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Sunday: It rained later as I worked for several hours inside the closed dome.
Physically collimating the big refractor was so challenging I risked everything and removed the objective. Removing the heavy lens in its cell is not a trivial matter! Supporting a 10lb lump in the depths of downward facing dewshield over a desk is apt to cause the jitters. The three, long, socket head, retaining screws are not only invisible but almost impossible to find with a long hex key on an extension. It must all be done by feel alone without scratching the front of the objective.
Physically collimating the big refractor was so challenging I risked everything and removed the objective. Removing the heavy lens in its cell is not a trivial matter! Supporting a 10lb lump in the depths of downward facing dewshield over a desk is apt to cause the jitters. The three, long, socket head, retaining screws are not only invisible but almost impossible to find with a long hex key on an extension. It must all be done by feel alone without scratching the front of the objective.
In the end I managed the task without dropping the lens. Nor letting the 8' long telescope swing viciously once it was no longer balanced by the lens! Last time it did swing. While I was perched high on a stepladder. The bare tip of the tube almost hit the objective right out of my hands, through the open slit and on down to the ground some 20' below! Lesson learned!
No such drama this time. I had a noose around the objective end of the tube with a loop on the other end of the cord wrapped around my foot. I also lightened the focuser end as much as possible and moved the three [tube] balance weights towards the lens end of their travel.
Of course the very last screw wouldn't come free of its T-nut. So I had a loose lens cell still deep in the now rotating dewshield. I used to think I was so clever trapping the dewshield flange behind the cell for simplicity. Not any more, I don't!
Once I had cleaned the back of the lens I refitted it back onto the tube without the stub dewshield. The thick, laminated, Baltic birch, plywood ring is a tight fit on the 8" diameter tube. The ring locks against the small flange on the end of the steel, duct tube. So the objective cell can be safely pulled against the ring without any risk of it pulling off the end of the tube. Push-off collimating screws through the objective cell flange provide the adjustable alignment.
A quick check through the Cheshire with a torch fitted with new batteries showed that my initial rough alignment was actually spot on. And I still hate the Orion Cheshire's foolishly thick, wire cross-hairs!
After lunch I shall remove the entire, 7" OTA from its tube rings using the pulley and block system. Then the stub dewshield will be slid along the main tube. To be held in place by nuts on the cell's pull screws behind the plywood ring. Whenever I need to collimate, in future, I just need to slacken the three nuts. I might even file keyholes so that the dewshield can rotated slightly to remove it or lock it into place. Then the obscuring dewshield can be easily withdrawn backwards. To allow free access to the collimating screws in the front of the cell.
The image above shows the full aperture, Baader solar foil filter in place on the front of the now-bare, objective cell. I made the filter holder from a modified baking tin. Using double sided tape for a snug fit and excellent grip without marking the iStar cell. The looseness of the filter foil is deliberate. Tight and flat foil ruins the view of the sun.
Fitting the stub dewshield to the main tube was a non-starter. There is one weight rail, three U-shaped handles, the finder base and the focuser backplate to come off first. All of which would need distant nuts to be removed. Inside the tube, at arms length, with my hand forced through the sharp-edged baffles. I decided to make the long dewshield smaller in diameter to match the plywood ring. Then it only needs a couple of wood screws removed to allow it to slide back or forth.
Tomorrow is promised to be cool but sunny! Hopefully back to solar observing.
Monday: I'm still waiting for my Herschel prism tracking number 5 days after confirmation of order 6.2.19. No track and trace number for £16 postage? Who are they kidding? Registered on their website but still no sign of my order on their website order history. No response to entering the order number. No response to my emails requesting a tracking number.
Still waiting to hear about my TS binoviewer misalignment. First reported on 15.1.19. Confirmed they received the binoviewer back for examination on 29.1.19.
No such drama this time. I had a noose around the objective end of the tube with a loop on the other end of the cord wrapped around my foot. I also lightened the focuser end as much as possible and moved the three [tube] balance weights towards the lens end of their travel. Of course the very last screw wouldn't come free of its T-nut. So I had a loose lens cell still deep in the now rotating dewshield. I used to think I was so clever trapping the dewshield flange behind the cell for simplicity. Not any more, I don't!
Once I had cleaned the back of the lens I refitted it back onto the tube without the stub dewshield. The thick, laminated, Baltic birch, plywood ring is a tight fit on the 8" diameter tube. The ring locks against the small flange on the end of the steel, duct tube. So the objective cell can be safely pulled against the ring without any risk of it pulling off the end of the tube. Push-off collimating screws through the objective cell flange provide the adjustable alignment.
A quick check through the Cheshire with a torch fitted with new batteries showed that my initial rough alignment was actually spot on. And I still hate the Orion Cheshire's foolishly thick, wire cross-hairs!
After lunch I shall remove the entire, 7" OTA from its tube rings using the pulley and block system. Then the stub dewshield will be slid along the main tube. To be held in place by nuts on the cell's pull screws behind the plywood ring. Whenever I need to collimate, in future, I just need to slacken the three nuts. I might even file keyholes so that the dewshield can rotated slightly to remove it or lock it into place. Then the obscuring dewshield can be easily withdrawn backwards. To allow free access to the collimating screws in the front of the cell.
The image above shows the full aperture, Baader solar foil filter in place on the front of the now-bare, objective cell. I made the filter holder from a modified baking tin. Using double sided tape for a snug fit and excellent grip without marking the iStar cell. The looseness of the filter foil is deliberate. Tight and flat foil ruins the view of the sun.
Fitting the stub dewshield to the main tube was a non-starter. There is one weight rail, three U-shaped handles, the finder base and the focuser backplate to come off first. All of which would need distant nuts to be removed. Inside the tube, at arms length, with my hand forced through the sharp-edged baffles. I decided to make the long dewshield smaller in diameter to match the plywood ring. Then it only needs a couple of wood screws removed to allow it to slide back or forth.
Tomorrow is promised to be cool but sunny! Hopefully back to solar observing.
Monday: I'm still waiting for my Herschel prism tracking number 5 days after confirmation of order 6.2.19. No track and trace number for £16 postage? Who are they kidding? Registered on their website but still no sign of my order on their website order history. No response to entering the order number. No response to my emails requesting a tracking number.
Still waiting to hear about my TS binoviewer misalignment. First reported on 15.1.19. Confirmed they received the binoviewer back for examination on 29.1.19.
Click on any image for an enlargement.
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