Quote:
Originally Posted by Saturnine
Hi Alan.
Enjoyed your story, having done much the same several years ago. Wanted a larger diameter finder for my 12.5" dob and saw the adds on Ebay for the 70 X 300mm refractors so bought one for $45, at the time
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Worked out, as you have done, that the baffles were useless, reducing the effective aperture to what I worked out, to about 40mm and the included eyepieces and barlow were better off in the bin and were only the .945" type, 24.5mm I think. Did as you have done and cut the length of the drawtube by half and carefully machined out the plastic at the eyepiece end to accommodate an 1.25" correct image diagonal. Removed the tripod mounting interface as well and made up some 80mm ID rings and standard finder sized dovetail.
Didn't see any need to remove the objective, so the glue etc didn't concern me but painting the inside of the dewshield with flat black helped reduce stray light. All up, for less than $100, including the 1.25" diagonal and 32mm plossel I ended up with a quite serviceable 9 X 70mm finder with a field of view of about 5 deg. At that magnification false colour is not a problem and the field is sharp almost to the edge.
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Thanks for your adventure as well. As for my own, there's more to come, much more.