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William Optics Star71II or GT71?

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18 replies to this topic

#1 Poochpa

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Posted 17 January 2020 - 12:00 PM

I’m trying to decide between a WO Star 71 II and GT71 for a lightweight travel scope for imaging with either a DSLR or cooled OSC camera.  The Star 71 is lighter and has a larger imaging circle (48mm v 44mm), a benefit if I decide in the future to go full frame. The GT71 could be used with or without the reducer/flattener and is slightly faster than the Star71 (f/4.7 v f/4.9), when using the Flat6AIII .8x reducer/flattener.  On the other hand, the Star71 has the corrective lens elements built-in, so no need to worry about getting the right back focus adjustment dialed in when using a reducer/flattener.  However, it would seem to me that there is more potential for miscollimation, especially after shipping from overseas, with the Star71’s 4 lens elements versus the GT71’s 3 elements. Most important to me is image quality, so what do you think? And just so you know, I’m sticking with William Optics, after owning two other great scopes from them. Thanks.
Mike



#2 gene williams

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Posted 17 January 2020 - 12:33 PM

I’m trying to decide between a WO Star 71 II and GT71 for a lightweight travel scope for imaging with either a DSLR or cooled OSC camera.  The Star 71 is lighter and has a larger imaging circle (48mm v 44mm), a benefit if I decide in the future to go full frame. The GT71 could be used with or without the reducer/flattener and is slightly faster than the Star71 (f/4.7 v f/4.9), when using the Flat6AIII .8x reducer/flattener.  On the other hand, the Star71 has the corrective lens elements built-in, so no need to worry about getting the right back focus adjustment dialed in when using a reducer/flattener.  However, it would seem to me that there is more potential for miscollimation, especially after shipping from overseas, with the Star71’s 4 lens elements versus the GT71’s 3 elements. Most important to me is image quality, so what do you think? And just so you know, I’m sticking with William Optics, after owning two other great scopes from them. Thanks.
Mike

I once had a somewhat rare William Optics five element GTF80mm with the field flattener built in.  I loved that scope, and wish I still had it.  That scope made me biased towards systems with the field flattener built in, because setup was so easy.  All I know is that the images I have seen on astrobin from either scope look great.  


Edited by gene williams, 17 January 2020 - 12:51 PM.


#3 georgian82

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Posted 18 January 2020 - 02:11 AM

I would go with the GT71 all day long. The Star 71 gives weird star shapes and you would need to stop it down using a step down ring in the front element to make that go away.

Other alternatives are the Meade 70mm f5 petzval (I have one and very happy with it), the new TS optics 76mm f4.5 (https://www.teleskop...nung-F-4-5.html) and I believe William Optics is coming out with a 70mm f5 version of the red cat this year which should be another petzval design. Finally, don’t forget about the Stellarvue SV70T...similar to the GT71.

Edited by georgian82, 18 January 2020 - 02:14 AM.

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#4 Joe G

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Posted 18 January 2020 - 02:55 PM

I believe some of the previous Star 71s gave "weird" stars, but that was some time ago.

 

I have the newer version.  Stars look okay to me?

 

https://www.flickr.c...57694685889534/


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#5 Poochpa

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Posted 18 January 2020 - 04:16 PM

I believe some of the previous Star 71s gave "weird" stars, but that was some time ago.

 

I have the newer version.  Stars look okay to me?

 

https://www.flickr.c...57694685889534/

 

Joe, stars look good.

Mike


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#6 georgian82

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Posted 18 January 2020 - 05:01 PM

I believe some of the previous Star 71s gave "weird" stars, but that was some time ago.

I have the newer version. Stars look okay to me?

https://www.flickr.c...57694685889534/


Got it. I was under the impression both version had the same issue. The stars look good to me...I retract myself then from my initial comment :)
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#7 OldManSky

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Posted 18 January 2020 - 08:39 PM

Tough call.  I bought the GT71 about 5 months ago, and have really been enjoying it.  With the Flat6AIII, I get nice round tight stars all the way out to the edge of my field.  Performance and lack of CA are excellent.  I kind of like the idea of being able to adjust the spacing after the flattener, though I can certainly see the upside of having it essentially built-in to the scope and not needing to do so.

I think either would be a very good choice.


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#8 lakerunr

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Posted 25 January 2020 - 09:49 PM

I'm trying to make the same choice. I currently have a Zenithstar 73, 2018 model, which is great for visual or entry level AP, but as I gain experience in AP, I see the shortcomings of the doublet configuration. Especially after using the WO FLT132 triplet I acquired last Fall. So I'm looking for a faster, crisper wide field rig, and like you I prefer to stay with WO.

