A night with a RASA8

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Jean-Francois
Posts: 360
Joined: Sun Oct 13, 2019 10:52 am
Location: Germany

A night with a RASA8

#1

Post by Jean-Francois »

Hello,

I did in the past weeks several "serious" imaging with my new equipment (RASA8 and QHY-268 + FCCT-II and filters).

Some of the targets are in the swan constellation. Here only the images taken in one night with the Halpha filter (6 nm for F2 system).
I used SharpCap Pro and the Live Stack tool. The RASA8 is mounted on my EQ8Rh mount in parallel with my Newton 10" telescope, note that no guiding was used. All the images are done during the night from 4. to 5. August (from 23:50 to 02:09).
Each target is the result of 5 images of each 1 minute exposure ... so only 5 minutes total exposure.
I take a dark image before imaging. No offset or no flat correction are used.

Here all images together (and reduced to 40%):
Eine_Nacht_im_Schwan_40.jpg
Eine_Nacht_im_Schwan_40.jpg (966.96 KiB) Viewed 811 times
Here the position of the images in the sky:
Sky_observation_1.jpg
Sky_observation_1.jpg (216.58 KiB) Viewed 811 times
Sky_observation_2.jpg
Sky_observation_2.jpg (164.33 KiB) Viewed 811 times
Regards,
Jean-Francois
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admin
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Re: A night with a RASA8

#2

Post by admin »

Hi Jean-Francois,

stunning images, especially for 5 minutes each target :)

The wonders of an f/2.0 optical system!

cheers,

Robin
Jean-Francois
Posts: 360
Joined: Sun Oct 13, 2019 10:52 am
Location: Germany

Re: A night with a RASA8

#3

Post by Jean-Francois »

Hello Robin,

Yes, I was surprised too.
It is necessary to take care to not overexpose the images with long exposure time (not on the stars but on the nebula itself).
I did the images with no moon and low background light (the milky-way was easily visible).

In a different message, it is about some rats.
The last days, during the processing of my NGC7000 images, I see a small rat and a big elephant (or mammoth).
I do not understand why the people name it the Pelican nebula.
NGC7000_elefant_and_mouse.jpg
NGC7000_elefant_and_mouse.jpg (307.33 KiB) Viewed 798 times
Regards,
Jean-Francois
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admin
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Re: A night with a RASA8

#4

Post by admin »

Awesome artwork :) Quick, make an NFT from it and get rich quick! :D

cheers,

Robin
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: A night with a RASA8

#5

Post by timh »

Hi Jean-Francois,

Really interesting and impressive. Great pictures and I love your sky globe summary of what you have been able to cover.

I can see the attraction of F2 when it works that well and the RASA8 a an intriguing scope. Do you have dark skies where you are? I was just thinking that here under Bortle 6 skies narrow band might often be a necessary option - but also read that the RASA8 has limited backfocus distance - so filter changing slower - and that - because of the camera position - the connecting cables have to run across the corrector plate? Interested to know your views and how you deal with these potential issues - whatever you are doing it certainly works well!

thanks
Tim
Jean-Francois
Posts: 360
Joined: Sun Oct 13, 2019 10:52 am
Location: Germany

Re: A night with a RASA8

#6

Post by Jean-Francois »

Hello Tim,

I have the RASA 8 since last year. At the beginning, I installed my old Horizon-C camera.
But the results were not so good. In the meantime, Baader released the FCCT tool (a camera tilter with filter).

You are right, the backfocus of the RASA 8 is very short.
Not only that, but a backfocus error of 1 mm is already too much. You can refocus the image, but it will be not nice over the full field.
The FFCT tool is delivered with 2 shims of 0.5 mm for adapting some manufacturing difference.

I adjust the QHY-268M camera on the RASA with the FCCT before disconnecting the camera for transport to the south of France (~3 weeks ago).
In France, I remount the camera on the RASA and I take my first "woua!" image of NGC7000 with the Live Stack of SharpCap.
It was very impressive to see after few minutes the North America nebula on the computer screen like on the image above.
I readjust the camera in the field. I dismounted all the part before travel back to home.
After the holidays in France, I reinstall all my equipment at home ... and it was the pictures above. In between no new alignment of the camera.

I'm in the village centre around 30 km south of the south of Munich. The nights are OK, I can see the Milky-Way above and near the horizon.
One limiting point is : all the streets and houses (church) illuminations limit my eyes adaptation. I'm maybe somewhere between Bortle 4 and 6.
I have the EAGL4 mini computer, it has an photodiode for the sky brightness measurement. I did not us it until today, I will try it.
For the narrow band, I will say that it is a "must to have" ... Ha and O-III (for S-II that is a different question).
Note that the RASA with FD=2 needs special narrow filter. I use the 6 nm for F/2.

