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The new iStar lens has arrived. Superbly well packed, in multiple layers, it took quite some time to unwrap it. As is usual with these large objectives it is surprisingly heavy.
The objective looks flawless. An unusual feature are the usual element separation tabs being transparent. I have never seen or heard of this before. At f/10 and offering H-alpha correction it should provide a better match for the nominally f/10 PST etalon than hitherto. Until now I have been using an ancient CR150HD f/8 with a weak 1.125x, Baader GPC.
Having confirmed the dimensions match the drawing I can go ahead and make an adapter ring in plywood and aluminium. This will support the lens and its cell on the front of the 160mm steel tube. Both the front and back of the cell are 168mm in diameter.
As discussed earlier, the cell cannot enter the smaller, main tube. So it will need support for the rear of the cell to avoid sagging from the cantilevered load. Otherwise it will just hang from the three, M5 collimation "pull" screws. Albeit under tension from the three "push" screws.
As discussed earlier, the cell cannot enter the smaller, main tube. So it will need support for the rear of the cell to avoid sagging from the cantilevered load. Otherwise it will just hang from the three, M5 collimation "pull" screws. Albeit under tension from the three "push" screws.
At the same time, the M5 collimation "push" screws need a hard surface to press against to avoid denting over time. Which might cause a change in collimation. So I shall make an aluminium ring to carry out both functions. The ring will be screwed to the front of the plywood ring which will be a tight fit on the main tube. While being safely restrained by the tube's small, curved flange.
I suppose hard pads could easily be provided in the face of the plywood, adapter ring for the push screws to press against. This would ease construction and avoid having to search for a piece of aluminium large enough to make a ring. I prefer a plywood ring because it adds no excessive weight to the front end of the telescope.
Most refractors end up nose heavy. Which means they must be lowered down through the tube rings to compensate. Which reduces the comfort level for overhead objects even with a star diagonal in place.
The popular 6" refractors were typically nose heavy and often looked poor on a mounting. Unless carefully posed at the half way mark with the brakes on. I turned an iron doughnut to go inside the focuser end of mine to achieve a more "cosmetic" balance point. It did, but made the already heavy OTA a real burden for lifting high above head height. It had to be lifted high to go onto the MkIV mounting on its tall, welded pier. Made even higher, later on, by the wheels. It's no wonder I did so little serious observing!
I suppose hard pads could easily be provided in the face of the plywood, adapter ring for the push screws to press against. This would ease construction and avoid having to search for a piece of aluminium large enough to make a ring. I prefer a plywood ring because it adds no excessive weight to the front end of the telescope.
Most refractors end up nose heavy. Which means they must be lowered down through the tube rings to compensate. Which reduces the comfort level for overhead objects even with a star diagonal in place.
The popular 6" refractors were typically nose heavy and often looked poor on a mounting. Unless carefully posed at the half way mark with the brakes on. I turned an iron doughnut to go inside the focuser end of mine to achieve a more "cosmetic" balance point. It did, but made the already heavy OTA a real burden for lifting high above head height. It had to be lifted high to go onto the MkIV mounting on its tall, welded pier. Made even higher, later on, by the wheels. It's no wonder I did so little serious observing!
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