Celestron RASA



Imaging in the uk is always a challenge due to the number of good imaging nights we get each year , to make the best of these all to infrequent nights a fast optical system gives you a great advantage , so when the new Celestron rasa came to the market it seemed to offer just what the doctor ordered a F ratio of 2.2 , Focal length of 620mm and a huge 70mm flat imaging circle which should cover any ccd camera inc my starlight xpress sxvf m25 OSC camera ( probably the easiest way to get RGB from this scope) and my SXVF h35 the later being a 35 mm full frame chip , I also suggest a round camera like the Starlight xpress cameras are most suited for this scope , but Celestron do show DSLR cameras being used.

Read on for my opinion



For a start the RASA is a imaging only scope with the camera mounted up front very similar to a SCT with a faststar attachment , so no looking through this scope.

On unpacking the scope it soon becomes obvious this is a substantial scope longer ,than a STD 11" sct and at about 20kg quite heavy as well, just about a 1 man scope.
There are 2 dovetail bars one for mounting the scope on a mount and the second I am informed for mounting accessories like guide scope etc , but wonder if its also for rigidity purposes as well.
I do like the lifting handle at the cell end but does leave you wondering what to hold at the other end !

At the rear are 2 mirror locks which are supposed to ensure that after focusing that the dreaded sct mirror flop does not occur , I am slightly concerned about this as a lot of imagers will use motor focusing and use autofocsing during the imaging night , something you can not do if the mirror is locked in place ! and might rule out remote use of this scope.

For focusing there is a very nice 2 speed feathertouch focuser which as you would expect works very smoothly and I believe it was also selected so a motor could be attached easily (feather touch will sell you one for a suitable amount of money) .last up at the rear is a maglev fan which Celestron suggests will improve cool down time of the scope as of course its a closed system.

At the business end of the scope , the permanently mounted optical flattener is mounted in the corrector plate , you might just be able to see the collimation screws for the flattener and I am hoping that the scope comes well factory collimated, as the depth of focus at f2.2 is tiny and even though personally I am quite willing to fine tune any of my equipment to get the best from it , a lot of people would find this more of a unwelcome challange.The central lens is also covered with a clear glass filter assembly and this can be removed so you can fit a special light pollution filter supplied by celestron , this being at a extra cost

With the scope comes 2 adaptors for mounting cameras to the scope , these are well made and very robust, one is for mounting a dslr camera ( the preverbal 55mm back focus) and the the other has a 48mm thread , I do think celestron has missed something here and unless you are going to use a small ccd with this scope ( unlikely ) this will produce a lot unnecessary vignetting and more thought could have been given to this and purpose made adaptors are almost a must.
I thought I would show the supplied battery pack to operate the fan , it must have taken celestron a long time to find something that is this bad , and you would be disappointed if you got this out of a Christmas cracker , a small thing I know :) .

Lastly there seems to be no thought given to cable management , it is suggested that you tape any wires tidily out of the way as good as you can , seems so arbitrary to me and unsatisfactory again I see some kind of cable holder being made later.

Next up attempted first light



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