New wo gt71 focus issues

[ninjageezer]

Just upgraded my WO scope for a WO GT 71 ,i also bought the WO Field flat 6AIII.

fitted the camera and the spacers recommended to get the 55mm and then adjusted the FF to 64.1 mm as per instructions and noticed i had only 10mm of focus tube left .

i finally got chance to test tonight but not have much joy.  i can get a great focus curve no issues but when i try and adjust the FF and start to get near better edge stars i literally cannot use the eaf as its ran out of tube.i have no idea why .....please help i had no issues with my last WO z73 .

[ninjageezer]

this picture may help ,please anyone with a GT 71...

[newbie alert]

You've not fitted the reducer the wrong way around have you?

I've seen someone else do this, who's name I'll hide to save embarrassment....ehh Simon🫢

[david_taurus83]

How much drawtube have you left when in focus? I had the older GT71 and Flat 6II and I'm sure I had about 30mm of drawtube available. The difference with my scope was I didn't have the rotator fitted like you have. 

[david_taurus83]

49 minutes ago, newbie alert said:

You've not fitted the reducer the wrong way around have you?

I've seen someone else do this, who's name I'll hide to save embarrassment....ehh Simon🫢

No it's the right way. The M63 end goes to the scope with the M48 end on camera side.

[900SL]

Are you saying that you need to increase the backspacing by 10mm to get good corner stars, which uses up your 10mm of available focus?

  From memory I have 30 mm without the WO rotator and around 15mm with the rotator. You should be able to reach focus. Try removing the rotator if you are struggling and rotate the scope in the tube rings to get correct camera orientation 

The image train and reducer look ok, 55mm from back of 6Aiii to SENSOR? 

You shouldn't need to adjust the 6Aiii by more than a couple of mm max either way, I increase mine by 1mm to allow for a filter.  The EAF should still work as long as you have set appropriate limits

Try without the rotator. Report back on backspace (55mm?) and offset on 6Aiii (9mm?) and focus tube rack out (30mm?)

 

Edited February 24, 2023 by 900SL

[ninjageezer]

Thanks to all I will try without the rotator when and if we ever get a clear night lol......had the new scope 2 weeks first try last night until clouds came in..

WO quote something like 9.1 mm  on the adjustment  + 55mm std back focus when using the Field flattener. I tried this but stars  still bad ,I also read somewhere that another user found his sweet spot at 12.5 mm on the adjuster I don't have enough focus tube left to try that , will see without the rotator.

[StevieDvd]

Looking at the data for the reducer and your scope as you have it setup then my calculation for the adjuster setting is about 8.7mm

Reducer Back focus	64.1
Camera sensor inset	-17.5
Filter Drawer	-21
Spacer	-17.5
Add filter refraction	0.6
Adjustment needed	8.7

That's assuming your PlayerOne camera has a 17.5mm spacing, the filter drawer takes up 21mm, you have an added 17.5 spacer and the filter adds about 0.62 to the spacing.

As you now have a rotator before the reducer the focuser has had its adjustment range reduced. Any error that increases the spacing distance is going to reduce the adjustment range further.

The 55mm value is based on a DSLR with a standard adapter for the camera fitted, for telescopes having a 'standard' 55mm back focus.  So an adjustment of 9.1mm would be correct for a DSLR without the filter drawer.

HTH

Steve

 

[ninjageezer]

On 24/02/2023 at 15:05, StevieDvd said:

Looking at the data for the reducer and your scope as you have it setup then my calculation for the adjuster setting is about 8.7mm

Reducer Back focus	64.1
Camera sensor inset	-17.5
Filter Drawer	-21
Spacer	-17.5
Add filter refraction	0.6
Adjustment needed	8.7

That's assuming your PlayerOne camera has a 17.5mm spacing, the filter drawer takes up 21mm, you have an added 17.5 spacer and the filter adds about 0.62 to the spacing.

As you now have a rotator before the reducer the focuser has had its adjustment range reduced. Any error that increases the spacing distance is going to reduce the adjustment range further.

The 55mm value is based on a DSLR with a standard adapter for the camera fitted, for telescopes having a 'standard' 55mm back focus.  So an adjustment of 9.1mm would be correct for a DSLR without the filter drawer.

HTH

Steve

 

Hi Steve that's the distances I got exactly....I tried about that distance but stars not good so that's when I tried to increase the FF to 10mm and ran out of focus tube ,I have now removed the rotator and flipped the OTA in its rings .my approx focus now gives me 25 mm of tube left to play with. Also i can rotate the OTA within the rings about 80 degrees either way if needed. I will have to wait until we finally get some clear skies as ATM I seem to be living under permanent clouds.....

