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C8-RASA - progress (with image)

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#1 bobzeq25

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Posted 27 September 2019 - 10:09 AM

The difficulty I (and others) had with the C8 RASA was the F2 systems extreme sensitivity to tilt.  Spacers that had worked fine with other scopes were a problem.

 

I decided to brute force the problem, to see if the scope was an issue.  Got a PreciseParts spacer that replaced almost everything with a hunk of metal that had only one threaded connection.  It's shaped like the Celestron t-thread adaptor on the bottom, goes out the correct distance, and accepts the 183C camera (without the cameras threaded ring).  I retained the Celestron retaining ring for the scope end, that shouldn't introduce tilt, and makes camera rotation easy.

 

Below are the results.  Click on the picture for readability.  The FWHM is in pixels, multiply by 1.2 to get arc sec.  Comments on field flatness or tilt welcomed.  Those are beyond good for me, I don't think my SV100Q is as flat.

 

Here's the resulting image.  The night was really uneven, with FWHMs ranging from that 2.5 ish to over 4.  Guiding sometimes went over 1.0.  I dropped everything with a FWHM over 4, that cut out 1/3 of my 30 second frames, leaving me with 245.  Not great, but it shows I'm on the way to achieving what I wanted to.   Decent images in Bortle 7 without 10 hours or more total imaging time.  This is 2 hours, with a one shot color camera.  There'll be better cameras down the road.

 

I used Celestron's IDAS style LP filter.  I have signal to burn, so that's not an issue, but I still don't like the star color much.  Tradeoffs.

 

Don't tell Jerry.  <grin>

 

https://www.astrobin.com/ky6juu/

 

For those who don't know, my age makes imaging in dark skies impractical, except possibly with my camera tracker.

 

C8 RASA.jpg


Edited by bobzeq25, 27 September 2019 - 10:14 AM.

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#2 RRod

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Posted 27 September 2019 - 11:02 AM

That is pretty good!! Would you be able to provide more information about the PreciseParts and the specs? So I could order that. Are you using a filter slider?

 

Thank you

 

Rodrigo



#3 bobzeq25

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Posted 27 September 2019 - 11:12 AM

That is pretty good!! Would you be able to provide more information about the PreciseParts and the specs? So I could order that. Are you using a filter slider?

 

Thank you

 

Rodrigo

Go to the precise parts website, build your adaptor.  There are options listed there.  Mine is Rasa 8 inch, 183 without ring.

 

First, you'll want this, to compute the spacing.

 

https://celestron-si...dapter_Rev1.pdf

 

I'm waiting for the Baader filter slider.


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#4 rgsalinger

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Posted 27 September 2019 - 11:17 AM

Were you able to get PP to make the adapter with those 60 degree slots? That would seem like a wonderful improvement as you can then frame things as opposed to screwing something in and being subject to whatever angle you end up with.

Rgrds-Ross



#5 bobzeq25

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Posted 27 September 2019 - 11:24 AM

Were you able to get PP to make the adapter with those 60 degree slots? That would seem like a wonderful improvement as you can then frame things as opposed to screwing something in and being subject to whatever angle you end up with.

Rgrds-Ross

Yes, even though they don't show on the order form, the part automatically comes with the slots (I verified that with email before ordering.  As someone once said to me, I'm a guy for who this is not the first astro-rodeo <smile>). 

 

Their purpose is collimation.  I see absolutely no need to mess with that on mine.  If it ain't broke....

 

But, if you had to, that PP adapter gives you enough room to sneak an Allen wrench in, I think.


Edited by bobzeq25, 27 September 2019 - 11:29 AM.

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#6 RRod

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Posted 27 September 2019 - 01:39 PM

Is this the one you chose:

 

sp.JPG

 

Thank you

 



#7 bobzeq25

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Posted 27 September 2019 - 02:36 PM

Is this the one you chose:

 

attachicon.gif sp.JPG

 

Thank you

No.  Than could work, but I don't see how you'd rotate the camera.  I got plain Rasa 8, which uses the Celestron clamp ring.

 

Try both, the site gives you a 3D picture.


Edited by bobzeq25, 27 September 2019 - 02:37 PM.


#8 RRod

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Posted 27 September 2019 - 04:58 PM

Thank you

#9 Joe G

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Posted 27 September 2019 - 08:45 PM

Bob, I think the stars came out pretty good!  Don't mind the color, but I do like the shape given the RASA system.

 

OMG, an IDAS filter.  I guess you have gone to the darker side.  In your terms: <grin>



#10 APshooter

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Posted 28 September 2019 - 06:30 PM

Congrats!  I was hoping someone would post flatness images.  Do you find this solves any problems over the filter drawer idea?  Oh, and for the record, I'm very happy with my filter drawer, just asking.


Edited by APshooter, 28 September 2019 - 06:31 PM.


#11 bobzeq25

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Posted 28 September 2019 - 11:13 PM

Congrats!  I was hoping someone would post flatness images.  Do you find this solves any problems over the filter drawer idea?  Oh, and for the record, I'm very happy with my filter drawer, just asking.

I have no idea.   My old spacers clearly were not up to the task.  So I hit things with the biggest hammer I could find (a solid block, from a good source, with only the one essential threaded connection).  That seems to have worked, now I have a baseline to measure other setups against.



