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Looking for my first APO

Refractor
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#1 MattSimmons

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Posted 24 January 2023 - 07:42 PM

I have been imaging for almost 3 years now. My current main rig is a Quattro 200P on an EQ6, with a Canon 90D APS-C (soon to be modified) or an ASI533MC. I shoot at 800mm and 600mm with the use of a flattener @800mm and a Starizona Nexus @600mm. I also have a 135mm, 35mm and 16mm Canon lenses for wide field and Milky way shots. As you can see I have a pretty large gap between 135mm and 600mm I would like to fill - something in the 250mm-400mm range. So, I am looking at getting a good APO to fit the bill. I have a budget of $2500 to spend on the OTA + reducer/flattener, so higher end stuff like Tak, AP, and SV are probably out. What would you get in that focal range? Some that I have looked at are:

 

  • Esprit 80
  • WO Redcat 71
  • Askar - several models in this range
  • Orion EON
  • Radian 75
  • Astrotech - several models in this range. The new AT90CFT looks interesting, but its not out yet
  • SW 190 Mak-Newt (not an APO)

 

Ideally, I would like to keep the f-ratio under f6 -- I'm used to shooting f4 or less. I also want to stay away from camera lenses as I have found them 1)difficult to hold focus, and 2) are limited for backfocus. I like OAG guiding, but 42mm backfocus usually means choosing between a filter or the OAG.



#2 Achernar

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Posted 24 January 2023 - 08:39 PM

Have you looked into an Astro-Tech 80mm EDT? It's an F/6 but with the matching field flattener and focal reducer it's an F/4.8 system with a focal length of 384mm. With your camera the true field will be just under 1.7X1.7 degrees. I obtained this photo with this telescope and a ZWO 533MM monochrome camera. Both this telescope with the focal reducer and field flattener will run you about $1,200.00.

 

Taras

Attached Thumbnails

  • m-42 and m-43_LRGB_small.jpg

Edited by Achernar, 24 January 2023 - 08:41 PM.

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#3 revans

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Posted 24 January 2023 - 08:41 PM

My first impression is that you have a lot of experience imaging with reflectors and mostly are looking for shorter focal length.  I have used the Esprit 80 and it is a good scope at 400mm focal length but is somewhat expensive compared to other scopes that would probably perform as well.  But instead of a refractor you might try what I am in the process of doing and put a hyerstar 6 v4 on a C6.  The hyperstar and filter drawer and adapter for your camera would run roughly $600 and you can get a new C6 for roughly $850 or a used one for hundreds less.  They are pretty ubiquitous.  Anyway, I've decided to give that route a try and see what happens.  Imaging at 300mm focal length at f2 with 150mm of aperture can't be all bad :)

 

Rick



#4 MattSimmons

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Posted 24 January 2023 - 08:49 PM

My first impression is that you have a lot of experience imaging with reflectors and mostly are looking for shorter focal length.  I have used the Esprit 80 and it is a good scope at 400mm focal length but is somewhat expensive compared to other scopes that would probably perform as well.  But instead of a refractor you might try what I am in the process of doing and put a hyerstar 6 v4 on a C6.  The hyperstar and filter drawer and adapter for your camera would run roughly $600 and you can get a new C6 for roughly $850 or a used one for hundreds less.  They are pretty ubiquitous.  Anyway, I've decided to give that route a try and see what happens.  Imaging at 300mm focal length at f2 with 150mm of aperture can't be all bad smile.gif

 

Rick

I have a C8 with Hyperstar v3. Imaging at f2.2 is awesome, but I am not a fan of the hypersensitive collimation, nor the odd diffraction spikes you get from the cables hanging out in the image path. I have been intrigued by what Cuiv is pulling off with the setup though. Have you thought about the filters you will need to manage that fast of an optical train? I have also had an eye on the Sharpstar 150 hyperbolic reflectors - f2.8...



#5 KTAZ

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Posted 24 January 2023 - 09:28 PM

OP is looking for a refractor...not a reflector.