[StevieDvd]

Two things:

1. You can probably check the in/out focus range during the daylight if you have a far off building/aerial etc

2. Your EAF is not hitting a limit is it? And not the focuser itself maxing out.

[ninjageezer]

17 hours ago, StevieDvd said:

Two things:

1. You can probably check the in/out focus range during the daylight if you have a far off building/aerial etc

2. Your EAF is not hitting a limit is it? And not the focuser itself maxing out.

Hi Steve I checked and reset to make sure the EAF is at 0 when focus tube is in to the max .messed about in the daytime yesterday and when focussed on far objects I had about 25mm left without the rotator so should be ok as far as tube travel now.

[scotty38]

As you know, I think, you need the 55mm from the back of the Flat6A to the sensor and then, for the GT71, you need the Flat6A adjusting to 9.1mm.

Looking at your image it doesn't look like it's anywhere near that setting, looks closer to 0mm, is that how you have it?

[StevieDvd]

If you need/prefer to add the rotator back, then perhaps there is an extender available for the focuser.

[Laurin Dave]

As @scotty38 says to start with you need to adjust the flattener to 9.1mm.  I found with mine that in-order to fine tune the flattener spacing (from 9.1) I needed to remove the rotator to get some extra back focus.  Once I'd got the spacing correct I put the rotator back and all was fine. Hopefully be the same with yours

[david_taurus83]

20 minutes ago, scotty38 said:

As you know, I think, you need the 55mm from the back of the Flat6A to the sensor and then, for the GT71, you need the Flat6A adjusting to 9.1mm.

Looking at your image it doesn't look like it's anywhere near that setting, looks closer to 0mm, is that how you have it?

 

6 minutes ago, Laurin Dave said:

As @scotty38 says to start with you need to adjust the flattener to 9.1mm.  I found with mine that in-order to fine tune the flattener spacing (from 9.1) I needed to remove the rotator to get some extra back focus.  Once I'd got the spacing correct I put the rotator back and all was fine. Hopefully be the same with yours

It's correct. If you undo the knurled ring and wind it back to the front section you would see that the rear section is on around 9mm on the scale.

[scotty38]

Good point, I must admit I was imagining mine was with the knurled bit at the marker but it's not in front of me 🙂

[david_taurus83]

I should add that when I had my GT71 and Flat6AII I never got perfect corners with either 600D or 1600MM. I was forever chasing it and changing back spacing. It's a road to madness!

[900SL]

The flat 6A111 can have tilt induced when you tighten the knurled adjuster, due to tolerances in the threads and flatness of machining. It's a nice idea but I noticed a few users on cloudy nights had this issue and replaced the focus ring with either a machined spacer of the required thickness, a 3D printed spacer with parallel faces or simply wound it all the way in and used a separate spacer and shims to get the correct backfocus and field flatness. 

 

Mine seemed OK so I simply set it to the correct backfocus and wound silicone self fusing tape round it. I use a shim to allow for filters

[StevieDvd]

The camera fitted in the pictures looks like it has tilt adjusters in case that's an issue for @ninjageezer I could be mistaken though.

[ninjageezer]

On 26/02/2023 at 10:18, scotty38 said:

As you know, I think, you need the 55mm from the back of the Flat6A to the sensor and then, for the GT71, you need the Flat6A adjusting to 9.1mm.

Looking at your image it doesn't look like it's anywhere near that setting, looks closer to 0mm, is that how you have it?

the locking ring is at about 0 thats what you can see..

[ninjageezer]

On 26/02/2023 at 10:33, Laurin Dave said:

As @scotty38 says to start with you need to adjust the flattener to 9.1mm.  I found with mine that in-order to fine tune the flattener spacing (from 9.1) I needed to remove the rotator to get some extra back focus.  Once I'd got the spacing correct I put the rotator back and all was fine. Hopefully be the same with yours

Do you currently have a GT71 

[ninjageezer]

2 hours ago, StevieDvd said:

The camera fitted in the pictures looks like it has tilt adjusters in case that's an issue for @ninjageezer I could be mistaken though.

the camera does have tilt adjusters ,why is this an issue ? they are not adjusted for anything currently.....i thought the idea of tilt adjusters was a bonus ? sorry i must be missing something....

[ninjageezer]

On 26/02/2023 at 11:03, david_taurus83 said:

I should add that when I had my GT71 and Flat6AII I never got perfect corners with either 600D or 1600MM. I was forever chasing it and changing back spacing. It's a road to madness!

not want i want to hear lol,wish i had kept the Z73 lol....perfect corners using the field flattener on that .

[900SL]

https://www.cloudynights.com/topic/790549-need-help-setting-up-wo-flt-91-w6aiii-flattener/?p=11952246

 

 

[StevieDvd]

1 hour ago, ninjageezer said:

the camera does have tilt adjusters ,why is this an issue ? they are not adjusted for anything currently.....i thought the idea of tilt adjusters was a bonus ? sorry i must be missing something....

Hopefully you don't have an issue but as @900SL had mentioned possible issues needing some spacers for fixing tilted camera, you would not need spacers as your camera has the option too adjust the tilt (if needed). Sorry if I have worried you.