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C8RASA - some (unavoidably belated) answers for rgsalinger, maybe others

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7 replies to this topic

#1 bobzeq25

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Posted 18 September 2019 - 12:40 PM

"Please do this. I need to see someone do it and report on it for whom this is not their first astro-rodeo.

 

My fears are:

1. Extreme difficulty in collimation and or frequency of collimation.

2. How to put anything other than a DSLR on it - filter wheel is NEVER going to work.

3. Focusing it at F2 will be a nightmare and need to be done every hour.

I have only ever seen one RASA in operation. That was an 11" about two years ago. The guy was using a round color camera - Starlight Express as I recall - and was setting up at around 7PM in the summer. I chatted with him for a while and he was really positive about the scope. I came back 3 hours later and he was still trying to get collimation and/or focus working properly. I do not recally how he automated his focusing. That put me off permanently on RASA and Hyperstar.

I am a person who prizes ease of operation above absolute quality. I want to have fun, not spend my night searching out USB cabling problems or why software doesn't play nice with other software. So, I'm dying to hear from someone who makes this new puppy operate easily.There must be a ton of RASA owners on this forum, though."

 

1.  My RASA came almost perfectly collimated, per the Celestron test.  I'm not about to mess it up trying to remove "almost".

 

2.  I'm using a 183 color astro camera.  Can't see why people would want to use anything else, maybe a 183mono with a filter drawer.

 

3.  Focus is _really_ easy, either manually or with the Celestron motor.  The configuration of the scope means you need almost no focus travel, so the single speed focuser is geared _way_ down.  I'm using autofocus, you could "get away" without it, at a small cost to image quality.

 

No software issues, I integrate everything seamlessly with Voyager.  I had a friend with a 3D printer (doesn't everyone have one of those?  <grin>) make me a wire loom that was posted on the Internet.  Using it is easy, and it greatly reduced diffraction spikes from the wires.  Which weren't that bad even before I started using it.

 

The advantage over Hyperstar is that everything is optimized for F2.  The disadvantage is that it's a one trick pony, and a Barlow is unlikely to work well.

 

The unanticipated issue is how sensitive it is to tilt.  Still working on that, a PreciseParts spacer is on order.  Also the field is not as flat as I would have hoped (still, it's decent) wondering if varying a little from Celestron's spacing would improve that.  Anyone reading this who can tell me?


Edited by bobzeq25, 18 September 2019 - 12:44 PM.

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#2 kingjamez

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Posted 18 September 2019 - 12:49 PM

Agree on all points, especially #3. I read all the doom and gloom about focus issues and an aluminum body. Just simply not a problem. The focus knob is so well geared that this is probably one of the easiest imaging scopes I've ever used in regards to focusing. 

 

I'm hoping the yet to be released tilting Baader filter slider solution will offer a fix to the tilt issues. 

 

I bought a precise parts M87 to Baader S70 dovetail so I could use the Baader UFC. I had to turn it down on my lathe because precise parts wouldn't make it with a short enough optical length. I can affirm though that 1.5mm too much backfocus is BAD and the field gets curved, quickly. 

 

I have both the 183 mono and color, but mostly use the mono so far. Maybe that will change when I go after M31.

 

-Jim


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#3 APshooter

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Posted 18 September 2019 - 04:40 PM

I love my Rasa. It's no exaggeration when I say it has redefined imaging for me. I have some very nice scopes sitting on shelves right now, unused, because imaging with the Rasa let's me capture images in hours instead of days. And strings of clear days are often what I don't have.

+1 on all the points regarding focusing, etc. I did add temperature compensation through my Feathertouch focuser, which means I check my images at the 30 minute mark and again after an hour. Almost always the focus hold very well. Gone is the need to pause to refocus. Gone too is the need for expensive or finicky automaton software. I have not nor do I plan to guide my Rasa.

I think if had more savings I would buy both the 11in and 36cm Rasas. I still have the 11inch in my sights, and have given the 36 a hard look this summer.

#4 SXBB

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Posted 19 September 2019 - 03:47 PM

I'm planning on picking up an 11" but one thing is making me wait.  The focusing system of the 8" & 14" are a significant upgrade compared to the 11".  I'm hoping that the "Super-Stable" focusing system will be added to the 11" soon!  Not having to lock down the mirror and having no mirror flop while still being able to automate focus is an upgrade that I don't want to do without.  I'm wondering if maybe we'll hear something at AIC in November... 

 

Kudos to John Hayes for helping design the new focusing system!

 

Best,

 

Bruce


Edited by SXBB, 19 September 2019 - 04:00 PM.


#5 elfuma

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Posted Yesterday, 12:42 PM

I'm planning on picking up an 11" but one thing is making me wait.  The focusing system of the 8" & 14" are a significant upgrade compared to the 11".  I'm hoping that the "Super-Stable" focusing system will be added to the 11" soon!  Not having to lock down the mirror and having no mirror flop while still being able to automate focus is an upgrade that I don't want to do without.  I'm wondering if maybe we'll hear something at AIC in November... 

 

Kudos to John Hayes for helping design the new focusing system!

 

Best,

 

Bruce

Bruce, can you please elaborate more on this? I'm asking because I'm considering buying a RASA, and since I intend to automate as much as possible, the focusing and mirror locking are important aspects for my decision. My eyes were on the 11" model, but now I've understood that the 8" and 14" versions have a better focusing system, and more important they have mirrors which do not require to be locked?


Edited by elfuma, Yesterday, 12:42 PM.


#6 kingjamez

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Posted Yesterday, 12:48 PM

I have a bit of flop on my RASA8, but only enough that I have to refocus when I meridian flip, otherwise it's not noticeable. The focusing system on the 8 is very fine and my Celestron Focus Motor is a good match with plenty of repeatable accuracy. Obviously, one must use a guidescope with a RASA and I've never had any issues with differential flexture or mirror flop causing problems. 

 

-Jim


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#7 SXBB

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Posted Yesterday, 01:29 PM

Bruce, can you please elaborate more on this? I'm asking because I'm considering buying a RASA, and since I intend to automate as much as possible, the focusing and mirror locking are important aspects for my decision. My eyes were on the 11" model, but now I've understood that the 8" and 14" versions have a better focusing system, and more important they have mirrors which do not require to be locked?

Hi elfuma,

As Kingjamez said, with the newer focusing/mirror stabilization used on his 8' & also the 14" versions, mirror flop is minimal, and focus is very repeatable. Honestly, I haven't read of anybody complaining about the focusing/flop in the 11" version but the new system does away with mirror locks which I'd like. I'm told that Celestron has a huge amount of inventory to go through before they will possibly upgrade the 11" to the new system so it may be a while. I'd love to hear from some of the owners of the 11" RASA about their experiences with flop/shift/repeatability. Is it worth putting off the purchase? I'm not sure. I hope to learn more at AIC next month.

Best,

Bruce

Edited by SXBB, Yesterday, 02:02 PM.


#8 elfuma

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Posted Yesterday, 01:35 PM

Thank you, guys.

 

Let me just add some more details to my first comment. I'm planning to use the RASA with a FF DSLR, so the 8" and 9.25" models are a no-go. The 14" is a dream but no way I will spend that much (yet). The only one left is the 11", so yeah it would be great to hear from those who have it :)

 

Luca




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