William Optics FLT 91 - imaging

[PadrePeace]

Who supplied this?

[scotty38]

I accept it may not cause this but is the back focus all set ok as I know there has been various settings given out for the 6AIII?

[Adam J]

2 hours ago, scotty38 said:

I accept it may not cause this but is the back focus all set ok as I know there has been various settings given out for the 6AIII?

Spacing would not cause an issue in the centre of the feild like this. 
 

I believe that these scopes Guarantee 95% Strehl too....

Edited May 6, 2021 by Adam J

[PadrePeace]

3 hours ago, PadrePeace said:

Who supplied this?

Still don’t know who supplied this? 

[scotty38]

1 hour ago, Adam J said:

Spacing would not cause an issue in the centre of the feild like this. 
 

I believe that these scopes Guarantee 95% Strehl too....

Well it just shows what I know as I thought the centre looked ok

[scotty38]

Ok fair enough I zoomed in a bit 🙂

[kbrown]

I just received mine yesterday. Only been able to test it a little bit visually tonight between the patches of clouds. Here's my initial thoughts:

• Feels like a solidly built piece of kit.
• Focuser had some rough spots when going through from one extreme to another. A bit of silicone grease on the rack took care of that. Didn't have to adjust any screws.
• Was surprised not to be able to focus in enough with my Ascension 2" 90° Dielectric Star Diagonal using any of my 1.25" eye pieces. Had to "shorten" the diagonal by 18mm by printing a new EP holder for it.

Overall I'm very pleased with it so far. Next time it's clear I'll pop in my ZWO ASI183MC Pro together with my HoTech SCA Field Flattener and capture some images.

 

Edited May 7, 2021 by kbrown

[kbrown]

On 30/04/2021 at 17:42, kbrown said:

Can any of you give me an idea what sort of weight the focuser on the WO FLT91 can handle? I think this is my current favourite to get.

Answering my own question as I received this information from WO:

"Focuser loading capacity is around 8-10Lbs. If you have a heavy loading you will need to add some extra tension using two screws located on the top of the focuser."

 

[Ken999]

I received  a replacement for my FLT91 that was giving me problems; it was most likely a first run lemon, but the great folks at William Optics and my retailer Ontario Telescope turned it around quickly and dropped off a new FLT91 and 6AIII flattener for me to try out.  Out of the box, after snugging down a few screws that were holding the focus assembly in place, I was good to go. Steve at Ontario telescopes consulted Gary Palmer who said he gap distance on the flattener/reducer must be 3.45mm for a 55mm back focus. First light image attached. I am very impressed with the optics, coming from someone who has only used the RedCat51. For this image of C34, I used an ASI294MC Pro guided by an ASI290MM and an optolong L-enhance filter. 56x180s frames under Bortle 5 skies.

[AstroDoc1]

I just received this scope and flattener.

is 3.45mm definitely the correct flattener gap space for a 55mm back focus with the ZWOasi2600mm camera?

I thought I read somewhere it should be 5.4mm. I need confirmation.

thanks,

brian

Edited July 31, 2021 by AstroDoc1

[Tony Bell]

On 31/07/2021 at 18:01, AstroDoc1 said:

I just received this scope and flattener.

is 3.45mm definitely the correct flattener gap space for a 55mm back focus with the ZWOasi2600mm camera?

I thought I read somewhere it should be 5.4mm. I need confirmation.

thanks,

brian

Hi Brian did you find the answer to the adjustment on the Flattener ? 3.45mm or 5.4mm ?  Just got my FLT91 and flattener and want to fit ZWO EFW and ASI 1600 mm Pro Mono.  

[AstroDoc1]

On 24/08/2021 at 16:42, Tony Bell said:

Hi Brian did you find the answer to the adjustment on the Flattener ? 3.45mm or 5.4mm ?  Just got my FLT91 and flattener and want to fit ZWO EFW and ASI 1600 mm Pro Mono.  

Definitely 5.4mm is the starting gap then adjust from there to improve the star shapes in the corners. I use a backfocus of 56mm because I add 1 mm for the 1/3 thickness of the filters. Let me know how you make out.

Brian

[newbie alert]

Nice mount

[iantaylor2uk]

I use a WO 81 GT IV with a 1x Hotech SCA flattener and the ASI Air Pro tells me the focal length is 475 mm and I've had some great images from it. I guess if you went for a 91 with a reducer it would be a similar focal length so the only advantage would be the slight increase in aperture.

[licho52]

I am quite happy with the performance of mine, found that using 2mm filter the backfocus is 6.1mm.  I might fiddle more but tbh, not really.  I can safely say I've never had a better scope. 

 

[Limerick John]

On 07/05/2021 at 10:51, kbrown said:

I just received mine yesterday. Only been able to test it a little bit visually tonight between the patches of clouds. Here's my initial thoughts:

• Feels like a solidly built piece of kit.
• Focuser had some rough spots when going through from one extreme to another. A bit of silicone grease on the rack took care of that. Didn't have to adjust any screws.
• Was surprised not to be able to focus in enough with my Ascension 2" 90° Dielectric Star Diagonal using any of my 1.25" eye pieces. Had to "shorten" the diagonal by 18mm by printing a new EP holder for it.

Overall I'm very pleased with it so far. Next time it's clear I'll pop in my ZWO ASI183MC Pro together with my HoTech SCA Field Flattener and capture some images.

 

Hi. I picked up a new FTL 91 last week and have the same issue getting focus with 1.25" eyepieces. I tried two diagonals, both William Optics but hit the stop just before focus could be achieved. Did this affect getting focus with your ASI camera? I am considering returning the scope to the dealer.

[kbrown]

19 hours ago, Limerick John said:

Hi. I picked up a new FTL 91 last week and have the same issue getting focus with 1.25" eyepieces. I tried two diagonals, both William Optics but hit the stop just before focus could be achieved. Did this affect getting focus with your ASI camera? I am considering returning the scope to the dealer.

No it didn't as for imaging you don't typically use a diagonal at all.

Regarding the focuser I did have some additional woes with it but I managed to get it to operate really well. Here's more info on that: http://knowhere.myqnapcloud.com/WordPress/2021/08/23/adjusting-william-optics-flt-91-focuser/

[900SL]

On 12/09/2022 at 02:35, kbrown said:

No it didn't as for imaging you don't typically use a diagonal at all.

Regarding the focuser I did have some additional woes with it but I managed to get it to operate really well. Here's more info on that: http://knowhere.myqnapcloud.com/WordPress/2021/08/23/adjusting-william-optics-flt-91-focuser/

Does this run the risk of moving the collimation out between objective and reducer? Are the brass screws used for alignment of the focus tube? 

[kbrown]

4 hours ago, 900SL said:

Does this run the risk of moving the collimation out between objective and reducer? Are the brass screws used for alignment of the focus tube? 

I might be wrong but honestly I don't think so. The screws got plastic tips on them which just sit int the groove of the focuser tube. I think they're just meant for locking the tube in place. I don't think they are meant for adjusting it. Mine's been totally fine after I opened it...