How to adjust tilt of SW 2" crayford? More than 80 thou untrue at camera end!

[pipnina]

I was wondering why my new (second hand) refractor was showing astigmatism on one side, coma in the center, and fuzzy stars on the opposite side last night. I figured the most likely cause would be focuser slop as the previous owner took it apart to remove their ZWO EAF. And then I also messed around with it to add my own ZWO EAF.

Sadly, I could only affix the EAF via the hole for one of the tilt tension grubsrews, and I really hope that only one is necessary for getting the tension across the spindle correct because I don't know how else to attach the EAF...

I noticed when tightening and loosening the main tension screw, the focuser would shift up and down, but figured erring on the tenser side would be better. Seemingly not as it caused the EAF to skip steps and still wasn't true to the optics...

I used my dad's dial test indicator and the focuser's very convenient 360 rotation feature to see how much the focuser runs out with a 180 rotation. Turns out it is likely more than 80 thou! That's about 2mm near the camera, and I think that's almost certainly enough to disturb my images and give me the astigmatism, coma and blobby stars...

I'm really hoping there's a good way to adjust it because tomorrow might be the last good imaging night for a while : (

Any help greatly appreciated!

here's a non-raw image to show the problem (astigmatism in bottom left), as well as two abberation inspector samples from raws in pixinsight.

 

 

[pipnina]

Still no luck. I've tried fiddling with a few adjustment screws to no avail. For some reason the focuser barrel just won't sit parallel to the scope tube! Measured the error both on the blue part of the camera's outside diameter and on the focuser barrel and it's consistent between the two, so I am fairly confident that it's the barrel not sat right in the focuser itself.

Some pics of the focuser

[Budgie1]

I don't know it will help with your problem but, when I fitted the ZWO EAF to this focuser on both my Evorstar 80ED DS Pro & 100ED DS Pro I didn't remove one of the grub screws of the shaft. There was enough thread to be able to leave them in place and use washers to pack out the EAF securing screws to lock it in place.

Also note I turned the flat plate up the other way to how you have it, to git a flat surface for the washers.

[pipnina]

26 minutes ago, Budgie1 said:

I don't know it will help with your problem but, when I fitted the ZWO EAF to this focuser on both my Evorstar 80ED DS Pro & 100ED DS Pro I didn't remove one of the grub screws of the shaft. There was enough thread to be able to leave them in place and use washers to pack out the EAF securing screws to lock it in place.

Also note I turned the flat plate up the other way to how you have it, to git a flat surface for the washers.

Interesting. Maybe that screw is pushing down on the tension pad after all... I'll have to check that.

I take it you don't really need the side tension grub screws and can just rely on the center one?

Also i put the flat plate in such a way to increase the flat surface area the plate would have on the focuser, given how hard it was to get it to behave at all haha

[Budgie1]

16 minutes ago, pipnina said:

Interesting. Maybe that screw is pushing down on the tension pad after all... I'll have to check that.

I take it you don't really need the side tension grub screws and can just rely on the center one?

Also i put the flat plate in such a way to increase the flat surface area the plate would have on the focuser, given how hard it was to get it to behave at all haha

Just to be clearer, all the grub screws are still in place, I didn't remove any of them. The smaller ones are screwed into the casing enough that it leaves 2 or 3 threads for the EAF screw to use. 

The larger central grub screw for the pad adjustment works as normal.

[StevieDvd]

If the grub screws work like the SW crayford the outer ones keep the tensioner leel and the middle locks it in place.  Personally I'd avoid using them for the EAF.  The four outer screws (I believe) hold the focuser controls to the focuser body. I would check the size of these screws and get slightly longer ones and use 2 of them to hold the EAF bracket. You may need to enlarge the bracket hole/slot and use washers but that would avoid messing the focuser tensioner functionality.

I ewcwntly fitted an EAF to the Evolux 62ED but used a different optional EAF bracket as can be seen here to get a decent fit.

[michael8554]

Hope you find the problem.

But in any case, wouldn't the focuser tube be better supported on the bearings, so have less chance of sagging, if it was almost fully retracted, and a suitable extension added ?

Michael