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Celestron RASA replacement

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#1 pyrasanth

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Posted 12 August 2020 - 04:13 AM

Some of you may be aware that Celestron replaced my RASA 11" V1 with a new RASA V1 as the tilt issue could not be resolved on the original instrument. I guess it was cheaper for Celestron to replace a five year old instrument than spend time investigating what the original issue was.

 

I kept the replacement in the box for nearly a year as I was using the C14 Edge on the mount- I don't as yet have 2 beefy mounts.

 

I replaced the Edge OTA with the new RASA and managed to get first light last night using the Baader UFC spaced at 55.30 mm & camera back focus at 17.5 mm with no allowance for filter effects (since the stock clear filter was removed I presume adding your own filter puts everything mostly back as it was). This gave me the 72.80 mm required

 

I used the Astronomik CLS CCD filter and the camera on a 2x2 Bin (I could not use 1x1 bin as the SkyX was crashing with an out of memory error- I need to look at that).

 

I focused manually as I did not have the auto focuser fitted which will, later, be the Optec Quicksync which does a good job provided the initial step sizes are dialed in correctly. At 3.00 am this morning the seeing was good but the transparency horribly spoilt by misty cloud but I managed 80 10 second test subs of NGC7331.

 

For the first time ever the field looked really flat and sharp even focusing by eye I managed a FWHM of average 2 pixels. This will be a lot better now I've fitted the auto focuser this morning.

 

I'm pleased with the result given by the replacement.

 

One last tip for the camera placement. If your using the Baader UFC you need to remove the Celestron Stock filter as this sits 3-4 mm proud of the camera base which will prevent the Baader UFC from sitting straight and it will be at the wrong back focus unless compensated for in your measurements. This is a hassle not needed but it does prevent the use of the excellent Astrondon LPR filter which would have the same constraints. I also greased the camera locking ring with Dow Corning high vacuum grease to ease the ring placement which screwed on butter smooth.

 

I've attached the 13 minute image which is cropped to fit on the forum but the stars are true right to the edge of the field and the CCD inspector result.

 

I wish all of you clear skies....stay safe.

 

Best wishes

Mark

 

First Light New RASA.jpg

 

NEW RASA FIELD.jpg


Edited by pyrasanth, 12 August 2020 - 04:16 AM.

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#2 Professor2112

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Posted 12 August 2020 - 06:21 AM

Awesome results!  NGC7331 has been a goal of mine for a while now but misty tropical nights have been making my subs have this “red fuzz” all over the images(dew I believe?).  Also, it’s the last 4 digits of my cell number, so I like to call it “the cell phone cluster” when referring to it to my wife lol.  Well done!


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#3 Ladyhawke

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Posted 12 August 2020 - 06:30 AM

Awesome results!  NGC7331 has been a goal of mine for a while now but misty tropical nights have been making my subs have this “red fuzz” all over the images(dew I believe?).  Also, it’s the last 4 digits of my cell number, so I like to call it “the cell phone cluster” when referring to it to my wife lol.  Well done!

Professor2112, now that's a proper member name. Rush on :)



#4 Professor2112

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Posted 12 August 2020 - 06:50 AM

Professor2112, now that's a proper member name. Rush on smile.gif

Absolutely! Your quote is one of my fav songs btw! 

 

Now back to the “cell phone cluster”! lol.gif 
 

still can’t get over how crisp everything is in this image! And at only 13 mins that’s a lot of data! Considering you can see the main background galaxies which are 200-300 million lys away!  I just ordered an 8” Edge HD today and will definitely have to consider hyperstar!


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#5 pyrasanth

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Posted 12 August 2020 - 06:50 AM

Awesome results!  NGC7331 has been a goal of mine for a while now but misty tropical nights have been making my subs have this “red fuzz” all over the images(dew I believe?).  Also, it’s the last 4 digits of my cell number, so I like to call it “the cell phone cluster” when referring to it to my wife lol.  Well done!

Thanks- it's been a long time coming. In the 5 years I had the original RASA I only obtained one image of the double cluster that had a reasonable flat field-the rest of the images were really badly out of focus down 1/3 of the field because of tilt. I hope this is now firmly behind me as the camera will stay on the RASA for the foreseeable future. I'm terrified to remove it now I have a good result.

 

NGC7331 is a superb target if you can get the right conditions. I've imaged it with the C14 and the detail was superb being a much longer focal length like over 6 times greater. However it might be possible to get a larger image scale by drizzling the 1x1 bin subs- not so much to capture more detail but use the software to resample which seems to do a better job than the PI standard resample tool.

 

The nights are now getting darker earlier and for longer. I can't wait for the right conditions and spend a whole evening with the RASA on this target.


Edited by pyrasanth, 12 August 2020 - 06:53 AM.

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#6 pyrasanth

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Posted 12 August 2020 - 06:56 AM

Absolutely! Your quote is one of my fav songs btw! 

 

Now back to the “cell phone cluster”! lol.gif 
 

still can’t get over how crisp everything is in this image! And at only 13 mins that’s a lot of data! Considering you can see the main background galaxies which are 200-300 million lys away!  I just ordered an 8” Edge HD today and will definitely have to consider hyperstar!

Thanks- The RASA's are light buckets they really do suck in the photons and the ASI6200 camera being CMOS and very low noise with small pixels can take advantage of that. It was a shame I could not test on the 1x1 bin but the software had an issue which I can't repeat this morning so perhaps a 1 off. I do intend to capture at native 1x1 bin to avoid any initial software binning anomalies then look at the options for resampling or drizzling.  


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#7 Professor2112

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Posted 12 August 2020 - 11:42 AM

Thanks- it's been a long time coming. In the 5 years I had the original RASA I only obtained one image of the double cluster that had a reasonable flat field-the rest of the images were really badly out of focus down 1/3 of the field because of tilt. I hope this is now firmly behind me as the camera will stay on the RASA for the foreseeable future. I'm terrified to remove it now I have a good result.

 

NGC7331 is a superb target if you can get the right conditions. I've imaged it with the C14 and the detail was superb being a much longer focal length like over 6 times greater. However it might be possible to get a larger image scale by drizzling the 1x1 bin subs- not so much to capture more detail but use the software to resample which seems to do a better job than the PI standard resample tool.

 

The nights are now getting darker earlier and for longer. I can't wait for the right conditions and spend a whole evening with the RASA on this target.

 I’m hoping to get decent results with the 8” edge at native FL and then when I can get the 0.7 Reducer on that as well on a Sky-Watcher EQ6-r pro mount. Right now I have an Orion compact 80 mm refractor for a guide scope and a starshoot mono pro for a guide cam. Hoping that camera is sensitive enough for an OAG if the guidescope doesn’t get me good enough guiding. So far I’m impressed as when I was imaging M 51, I had It looping 1.5s. exposures and I could actually see M 51, fuzzy spiral arms and all.  More data on your target though and I believe you’ll have an extremely pleasing result! 




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