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Mono vs Color RASA

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#1 Mmarett

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Posted 17 January 2020 - 08:45 AM

I’m always looking for more information on my next potential upgrade. I live in a heavily LP area, call it bortle 9, basically downtown Manhattan equivalent. I get okay shots with my current 80mmED. I want to upgrade either to a 120mm APO refractor or an RASA/Hyperatar. Now my question is, what is more ideal in a LP region? I shoot mono with the Refractor and would shoot mono with the next refractor but if I went to an RASA is likely switch to color with maybe an LP filter. Since I am so LP do I need to always stay with mono? At f/2 would I wash out right away? I really wouldn’t like to shoot mono with the RASA because then I have to get up all night and I like to shoot on work night. Open to al thoughts and suggestions about a intermediate RIG for a LP area. Don’t worry about mounting. Assume it will be perfectly mounted for this discussion 



#2 jdk

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Posted 17 January 2020 - 09:17 AM

I really wouldn’t like to shoot mono with the RASA because then I have to get up all night and I like to shoot on work night.

This is why I gave up on mono on mine. It's not impossible but you should pretty much either be ready to babysit it all night or integrate different filters on different nights (I've done both and it is irritating). If you go the RASA route, I would go color. But I'm not sure how much a LP filter will help in a bortle 9 site.

 

In that heavy of light pollution my guess is that the stronger argument is in favor of mono with narrowband filters, which makes the refractor option more appealing because you can automate with a filter wheel. 



#3 RJF-Astro

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Posted 17 January 2020 - 09:27 AM

A plus for narrowband is that you can do a lot with two filters: Ha and O3. That means you can do Ha on one night and O3 on the other, or swap only once. I would really make this my focus in bortle 9.

 

I plan to get a RASA too, but I want to keep one high focal length scope for LRGB galaxies and clusters (the 6RC). That is because of it's focal length, but also being able to use a filter wheel.


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#4 Madratter

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Posted 17 January 2020 - 09:38 AM

In that site, I would stick with Mono. Now if you're willing to travel to better skies, then a RASA might make huge sense since you can polish off a picture in one night instead of needing to travel multiple times to get an image.



#5 pyrasanth

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Posted 17 January 2020 - 09:43 AM

I use a RASA 11 with a QHY168C camera under Bortle 8/9 sky conditions.

 

The Celestron RASA either the 8, 11 or 14 work at very fast focal ratios of F2. If you put very little time into your imaging you can still produce fabulous results.

 

A mono camera will capture so much light that even on the faintest objects- provided they can be captured above the ambient light pollution you would only need an hour between each filter and just use 2-3 hours on a colour CMOS camera.

 

If I had to choose 2 filters from my collection it would be the Celestron/Astrodon LPR filter & the Optolong LE enhance.

 

If you search for my posts all the images in the last few months have been captured with the RASA 11 & the QHY168C and not one image is under condition better than Bortle 8. The only limitation is your willingness to give it a go and a bit of experimentation.


Edited by pyrasanth, 17 January 2020 - 09:43 AM.

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#6 pyrasanth

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Posted 17 January 2020 - 09:46 AM

In that site, I would stick with Mono. Now if you're willing to travel to better skies, then a RASA might make huge sense since you can polish off a picture in one night instead of needing to travel multiple times to get an image.

I would if possible get 2 cameras. I would capture the RGB with a CMOS colour & the L with a mono. The results would be spectacular & not a lot more integration time as for every 2-3 hours of colour you would only need 1/3 for the L.



#7 klaussius

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Posted 17 January 2020 - 09:49 AM

This is why I gave up on mono on mine. It's not impossible but you should pretty much either be ready to babysit it all night or integrate different filters on different nights (I've done both and it is irritating). If you go the RASA route, I would go color. But I'm not sure how much a LP filter will help in a bortle 9 site.

 

In that heavy of light pollution my guess is that the stronger argument is in favor of mono with narrowband filters, which makes the refractor option more appealing because you can automate with a filter wheel. 

I image at bortle 9 with an F5, and I'm limited to maybe 60s subs in very good nights if I don't care about star colors.

 

With a RASA, you'd be nearly doing lucky imaging at 9s tops, more realistically 4s. And that's with a LPF.

