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Filter Options for RASA 11

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#1 MountainAir

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Posted 20 March 2021 - 01:59 PM

I have a dilemma I'm trying to solve without going broke.

 

I have a RASA 11 V2, with ASI6200MC-Pro and ASI6200MM-Pro cameras.

 

For the mono camera, I use the Baader UFC system with 50x50mm square Baader f/2 HighSpeed filters.  Narrowband filters on the RASA really should have a shifted bandpass, otherwise you lose too much light with "normal speed" filters.  It has worked great, except Baader still does not have the OIII filter in stock so this camera and filter setup has been next to useless.  Well, that's too harsh -- I have been capturing Ha and SII data, but will have to supplement it with OIII data next year (since my targets are drifting out of season).

 

For the OSC camera, I have the Celestron Light Pollution Imaging Filter for RASA.  I believe this filter may actually be made by Astrodon, but that could have been a rumor.  Anyway, it seems to be a great filter -- it handles my Bortle 6 skies well, and the colors it produces are pretty natural.  The problem that I have is the Baader UFC telescope adapter is not built to Celestron's custom adapter specs.  It sits flat on the lens group instead of having negative space, so it ends up sitting on top of the Celestron filter ring screwed into the RASA.  This is a horrible oversight, and it means I cannot use UFC with this filter because it introduces spacing and tilt issues.

 

In a simple world, I would just sell the Celestron filter (as good as it is) and buy a replacement 50x50mm filter for the UFC.  However, I don't see any of those available (such as the Triad Ultra Quadband, which only appears to be available in 65mm square sizes), plus they are not band-shifted to work with ultra-fast optical systems like the RASA.  Am I missing some good options?

 

I've looked into various other solutions.  I started with PreciseParts.com but I need the solution to be spacing-adjustable.  Then I came up with a PreciseParts adapter that connects to the Baader M68 Varilock, but then that needs an M68 gender changer to the ZWO 68mm tilt adapter that I can't seem to find anywhere.  I could just adapt it to the existing m54 tilt adapter I suppose, but I was hoping to keep everything M68.

 

I've also looked into some very interesting custom-engineered solutions that also allow precise tilt and spacing adjustment via micrometers... but they are expensive and I'd rather not spend more for an adapter than the filter I'm trying to save.

 

Anyway, is there some option out there that I am missing?  Other than selling the OSC, of course (I love my mono, but with the RASA able to capture so much light it makes OSC cameras much more practical, especially since I can't mount a filter wheel).

 

Thanks in a advance.



#2 bobzeq25

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Posted 20 March 2021 - 02:42 PM

I'm planning on using these with my C8 RASA.  The filter may be of interest to you.  Note that it's for emission nebulae, ONLY.

 

https://agenaastro.c...-backfocus.html

 

https://astrohutech....la-booster-nbx/

 

I've also used custom PreciseParts adapters, specced to avoid spacers.  I've had no luck with setups requiring spacers, at all.  It's unlikely many are made to adequate standards of parallelism.  The PP adapters have worked, first light with the Artesky last night was very promising.


Edited by bobzeq25, 20 March 2021 - 02:46 PM.


#3 RogeZ

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Posted 20 March 2021 - 02:46 PM

You are missing a great option, the Astronomik MaxFR. I had them in my 11" V2 RASA in 50x50mm. They are great!



#4 pyrasanth

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Posted 20 March 2021 - 02:46 PM

I have exactly the same setup as yourself and use the Astrodon/ Celestron LPR filter with the Precise parts custom adapters that screw over the central camera assembly mounting and fit the Baader UFC dovetail. I think you will be very surprised to learn that most of the tilt introduced into the RASA system comes from the accumulated errors in the adaptors and not the imaging train. You may get away without needing tilt adjustment if your adapters are built with enough quality with regard to maching accuracy.

 

I ordered the precise parts adaptor at 21 mm for the ASI6200 and using the Baader variable spacer of 15-20mm I was able to dial in a pretty good flat field. I suggest if possible you try and get a compromise on spacing so you can use with more than 1 camera using the variable spacer.

 

I have a full set of the fast filters for the RASA that I purchased a few years back and these work very well with the mono ASI6200 camera.

 

I've shown the adaptor I use below.

 

ADP1_CN.png    ADP2_CN.png


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#5 MountainAir

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Posted 20 March 2021 - 04:05 PM

You are missing a great option, the Astronomik MaxFR. I had them in my 11" V2 RASA in 50x50mm. They are great!

They look fantastic for narrow band, but they don't seem to have a quad-band version for OSCs (I already have 2 out of the 3 NB f/2 filters I bought from Baader).  They are also very expensive, at almost $2000 US for 3 NB filters (6nm).  And maybe I'm missing it, but I don't see 50x50.  I only see 50mm round.

 

I did stumble across Aluxa at one point, but didn't recall hearing about them in the forums.  They have a 5-band-pass filter that looks interesting, and they say they can do custom sizes.  I'm not sure if they'll work with an f/2 OTA, though. 

 

https://www.alluxa.c...and-filter.html


Edited by MountainAir, 20 March 2021 - 04:09 PM.


#6 RogeZ

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Posted 20 March 2021 - 05:08 PM

Astronomik makes 50x50mm, I had them.

On the RASA, you must either keep bandpasses large or get preshifted filters with medium bandpasses. I would be worried of any of the multiband filters are they tend to be narrow.

#7 bobzeq25

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Posted 22 March 2021 - 07:19 PM

Astronomik makes 50x50mm, I had them.

On the RASA, you must either keep bandpasses large or get preshifted filters with medium bandpasses. I would be worried of any of the multiband filters are they tend to be narrow.

The Hutech NBZ duoband is specifically designed for fast scopes, and has a decently narrow bandwidth (10nm-ish?).  Check out the bandwidth curves with various speeds.

 

https://www.sciencec...filters/nbz.htm


Edited by bobzeq25, 22 March 2021 - 07:20 PM.


#8 CloudGazer

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Posted 10 April 2021 - 03:08 PM

IDAS has a dualband filter (Ha/O-III) for very fast scopes.  Check out the curves here: https://www.firstlig...-dual-band.html

 

Not 50x50, but 48mm and 52mm... But I believe you can get a 48mm round slider for the Baader system, and that should not vignette the RASA 11?


Edited by CloudGazer, 10 April 2021 - 03:09 PM.


#9 bugbit

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Posted 10 April 2021 - 06:16 PM

I made this earlier this week for my own reference but it may have some relevance here, This is for a RASA 11 and it shows how big of a area is needed to cover the light cone at 0.7 inches above the sensor.

 

 

F2.2 light cone via round and square filters at 0.7 inch in color.jpg Annotation 2021-04-05 181222.jpg


Edited by bugbit, 10 April 2021 - 06:37 PM.



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