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Looking for William Optics FLT91 Owners

Astrophotography Refractor
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#1 Jim Waters

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Posted 24 May 2024 - 11:53 AM

As the title says, I am looking for William Optics FLT91 owners.  I am not sure if this post belongs here or in 'Refractors'.  The scope will only be used for astrophotography using an ASI2600MC Pro (APS-C) camera.

 

What are your opinions on the scope, do you like the images it produces ...etc?  I will be using the WO Flat 68III.  What adapter do I need to use the Flat 68III?  I have seen conflicting information.  Is the star-field flat with pinpoint stars in the corners?

 

Thx



#2 hyiger

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Posted 24 May 2024 - 12:11 PM

Hi Jim, before I drop money on a scope, I usually head over to AstroBin and look for examples with that scope combination with my mount. A lot of time people upload the FITS so I can download that and pixel peep to get an idea of the quality. That said, a guy in my club has the FLT91 and uses it with ASI6200MM and claims "it's my best scope" (subjective opinion of course)

 

I now own 3 William Optics scopes and they've all been winners although I've heard stories about the Pleiades series having coma issues. 


Edited by hyiger, 24 May 2024 - 12:14 PM.

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#3 Jim Waters

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Posted 24 May 2024 - 12:30 PM

Thanks hyiger.  I haven't seen many posted FLT91 images on astrobin.  I am searching YouTube now for reviews.



#4 cmanley134

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Posted 24 May 2024 - 12:37 PM

Thanks hyiger.  I haven't seen many posted FLT91 images on astrobin.  I am searching YouTube now for reviews.

If you go to the "Equipment" tab under "Explore" you can search for images captured with the FLT91. For me it shows there are 21 pages of results, so a bit over 1000 images to browse through. 


Edited by cmanley134, 24 May 2024 - 12:37 PM.

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#5 Jim Waters

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Posted 24 May 2024 - 12:55 PM

Thanks !



#6 DeepSky Di

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Posted 24 May 2024 - 01:21 PM

I have a GT81 that I love. However, WIFD came out and to me the idea makes sense, particularly for RedCats, if you want to add a focuser and / or travel. The GT81, ZW81 and RedCats have been converted to WIFD. FLTs have not so far. Pleiades 111 is WIFD but according to a review I watched, has some configuration issues which are being resolved.


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#7 hyiger

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Posted 24 May 2024 - 01:30 PM

I have a GT81 that I love. However, WIFD came out and to me the idea makes sense, particularly for RedCats, if you want to add a focuser and / or travel. The GT81, ZW81 and RedCats have been converted to WIFD. FLTs have not so far. Pleiades 111 is WIFD but according to a review I watched, has some configuration issues which are being resolved.

I replaced my GT81 with the WIFD version since on the former I had focusser sag causing tilt. The WIFD is a massive improvement plus the tube is shorter which is a bonus. I had my eye of the Pleiades 111 but heard about too many people having coma issues with it. I suppose that's almost to be expected with a 7 lens setup? Although at that price I expect it to not be an issue. 


Edited by hyiger, 24 May 2024 - 01:30 PM.

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#8 Dynan

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Posted 24 May 2024 - 02:11 PM

This is a tilt analysis in ASTAP. It does however show the FHD of all stars including the corners. This is with the 68III f/1.0 flattener.

 

I will say that the tilt can get worse in certain positions owing to the flex in the WO focuser. Sometime worse than other, yet still yields a great image.

 

Sombrero Tilt.jpg


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#9 Jim Waters

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Posted 24 May 2024 - 04:02 PM

Thanks everybody.

 

A friend suggested I check out the Stellarvue SVX90T.  I also got 3 direct messages from WO owners saying that they have been having issues with tilt with the 3" WO focuser.  After taking to Stellarvue over the phone for 15 minutes I decided to jump ship and get the SVX90T Imaging Version.

 

SVX90T Imaging Version - $2,695 Total cost

- Includes full frame field flattener designed for the scope

- Rings, ring standoffs and D mounting plate

- 90mm

- 540mm F.L.