 

Maybe a dual narrowband would allow longer shots but I still think a RASA would be a waste in bortle 9.


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#8 pyrasanth

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Posted 17 January 2020 - 09:54 AM

I image at bortle 9 with an F5, and I'm limited to maybe 60s subs in very good nights if I don't care about star colors.

 

With a RASA, you'd be nearly doing lucky imaging at 9s tops, more realistically 4s. And that's with a LPF.

 

Maybe a dual narrowband would allow longer shots but I still think a RASA would be a waste in bortle 9.

You clearly don't have a RASA and I respect your opinion but your post is just wrong.....on nearly all counts. I image in a Bortle 8/9 site, have great star colours & good images and I can use long subs. The theory is fantastic on paper but the reality in respect of optimal sub length is somewhat different.

 

I'm currently imaging M51 with 2 minute subs & getting great detail with the Optolong LE enhance filter to try & get a smattering of any HA that may be found.

 

Imaging processing techniques & longer integrations can make up some of the disadvantages of not being under dark skies. A fast focal ratio also helps pull the differences closer- hence my love of fast optics in less than optimal conditions.

 

The RASA is so good that I'd keep it in preference to my C14 keeping image scale out of the considerations.


Edited by pyrasanth, 17 January 2020 - 10:13 AM.

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#9 bobzeq25

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Posted 17 January 2020 - 10:35 AM

I’m always looking for more information on my next potential upgrade. I live in a heavily LP area, call it bortle 9, basically downtown Manhattan equivalent. I get okay shots with my current 80mmED. I want to upgrade either to a 120mm APO refractor or an RASA/Hyperatar. Now my question is, what is more ideal in a LP region? I shoot mono with the Refractor and would shoot mono with the next refractor but if I went to an RASA is likely switch to color with maybe an LP filter. Since I am so LP do I need to always stay with mono? At f/2 would I wash out right away? I really wouldn’t like to shoot mono with the RASA because then I have to get up all night and I like to shoot on work night. Open to al thoughts and suggestions about a intermediate RIG for a LP area. Don’t worry about mounting. Assume it will be perfectly mounted for this discussion 

I have a C8 RASA, and five years of experience with other scopes.  I purchased it for my Bortle 7 skies.  I was getting to a point where good images were multinight projects and I could see I was going to need 10+ hours of total imaging time.  F2 gathers light fast, reducing total imaging time.

 

It has benefits and drawbacks, both are significant. 

 

I first used a 183 one shot color cam.  It did great, here's an image of M45. 

 

https://www.astrobin.com/t5173s/B

 

To get that detail and so much of the dim dust in Bortle 7, with only 1.8 hours of total imaging time, is amazing.  BUT...

 

Proper subexposure was 10 seconds.  More saturated a _lot_ of the image, removing color.  So, 1.8 hours was 662X10".  I knew this was going to happen, and had built a new PixInsight computer in anticipation.  16 cores, 32 threads, it preprocesses 32 subs simultaneously.  Neat to watch.  Once you have the stack, things are back to normal.  (the fast computer is sill useful)

 

I've now also purchased a 183 mono.  The plan is to use it for luminance and H alpha, maybe O(III).  Just getting started with that.  Maybe on separate nights, getting flats with each camera and filter is an issue.

 

The last thing is not small.  At first my images were horrible, stars at one place or another were distorted.  Sometimes even donuts.  It varied every time I took the camera off to shoot darks and bias, and put it back on.  Five years of experience (and PixInsight data) told me it wasn't likely to be collimation, but tilt, maybe spacing.  Likely either in the Celestron camera adaptor or my spacer.   I took a brute force approach, and replaced everything with a one piece PreciseParts adaptor of the "right" optical length.  That pretty much fixed it, there's a bit of a perfectionist issue left, seen if you "pixel peep".  Part of it may be getting that "right" length, especially using different filters. 

 

https://www.cloudyni...pacing-mystery/

 

Maybe tweaking collimation, not going to mess with that right now.

 

F2 gives you a lot, but it's very demanding.  Either PixInsight or CCDInspector is likely mandatory to get it working well.  I hope Baader comes out soon with their much delayed FCCT, a filter drawer system with adjustable tilt.  RASA gives better stars than Hyperstar, but getting them good is not trivial.  I haven't used Hyperstar, but it's unlikely to be much easier.

