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Note the cross on the Dec axis housing in the image, below right. This is the theoretical centre of mass. Since the counterweights balance the OTAs the centre of mass cannot be anywhere else. A vertical line should pass through the centre of the pier but is slightly offset to the north. Still, close enough I think to avoid toppling piers.
I have refitted the hinged tube rings for the 6" H-a telescope to the 30" long saddle. No point being without a working solar instrument while I design and build the new one. Still unsure how best to proceed. I'd like to build a skeleton tube design. It might even be worth getting some more of the same square tubing and joints as I used on the folded version of the 7". I wanted to be able to adjust the D-ERF without dismantling.
Then I can experiment with open and closed OTAs to confirm internal, thermal effects from solar heating. Though a full aperture D-ERF will hopefully keep the "insides" much cooler than the present, internal D-ERF version. Fortunately [?] the seeing is poor at this time of year with the sun being so low. Particularly when it is traversing directly over the house roof. So any changes from closure of an open framed refractor will be hard to detect. Is there any point in making an open framework if I don't need to adjust an internal D-ERF?
I do want to try to stiffen up the tail end of the drooping etalon and filter stack. Something like a finder ring mounted on a Newtonian style spider [or two] would do. The support provided must be independent of telescope orientation and adjustable for centring.
I really don't want
anything interfering with manual access to these parts for dismantling
and re-assembly. Which suggests an adequate cross section rather than
minimal. The tube struts should probably extend from end to end of the entire OTA. Right back to the camera.
Latest image of the mounting with only the 6" f/8, PST modded, H-alpha and the Vixen 90mm aboard. Picture taken from the veranda through the open slit from the west without flash. I have added a couple of small weights to the lower saddle to help the balance. The 6" f/10 will be 30cm or about a foot longer. Note how moving the mounting 2" north still allowed room for the RA stepper motor, drive belt and housing. Though it was quite close.
I have tried both T2 and 2" fittings for the filter stack and neither is stiff enough without external support. Being able to see physical droop of the camera or binoviewer is hardly an adequate sign of competence. Though a cynic might suggest that it avoids the need for a tilt plate for the camera.
I found a single 5Kg weight out-balanced the 6" H-a scope. So I added the 90mm outboard for white light views and imaging. A quick, flash picture, snapped in the darkness of the dome, proved I am ready if the sun ever comes out again. I had to move the 6" tube rings slightly closer together to bring the Vixen rings inboard enough not to overhang the focuser.
As an aside, the 50mm x 1.5mm O-rings I ordered back in early December finally arrived. I'll wait until daylight to see if they are any better than those that proved to be too thin for the PST etalon. Meanwhile I have ordered some 1.7mm Ø, elastic, fishing leader to try that. There must be something out there which will reduce the friction of PST etalon tuning without causing slop. I have tried the whole range of 1.5mm Ø O-rings. My thinking was that they would be thinner with more stretch and vice versa. The latest will, have no stretch at all. Well, the new O-rings proved to be no better than anything else I have tried so far. I will now pin my hopes on the 1.7mm Ø, elastic fishing leader.
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