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Thread: 35mm adapter

  1. #1

    Default 35mm adapter

    I have purchased all of the parts i need to make a 35 mm adapter, however i am finding it impossible to get the correct spacing between all the parts. I am using a lens from an old Olympus OM-1 35mm camera. So if i understand correctly, if i can get the correct amount of space between the lens and my focusing screen, it will exactly simulate the range that i can focus on with my OM-1. No matter what distance i use, however, i cannot get the same range. Is there something else thats going on inside of the OM-1 that i dont know about? Any suggestions on building this would be appreciated.

  2. #2

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    i seem now to have gotten as close to the correct distance between my focusing screen and lens as possible, however the difference between in and out of focus is not as sharp as when the lens is atached to my OM-1 (there is a much longer depth of field on the adapter). Also, the focusing ring is less sensitive when attached to the adapter (objects stay in focus for large turns of the focusing ring, rather than going out of focus with just a tiny turn like with my OM-1)

    What is going on here?

  3. #3
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    Quote Originally Posted by mbrown3391 View Post
    however the difference between in and out of focus is not as sharp as when the lens is atached to my OM-1 (there is a much longer depth of field on the adapter).
    If I undersatand correctly, the reason here is ONE of the factors affecting DOF is the size of the "sensor" makes a diference. Your 35mm "sensor" on your OM1 will be significantly bigger than the CCDs/CMOS on your video camera.
    Tim

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    Tim - I think you may have not totally grasped how these work.

    In essence you are using your video camera to film the image produced by another camera.

    To get the full effect the projected image from the objective lens is foussed onto a frosted glass screen ( often) at 35mm neg size as opposed to the 6mm CCDs common in consumer cameras. The camera is then set to macro to focus on the screen.

    The glass screen is spun on some models to reduce unwanted images of the screen texture.

    I have never used a adaptor but intuitlively i can see there are downsides. You are using all the camera glass on a macro setting - perhaps not something the camera lens in optimised for. You are also using another set of lenses and seeing the image second hand via the screen.

    This must produce much softer images overall not to mention other possible sources of abberation.

    Given that shallow dof is merely one tool in the box I do question the current fashion for hanging all that crap infront of your camera.

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    Quote Originally Posted by Mark W View Post
    Tim - I think you may have not totally grasped how these work.
    Actually what I failed to grasp was that what mbrown was trying to make was a DOF adapter (something I do understand since Guru's (I think) excellent description a few weeks back).

    I don't know what I thought a 35mm adapter was - but I didn't twig that the two were being used synonymously.

    My bad. Sorry for wasting everyone's time.
    Tim

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