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The OTA is now propped between the bottom of the observation slit on the base ring and a stepladder on the observatory floor. I wanted to focus the telescope on distant trees. The step in the inverted framework prevents the telescope sliding forwards. Scraps of timber allow adjustment of pointing altitude. The stepladder can be slid sideways for azimuth adjustment.
I am still working on the folded 7" refractor design as I go along. Here I have fitted the stumpy dewshield by trapping it behind the objective cell. The three collimation, pull screws pass right through the dewshield flange. The push screws press the dewshield against the objective mounting plate. So the objective can still tilt relative to the framework using the standard collimation screws.
I am presently fine aligning the folding flats [mirrors.] The second flat [mirror] is beyond arm's length from the focuser. Which makes optical alignment very time consuming. I always intended to make the 2nd mirror adjustable from the back plate via screwed rods and control knobs. I'll have to look at that idea again. Particularly if I cover the framework and lose the already limited access to the mirror collimation, wing nuts.
Note how nicely the focus falls regardless of the view being straight through or via a 2" dielectric star diagonal. The straight through view needs a slightly longer 2" extension. Which is presently on the H-a telescope. I think I'll get a 2" push fit to 1.25" Baader Clicklock to hold the imaging camera. The usual radial thumbscrews are often inaccessible when faced with any kind of flange. The worst being tilt plates. It can be impossible to reach the thumbscrews with these. Being sprung, the collimation T-bars can be squeezed by hand to check the desired direction of travel. This is proving a useful time saver.
Note how the direct light from the objective can be seen through the open focuser. This light has passed through the initial and only baffle plate. [Image right] This is because I don't have a baffle pipe fitted to the FT. Which I had fitted to the earlier, Vixen 2" focuser.I need a much larger pipe with the 3.5" FT focuser but can't just add a pipe onto the FT drawtube. Or it will be pushed off when the drawtube is fully racked in. Nor do I want to lose the excellent baffling and matt black inside the FT drawtube by fitted a smaller baffle pipe inside it.
Some folded refractors use a second flat baffle with a figure of eight cut out of it. It needs an oddly shaped cut-out because of the folded beam being reflected back and forth. Other folded refractors are built up of many baffles on rails. These are very time consuming to mark and out and cut holes to allow the folded light beam to travel back and forth.
The improvement in contrast is really quite startling with a temporary, blackened pipe fitted to shield the direct light from the objective. Without it, half the [terrestrial] field of view is bright white! With the distant trees milky, soft and misty. The problem is that the direct light coming from the objective, via the short cut, is not only bright but seriously out of focus. This is because it is at about half the true focal length without the intervening, folding, flat mirrors.
I can't just add tubular dewshields to the folding, mirror cells either. Because of the complexity of the folded and tapering beam bouncing back and forth. Both mirrors are tilted. So adding a tube to either of them will just block some light from reaching the mirror. The longer the tube the more light is lost.
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