- f/6

- No rotator

- US made and US phone support

 

William Optics - ($1,998 + $656) $2,654 Total cost

- 540mm F.L.

- f/5.9

- Manual rotator

- Flat68III - $656

- Made in Taiwan and limited email support

 

 

EDIT - I just ordered the SVX90T


Edited by Jim Waters, 24 May 2024 - 04:03 PM.

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#10 Dynan

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Posted 25 May 2024 - 04:15 AM

FCD 100 vs. Fluorite. Let us know the final analysis.



#11 RogerM

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Posted 25 May 2024 - 03:47 PM

I got the FLT91 back when it was first released in 2021 but was also considering the predecessor to the 'x' series (SV90TBV) at that time.  I'm happy with this scope so far and it will be nice to read your impressions of the SVX90T....there's an image of LDN 134 on Astrobin that really shows off what this APO can do!


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#12 Christine_Z

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Posted 26 May 2024 - 09:49 AM

Hi,

I use the FLT91 in front of an ASI2600MM Pro with the 68III flat.

You can see some of my images on astrobin. I also have the 6AIII reducer/flattener as well, that sees almost no use.

 

My only gripes with the FLT are:

1) the stock focuser required some work to get it stable for an heavy image train. It is fine now, but I had to do surgery on it.

2) A robotic focuser required adaptors due to the non-standard size of the dual speed pinion shaft (at least it did for me with a PLL Sesto-Senso-2)

3) It's heavy! I keep my AP rig in a single large Stellarvue case (and I can barely lift the case with its contents - to be fair, it includes everything that I use for AP except the battery box, so much more than the weight than what ultimately gets mounted. Computer, extra camera, extra harnesses, the reducer)

 

Things I like about FLT91

1) the built in Bahtinov mask...for those evenings when NINA's focus routine is being problematic.

2) The rotator...mine works very well, and is heavy duty. 

3) the stock focuser: Assuming my focuser issue was a quality control adjustment issue, the stock focuser holds focus even with my heavy image train at high angles without being locked, yet it is very smooth and a robotic focuser easily handles the job.

4) The WO rings...I love that they have three sets of tapped holes for extra accessories. This comes in very handy for a dedicated AP setup. (I think these are some of the nicest rings I have used)

5) The optics! As for the optics though, they are excellent, although I have never used the scope visually...I should try that someday...lol I have no gripes about color, although I shoot pretty much narrowband only. But going from O-III to S-II does not require a refocus, although I do it anyway, so that tells me this triplet has good color correction.

 

For those considering an FLT91, my mount can easily handle the 18kg setup, but mass/weight is something to consider for a fully decked out 90mm scope being used for AP. The Stellarvue is .5kg less than the WO FLT91. I think the Stellarvue flattener is less massive too. The 68III is a huge piece of glass. I do not know how the image circles compare, but I get nice and round in the corners with an APS-C chip with easily corrected and minor vignetting, which is most likely due to the adaptors and 36mm filters rather than the 68III. The WO 6AIII reducer is significantly lighter and smaller, but cropping is necessary with an APS-C size chip, which negates the reason for the reducer other than having slightly faster scope.

 

(the 18kg includes: the FLT91, custom flat panel on the front, robotic focuser, two 9" ADM Losmandy plates, WO rings, WO 68III flattener, adaptors, WO 7 position 36mm filter wheel, ASI2600MM Pro camera, wiring harnesses, Stellarvue 80mm guide scope/rings and saddle and an ASI 290mm guide camera, laser finder) Sure it could be lighter, but often I replace the regular guide scope with a Redcat for widefield so it sits on top of the FLT91's top plate and puts me at about 22kg.


Edited by Christine_Z, 26 May 2024 - 03:45 PM.

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#13 Dynan

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Posted 26 May 2024 - 12:34 PM

And if you have any backfocus issues, Christine (above) it the source for cures. :smile:



#14 Christine_Z

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Posted 26 May 2024 - 03:55 PM

This is a tilt analysis in ASTAP. It does however show the FHD of all stars including the corners. This is with the 68III f/1.0 flattener.

