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RASA 11" vs RASA 8" for EAA

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#1 chef

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Posted 06 May 2019 - 08:06 AM

Hello Everyone,
Can someone please advise, whether RASA 11" will give much better results in EAA over RASA 8" ?

I am complete beginner in AP/EAA and I just bought camera ASI294MC Pro for EAA.

For visual observing is aperture one of the most important parameter to be able to see more DSO objects, but I dont know, if for EAA is aperture also the most important parameter (especially, when RASA 11" cost twice times more, than RASA 8").

 

Thx



#2 Rickster

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Posted 06 May 2019 - 10:41 AM

The 11 inch will gather 90% more photons than the 8 inch.  And photons are signal (information).  So, yes, the 11 inch will give better performance.  The 11 inch, at f2.2 would also be a better match (in terms of arc sec/px) for the 294 than the 8 inch.  If the added cost, weight, mount requirements and storage space are not a problem, then I would think that you would be a lot happier with the 11 inch.


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#3 chef

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Posted 06 May 2019 - 11:49 AM

Thanks a lot for advice.

So I will focus on RASA 11" .



#4 Ubuntu

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Posted 09 May 2019 - 09:23 AM

Hello Everyone,
Can someone please advise, whether RASA 11" will give much better results in EAA over RASA 8" ?

I am complete beginner in AP/EAA and I just bought camera ASI294MC Pro for EAA.

For visual observing is aperture one of the most important parameter to be able to see more DSO objects, but I dont know, if for EAA is aperture also the most important parameter (especially, when RASA 11" cost twice times more, than RASA 8").

 

Thx

Basically the only difference will be the focal length, because both are F2.

So your FOV will be 1.5 times smaller with the 11" than with the 8", giving more details.


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#5 OleCuss

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Posted 09 May 2019 - 11:45 AM

Yes, with the 11" one would expect the FOV to be smaller.

 

The focal length will be longer but that could be a significant benefit when using the ASI294 because you will have less under-sampling.

 

The 11" will be considerably heavier and longer and that means you need a more robust mount than you would need with the 8" RASA.

 

Cool-down will be slower with the 11".

 

I think there are lots of reasons to like the 11" over the 8", but I think that if I had the budget to buy one or the other I'd probably stick with the 8".

 

The 8" has an image circle more appropriate for an APS-C or 4/3rds sensor.  Cool-down is faster.  I have an ASI183 so I don't have to be under-sampled all that badly even with the shorter focal length.  As I get older I appreciate smaller/lighter equipment more.  I don't have to use a heavier mount with the 8" RASA.

 

I do have a bigger mount so I could actually mount the 11" fairly nicely on that, but if I want to travel?  The lighter mount and OTA are much easier to deal with and part of what I'd want the RASA for would be for public outreach.

 

If I were planning to just leave the OTA on a big mount in the observatory and if I had a full-frame camera - I'd be in the slam-dunk category for the 11" RASA.


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#6 Astrojedi

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Posted 11 May 2019 - 11:02 PM

How do you define a better image?


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