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Lunar Imaging with RASA?

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#1 Thundermoon1994

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Posted 12 February 2020 - 01:11 PM

Hi everyone,

 

I am looking to take my deep sky imaging in a new direction (currently 80mm refractor), and I think I've chosen the RASA 8.  I also enjoy lunar imaging with the 80mm.  Are there any practical concerns about lunar imaging with the RASA and my ASI178MM/183MC?  I can't think of anything, but I also can't find a single lunar image taken with the RASA in this forum.undecided.gif   Given that the focal length of my refractor and the RASA are within 4% of each other, I feel like the changes in processing workflow would be rather minimal.

 

 

Thanks,

Damien



#2 Stellar1

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Posted 12 February 2020 - 01:18 PM

The RASA is a speed demon of a scope, meant specifically for capturing and recording the faintest of light. From a technical POV i cant really say but, from a design POV, it may be like shining a floodlight 

into a pair of night vision goggles.


Edited by Stellar1, 12 February 2020 - 01:32 PM.

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#3 Jim Waters

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Posted 12 February 2020 - 01:43 PM

The scope is too fast and the F.L. too short.  Get a 8" Celestron EdgeHD.

https://www.celestro...y-cg-5-dovetail

 

EDIT - Do not get the RASA for Lunar imaging.


Edited by Jim Waters, 12 February 2020 - 02:39 PM.

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#4 bobzeq25

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Posted 12 February 2020 - 02:13 PM

Hi everyone,

 

I am looking to take my deep sky imaging in a new direction (currently 80mm refractor), and I think I've chosen the RASA 8.  I also enjoy lunar imaging with the 80mm.  Are there any practical concerns about lunar imaging with the RASA and my ASI178MM/183MC?  I can't think of anything, but I also can't find a single lunar image taken with the RASA in this forum.undecided.gif   Given that the focal length of my refractor and the RASA are within 4% of each other, I feel like the changes in processing workflow would be rather minimal.

 

 

Thanks,

Damien

It should work, but I'm not sure here's much benefit of the RASA on something this bright.  Maybe not any, there is a central obstruction and the wires.  I wouldn't expect images to be significantly better than the 80mm.  Lunar is mostly limited by seeing.  You want to shoot a video, and use lucky imaging.

 

I'd be using one of my refractors for lunar.

 

EDIT.  The issue raised below about extending the focal length.  I would imagine adding a Barlow to a RASA would be significantly detrimental to the optics.


Edited by bobzeq25, 12 February 2020 - 03:05 PM.


#5 Wouter D'hoye

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Posted 12 February 2020 - 02:27 PM

Hi,

 

at the focal lenght and speed of the RASA there will be little or no advantage for lunar imaging over your 80mm telescope. The focal length of the RASA is too short to get a boost in resolution, even with the tiny pixels of the ASI178 the rsolution of the system is about 1.2 arcsec/pixel. To get an resolution advantage out of the 8" aperture you'll need a longer focal length. 1,2 arcsec is also pretty much the resolution of your 80mm telescope, and for imaging with the ASI178 the system needs to be around f/11.

 

So, can you use the RASA.. Probably, yes. Would it be any better for lunar imaging than your current 80mm scope. No, unless you can extend the focal lenght.  But that is usually not what a rasa is build for.

 

Kind regards,

 

Wouter.



#6 jgraham

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Posted 12 February 2020 - 03:04 PM

If the moon is in the sky I almost always grab a quick image if for no other reason to take a peek. My fast scopes like my classic 5.5" f/1.6 and 8" f/1.5 Schmidt Cameras (converted to digital) and my 5.5" Comet Catcher do a fine job capturing full disk images of the moon. No reason not to have a bit of fun with your RASA.

Enjoy!

#7 MikeMiller

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Posted 12 February 2020 - 03:32 PM

This is one of the reasons I got an EdgeHD 8 and Hyperstar. The combination is more expensive, but I can use f/2.1, f/7, and f/10 depending on my needs.

 

An EdgeHD 8 with the .7 reducer makes the full moon almost perfectly fit on a 4/3 sensor like the Horizon or ASI1600.

 

Even at f/7 I need to use a filter to cut down on how bright the moon is.


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#8 photoracer18

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Posted 12 February 2020 - 03:32 PM

On the other tack having taken my first lunar image back in 1964 I would say full disk images are a total waste (except for Lunar eclipses). Get something longer and get some real details. As has been said with that camera you want something about F11 so a regular SCT or a faster MCT would be a better match (even a long focus refractor). You can always use an FF/FC to get a wider view.


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#9 Tom Glenn

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Posted 12 February 2020 - 03:58 PM

Any scope can take a nice image of the Moon, and so there is no reason this one cannot.  It would not be the ideal choice for an exclusive lunar scope, but that's not what the OP is asking.  If the decision to get the scope is driven by its performance in DSO imaging, there is no reason it cannot be used to catch a quick image of the Moon.

 

 

On the other tack having taken my first lunar image back in 1964 I would say full disk images are a total waste (except for Lunar eclipses). Get something longer and get some real details. 

 

This would only be true if you have some unusually high standards for what qualifies as "real details".  The benefit of the ASI183 camera that the OP plans to use is that it has a fairly large sensor with small pixels, so even at modest focal lengths can produce detailed images.  And many people like to have images that include the entire lunar disk.  


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#10 Thundermoon1994

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Posted 12 February 2020 - 04:24 PM

Any scope can take a nice image of the Moon, and so there is no reason this one cannot.  It would not be the ideal choice for an exclusive lunar scope, but that's not what the OP is asking.  If the decision to get the scope is driven by its performance in DSO imaging, there is no reason it cannot be used to catch a quick image of the Moon.

 

 

 

This would only be true if you have some unusually high standards for what qualifies as "real details".  The benefit of the ASI183 camera that the OP plans to use is that it has a fairly large sensor with small pixels, so even at modest focal lengths can produce detailed images.  And many people like to have images that include the entire lunar disk.  

Yep. This.

 

I already have a C8, which I would use if I wanted to do long focal length work on the moon.  I've done some of that, but I really do enjoy full-disk imaging of the moon with the 183.  Those small pixels certainly help the 80mm scope "punch above its weight" when it comes to resolving features in my images. 

 

My decision to buy the RASA is only based on its performance on faint fuzzies.  My question was just around whether it could do as well of a job as my current approach.  If I'm out and set up early, why not grab a few videos of the moon?

 

 

Thanks,

Damien



#11 Tom Glenn

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Posted 12 February 2020 - 04:36 PM

Damien, as Wouter said above, under most circumstances, the RASA will not outperform your 80mm scope, unless you extend the focal length.  But it may not be as easy to extend the focal length enough, and at that point, you would use the C8 anyway.  

 

I do have a question though, because I'm not familiar with this scope, but I know it has a unique optical design and the camera goes in front.  My question is whether it is even possible to insert a barlow into the light path and come to focus, since there are probably somewhat strict back focus requirements.  And if you are able to come to focus with the barlow, is the field still well corrected?  If you cannot lengthen the focal length at all, then imaging at 400mm focal length will be very limiting on the Moon.  If you can double that to 800mm though, the entire Moon will still fit on the ASI183mm sensor, and will have very reasonable resolution across the image.  




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