 

Bottom line.  If you've been imaging less than a year, are looking for a cheap and easy scope, RASA (or Hyperstar) may not be for you.  But, good gracious, they suck down photons _fast_ <smile> which is helpful in light pollution.

 

Different but important issue.  Are you doing gradient reduction in processing?  I think it's a must in light pollution.  Moreso than broadband light pollution filters, which also have drawbacks, and mostly work on emission nebulae, where narrowband is far better.  I pretty much don't use them, although the RASA may or may not change that some. 

 

The plan is to (instead) combine H alpha, and maybe O(III), with one shot color on emission nebulae.  LRGB (L one shot color) on broadband targets like galaxies, the RGB data from a color camera.  Still early days, I only got the scope 6 months ago, only got it working well 3 months ago.


Edited by bobzeq25, 17 January 2020 - 11:21 AM.

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#10 klaussius

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Posted 17 January 2020 - 11:07 AM

Proper subexposure was 10 seconds.  More saturated a _lot_ of the image, removing color.  So, 1.8 hours was 662X10".  I knew this was going to happen, and had built a new PixInsight computer in anticipation.  16 cores, 32 threads, it preprocesses 32 subs simultaneously.  Neat to watch.  Once you have the stack, things are back to normal.  (the fast computer is sill useful)

How long does such a stack take?

 

Trying to compare... not using PI, but my stacks are about ~320x30" and it takes forever (4 threads only). I usually let it work overnight, and it takes at least the whole night, so a few hours.


Edited by klaussius, 17 January 2020 - 11:08 AM.


#11 bobzeq25

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Posted 17 January 2020 - 11:12 AM

How long does such a stack take?

 

Trying to compare... not using PI, but my stacks are about ~320x30" and it takes forever (4 threads only). I usually let it work overnight, and it takes at least the whole night, so a few hours.

Maybe an hour for stacking (integration)?  I do tend to get it running, and go away and do something else.

 

Much less for calibration, cosmetic correction.  I wait for those.  In between for debayering and star alignment.

 

You can pretty much assume 32 threads will work on subs 8 times as fast as 4.  Because PI is very effectively multithreaded.  I also use Linux, which speeds things up.


Edited by bobzeq25, 17 January 2020 - 11:14 AM.

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#12 Brule

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Posted 17 January 2020 - 11:22 AM

With regard to doing narrowband on the RASA keep in mind you can't effectively use the more narrow 3nm filters like you can with your refractor, as it will get a ton of signal loss at that speed. Currently, there are the Baader highspeed f/2 filters, which I have seen reports are around 10nm (though not confirmed by Baader), and some even prefer Astronomik 12nm as being better for the RASA. So it's a tradeoff. You get that fast speed to allow you to capture more data in a given time frame, but you can't use the more narrow filters which more effectively cut out light pollution. Now, how much of it is a trade off in favor of one setup vs another, I'm not sure, and maybe depends on the person and their post-processing skills. If it helps, here is some analysis done by mxcoppell comparing an 85mm f3.85 refractor using 3nm filters with the RASA at 5nm & 12nm. You can see for yourself the difference in the images.

 

That said, I actually have a RASA 8 on the way, and already have an 80mm refractor with a narrowband setup. I'm more getting it for fun than anything else. I think if I only wanted the best data with my bortle 8 skies, then I'd just stay with my 80mm refractor, invest in better Chroma 3nm filters, and spend longer on a given target. However, I decided I enjoy the process of equipment setup and capturing data as much as the end result, so the RASA sounded like more fun.

 

For broadband of larger DSOs (m31, m33, m45) I think the RASA will be great.

 

 


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#13 bobzeq25

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Posted 17 January 2020 - 11:30 AM

With regard to doing narrowband on the RASA keep in mind you can't effectively use the more narrow 3nm filters like you can with your refractor, as it will get a ton of signal loss at that speed. Currently, there are the Baader highspeed f/2 filters, which I have seen reports are around 10nm (though not confirmed by Baader), and some even prefer Astronomik 12nm as being better for the RASA. So it's a tradeoff. You get that fast speed to allow you to capture more data in a given time frame, but you can't use the more narrow filters which more effectively cut out light pollution. Now, how much of it is a trade off in favor of one setup vs another, I'm not sure, and maybe depends on the person and their post-processing skills. If it helps, here is some analysis done by mxcoppell comparing an 85mm f3.85 refractor using 3nm filters with the RASA at 5nm & 12nm. You can see for yourself the difference in the images.

