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Rasa 8" OSC vs Mono and Baader Highspeed F2 Filters

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#1 caseyfinn

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Posted 14 August 2019 - 11:01 PM

I still consider myself to be a newbie in this hobby .... but

Last night I was checking out the differences between single images of the veil nebula from a month ago while taking new images. I recently "invested" in a dedicated Celestron light pollution filter and Baader's highspeed F2 narrowband filter set for a Rasa. I image under a suburban sky dome,  maybe Bortle 6/7.  Seeing and transparency usually are good here in the desert (except during the monsoon season).

This first image was taken using a Triad filter at unity gain for 120 sec. with an ASI183mc. A masked stretch applied:

 

Veil_Nebula__1x1_120.000secs_0.50C_00002056.jpg

 

https://drive.google...iew?usp=sharing

 

 

This image was taken last night under a lot of moonlight with the same camera but mono, ASI183m, and a celestron  light pollution filter and baader ha F2 filter. Unity gain but only 60 sec. :

 

HA__Tycho_2687_948__1.00mins_0.50C_00005363_c_r.jpg

 

https://drive.google...iew?usp=sharing

 

Contrast between the color camera and mono camera is remarkably improved. As for signal to noise ratio, the difference is a large factor. It seems like the jump in sensitivity from DSLR to one shot color is about the same jump from OSC to mono for deep space imaging. Another benefit of mono is how fast pixinsight rips through the load. After reading time and again on the benefits of mono vs osc I'm glad I made the jump. 

 

F2 filters (o3 and s2 reveal great detail also) work very well. I have no experience with any other brand or type but these seems very sensitive. Using a fairly small sensor with tiny pixels combined with small filters (1.25") and a really fast astrograph seems like a very efficient and not to expensive imaging system.

 

I just got a hyperstar cable manager to remove the funky spikes but haven't tried it out yet.

 

 

 

 

 

 



#2 44maurer

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Posted 15 August 2019 - 12:47 AM

why are you using a LP filter with the narrowband filter?


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#3 RogeZ

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Posted 15 August 2019 - 05:41 AM

Also, Triad filters cannot be used with RASAs. You are losing a lot of light due to shift.
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#4 elmiko

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Posted 15 August 2019 - 01:00 PM

I don't see any color or barely any signal?? Your targets are light grey.

Mike



#5 kingjamez

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Posted 15 August 2019 - 01:18 PM

The Triad is all but useless on the RASA.

 

I use an Optolong L-eNhance and it's performance in Ha leaves a lot to be desired. I'm looking for a filter like the L-eNhance with wider bandpasses so that the significant shift due to F/2 doesn't wipe out the Ha.

 

I'd like to see a comparison between the OSC with the Celestron LPR filter and the Baader F/2 Filters on the 183m with equal times between (for instance 3 hours OSC, 1 hour Ha mono, 1 hour O3 mono, 1 hour S2 mono).

 

The current shootout for my RASA8 is between the L-eNhance on OSC (ASI183MC) and 12nm Ha and O3 on an ASI1600mm-c camera. If the skies will cooperate I'll have the comparisons soon.

 

How is your spacing? Where are your filters mounted? I noticed quite a bit of aberration in your corners that shouldn't be there on the 183MC with it's tiny sensor. 

 

-Jim


Edited by kingjamez, 15 August 2019 - 01:27 PM.


#6 kingjamez

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Posted 15 August 2019 - 01:23 PM

I don't see any color or barely any signal?? Your targets are light grey.

Mike

You have to debayer the color image from the 183mc. 

 

I also did a 120 second image of the veil last night on my RASA8 using the L-eNhance and the ASI183MC. I'll put it up here for reference when I get home tonight. It's pretty different than your triad filter example.

 

-Jim


Edited by kingjamez, 15 August 2019 - 01:25 PM.

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#7 caseyfinn

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Posted 15 August 2019 - 01:29 PM

"why are you using a LP filter with the narrowband filter?"

 

I tried without and it seems there is more signal with the filter in place. I could certainly be mistaken though. I'm still testing/learning what works best. I'm guessing by your question you think it's a bad idea? My thought was to just leave it in place unless I go to a dark site because of local light pollution.

 

"Also, Triad filters cannot be used with RASAs. You are losing a lot of light due to shift."

 

I asked OPT what they recommend: the Triad. Amazing how little contrast came though. 

 

"I don't see any color or barely any signal?? Your targets are light grey.

Mike"

 

Sorry for such poor examples. They are single jpeg images and really don't look that great on CN. On my large UHD monitor  the original files look very different. They are gray still, btw.

 

Cheers


Edited by caseyfinn, 15 August 2019 - 02:56 PM.

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#8 kingjamez

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Posted 15 August 2019 - 02:27 PM

 

Sorry for such poor examples. They are single jpeg images and really don't look that great on CN. On my large UHD monitor  the original files look very different. They are gray still, btw.

 

Cheers

The color is quite good on the 183MC / triad image, and it's not a bad example, exactly what I'd expect. Why do you say it's gray? 

 

Here it is stretched and resized to fit the 500kb rule... overall there is more Ha than I thought initially, but that red halo is wicked.

Attached Thumbnails

  • Veil_Nebula__1x1_120_000secs_0_50C_00001964_c_RGB_VNG_ABE1.jpg

Edited by kingjamez, 15 August 2019 - 02:34 PM.