 

Looking at the two, the Star's built-in flattener is a definite advantage. But the GT71 has the new CNC Handlebar, which I also have on the FLT132. I find this a great convenience for set-up/take-down since I don't have an observatory. Also, the slide-base guide scope or rings are easier to deal with.

 

The external flattener, Flat6AII, also allows mounting a 48mm filter. I used this with both the Flat73 on my Z73 and the Flat68III on my FLT132 when using a OSC camera. Not significant if you are only using a mono camera and filter wheel.

 

Just my $0.02, clear skies!


Edited by lakerunr, 26 January 2020 - 07:39 PM.


#9 Freakshow

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Posted 05 February 2020 - 03:48 PM

The Star71 II does not have a built in reducer or flattener.  It is a design called Petzval similar to the Televue 101IS and the Takahashi FSQ-106EDX4.  Most of the Petzval scopes are in the $6000++ range.  WO seems to be one of the few that can make one affordably.  The spacecat line has a fine tune adjustment for sensor tilt--also worth considering.



#10 Freakshow

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Posted 05 February 2020 - 03:58 PM

This poster uses a Star71 mkII.  I think the stars look good.  Thoughts?  

 

https://www.cloudyni...l=+wo +star +71


Edited by Freakshow, 05 February 2020 - 03:59 PM.


#11 Poochpa

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Posted 05 February 2020 - 04:14 PM

This poster uses a Star71 mkII.  I think the stars look good.  Thoughts?  

 

https://www.cloudyni...l=+wo +star +71

I think so, but it's hard to tell without seeing a single unprocessed frame.

Mike

P.S. Still undecided between the Star71II and the GT71.



#12 sg6

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Posted 05 February 2020 - 04:41 PM

My preference would be the GT71 with a flattener and/or reducer.

The Star 71 are nice and if you get a good one they are very good, however accurate alignment of the 4 elements has been known to not be as good as expected.

 

Usually prior to sale/receiving they are sent for checking and alignment. The Mk1 were poor, the MkII a fair but better, but still a good number are adjusted for better performance.

 

With the Flat6AIII you have an easily adjustable flattener.

 

Now a minor point: According to the WO site they say "Discontinued".

Might be there is a newer GT71 but cannot see mention of such.

 

WO do seem to have a habit of making a good scope, then ceasing it/them.



#13 OldManSky

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Posted 05 February 2020 - 08:16 PM

The GT-71 isn't discontinued.  It's in stock at WO and several vendors.

 

https://williamoptic...1-apo-refractor

 

 

 

That's the one I bought late last year.  I've been very pleased with it.  I chose it over the Star71 largely because of the "flexibility" -- use the flattener, don't use the flattener.  Adjust the flattener for optimal spacing.  Take it off to put on a barlow.  Etc.

 

Imaging has been terrific with it.  

 

 

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  • gt71_oncem25.jpg

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#14 Freakshow

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Posted 06 February 2020 - 01:17 AM

Let us make life more difficult...WO has announced a redcat71 and a redcat91.  imho a redcat71 would best the star71 and gt71 because of the abilty to fine tune for image sensor tilt.



#15 sg6

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Posted 06 February 2020 - 05:24 AM

Just going to throw that in myself, 2 new scopes.

Guess the Redcat 71 replaces or will replace the Star71.

 

Will agree with Freakshow, consider the Redcat71.

 

Now will they appar the the next Astro show here in March. Somehow doubt it owing to the background nature of the show. But something to look out for.

 

Note to self: Leave wallet and all card at home. Take just enough for coffee and food.



#16 OldManSky

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Posted 06 February 2020 - 08:30 AM

The Redcat 71 does look amazing...I'm not a fan of the helical focuser though.  Makes autofocus more difficult.  Not impossible, of course...



#17 Freakshow

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Posted 06 February 2020 - 01:47 PM

I saw a blue redcat71 that had rack and pinion. Might be an option.
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#18 OldManSky

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Posted 06 February 2020 - 03:07 PM

I saw a blue redcat71 that had rack and pinion. Might be an option.

Would that be a bluecat? :)



#19 Poochpa

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Posted 10 February 2020 - 01:33 PM

Thanks everyone for your input. A used GT71 came up in the CN classifieds last week and I bought it. While it's the older generation without the Bahtinov mask built into the lens cover, it came with a Flat6AII flattener/reducer and the M63 Camera Angle Rotator.

Couple of questions:

What's the difference between the Flat6AII and III?

The Camera Angle Rotator is very stiff to turn. So much so that it unscrews from the focuser when turned CCW. Is there a way to adjust it? I see 3 grub screws in the housing, but I'm not sure if they adjust the rotational friction or are just for positioning the engraved degree markings. Thanks.

Mike




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