#12 lucutes

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Posted 05 October 2019 - 05:56 PM

How are the new spacer from PP working?



#13 RogeZ

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Posted 04 January 2020 - 03:42 PM

Bob: 

Sorry to resurrect old thread. Can you post CCD inspector curvature profile from your recent M45 image?

 

Thanks sir!



#14 bobzeq25

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Posted 04 January 2020 - 04:23 PM

How are the new spacer from PP working?

 

 

Bob: 

Sorry to resurrect old thread. Can you post CCD inspector curvature profile from your recent M45 image?

 

Thanks sir!

Nope, don't have CCDInspector.  If you want to purchase and send me a copy.... <grin>

 

I looked at my reference sub for M45 in PI.  The data is insignificantly better (5%?) than what I showed in post #1 here.  Slightly better night, probably.

 

A key thing is that the camera has been mounted/unmounted several times in between.  Both to the PP adapter, and to the scope.  No attempt is ever made to center the flange (there's some slop).  This appears to be robust.

 

Bottom line.  My images, what I show in post #1, and the AberrationInspector data, is "good enough" for me.


Edited by bobzeq25, 04 January 2020 - 04:25 PM.


#15 RogeZ

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Posted 04 January 2020 - 05:51 PM

Bob:

 

While I cant share my license, I can analyze your stack file. If you post me a link I will download, analyze and post. Just the plan stack would be great.

 

BTW: The Artesky adapter I have is basically the same as the PP you are using.

 

Thanks,

 

Roger M



#16 bobzeq25

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Posted 04 January 2020 - 07:13 PM

https://www.dropbox....s 2019.fit?dl=0

 

Anyone at all should feel free to analyze it, process it, etc.  If you publish/post your results please give me credit for the data.  In this thread, it's understood.

 

Note that the stack is not as good as the reference image was.  My usual variability in seeing, my subframe selector criteria was FWHM < 3.5 arc sec, eccentricity < 0.60.


Edited by bobzeq25, 04 January 2020 - 07:14 PM.


#17 RogeZ

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Posted 05 January 2020 - 12:17 PM

Thanks Bob.

 

Here is the CCD Inspector plot of your image. I can attest that your image is way flatter than any of my images. I had to convert the image to JPEG as CCD inspector does not support 32 bit files.

 

Attached are both files

Attached Thumbnails

  • Bob's M45 curvature.JPG
  • Bob's M45 curvature map.JPG

Edited by RogeZ, 05 January 2020 - 12:30 PM.


#18 RogeZ

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Posted 05 January 2020 - 12:24 PM

Compare that to mine... I have a feeling the more "out" you go with the sensor the worse it will be for RASA. If anything you to be in...

Attached Thumbnails

  • Roger's M31 curvature map.JPG
  • Roger's M31 curvature.JPG


#19 ChrisWhite

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Posted 05 January 2020 - 02:00 PM

Roger, are you also seeing issues in your stars at the corners?  CCDI is kind of funny sometimes.  I get a curvature plot like that for my Edge 9.25 with a 1in sensor, but the field is perfectly flat.  I'm guessing its because there are not very many stars to analyze in my small FOV, but still... how do your stars look?



#20 RogeZ

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Posted 05 January 2020 - 02:29 PM

Chris, yes my stars are quite bad. I will post an image soon that I took a couple of nights ago...

#21 bobzeq25

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Posted 05 January 2020 - 03:17 PM

Compare that to mine... I have a feeling the more "out" you go with the sensor the worse it will be for RASA. If anything you to be in...

I would interpret that as a spacing issue.  It's possible I lucked out when I specified, and PP made, my camera mount/spacer.

 

Thanks so much for doing that.  It reinforces my belief that I'm "good enough".

 

Here it is as a 16bit unsigned integer tiff.  Two reasons.  I'm curious if it makes a difference.  I break out in hives when it comes to images, technical data, and jpgs these days.  <smile>  Don't ask.

 

Mess with it or not, as you see fit (get it?  <grin>)

 

https://www.dropbox....s 2019.tif?dl=0

 

Minor tip.  Such format transitions are trivial in PI.


Edited by bobzeq25, 05 January 2020 - 03:18 PM.


#22 RogeZ

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Posted 05 January 2020 - 03:54 PM

Bob l will get to it :)

 

Mess with it or not, as you see fit (get it?  <grin>)

lol



#23 RogeZ

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Posted 05 January 2020 - 03:54 PM

Btw what was your spacing on the PP adapter? Whats exactly your image train?



#24 RogeZ

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Posted 05 January 2020 - 03:59 PM

Made a significant difference for the better.

 

I would guess the compression took a toll on star shapes and ended up skewing the data.

Attached Thumbnails

  • Bob's M45 TIF 3d curvature.JPG
  • Bob's M45 TIF curvature map.JPG


#25 RogeZ

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Posted 05 January 2020 - 04:06 PM

Here is my M31 image.

 

get.jpg?insecure

 

I have to admit, I think the above image is a great win for the RASA8. I'm in Bortle 8/9 skies, shooting mono with the 1600MM and an Astronomiks CLS-CCD. To be able to see the galaxy in such detail is thrilling to me. I have also "successfully" captured M81, M82, M101 so there is potential to the scope.

 

M31 is 2.7hr image composed of 1min exposures at unity gain


Edited by RogeZ, 05 January 2020 - 04:06 PM.



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