with the 1.25" in a 36mm holder (I'm assuming 36mm because you mention the STT. Vignetting isn't too bad and matters little for the science work.
 
Dan


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#10 happylimpet

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Posted 29 July 2021 - 03:22 AM

I have a free slot as well and would really like something for monochrome images of galaxies but don’t know what. I thought about using a generic light pollution filter but from what I’ve read you’re usually better off not using one. The IR filter is an interesting idea but I worry how well it blocks light pollution.

For me, very well. Light pollution is much better generally in the IR - people dont bother lighting up the sky in IR any more than they do by mistake, which is possibly a lot less now that incandescent bulbs are being phased out. At least LED lights are restricted pretty much to the visible spectrum.



#11 OldManSky

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Posted 29 July 2021 - 07:34 AM

The STT has a real shutter. There's little need for a dark filter.

Right...I forgot they had mechanical shutters.  



#12 Peregrinatum

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Posted 29 July 2021 - 10:40 AM

I have an Atik 9 slotter, #8 is an Hb which I never use but thought was a good idea at one time, #9 is a dark and I use this when I shoot my flat darks inside the house



#13 medderx

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Posted 31 July 2021 - 02:08 AM

ZWO 850nm longpass is fun for highly obscured galaxies, or for just getting a different take. M42 for example shows much less nebulosity and many more stars. That would be my suggestion, or the 685 as you suggest.

 

Im surprised you dont find a use for the clear filter. I find one very useful for imaging faint targets like obscure comets and KBOs.

Yeah I think I will go with an IR or a sloan i' which is 695-844. An 850 I think would be pushing it for me since I'm at f/10 and my QE down there is about 20%. 


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