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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.



#12 beeboman82

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Posted 13 August 2020 - 03:52 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.

I am thinking of giving the AT 0.8x reducer/flattener specific to the AT60ED a try.  I think maybe the general AT 0.8x unit is the same as the Orion unit as those both appear to have 42 mm threads, and I agree from your image that it does not look quite up to the task.  The ATRF60 has 48 mm threads which seems consistent with support a larger flat imaging circle...not sure if it will cover a full frame though (product description says "large format DSLR chip"...not certain what that means).

 

Brian



#13 aa5te

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Posted 13 August 2020 - 04:00 PM

I am thinking of giving the AT 0.8x reducer/flattener specific to the AT60ED a try.  I think maybe the general AT 0.8x unit is the same as the Orion unit as those both appear to have 42 mm threads, and I agree from your image that it does not look quite up to the task.  The ATRF60 has 48 mm threads which seems consistent with support a larger flat imaging circle...not sure if it will cover a full frame though (product description says "large format DSLR chip"...not certain what that means).

 

Brian

I was able to try mine out a few nights ago and it works almost perfectly to the corners on my APS-C sensor. You can detect a slight elongation of the stars in the corners, but light-years better than AT 0.8x, Orion 0.8x, or the Televue.


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#14 onesillyhatch

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Posted 15 August 2020 - 01:29 PM

I was able to try mine out a few nights ago and it works almost perfectly to the corners on my APS-C sensor. You can detect a slight elongation of the stars in the corners, but light-years better than AT 0.8x, Orion 0.8x, or the Televue.

This is with 1.0x flattener?  Which flattener did you get?  I’m looking at this setup for Astrophotography.  Cheap if it works.  I am also not using full frame 



#15 awong101

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Posted 15 August 2020 - 08:28 PM

I'm a beginner like you and I just completed gathering my basic setup. Except that I don't have any of the lens you mentioned (although I should have a Spacecat 51 inbound soon!)

 

I've been interested in the Red/Spacecat 51 ever since I decided this is a hobby I want to pursue and start. Simply because I think sub-300mm focal lengths are beginner friendly. And here is why:

 

My journal to astronomy actually started with a Celestron SLT130 for viewing only, with its focal length at 650mm. While I was able to find a few (BRIGHT) targets such as the moon, Jupiter, Saturn, I was absolutely lost in the night sky and honestly, that telescope made me lose interest in astronomy. 

 

And this is why I am starting my astrophotography journey with lower focal lengths, starting with the Rokinon 135mm.

 

Lately, I've been reading a few discussion about the Red/Spacecat 51 being well, the "luxury item" of astrophotography. I definitely can see why some may arrive at that perspective because at 250mm, it IS a wide field of view and perhaps it's not going to be great at fine details. Not to mention, as much as I've wanted my Spacecat 51, I think it's overpriced, and the used market isn't much better because it is completely out of stock. I think William Optics lucked out by essentially having a monopoly in the 200mm range.

 

However, I still think there's value in the Red/Spacecat 51 for me, and other people as well. I think it'll serve its purpose as a great stepping stone for a beginner into the realm of actual telescope range.

 

In case you were wondering, I am reusing the ball head that came with my tripod.

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#16 aa5te

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Posted 15 August 2020 - 08:41 PM

This is with 1.0x flattener?  Which flattener did you get?  I’m looking at this setup for Astrophotography.  Cheap if it works.  I am also not using full frame 

No, the 0.8x FF/FR for the AT60ED, model number ATRF60. The AT60FF (1.0x flattener) also flattens it all the way out to the corners as well.


Edited by aa5te, 16 August 2020 - 04:11 PM.


#17 Cometeer

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Posted 16 August 2020 - 04:03 PM

I think the Sharpstar 61edphii is a worthwhile redcat competitor. It’s 275mm with the flattener at F4.5, compact, and has a nice rack and pinion focuser. Priced around the same or slightly less depending on where you purchase from. 



#18 celeron787

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Posted 17 August 2020 - 04:53 AM

Just an update. I got the redcat in the end, didn't want to deal with any flatteners/reducers. So just a direct T mount to my camera.
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#19 davidparks

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Posted 17 August 2020 - 12:52 PM

I'm extremely happy with my Redcat 51.  Flat to the edge using APS-C sized ASI2600.  Very sharp, and back focus hasn't been an issue with the helical focuser (although I still tend to build a standard ~55mm train with OAG, Filter, and ASI Cam)

 

I hope you find the RC51 experience as rewarding as I do waytogo.gif

 

These are not post processed, just live stacked with ASIAIR Pro.

(clicky picky for details)

 

Sadr/Crescent
Redcat / CEM40 / ASI2600 / ASIAIR Pro
Redcat / CEM40 / ASI2600 / ASIAIR Pro
Redcat 51 / AZGTi

Edited by davidparks, 17 August 2020 - 12:53 PM.

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#20 Beevo17

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Posted 17 August 2020 - 04:17 PM

Without a doubt, the RedCat is a better choice. 

 

[a] William Optics have superb optical qualities.

[b] The RedCat is an astrograph; no reducers or flatteners required.

[c] Build quality of WO scopes is also excellent.

[d] The RedCat is f/4.9, pretty darn fast.

 

The only negative is a helical focuser, which takes some getting used to. But with a little practice and using the included excellent Bahtinov mask you’ll get good at it. The scope will hold focus for quite a while unless you have wild temperature changes. And there are now a few options to motorize the focuser if you want to.

 

I have a RedCat and a WhiteCat; run them as a pair with a WO Star 71 quad as a guider. With the ASI ZWO 1600 as a camera you get a wonderful FOV and sharp stars. 

 

RedCat all the way.


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