14/15th April 2019

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Sunday: I brought down the 7" OTA and removed the objective, tailpiece, handles, weight rail and Vixen focuser. Then shortened the main tube by 150mm/ 6". The FTF is about 30mm longer than the Vixen both at minimum length. The turned base ring adds another 20mm. So I added 50mm to the difference. This should allow me to reach focus with the 2" Lacerta prism and binoviewer. It is very easy to add 2" extenders but far more difficult to reach inward focus.

A slight worry is the great difference in weight between the two focusers. Weight at the tail end means moving the OTA up through the rings. There isn't an an awful lot of clearance now. So I'll just have to move the offset weights for the 6" H-alpha 'scope to the top of the 30" long saddle. I already had weights up there but moved them down to the focuser end. This was to balance the added weight of the offset 6" mounted, via tube rings, on the saddle.

After spending so much time on the backplate I changed my mind. I have decided to sandwich the original [saucepan] tailpiece with the focuser collar and base ring. This required I turn a shoulder on the custom base ring. Meanwhile I shall be looking for another saucepan with much less taper.

I put the laminated plywood internal rings back in the lathe and turned the outer surface to better match the saucepan's curve. Then I was able to make use of the original collimation springs in the shorter gap. I reconsidered the sandwich when I realised that I was merely duplicating the FTF rotation system. The custom base ring needs to be firmly anchored to the saucepan base. Then the FTF collar can do its thing.

Springs are probably a bad idea with such a heavy focuser on an equatorial mount. It would tend to sag around the optical axis in all positions. So I need to add push screws for locking the collimation as well. All this would be far better done on a straight-sided pan base.

I now have the 7" refractor in pieces just as the sky clears.  The Moon is high in the south, the sun has an interesting spot and my new camera is sitting uselessly on my computer desk.

Monday: I refitted the tapered tail end with the springs and large washers keeping the custom base ring rigidly in place. Then I dragged the bare tube upstairs to the observatory and fitted the objective back on. Then the big focuser was attached to the updated tailpiece.

I fitted the 7" and re-balanced the telescopes while duplicating the offset weights. Still a little extra care in balancing is required. I have moved the 7" main tube higher in the rings for more floor clearance as the sun climbs higher.

Finally I was able to find the sun and try the new focuser. It is an absolute delight to use after my struggles with the floppy/tight Vixen. No more sag and the focusing action is superb. It seems I overdid the shortening of the main tube when the WO Barlow is on the binoviewer nose. So I added a short 2" extension to bring the draw tube to half way.  Without the Barlow I should finally have low power binoviewing.

The bridge on AR2738 has moved towards one end of the spot. My first clear, visual view of super-granulation at 140x and 170x thanks to the binoviewers. The sun spot is spectacular!

A quick glance in H-alpha also showed the bridge against a large dark spot. With two large prominences visible.

13.30: Stopped for lunch. I shall be back out there with the ZWO camera and laptop this afternoon. Though I could see fine surface detail in both WL and H-a I seeemed unable to capture it.

Click on any image for an enlargement.

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