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  #41  
Old 12-05-2020, 11:06 AM
JA
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Hi EH,

I'm sure you will do well with that combination given the APS-c sized sensor on the XT2. If the XT2 uses an internal UV/IR filter similar to the original Fuji Pro1 or XE1, then you'll also find very good Hydrogen Alpha response compared with other unmodified mirrorless or DSLR cameras.


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Last edited by JA; 12-05-2020 at 11:20 AM.
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  #42  
Old 12-05-2020, 11:19 AM
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The_bluester (Paul)
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Originally Posted by jahnpahwa View Post
Sorry to jump in here, but has anyone an opinion on the celestron edgeHD 8" with fastar at F2-ish? I guess this ends up being comparable to a RASA of the same size (though I assume RASA has different/superior flattening?) but has the added flexibility of being able to image at f10 and also be used visually?

I ask because I'm sort of in the same boat, thinking about an OTA to complement my 8" F5 newt... and figure that the 8"edgeHD gives me focal lengths either side of this.

(again, sorry to hijack!)

JP
From what I have seen and read (As far as I know, Celestron don't make the Fastar any more and have not for ages, but the same comments apply to the Hyperstar) you can get some pretty startling results out of them, however they can be absolute murder to collimate, and at F2 are just as touchy about spacing and tilt as a RASA and you will likely need to collimate every time you fit it. Add to that that by the time you get a new Hyperstar in your hands, between the exchange rate and GST and freight you will spend two thirds of the price of a RASA 8.

If a Hyperstar for my CPC925 came up secondhand at a good price I would be tempted, but if I wanted F2 new, I think I would just go buy a RASA.
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  #43  
Old 12-05-2020, 11:24 AM
Emuhead (Andrew)
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Originally Posted by JA View Post
Hi EH,

I'm sure you will do well with that combination given the APS-c sized sensor on the XT2. If the XT2 uses an internal UV/IR filter similar to the original Fuji Pro1 or XE1, then you'll also find very good Hydrogen Alpha response compared with other unmodified mirrorless or DSLR cameras.


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JA
Yes its actually surprisingly good for Ha.. this image of mine was 12x120s images.
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  #44  
Old 12-05-2020, 11:31 AM
jahnpahwa (JP)
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Originally Posted by The_bluester View Post
From what I have seen and read (As far as I know, Celestron don't make the Fastar any more and have not for ages, but the same comments apply to the Hyperstar) you can get some pretty startling results out of them, however they can be absolute murder to collimate, and at F2 are just as touchy about spacing and tilt as a RASA and you will likely need to collimate every time you fit it. Add to that that by the time you get a new Hyperstar in your hands, between the exchange rate and GST and freight you will spend two thirds of the price of a RASA 8.

If a Hyperstar for my CPC925 came up secondhand at a good price I would be tempted, but if I wanted F2 new, I think I would just go buy a RASA.
Ah yes, the collimation would become quite a drag! Thanks for that reminder
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  #45  
Old 12-05-2020, 11:48 AM
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From what i read, SCT's dont need collimation that often (not like newtonians which need it every time you use it).
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  #46  
Old 12-05-2020, 12:31 PM
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As a basic scope no they dont. Visually I tweaked my C925 every few months, but sometimes I left it go for a year or more.

Photographically I checked it at the start of each session, but for a Hyperstar they are super touchy and if you remove it you really need to at least re check it each time.
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  #47  
Old 12-05-2020, 01:37 PM
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So heres an interesting question:

https://www.baader-planetarium.com/e...stian-voltmer/

This shows an image taken with a Fuji XT3 on the front of a RASA 8, but if you look closely there are 90 degree diffraction spikes in the image... which made me question if this could have been taken with the Fuji? I thought those kind of diffraction spikes are created with dedicated astro camera power cables split at 90 degress, and not a fully self contained mirrorless camera body. Odd right?

Also, I can buy a T-2 Fuji wide-adapter that is 8.3mm thick, along with the Fuji back focus of 17.7mm brings this distance to 26mm, however the RASA 8 back focus is only 25mm (so im 1mm too long...) which is why i looked closer at that image in the first place. However there is a clear filter inside the RASA which im hoping adds that 1mm.. does/can this happen? The article does say to leave that in, so im hoping for the best really...

Last edited by Emuhead; 12-05-2020 at 02:02 PM.
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  #48  
Old 12-05-2020, 01:49 PM
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He may have added lines/cables to deliberately create spikes.
Or added them in post-processing, some people prefer spikes.

Come to think about it, wouldn't the rectangular camera body create spikes if it intrudes into the light path.

I suppose you could sand/file off 1mm off that adaptor if you can't find focus.
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  #49  
Old 12-05-2020, 01:56 PM
Emuhead (Andrew)
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Filing, yes i suppose I could do that. Hopefully the remaining threads can still hold the camera.. :|
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  #50  
Old 12-05-2020, 01:58 PM
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Quote:
Originally Posted by Emuhead View Post
So heres an interesting question:

https://www.baader-planetarium.com/e...stian-voltmer/

This shows an image taken with a Fuji XT3 on the front of a RASA 8, but if you look closely there are 90 degree diffraction spikes in the image... which made me question if this could have been taken with the Fuji? I thought those kind of diffraction spikes are created with dedicated astro camera power cables split at 90 degress, and not a fully self contained mirrorless camera body. Odd right?
Light will diffract at the edges/corners of the camera if it protrudes in to the field of view. Since the central obstruction of the RASA-8 is 93mm in diameter, anything larger, like the 133mm wide Fuji XT-2 or XT-3 could create such issues, although I am a little surprised how sharp and symmetrical the spikes appear.
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  #51  
Old 13-05-2020, 04:28 PM
Emuhead (Andrew)
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Closing the loop on this, the 25mm back focus 'increases' to 26mm if the filter is added. This was was confirmed by Baader. So should be good to go.

Also, this blog is incredibly helpful too.
https://cloudbreakoptics.com/blogs/n...y-pixel-part-1

Last edited by Emuhead; 14-05-2020 at 10:33 AM.
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