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New Imaging Refractor - Another "Spend my money" post

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#1 zakry3323

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Posted 09 October 2019 - 09:57 PM

Hey folks,

 

I've been saving up for a good bit for my first well-corrected fast refractor for wide-field imaging. After I sell a spurious AVX, I'll have about 2k to play with. 

 

I've had the very good fortune of getting to borrow a buddy's first edition WO Star71 and I love it. Nice big field, faster than what I'm used to dealing with, and no bloating in the blue channel. The gold trim doesn't excite me, but to each their own. I've got some questions and I hope you might have some suggestions for me. 

 

The Star71's optics are apparently a proprietary design - 5 elements including a flattener in the tube. I've been looking at the second edition Star71 and GT series, as well as redcats both current and keeping in mind the possibility of new petzvals 71 and 91mm from WO. Just from those choices, I've got what, 3 similar speed and aperture scopes with 3 different optical designs.

 

I'm wondering what advantages a petzval design might have over a more traditional triplet. I know that they're fast for the aperture and well-corrected, but I wonder if they're as versatile as say, a bit longer and slower triplet that would allow me to use both a flattener at native focal length as well as a reducer/flattener for a wider field and faster ratio. 

 

2k is a lot of money for me, likely this will be a scope that I have for a long time, and I'd like to be exceedingly careful in coming up with something that I'm happy with. 

 

I'd really appreciate your advice and suggestions. Currently looking at the AT92 and Stellarvue SVX080T along with all the WO options. 



#2 rockstarbill

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Posted 09 October 2019 - 09:58 PM

AT92, easy answer.


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#3 zakry3323

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Posted 09 October 2019 - 10:00 PM

AT92, easy answer.

Lol, thanks Bill :)


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#4 rockstarbill

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Posted 09 October 2019 - 10:08 PM

Lol, thanks Bill smile.gif

The one gotcha will be a quality field flattener for it. Astronomics was going to work on one, may want to check with them on that.


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#5 OldManSky

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Posted 09 October 2019 - 10:27 PM

I got the new 2019 version GT-71 just over a week ago.  I'm enthralled.

I really like the new handle-top on the tube rings, which doubles as a guide scope mount.

Stars are tiny and tight, color is terrific.

The adjustable flat 6AIII gives a perfectly flat field across my little 183MM camera, and is supposed to be flat out to a 43mm circle.  The adjustability is great.

With the 0.8x flattener/reducer, I'm at 336mm FL and f/4.73.  Same-length exposures as I was doing with my f/5.9 Z61 show clearly the advantage of that extra stop.  I haven't tried it without the flattener yet, but it *is* nice to have that option.

The cost of the scope, the reducer/flattener, and the camera angle adjuster come to about $100 below the Star71.  The new GT-71 does only come in gold so far, though -- while the Star 71 is in-stock in blue in several places smile.gif

I've owned a lot of very nice doublets (Tak FS60C, Tak Sky90, TeleVue TV86, WO Z61), and a Nagler-Petzval (NP101)...this is my favorite refractor to date.  Did I mention I'm enthralled? smile.gif

 

 

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#6 scadvice

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Posted 09 October 2019 - 11:06 PM

The current WO Star 71mm are a four element in 3 groups (2-1-1- configuration) at F4.9.  While I have not used one of these I did however have a WO GTF 81mm 5 element Gran Turismo F5.6. It was a fine scope with very good correction. So I don't think you could go wrong with the Star. I understand the Strehl minimum standard is .95... but no test report. 

 

But... Comparing side by side only 70mm OTA's, I suggest reading about this one as I believe it's worth considering over the Star. 

 

https://www.stellarv...plet-refractor/

 

This is the Stellarvue SVX070T Premier Apochromatic Triplet Refractor at F/6. It comes with a .8X dedicated field flattener/focal reducer included that gives you a F/4.8 wide field for about $1300. So for 200 bucks more you get a hand figured and made in the US optic's.with a .98 Strehl minimum standard and a Zygo test report. You also get the hinged mounting rings and a case just as you do with the WO.

 

 

 

Anyway, the Stellarvue SVX070T is my suggestion. I have the SVA130T which is the finest optic's I've ever owned at  a .992 Strehl.


Edited by scadvice, 10 October 2019 - 12:10 PM.

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#7 zakry3323

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Posted 10 October 2019 - 01:44 PM

Thanks folks! You've given me much to chew on!



#8 zakry3323

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Posted 10 October 2019 - 04:48 PM

The one gotcha will be a quality field flattener for it. Astronomics was going to work on one, may want to check with them on that.

I called up today and confirmed that a flattener is in the works. It's doubtful that it will be available soon, but will hopefully be stocked in the beginning of 2020. 

 

I asked, and was also told that there won't be a dedicated reducer/flattener for the AT92, but there are folks out there that have been getting results they like with the .8x ATR8 reducer/flattener. That however, is also out of stock, with hopes of it coming back around the same time as the dedicated flattener. 

 

This is very intriguing. 506mm is a little long for the targets I want to dig into without having to do mosaics. 404mm at F/4.4 though...



#9 Esso2112

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Posted 10 October 2019 - 05:29 PM

I have the SVX80T that came with the risers and bolted on rings. It is an excellent scope and with the attached rings, rock sold. I did some tests with a full frame camera and the included flattener and it looks good. Haven’t done any serious imaging yet. Visually, it is excellent. 

 

I also just started playing with a Redcat 51 (new version) and it is an impressive little scope. Out of the box, no tilt, which has been an issue with the earlier versions. With my full frame camera, it yields an 8.5 degree field of view. 

 

Personally, I’d go with a little more focal length and aperture than the redcat 51. It’s a bit limited due to focal length, but as a second imaging scope it is a great scope. 


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#10 zakry3323

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Posted 10 October 2019 - 06:26 PM

I have the SVX80T that came with the risers and bolted on rings. It is an excellent scope and with the attached rings, rock sold. I did some tests with a full frame camera and the included flattener and it looks good. Haven’t done any serious imaging yet. Visually, it is excellent. 

 

I also just started playing with a Redcat 51 (new version) and it is an impressive little scope. Out of the box, no tilt, which has been an issue with the earlier versions. With my full frame camera, it yields an 8.5 degree field of view. 

 

Personally, I’d go with a little more focal length and aperture than the redcat 51. It’s a bit limited due to focal length, but as a second imaging scope it is a great scope. 

I'm seeing preorders available for the SVX80T in two different versions, one with a 2.5" focuser, and one with a 3". I'm wondering what I can get away with, vignetting-wise. My train isn't all that heavy and my biggest sensor is on my ASI071. That's a $400 difference (not seeing any other differences) for the upgrade. It would be maxing out my budget either way, but I'd feel a lot more instantly gratified with a the optional reducer/flattener!

 

*Edit, opps I misread. There is no reducer/flattener option for the 2.5" focuser. Hmm. 


Edited by zakry3323, 10 October 2019 - 06:32 PM.

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#11 Esso2112

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Posted 11 October 2019 - 08:35 AM

I'm seeing preorders available for the SVX80T in two different versions, one with a 2.5" focuser, and one with a 3". I'm wondering what I can get away with, vignetting-wise. My train isn't all that heavy and my biggest sensor is on my ASI071. That's a $400 difference (not seeing any other differences) for the upgrade. It would be maxing out my budget either way, but I'd feel a lot more instantly gratified with a the optional reducer/flattener!

 

*Edit, opps I misread. There is no reducer/flattener option for the 2.5" focuser. Hmm. 

 

Correct, if you want the reducer you would need the 3” focuser. That is the version I have, but I don’t have the reducer. 




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