#1  
Old 09-11-2018, 04:42 PM
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Merlin66 (Ken)
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Bi wavelength filter!

https://www.cyclopsoptics.com/astron...d-filter-48mm/

Appears to give good filtering and suppression of background lighting.
Would need an OSC camera to separate and process the OIII and Ha images.
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Old 10-11-2018, 03:12 PM
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Lognic04 (Logan)
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You'll find it's just a rebranded UHC filter:
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Old 10-11-2018, 03:22 PM
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Merlin66 (Ken)
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Logan,
The tight transmission curves at OIII and Ha shows it's much more than an UHC filter.
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Old 10-11-2018, 09:52 PM
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Quote:
Originally Posted by Merlin66 View Post
Logan,
The tight transmission curves at OIII and Ha shows it's much more than an UHC filter.
Yes the peaks are much tighter in bandwidth on the dual narrowband filter compared with the UHC filter. Some time ago I had the idea of using a UHC filter in this way with a DSLR and using the BLUE channel for OIII, and RED channel for Ha. For a dark sky (no light pollution) one could even use the GREEN channel with either the dual narrowband or UHC filter. I had made a comparison of these together with a Nikon D800 sensor response. I will look for the comparison and post it here later.

Best
JA
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Old 04-03-2019, 03:36 PM
gb44 (Glenn)
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Possibly best filter for DSLR

Ken
Can you give us an update on this filter?
Did you buy it?

Cheers
GlennB
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Old 04-03-2019, 03:47 PM
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Glenn,
No, I didn't buy this filter.
I only do spectroscopy, so it wouldn't be of much help to me.

I see over on SGL that there are some members starting to use bi wavelength filters....early days.
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Old 04-03-2019, 03:48 PM
gb44 (Glenn)
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Ok thanks.

I also found this $300 filter.
https://www.cyclopsoptics.com/filter...pectra-filter/

GlennB
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Old 04-03-2019, 04:35 PM
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I had made a comparison of these together with a Nikon D800 sensor response. I will look for the comparison and post it here later.

Best
JA
Here is that comparison of the UHC filter & Dual Narrowband filter against the Nikon D800 spectral response. The curves are aligned by eye at 400 and 700nm.

As is evident the peaks are much tighter in bandwidth on the dual narrowband filter (Bandwidth = ~15nm OIII & ~18nm Ha [even less if the D800 response were to be included) compared with the UHC filter(Bandwidth = ~50nm OIII & ~28nm Ha [with D800 response included - brown line line on top graph]). At a fraction of the cost, or perhaps something that one might already have, I would give it a try in the same way as the dual narrowband filter is used on colour cameras, for "narrowish" - band imaging or of course stick to "normal" colour imaging with it to remove some light pollution.

Best
JA
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Last edited by JA; 04-03-2019 at 04:50 PM.
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Old 04-03-2019, 04:43 PM
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JA, et al,
I think Glenn was hoping to see some actual AP images with the bi-wavelength filter.....
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Old 04-03-2019, 05:03 PM
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Quote:
Originally Posted by Merlin66 View Post
JA, et al,
I think Glenn was hoping to see some actual AP images with the bi-wavelength filter.....
Hi K,
He didn't mention wanting to see images otherwise I would have pointed him to the sample images in your original link. Image number 5 in particular is an excellent demonstration of a difference, purportedly of the effect with and without the filter.

Best
JA
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Old 04-03-2019, 07:28 PM
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I got the STC Duo from Cyclops a few weeks ago. Using it on an asi071 OSC.

http://www.iceinspace.com.au/forum/s...d.php?t=173501
http://www.iceinspace.com.au/forum/s...d.php?t=173374

Processed as an OSC image. Need long subs as the two bands are narrow (10nm). Need 10min subs with the filter -compared to 1.5min with just a uv/ir filter. I'm still capturing lights for these images.
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Old 04-03-2019, 07:39 PM
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Chris,
How does the SCT bi-filter compare with the smaller bi- wavelength version??
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Old 04-03-2019, 08:12 PM
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What's the other one you are talking about Ken? I got this one

STC Astro Duo-Narrowband Filter (48mm / 2")
https://www.cyclopsoptics.com/astron...filter-48mm-2/

Sorry, I get confused easily ...
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Old 04-03-2019, 08:41 PM
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Chris,
The term SCT threw me....
There are also bi and tri wavelength filters designed as full aperture SCT filters.
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Old 04-03-2019, 09:34 PM
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Oops. Yes STC filter. This is the best comparison I have of using the Duo filter, on the Tarantula.

First is 2.7 hours of 90sec lights with UV/IR filter.
Second is 2.8 hours of 6min lights with STC Duo narrow band-filter.

Ignore the difference in resolution - as the first image is binned 2x2, the second isn't.

Edit: the first shot is at f5.9 and the second with the duo is f5.0.
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Last edited by ChrisV; 05-03-2019 at 09:09 AM.
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Old 05-03-2019, 11:09 AM
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Interesting thread. I was wondering about this filter too as I use the UHC one currently. For me I dont think I can us the bi-wave, though this thread has me thinking, especially seeing the wavelength graph comparisons that I should look at stripping my OSC subs and try processing as Ha Si filtered data and see what i get.
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Old 05-03-2019, 11:20 AM
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Quote:
Originally Posted by sil View Post
Interesting thread. I was wondering about this filter too as I use the UHC one currently. For me I dont think I can us the bi-wave, though this thread has me thinking, especially seeing the wavelength graph comparisons that I should look at stripping my OSC subs and try processing as Ha Si filtered data and see what i get.
I would definitely try that as the OIII & Ha bands are typically "only" about 2 to 3 times wider with the UHC filter if we also take in to account the camera's Ha response. It would be great to see such.

Best
JA
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Old 05-03-2019, 02:21 PM
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Quote:
Originally Posted by Merlin66 View Post
Logan,
The tight transmission curves at OIII and Ha shows it's much more than an UHC filter.
Correct. That's why the stars don't bloat after 700nm.
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Old 05-03-2019, 05:13 PM
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Before getting the duo filter I used a UHC filter a fair bit. The duo is a very different beast due to the much narrower bandpass as others have mentioned. I'm guessing but think I'd need subs at least 5x longer to get background levels equivalent to those with the UHC filter. Might do a comparison on a dud night.
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Old 05-03-2019, 05:58 PM
glend (Glen)
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Chris the STC Duo certainly looks like a mono layered narrowband result. Good investment. I would be tempted to try it with my Nikon (when night's get cooler).
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