 

I am also thinking about my next purchase for a wide field scope. I have a reflector for long FL, a high end refractor for medium FL, and now want something in the range that you are looking at.

 

I'm leaning towards a Petzval design. I want to see more data on the Askar's and the Astronomics AT60EDP Petzval.


Edited by KTAZ, 24 January 2023 - 09:29 PM.


#6 revans

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Posted 25 January 2023 - 08:46 AM

OP is looking for a refractor...not a reflector.

 

I am also thinking about my next purchase for a wide field scope. I have a reflector for long FL, a high end refractor for medium FL, and now want something in the range that you are looking at.

 

I'm leaning towards a Petzval design. I want to see more data on the Askar's and the Astronomics AT60EDP Petzval.

I agree that the small petzval design scopes have many good points and I almost went for a FRA300 or FRA400.  The only drawback is that they are not designed for visual astronomy.  Because I don't want to restrict a scope to pure AP, I then looked at many well-made doublets with nice glass and some ED triplets.  I thought that AstroTech products were the biggest bang for the buck.  I guess a lot of people also like SVBONY but I don't see major dealers carrying their telescopes (could have missed one that does though I guess) although you could buy one on Amazon.  

 

Since I already have an Esprit 80, I decided ultimately to not buy a smaller aperture refractor but to add hyperstar to my C6 instead.  If I have problems with collimation or focusing that make it annoying to use (don't really know yet as I've just ordered it) then my backup plan is to use some camera fast telephoto lenses that I have.  They do have a reputation for soft stars and sometimes for a bit of CA, but I've not had focusing issues so far at least.  My solution is to use them with step-down rings or aperture masks to improve star quality.  I'd use a native f2.8 at about f3.6, a native f4 at about f5.6, and a native f5.6 at f7.  All of my telephoto lenses are pretty large aperture ranging from 72mm up to 165mm.  Not many people think of using camera lenses, but they are widely available used at pretty reasonable cost.  And I'm betting they can be tamed for AP by putting them on a V or Losmandy base plate, using cooled astrocameras with them, using step-down rings or the equivalent when needed, and providing them with guide scopes either by way of a twin saddle or adding something like a ZWO ring for the astrocam which allows mounting a mini-guide scope.  

 

If I didn't have the Esprit 80, then I'd probably want something like the AT72 ED II.  I think an FPL-53/lanthanum doublet would be fine and the price is right.

 

Rick



#7 revans

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Posted 25 January 2023 - 09:28 AM

I have a C8 with Hyperstar v3. Imaging at f2.2 is awesome, but I am not a fan of the hypersensitive collimation, nor the odd diffraction spikes you get from the cables hanging out in the image path. I have been intrigued by what Cuiv is pulling off with the setup though. Have you thought about the filters you will need to manage that fast of an optical train? I have also had an eye on the Sharpstar 150 hyperbolic reflectors - f2.8...

I have no practical experience with hyperstar yet.  The unit should arrive next week.  I was planning on using a cable router available from agena to avoid the star spike issue.  Youtube videos seem to show that this works well.  Have you used one?

 

Rick



#8 matt_astro_tx

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Posted 25 January 2023 - 01:05 PM

  • Esprit 80
  • WO Redcat 71
  • Askar - several models in this range
  • Orion EON
  • Radian 75
  • Astrotech - several models in this range. The new AT90CFT looks interesting, but its not out yet
  • SW 190 Mak-Newt (not an APO)

If it were my money, I'd go with either the AT80EDT from Astrotech (which is in stock), or the AT92 (which is not).  The Esprits have good reputations but I don't have any experience with them.  I think Radians are overpriced.


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#9 Sctom

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Posted 26 January 2023 - 10:42 AM

My new SV SVX90 arrived a few days ago and will be listing my SV SVR90 f7 Raptor soon here on CN.  I will be including the .8 FFFR and SV scope case.  PM me if you are interested.  I am maybe the 3rd owner.  Wanted a new shorter and forever scope for my retirement, but the older one is fine.




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