Tips for aligning 8mm projector with a condenser lens?

Discussion in 'Photography' started by Doc, Dec 5, 2006.

  1. Doc

    Doc Guest

    If the projected image from a movie projector is projected through a 4
    1/2" plano convex condenser lens to create an aerial image, if the
    light path from the projector is perpendicular to the plane of the
    condenser lens and is striking the exact center of the lens


    projector/lens [ ]-----light------|) condenser lens

    shouldn't it exit the opposite side of the lens exactly centered?

    To achieve such an alignment here's a plan I've come up with and am
    hoping for suggestions for any way to improve on it.

    To make the projector lens perpendicular to the surface the projector
    is sitting on which will be the same surface the condenser lens housing
    is sitting on, for the Y axis I thought I'd use a carpenter's rule
    sitting on the same surface as the projector and visually align it very
    carefully with the front of the focus ring on the projector, so the
    close and far edges of the focus ring are aligned and making this front
    edge parallel to the ruler by adjusting the projector height as needed,
    going under the assumption that the focus ring is going to be pretty
    accurately machined and for all intents & purposes exactly parallel and
    perpendicular to the projector lens. I can't directly butt the rule
    against the focus ring when the rule is straight up and down due to the
    way the projector is constructed so it has to be done visually unless I
    were to make or find a gizmo for this particular purpose that has a
    flat-edged protrusion that's perpendicular to the mounting surface to
    butt up against the focus ring.

    The Y axis of the condenser lens would be made parallel by careful
    construction of the housing and mounting the lens in it so that it's
    even all around. If it's perpendicular to the same surface that the
    projector has been made perpendicular to, the lenses should be parallel
    to each other on the Y axis, yes?

    To make the projector and condenser lens parallel to each other on the
    X axis, again using the projector focus ring as a guide, laying
    straight edges of different lengths against it at an angle with one end
    touching the surface the projector is sitting on and marking that
    point, doing this at 2 or 3 angles (I can't do one straight up and down
    for the same reason I can't butt the rule up against the focus ring
    described above.Various parts of the projector get in the way.) and
    using those points to draw a line to align the condenser lens, mounted
    similar to this:

    and aligning this lens housing with the line I've drawn.

    For centering the projected image, once the projector is made parallel
    to the surface they'll both be sitting on, and before cutting the hole
    for the condenser lens, I thought I'd assemble the "lens box" and
    project the image against the board the condenser lens is to be mounted
    on, find the center of that image with a caliper and center the hole
    for the lens at that point. Also marking exactly where the lens box was
    when I made the measurement.

    What I'm wondering, is there a better way of doing it than what I've

    Doc, Dec 5, 2006
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