Focuser slop when imaging towards the South

[symmetal]

Still trying to get optimum spacing/tilt with the ASI6200 and FLT98 I noticed after a meridian flip that the apparant tilt error lessened quite significantly. There is up/down movement of the focuser barrel in the scope when lifting the camera but no left right movement. As I am imaging towards the South the scope is on its side so the two tension screws on the top of the scope above the focuser barrel are now on the side of the scope. These now stop left/right movement but there is nothing to stop up/down movement. It would be nice to have a second set of tension screws at 90 degrees to the current ones to stop slop in both directions. As scopes just seem to have the one set of screws (or screw) does anyone have any ideas on stopping movement in the up/down direction when the scope is on its side.

Doing the current single set of screws up really tight reduces the up/down movement quite a bit, (when the scope's on its side), but it's then too tight to autofocus. Thin PTFE strips fixed to the barrel may help but before I order some, are there any other suggestions. 🙂

This movement was always there but with smaller sensors it didn't really cause an issue.

Alan

[Davey-T]

Had the same problem with a WO Star71, I was going to take it apart and fit a couple more of those brass tensioners opposite  the original ones but fell at the first hurdle as couldn't unscrew the focuser assembly from the tube, spent ages trying to shift it but only succeeded in making a dent in the tube with a ratchet strap.

I had the focuser nearly right in and used spacers to get focus,

Dave

Edited August 31, 2020 by Davey-T

[symmetal]

26 minutes ago, Davey-T said:

I had the focuser nearly right in and used spacers to get focus,

Good point. With the flat IV flattener I had before, the focuser was almost fully in so the slop was less than it is now I expect. The new WO Flat68III I now have to cover full frame, screws directly to the end of the focuser with a M92 thread so I'd need a M92 spacer which would have to be specially made I imagine.

On the FLT98 the whole focuser assembly unscrews from the main scope body I believe, so looking in from the front may yield a solution. There are some accessory mounting holes on the focuser body, 45 degrees either side of the focus tension screws so nylon screws in these holes tightened against the focus tube may help. If they were offset by 90 degrees it would be ideal. 🙂

Alan

[symmetal]

Actually found that the accessory mounting holes seem to do the trick. They have blanking grub screws and screwing a nylon M5 screw in until it lightly touches the tube seems to do the trick. An M4 screw needed screwing in more tightly to achieve the same. Luckily a US scope didn't have UNC/UNF threads here 😀. I've ordered some M5 (and M4) 10mm knurled screws from ebay which should solve the problem, possibly with some thread lock. The right side screws are over the etched focuser scale so it's probably best just to use the M5 on the left. This will probably add some tilt but at least it should be a fixed tilt which can be adjusted out rather than a wobbly tilt which depends on where the scope's pointing. 🙂 The accessory holes are actually offset closer to 30 degrees from vertical rather than 45 degrees but it still seems to work.

Alan