 

I will say that the tilt can get worse in certain positions owing to the flex in the WO focuser. Sometime worse than other, yet still yields a great image.

 

attachicon.gif Sombrero Tilt.jpg

I get very similar results with mine as well, and sounds like the same setup.

 

I custom built a flex harness that sits on the back portion of the lower supporting Losmandy plate. This holds the adaptor tubes and image train locked in place and is micro-adjustable in the x-y-z positions. The supporting harness itself is bolted to the lower D plate, but the yoke that holds the image train is between the flattener and the filter wheel. This allows about 8-10mm total of in and out focus travel which is plenty for the autofocus routine to run. But most importantly it eliminates all slop that could occur due to a heavy camera/filter wheel setup. After I did the focuser surgery on my stock focuser, I found it was not necessary, but I still use it.



#15 Christine_Z

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Posted 26 May 2024 - 04:09 PM

Thanks everybody.

 

A friend suggested I check out the Stellarvue SVX90T.  I also got 3 direct messages from WO owners saying that they have been having issues with tilt with the 3" WO focuser.  After taking to Stellarvue over the phone for 15 minutes I decided to jump ship and get the SVX90T Imaging Version.

 

SVX90T Imaging Version - $2,695 Total cost

- Includes full frame field flattener designed for the scope

- Rings, ring standoffs and D mounting plate

- 90mm

- 540mm F.L.

- f/6

- No rotator

- US made and US phone support

 

William Optics - ($1,998 + $656) $2,654 Total cost

- 540mm F.L.

- f/5.9

- Manual rotator

- Flat68III - $656

- Made in Taiwan and limited email support

 

 

EDIT - I just ordered the SVX90T

I think you made a wise choice. I would think that either scope are going to be excellent performers in the 90mm space, perhaps second or third only to the AP Stowaway and Tak FSQ85.


Edited by Christine_Z, 26 May 2024 - 04:10 PM.

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#16 Jim Waters

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Posted 26 May 2024 - 04:19 PM

Thanks Christine for your inputs.



#17 Dynan

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Posted 26 May 2024 - 04:37 PM

I get very similar results with mine as well, and sounds like the same setup.

 

I custom built a flex harness that sits on the back portion of the lower supporting Losmandy plate. This holds the adaptor tubes and image train locked in place and is micro-adjustable in the x-y-z positions. The supporting harness itself is bolted to the lower D plate, but the yoke that holds the image train is between the flattener and the filter wheel. This allows about 8-10mm total of in and out focus travel which is plenty for the autofocus routine to run. But most importantly it eliminates all slop that could occur due to a heavy camera/filter wheel setup. After I did the focuser surgery on my stock focuser, I found it was not necessary, but I still use it.

You and I were in many communications to help me solve my backspacing measurements. It worked out amazingly well. Thanks!

I we talked about your camera support, but with my eq mount, it wasn't doable.


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#18 Christine_Z

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Posted 26 May 2024 - 04:50 PM

You and I were in many communications to help me solve my backspacing measurements. It worked out amazingly well. Thanks!

I we talked about your camera support, but with my eq mount, it wasn't doable.

LOL,  it is now...I designed a roller bearing ring that fully supports in all orientations.


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#19 Dynan

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Posted 26 May 2024 - 11:57 PM

LOL,  it is now...I designed a roller bearing ring that fully supports in all orientations.

Sounds great! Can you share details (without giving away the farm)? :smile:



#20 Christine_Z

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Posted 27 May 2024 - 11:26 AM

I just replaced the yoke which I use for an alt-az mount with a ring that can be used on an equatorial mount. Think a guide scope ring, but one that allows frictionless axial movement kind of like a Crayford mechanism.


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#21 Dynan

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Posted 27 May 2024 - 02:07 PM

I just replaced the yoke which I use for an alt-az mount with a ring that can be used on an equatorial mount. Think a guide scope ring, but one that allows frictionless axial movement kind of like a Crayford mechanism.

Doesn't it affect the cords going to the camera?




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