• Stacey

First Light with the Celestron RASA 8

Updated: Oct 2, 2019

So, i'll start off by saying WOW. What a piece of equipment!

Those of you who know me quite well, know how nervous I can get...especially when it comes to using a new piece of equipment that has been loaned to me for review/test. The RASA 8 has probably given me the most nerves i have ever had about a scope....and you know what? I need not have worried one bit!

So when I first knew that I was going to be getting a RASA to try I started researching...I looked at many forums to see what tips folks had, joined groups on facebook and basically tried to learn as much as possible. I also reached out to hyperstar owners...those guys and gals being the masters at running a scope down at F/2.

One thing that came up repeatedly was "focusing is critical down at F/2". Also "you will absolutely need a motor focuser". So as the scope is on loan to me, the motor focuser wasn't really an option, so i started looking for other solutions that could help me, such as a bahtinov mask. Now here in the UK i couldn't find any masks, so if you venture into RASA territory it may be worth asking your friendly astro geek (who has access to a 3D printer) to print you one off.

The second big thing that came up was "you're going to need a dew shield"

Finally..."you're in bortle 8? Wow....what about that light pollution with such a fast scope?"

...and so now, I shall talk about all of these things and how they impacted me with my first night using the RASA.

I shall talk about the light pollution first. Where I live, it can be a massive issue in certain directions. I always describe my skies as bortle 6-8. My north view is soaked in air glow from Birmingham city centre and my southern view is a little bit better (towards the countryside) but towards peoples houses and a large residential area. I had read that Celestron made a light pollution reduction LPR filter for the RASA and David Hinds ltd (who loaned me the scope) were generous enough to let me borrow one. When I initially tried to fit this LPR filter, I had a massive fail...the original clear glass would not move one bit. I ordered a lens spanner from Amazon and this allowed me to remove the clear glass easily (i think it was just over-tightened at the factory)

I then needed to get it actually onto my mount (a skywatcher HEQ5 Pro). My mount has a puck which can hold a vixen bar, whereas the Celestron RASA 8 utilises a celestron CGE (losmandy) bar. Luckily the guys at Altair astro were there to save the day on that account...they were able to let me borrow a Altair Starwave Vixen to Losmandy adapter. I simply bolted this to my vixen bar and slotted it onto my mount. I tightened it up as much as i could, so that I knew when the RASA was on there it wasn't going to budge.

The main issue I found when mounting it, was even though it is pretty light (7.7kg)...there is only one handle on the rear and it is a bit cumbersome. I did have difficulty sliding it into position and help from a second pair of hands was definitely needed. I hope i'll get a bit better at putting it on and off as i use it more...but for now (for me at least) its a two man job.

Behold the beast :)

Once it was actually on the mount, it wasn't hard to balance....i was pleasantly surprised!

And so as the day wore on, the sky began to clear.

I carried everything outside, I forgot to use the cooling fan on the RASA...but i got everything else ready.

I attached my camera (an Altair 294C Pro TEC) to the front of the RASA using the supplied adapter and my 7.5mm extension tube (the RASA needs 25mm of back focus, the 294C Pro Tec has 17.5mm built in, which leaves 7.5mm). I quickly did my polar alignment and then fired up Sharpap to try and get the RASA into focus.

This was the moment I had been dreading....and for nothing! I set maximum gain on the 294C ProTec and I could instantly see stars with 100ms exposure (and even shorter). I quickly checked the collimation which looked absolutely fine and decided I was too eager and just wanted to crack on. I moved the focus in and out a bit until I settled on what I thought was the best focus I could get (with the naked eye of course). I then left the focus knob and carried on. That whole thing of not locking down the focus is a bit alien to me and I was not convinced that the focus would't shift.

I slewed around a bit and used plate solving to find Andromeda (Messier 31). I rechecked the focus, it was still absolutely as I left it.

So then I proceeded to gather some light frames. I opted for 30s at unity gain (391 with the Altair astro 294C Pro Tec ) and captured 33 of them. I did have to stop and pause the imaging run a few times due to some epic clouds rolling over.

After about an hour the scope started to dew up and so my imaging run came to an end. I could have used a hair dryer to clear it, but because of how wet everything was outside I decided against it. The conclusion here is, I definitely do need a dew shield. I'm going to try DIY'ing one as Celestron don't make a dedicated one for the RASA yet i believe.

That said, I had managed to capture 16.5 minutes of data...which sounds pitiful (but not when it's at F/2!).

I set about stacking. I had captured some dark frames...but hadn't done any flats. The lack of flats was quite useful though as it showed me the vignetting on this setup (RASA8 + 294C sensor). I've come to the conclusion I definitely will be using flats next time, so I don't have to crop the edges of my images.

Here's the raw stack with a moderate stretch.

You may also see a few odd diffraction spikes on this image, it's because I didn't trail my cables across the aperture very well.

The data was nice and easy to process. I used Astro Pixel Processor for stacking, calibration and light pollution removal (the LPR cut it down a lot, but not completely) and then I moved into Pixinsight for the rest of post processing.

This was the result, my RASA 8 "first light image":

Honestly? I couldn't be happier with it. This was a complete culture shock for me. I'm used to refractors and guiding and no collimation and taking exposures that can last up to 6 minutes. With this, things seemed simpler? The 30s exposures were a life saver when i saw a bank of cloud approaching...i simply hit pause and was able to salvage as many exposures as possible.

So my main things to improve on for next time are:

1. Sort my cables from the camera out, so they either a) cross the aperture nicely...so as not to have random diffraction spikes....or b) so they curve and thus are smudged out of the image a bit.

2. get my dew shield sorted, this will allow me to image for longer and also enable me to take some flats by placing my light source at the end.

So TL:DR...as far as first impressions go. I really like the RASA 8. I like it a lot.

Bring on some more clear skies!!!

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