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#9 caseyfinn

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Posted 15 August 2019 - 02:38 PM

"How is your spacing? Where are your filters mounted? I noticed quite a bit of aberration in your corners that shouldn't be there on the 183MC with it's tiny sensor."

 

I've cropped most of the oblong corners in the past and really haven't tried to play with the spacing as I was under the assumption that  my imaging train was the correct configuration/backspace: ZWO camera  attached directly to a starizona filter drawer then to the camera rotator/adapter from celestron. The celestron light pollution filter is screwed in place in place of the clear glass insert provided with the scope. If you have any recommendations please share. 

 

"I'd like to see a comparison between the OSC with the Celestron LPR filter and the Baader F/2 Filters on the 183m with equal times between (for instance 3 hours OSC, 1 hour Ha mono, 1 hour O3 mono, 1 hour S2 mono)."

 

I plan on more testing, and I'' try more of an apple to apple approach but I'd bet that the SNR from the mono F2 combo is going to be extremely effective. I'll repost here later, final images.



#10 kingjamez

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Posted 15 August 2019 - 02:55 PM

Last night I went a little nuts. I removed the clear filter from it's housing and replaced it with my L-eNhance filter. This would be a similar setup to yours with the Celestron light pollution filter. From then I used T-thread extensions to directly connect the ASI183mc with no filter drawer, but with pretty accurate spacing (25mm from surface of the T-Thread adapter to the camera sensor). I used the 11mm female-female ZWO adapter and a 7.5mm t-thread extension.

Here is aberration inspector of one of my subs and your 183mc sub.

Attached Thumbnails

  • His_RASA_Stars.jpg
  • My_RASA_Stars.jpg

Edited by kingjamez, 15 August 2019 - 10:45 PM.


#11 MikeMiller

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Posted 15 August 2019 - 03:41 PM

On stacking a LP filter with narrowband;

 

1. Compare the bandpass of the LP filter to the narrowband filter, you will see that there is no point in stacking them. (Yes, I know Baader is secretive about the bandpass of the f/2 filters, but it works mostly like a normal narrowband.)

2. Stacking filters in this way will change the light path distance and can mess up the focus and collimation of the Hyperstar. (Yes, it is that touchy. I also ran into this problem using the Starizona Canon EF lens adapter and f/2 camera lenses.)

 

I have found that using different filters causes some issues, since they have different focus requirements. I only ever use the f/2 Baader filters for Hyperstar now, and don't shoot with a LP or clear filter. I just create the luminance from combining the HaOIIISII data together.


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#12 caseyfinn

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Posted 17 August 2019 - 12:40 AM

Kingjamez:

 

I took some measurements but only have my sons school ruler, so ...

IMG_4537.gif

 

If you assume the female and male connectors negate each other then this total width looks like 18.5mm. I suppose you could use some of those shims ZWO provides to adjust in of out a bit but it might just be the difference between one filter or two filters in line like Mike previously mentioned.

 

 



#13 kingjamez

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Posted 17 August 2019 - 05:55 AM

Kingjamez:

 

I took some measurements but only have my sons school ruler, so ...

attachicon.gif IMG_4537.gif

 

If you assume the female and male connectors negate each other then this total width looks like 18.5mm. I suppose you could use some of those shims ZWO provides to adjust in of out a bit but it might just be the difference between one filter or two filters in line like Mike previously mentioned.

Thank you very much! I really appreciate it! I bought my Starizona Filter Drawer used so I'm wondering if the previous owner did something to make it longer... this helps. thanks again.



#14 flyboy9990

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Posted 17 August 2019 - 04:55 PM

"How is your spacing? Where are your filters mounted? I noticed quite a bit of aberration in your corners that shouldn't be there on the 183MC with it's tiny sensor."

 

I've cropped most of the oblong corners in the past and really haven't tried to play with the spacing as I was under the assumption that  my imaging train was the correct configuration/backspace: ZWO camera  attached directly to a starizona filter drawer then to the camera rotator/adapter from celestron. The celestron light pollution filter is screwed in place in place of the clear glass insert provided with the scope. If you have any recommendations please share. 

 

"I'd like to see a comparison between the OSC with the Celestron LPR filter and the Baader F/2 Filters on the 183m with equal times between (for instance 3 hours OSC, 1 hour Ha mono, 1 hour O3 mono, 1 hour S2 mono)."

 

I plan on more testing, and I'' try more of an apple to apple approach but I'd bet that the SNR from the mono F2 combo is going to be extremely effective. I'll repost here later, final images.

In the RASA manual it states 2 pieces of glass are NOT to be used so if your using a filter slider unscrew and remove the glass over the corrector group. My son and I also use the same Baadar high speed Ha filter/StarAzona filter slider but with the clear glass lens removed from our RASA11. I believe it's likely your elongated stars are coming from the extra thickness of having the large glass over the corrector group still installed. In the image below only a few mm have been cropped out just to clean up around the edges from dithering. Also, We only use OSC and it does absolutely fine with straight Ha simply because it collects so much light so fast. We took this shot last weekend:

Conditions: Dark sky site about 80% full moon

Camera: QHY247C Gain: 3000 Offset: 76

-20C

Subs 4 min

Total Exposure: 2hrs 8 min

 

Pelican Ha_Small.jpg

 

RASA is an incredible imaging platform enjoy your speed demon! It's affectionately known to my son as The Wonder Machine


Edited by flyboy9990, 17 August 2019 - 05:22 PM.

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