Dear Robin,
This is a second go – the previous attempt just vanished when I tried to add an attachment.
Yes, I’m local. We’ve met at the Cockermouth Astronomical Society.
The grism holder now has a screw thread (not a good one IMHO) and so I guess has the tube it fits in. There is no locking screw (very much a retrograde move). The holder seems to come loose easily. It was loose just now when I checked it and I’m sure it was tight when I put it away.
I attach a copy of my last solar spectrum. I seem to not be focused very well (but the loss of detail caused by the size limit on image uploads to the forum has reduced the precision a lot as well).
Regards,
David Perkin.