10" f/8 Testing-testing.

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At 4.30 this morning I was wide awake and moonlight was lighting up the curtains. I sneaked out as quietly as possible and set up the telescope. A few brief glimpses confirmed a nice sharp image at 80x before a solid lid of cloud slid across the sky and the moon just disappeared. So I went back to bed. The mirror cell fixing needs reinforcing as it, or the pot itself , is clearly flexing on the beams when I stand the telescope on its tail for storage. The sack truck and OTA wheeled axle both worked as intended. I still need a finder, sights and an adjustable balance weight. Just putting the Barlow in tipped the telescope towards very nose heavy! I haven't fitted the worms and motors back onto the MkIV yet so there is very little friction to keep things under control. This may be a good thing while I finalise the design.

My search for an ultralight OTA now seems slightly irrelevant thanks to the wheeled axle. Had I decided to use the wheels in the first place I could more easily have lived with the cardboard tube. Though the extra weight of such a long tube would still have to be controlled by the MkIV.

Adding a finder will change the balance towards the top of the tube. Logic suggests having an adjustable balance weight near the bottom to compensate. However, that would mean a potentially dangerous top heavy situation at times as I move to the other end of the telescope to balance it. A long threaded rod with an adjuster knob near the eyepiece could be fixed between the beams. The balance weight could still be situated at the bottom where it would do most good. Without the adjustable weight the OTA would balance much further up the tube. Requiring a much taller pier to support the OTA at its natural balance point.

A taller pier inevitably brings ladders into the observing equation. I often used a step ladder with my 6" refractor on the MkIV. Finding them quite comfortable and relaxing when I faced and leaned against the ladder. So having to use a step ladder isn't a major disaster. What would be better is a stepladder with much smaller distances between each step. I shall have to examine the possibility of modifying a lightweight aluminium stepladder to allow smaller height increments when observing. Still lots to think about.

I was up early again this morning and had the same problem with rapid clouding over. So I had some coffee and breakfast and killed some time on the computer. When I went out again the cloud had cleared to small balls of cotton wool. I set up the telescope again and enjoyed powers up to 200x. (10mm eyepiece)

The sky was bright blue but there was just enough contrast to spend half an hour staring at the moon and adjusting collimation and balance.

Ideally I think I need an adjuster which will move the OTA along relative to the MkIVs saddle. This will avoid adding adjustable weights to optimise the balance.Which in turn would need more counterweights on the declination axis. With further problems of imbalance while moving the mounting around the garden on the sack truck.

Update: It was clear this evening with countless stars competing with a brilliantly clear Milky Way. I spent a couple of hours panning across the sky before it clouded over. It started with strange streaks light searchlight beams then misted right over. Star images were small but not tiny. No sign of coma. Collimation is still slightly off.

Update: I saw a chance for a look at the half moon early one morning before it was fully light. It promptly clouded over and then teased me for an hour with only brief glimpses. I put the 15mm in and stared hard at Plato at 130x but couldn't seen any tiny craters. The problem with the main mirror collimation may be due to the threads catching in the holes in the rather thin bottom of the pot. I'll have to look into this because adjusting the wing nuts doesn't move the mirror smoothly enough. At first nothing happens and then I can see the secondary move over suddenly.

Update: Another hour struggling with cloud as I tried to observe the moon around dawn. Even with the naked eye I could see the moon was very "misty" due to invisible high cloud. Things did not improve through the telescope at any power up to 200x.

Collimation changes as I run the OTA around on its wheels. Getting it back into alignment is almost a random affair at the moment. Despite this, the wheels are incredibly easy to use to move the OTA into and out of its accommodation. Settling time at the eyepiece is quite short at around 1/2 second but is very sensitive to the slightest touch. I still haven't fitted the worms to the MkIV so the OTA movements are very free. I really need to see how the worms damp the vibration seen through the eyepiece. I only rarely used the 6" refractor without the worms fitted and most usually with the polar drive engaged. The mounting was so solid in that condition that I could safely take snaps of the moon at quite high powers with the camera simply handheld to the eyepiece.

Update: I had half an hour observing a low crescent moon at up to 200x. The moon was so low I was crouched double on a folding, wooden chair. Lots of low and high frequency thermal effects with occasional cloud before a total sky blanket arrived. Surprised by the number of small black craters standing out and the ruggedness of the terminator. Lots of contour shadowing. Collimation is going to become a nuisance unless I can park the telescope on a raised platform and leave it there!

Update: Moon at about 45 degrees altitude in a clear sky so I dragged the 10" out again. Any sense of sharpness is still an illusion. A strange effect. The moon looked sharp at a glance but staring proved it was impossible to focus on tiny details. I fitted the Cheshire to improve the alignment which was very poor at first despite the secondary being perfectly centred. This helped but not enough. A bright star showed ragged, soft edges both sides of focus in the 35mm. (60x) Back to the moon and I pushed powers up to 100x, 200x and even 300x on Plato but the softness remained.

I still need to improve the secondary support. It rotates almost of its own accord. I ought to set up the telescope in daylight and see what can be done with the Cheshire. The MkIVs drives should also be fitted but the sky has been so cloudy of late that I haven't been inspired to do much. Having such poor views of the sky from the back lawn doesn't help.

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I climbed a ladder set up against the shed today to remind myself how clear a view I could have over almost 180 degrees centred on the South. I may now build a wooden platform in front of the shed about 8' off the ground and 8' square using the shed as a stable support for the rear of the joists.

My original plan was to have the platform beside the shed but that would require felling a 40' birch tree which stands right beside the shed. (Which I am still keen to remove as it drips and sheds seeds and twigs year round onto the car, shed and back garden) Unfortunately the huge birch set the nominal width of the shed at 8' when I was designing it. I would have preferred it to be wider to allow more room to move around inside.

The platform can become a token, flat roofed carport in overall design. I demolished the existing dilapidated carport to build the wooden shed. A really massive affair using 4"x2" timbers clad in exterior grooved plywood.

While the intended platform may appear like a carport to the uninformed eye it will have a safety handrail and a planked floor where the roof should be. Concrete anchors will support the front posts. I might clad the windward, westerly side with plywood matching the shed for weather protections and a uniform appearance.

Whether the platform will gain a protective wall, roll-off roof observatory, or even a dome, is more unsure. A door in the gable end of the shed could offer covered access to the telescope housed between the rafters of the shed. The problem with this carport idea is the unlikely and really unwanted central post to support the mounting!

I wonder whether a suitably heavy arrangement of timbers attached to the corner posts of the carport floor would offer enough isolation for the mounting from the floor? These timbers could be well above head height  but hidden under the platform floor. Thus keeping the carport clear of internal obstructions.

I imagine the telescope will shake from my presence on the platform floor whether I move deliberately, or not. Though I could invest in thick isolating foam to avoid conductive vibration from my movements. Then mount the MkIV directly onto the floor through an aperture in the foam. Suitably heavy joists will help. I could even have cantilevered joists using 8" or 10" x 2" supported (on edge) by the shed's own roof timbers to support the  mounting.

Plenty of corner triangulation will avoid the platform swaying. Sturdy access stairs could be used to provide further swaying resistance if it were well anchored top and bottom. Pre-cast, pyramidal, concrete anchors with protruding galvanised metalwork are readily available at builders merchants.

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