For the cables (12V power and USB), you have 2 different ways ... some people want to have the diffraction pattern, the other not.
I design a curved cables holder and I printed it with my 3D printer. The cables are routed with an half circle, so that no diffraction pattern is visible.

One point ... the filter exchange is easy when no dew shield is mounted. It is more difficult with a dew shield and not possible if the target in near the zenith. In France, I used the dew shield and I pointed the telescope near the horizon for the filter exchange. After that I used a new function of SharpCap ... the Goto-to-Image. It works great, I loaded the last image and SharpCap slewed the telescope to the same position.

For the sky globe summary, I used Prism ... first perform the astrometry of each image (= plate solve), then "insert" the image in the sky chart. But ... I performed first a binning 2x2 while the images have too much stars :-)

And concerning what I was able to cover ... I did the image after reinstalling my equipment at home after travelling from France the full day.
After 2:00 it was necessary to sleep ... next morning I restart to work. So ... yes it is nice to have FD2 ... no more 10 hours exposure time :-)

Regards,
Jean-Francois
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: A night with a RASA8

#7

Post by timh »

Hello Jean-Francois

Thank you very much for that detailed and useful answer. It seems to me that there are difficulties but that they are all surmountable once you understand the system well enough. I did wonder about the FASTAR and now this option - but went in the end for almost the exact opposite - a long focus system and observing small fields in more detail. In view of what you have written about the dew shield (which would probably be necessary autumn and winter), the need for filters and the fine backfocus tolerance this seems to be one to consider for keeping in a more or less fixed set up with a large chip OSC camera and perhaps one of those L-extreme dual band filters that Menno uses? I do really like the idea of getting good images so quickly. thanks agaim
Tim
Jean-Francois
Posts: 360
Joined: Sun Oct 13, 2019 10:52 am
Location: Germany

Re: A night with a RASA8

#8

Post by Jean-Francois »

Hello Tim,

I read somewhere on the Baader webpage, that Baader itself mention that the RASA + FCCT tool is not so easy to use.
The user needs to have some skill with fine mechanic parts (you have several very small screws and you need to dismount the FCCT before installation on the camera). ... But with patience and calm fingers, you can install and adjust the camera on the RASA with the FCCT.

For the filter exchange ... in the future I will plan my imaging session(s) differently ... for example several targets with one filter per night.
Thank SharpCap GOTO-to image function, it is possible to centre the telescope several night after on the same targets with a different filter.

For the combination RASA + camera ... yes, it is better to mount one camera fix on one RASA. I say that while I know somebody with 2 RASA-11 (one with a mono camera (+ narrow filter) and the other with a colour camera) ... both mounted on a NTM mount.

Concerning the RASA vs Fastar ... the advantage of the RASA is that it is a complete telescope system developed from the beginning.
The Fastar or other similar system is an additional system designed after the main telescope ... so the optimum is on the side of the RASA.
But it is clear that the RASA system is only for imaging. The other system can be added on the normal Schmidt-Cassegrain system.

And yes, you have no perfect telescope for all the targets and different use.
Long focal for the planets, sun and moon high resolution images. Wide field for large sky region imaging.
Something in between while some target are larger as the moon but smaller as a large nebula region.

I have my RASA mounted in parallel to my Newton 10" on the EQ8 mount.
I do asteroid occultation with the Newton (+ QHY-174GPS + reducer 2.8) ... in the future I want to design an interface for changing quickly the QHY-174 camera to my spectrometer (without over stress the focuser). On the RASA, I have now the QHY-268 camera. The camera will stay on the RASA ... it takes too long time to dismount it for only short period.

Good evening,
Jean-Francois
timh
Posts: 515
Joined: Mon Aug 26, 2019 5:50 pm

Re: A night with a RASA8

#9

Post by timh »

Hello Jean-Francois,

Yes I guess that FASTAR is just out of date if you are interested in imaging. Wow. Two RASA 11's with different filters on two mounts - one OSC and one mono set up in parallel. That must be a perfect dream - if very expensive - set up !

Good luck with the spectrometer set up. That is also an interesting angle on this hobby to try

Tim
Jean-Francois
Posts: 360
Joined: Sun Oct 13, 2019 10:52 am
Location: Germany

Re: A night with a RASA8

#10

Post by Jean-Francois »

Hello Tim,

Not so expensive ... the 2 RASA11 are mounted on the same mount :-)

Sometime I use my both telescopes at the same time.
I did some asteroid occultations in parallel ... Newton 10" with 174-GPS camera and RASA8 with QHY-183 camera.

Regards,
Jean-Francois
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