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    Re: Dioptric correction
    From: Bill Morris
    Date: 2013 Jan 21, 14:05 -0800


    I use a product called CRC Penetr8, but I don't think it matters much what you used. The most important ingredient is patience. Apply the stuff and then leave the part in a warm place for a day or so. Repeat as necessary until things un- freeze. Be very careful about applying excessive torque. If it won't unscrew when you hold the parts in hands wearing domestic rubber gloves, you need more releasing compound, warmth and patience.

    A trap for the unwary is that sometimes threaded parts are locked into position with tiny grub screws, and you should look carefully for these with a strong lens. The head may be covered over with dirt or paint.

    It sounds as though you may have an inverting draw tube. The inverting lens is usually a two lens combination in its own little tube that screws into the end of the draw tube opposite the eyepiece end. I have attached a photo of one such. Most makers seem to have placed the crosswires at the focus of the eye lens, between the eye and field lenses of a Huyghenian eyepiece. If a Ramsden eyepiece is used, the cross wires are outside the eyepiece, beyond the field lens. The inverting draw tube is of course much longer than the other draw tubes.

    If you would care to send me a few photos off-list (or on) I may be able to sort things out for you.

    Bill Morris
    New Zealand
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