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Redcat 51 vs Astro-tech AT60ED

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#1 celeron787

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Posted 07 February 2020 - 10:35 PM

Hi, I'm new here and to this hobby. 

I have been doing some research on small refractors and have come down to these 2 options:

 

1.  William Optics RedCat 51 (Upgraded Version) + William Optics 48mm T-mount for Sony E-mount

 

2. Astro-tech AT60ED + Astro-tech 0.8x field flattener (no stock currently) + William Optics 48mm T-mount for Sony E-mount

OR

2.1 William Optics Zenithstar 61 + William Optics Flat61 1.0x Adjustable Flattener + William Optics 48mm T-mount for Sony E-mount

 

I'm pairing the scope with a Sky Adventurer and a Sony A6000 APSC camera.

These setups come down the similar pricing.

I'm leaning towards the Astro-tech/Zenithstar 61 but what I like about the redcat is that it's straightforward to use, I just need to buy a camera adapter.

 

Some questions:

1. Should I go for the 0.8x flattener or the 1.0x flattener? With the 0.8x, the focal length and f ratio becomes similar to the redcat. I like the fov with the 1.0x flattener but I've read that I shouldn't go more than 300mm focal length on a star tracker.

2. Any thoughts on the setup's stability on the Star Adventurer? The Redcat is slightly lighter because of lesser accessories.

 

Any insights would be appreciated!

 



#2 aa5te

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Posted 07 February 2020 - 11:12 PM

Welcome to CN!

 

I've been trying to find the best 1.0x flattener and the best 0.8x reducer/flattener for my AT66ED scopes, and I believe that the Astro-Tech 0.8x is the same as the Orion 0.8x.

 

I just received an AT60ED today, but haven't had time to test the 1.0x flatteners in it, but I did test my Orion 0.8x and my Televue 0.8x (TRF-2008) in it, and I've found the same thing that I found with the AT66ED - the Televue definitely beats the Orion in flattening to the corners on daytime views; I haven't been able to test on stars yet due to the typical rain and clouds. The Orion definitely doesn't flatten all the way out to the edges and in the corners; I've attached a pic of its behavior on the AT66ED in an extreme corner using the Orion 0.8x.

 

So what I'm sort of getting at here is that the Redcat will probably provide better edge performance vs. the Astro-Tech unless there's a magical 0.8x reducer/flattener out there.

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Edited by aa5te, 07 February 2020 - 11:19 PM.

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#3 celeron787

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Posted 08 February 2020 - 08:11 AM

With a APSC crop, edge sharpness shouldn't be an issue?



#4 aa5te

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Posted 08 February 2020 - 09:32 AM

That is with an APS-C sensor - Sony A6300.



#5 MalVeauX

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Posted 08 February 2020 - 11:21 AM

Heya,

 

I'd get the shorter one, that's faster, with the flattest well corrected field. So probably the Red Cat. The lighter weight and shorter length matters a lot too, when using the mount you're considering. Frankly though, for what you're doing, do you really need a scope versus just using a lens?

 

Very best,


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#6 celeron787

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Posted 08 February 2020 - 06:48 PM

Heya,

 

I'd get the shorter one, that's faster, with the flattest well corrected field. So probably the Red Cat. The lighter weight and shorter length matters a lot too, when using the mount you're considering. Frankly though, for what you're doing, do you really need a scope versus just using a lens?

 

Very best,

Thanks! I currently own a 18-135mm lens which I've used a couple of times and found that I prefer something a little more deeper, like the redcat or AT60ED.

I could get a samyang 135mm which is about 50% price of the redcat but focal length is the same as my 18-135mm lens. Other longer E-mount photography lenses cost more than the redcat.


Edited by celeron787, 08 February 2020 - 06:59 PM.


#7 celeron787

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Posted 08 February 2020 - 06:52 PM

That is with an APS-C sensor - Sony A6300.

Ah nice! Which mount are you using the A6300 with AT60ED on?



#8 aa5te

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Posted 08 February 2020 - 07:06 PM

Ah nice! Which mount are you using the A6300 with AT60ED on?

 

I haven't been able to test the AT60ED on the sky yet, but that shot with the AT66ED was with an Orion SkyView Pro, and I wouldn't suggest going longer than 400mm with a crop sensor on it. I do have the Skywatcher Star Adventurer Pro, but haven't tried it out yet.



#9 Woodbridge_Dave

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Posted 10 February 2020 - 07:57 PM

I had a Redcat but returned it because the edges were not flat on my full frame Nikon d810.  In retrospect I’m glad I returned it because it was only 50mm diameter.  Not sure what I was thinking when I bought it.  It seemed like a glorified finderscope.
 

IMHO I would go with a good 60mm refractor and a dedicated flattener.  It may take trial and error to find the right thing.  If you can step up to 80mm, I would recommend the SkyWatcher Esprit 80mm with flattener.  This has charmingly flat fields.



#10 celeron787

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Posted 11 February 2020 - 04:24 AM

I had a Redcat but returned it because the edges were not flat on my full frame Nikon d810.  In retrospect I’m glad I returned it because it was only 50mm diameter.  Not sure what I was thinking when I bought it.  It seemed like a glorified finderscope.
 

IMHO I would go with a good 60mm refractor and a dedicated flattener.  It may take trial and error to find the right thing.  If you can step up to 80mm, I would recommend the SkyWatcher Esprit 80mm with flattener.  This has charmingly flat fields.

Hi, I'm using an APSC crop sensor so I'm not too worried about the edges. Did you get the 1st release version or the upgraded version redcat? Any other issues with the redcat other than the edge flatness? 

A small 60mm refractor is probably the limit for a star tracker, anything larger will probably exceed the load capacity.



#11 Astrojedi

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Posted 13 February 2020 - 06:26 PM

I had a RC51 which I sold in favor of keeping the AT60ED for a couple of reasons:

 

1. The RC51 was the same weight was the AT60. As this was meant to be my portable / travel setup I went for the larger aperture for the same weight. The AT60 is also easier to use for visual given the standard focuser and backfocus.

 

2. Image quality was very close. The RC51 is a pretty sharp lens but the AT60ED was very close (and good enough) plus offered more focal length and resolution.

 

My AT60ED performs very well using the dedicated flattener with a full frame sensor. Only one corner has noticeably elongated stars but it is a trade off I could live with as I was getting a larger aperture scope. Surprisingly vignetting is also minimal - actually less than the RC51. Could likely have had something to do with the adapters / spacers I was using on the RC51.




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