Skywatcher 72ed ds pro focuser issue

[AstroNebulee]

Hi. 

I was out imaging tonight and noticed eggy stars in the top right and left corner of my images. I checked everything in the imaging train with my 294MC pro, spacers and field flattener where all screwed in perfectly into the focus draw tube but there seemed to be a little play in the tube and when rotating the focuser there was a slight wobble (is this flexiture?) on the left hand focus knob as it was turned and wasn't going round in a perfect circle. And also when taking my flats the white flat circle was more over to one side and not central. The right hand knob with the fine focus knob was turning beautifully. I took the scope in and in the attached image this screw arrowed was quite loose, so I've tightened it up and just checked all the others and now seems to be rotating better and no play in the tube. I'm just wondering has anyone else come across this before and do I need to tighten the grub screws in the focus knobs? Or anything else to look out for, or worth taking apart and greasing it. 

Edited January 20, 2022 by AstroNebulee

[banjaxed]

I fitted one of those focusers to my ST120 and they are quite a simple design. If you dismantle it you will be able to work out how it works and how to adjust it. Should you have any problems let me know and if I will strip mine down and try to explain it further.

[AstroNebulee]

9 minutes ago, banjaxed said:

I fitted one of those focusers to my ST120 and they are quite a simple design. If you dismantle it you will be able to work out how it works and how to adjust it. Should you have any problems let me know and if I will strip mine down and try to explain it further.

Thank you that's very kind of you. I have found this link to a few sheers on the focuser issues so will print off and have a look. If not I'll be glad if your help 👍 

It seems as though it was one of the paralising screws that was loose, hopefully tightening it has stopped the loppy looseness of the focus tube now but I shall take it apart this weekend and give it a good look. 

https://www.yumpu.com/en/document/read/22870696/adjusting-the-skywatcher-110-refractor-crayford-focuser-teleskop

Edited January 20, 2022 by AstroNebulee

[AstroNebulee]

Ultimately@banjaxedI'm going to try tonight to adjust my focuser. I think it's worked loose because the length of my FF, spacers and 294mc pro and before when tightening the focus lock screw the would moved the focus tube back a bit.

Now my understanding of it is to loosen the counters screw and paralleling screws left and right of the tension screw.

Then tighten the tension screw a bit, then re tighten the left and right paralleling screws.

This should then grip my focuser better and stop the wobble and play plus no movement when engaging the focus lock screw. 

I may have to take the focuser off to check that the Teflon bearing is parallel according to this image in the instructions. 

Edited January 21, 2022 by AstroNebulee
Images

[banjaxed]

Theoretically if the 2 parellizing screws are protruding the same then you should be good. I think you will be fine if you just take your time and tighten and loosen a little at a time.

[AstroNebulee]

Think I've sorted it now. Just undone the screws as I mentioned and tightened the tension screw a touch now I've no slippage on the focuser with my FF, spacers and 294mc pro attached. Before the focuser was stiff in a few places and now it's smooth. Also before when nipping up the focus lock thumbscrew the focus tube would move. Now when tightening the focus thumbscrew the tube stays in position. Here's a flat I've taken with the adjustment made and now central in the image and not off to one side as before. 

Edited January 22, 2022 by AstroNebulee

[AstroNebulee]

Update on my issue. I still have the eggy stars in the top right and left corners (I will include a single sub of the issue) one sub is normal framing and one is camera rotated 90 degrees.

Looking close there is slight eggyness in the bottom corners but not as much as top. Maybe seeing this closer the sensor is too close to the scope. Thinking it's a focuser sag issue with the extended weight on the back. My scope is balanced, correct back focus of 55mm and guiding is great for my mount at around 0.6-1.4 rms. I can adjust the tension grub screw again to give me more tension on the focuser tube, maybe that will help. 

I've contacted FLO and they suggested adjusting the focuser on the bottom again. I have a rotator so will fit this too. FLO have suggested a tilt adjuster along with the rotator and focusing tweak. I'm wondering tgaet the bevel shamfered bit (arrowed on the image) on the FF could be contributing to the off centre too as they step in a bit, and with the 2 thumbscrews on the visual back couikd be shifting it. I thought maybe to adjust the bearings on the top but FLO said best to just alter the bottom of the focuser. 

Edited January 28, 2022 by AstroNebulee

[AstroNebulee]

××Mods can you move this to the imaging help forum please. ××