 

That said, I actually have a RASA 8 on the way, and already have an 80mm refractor with a narrowband setup. I'm more getting it for fun than anything else. I think if I only wanted the best data with my bortle 8 skies, then I'd just stay with my 80mm refractor, invest in better Chroma 3nm filters, and spend longer on a given target. However, I decided I enjoy the process of equipment setup and capturing data as much as the end result, so the RASA sounded like more fun.

 

For broadband of larger DSOs (m31, m33, m45) I think the RASA will be great.

+1. 

 

I'm using 6nm Astronomik right now, thinking about getting 12.  Here's some data I developed re 3, 6, 12, unfortunately did not have access to data from the Baader high speed filters.

 

https://www.cloudyni...-3#entry9911447


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#14 Brule

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Posted 17 January 2020 - 12:13 PM

+1. 

 

I'm using 6nm Astronomik right now, thinking about getting 12.  Here's some data I developed re 3, 6, 12, unfortunately did not have access to data from the Baader high speed filters.

 

https://www.cloudyni...-3#entry9911447

Ah, this makes me feel good about using the 12nm Astronomik filters I already own. Thanks for the analysis. Yes, I haven't seen any side-by-side comparison between the Baader highspeed vs the 12nm astronomik, but everything I've read seems to suggest there is no difference or the 12nm is better.

 

When buying the RASA I also emailed Chroma asking if they have any NB filters in the works specifically for F2 and they said they have designed them but have not moved into production yet. I'm not sure how much more effective they will be, but will be interesting to see, assuming they actually surface.



#15 DrGomer

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Posted 17 January 2020 - 01:03 PM

For whatever reason, it feels like PI takes WAY longer to stack than DSS, even with PI batch processing.  These days, I use PI to blink and discard, then calibrate/stack in DSS, then process back in PI.  



#16 bobzeq25

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Posted 17 January 2020 - 06:17 PM

For whatever reason, it feels like PI takes WAY longer to stack than DSS, even with PI batch processing.  These days, I use PI to blink and discard, then calibrate/stack in DSS, then process back in PI.  

It takes longer to do anything well in PI.  If you don't want to spend the time (and the time needed to learn how to use the complex capabilities), it makes sense to use something simpler.  You can get very good results much easier/faster.



#17 pyrasanth

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Posted 22 January 2020 - 05:48 AM

For whatever reason, it feels like PI takes WAY longer to stack than DSS, even with PI batch processing.  These days, I use PI to blink and discard, then calibrate/stack in DSS, then process back in PI.  

We need to be careful with this approach. Do we truly get the same data back when we process in other packages?

 

I trust PI, even if it is a bit slower, to protect the data & produce consistent results across a given work flow.



#18 Mmarett

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Posted 22 January 2020 - 12:50 PM

Does anyone have any experience with a tri-band or quad-band filter on an RASA?

#19 caseyfinn

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Posted 23 January 2020 - 12:34 AM

Does anyone have any experience with a tri-band or quad-band filter on an RASA?

 

I’ve tried the original Triad and Omega NBP filters. The triad doesn’t let through much Ha but acts like an excellent O3 filter. The Omega works ok But halos around bright stars are quite strong. I’m curious also if anyone’s had good luck with Optolong L-enhance as it seems very popular, and it’s not a grand.  



#20 Tim

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Posted 23 January 2020 - 01:01 AM

I’ve tried the original Triad and Omega NBP filters. The triad doesn’t let through much Ha but acts like an excellent O3 filter. The Omega works ok But halos around bright stars are quite strong. I’m curious also if anyone’s had good luck with Optolong L-enhance as it seems very popular, and it’s not a grand.  

 

A guy on youtube used the Lenhance with his Rasa - I asked if he could see the difference between that and the F2 filters and he said no.. I am not sure that's the case but his images with the Lenhance filter looked good to me.  check it out on you tube and look for Roswell Astronomy I believe.




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