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Thread: Arca Swiss RM3D Tilt

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    Arca Swiss RM3D Tilt

    Wondering if someone can answer a question that's been puzzling me for a while.

    I've been reading about the Arca Swiss RM3D, and I'm wondering if, when you use front tilt, the lens is rotated about it's rear nodal point? i.e. as in a traditional view camera front standard design, so that the distance between the film plane (sensor) and the rear nodal point of the lens doesn't change as the lens is tilted - and consequently the subject shape isn't altered by the degree of tilt.

    The reason that I ask is that the lens boards for the Arca vary quite a lot in depth - e.g. recessed for the 24mm, very extended for the 120mm. I can't see how the RM3D keeps the rear nodal point of each lens on the axis of rotation (which would appear to be fixed) and thus avoids actually moving the entire lens assembly when tilted - which would alter the subject shape relative to the degree of tilt.

    I guess this question is equally applicable to the Sinar Artec which would appear to use a 'one-axis-of-rotation-suits-all' approach as well.

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    Re: Arca Swiss RM3D Tilt

    Hi,
    I have the Rm3D. You are right the lens boards do extend out pretty far as you get to longer lenses. The tilt mechanism is on the body and tilts the whole lens board from where it attaches to the body.

    I've never used a traditional view camera and am new to using tilts and shifts so I can't give you all the technical details that you are looking for. I hope by bumping this up some of our resident experts will chime in.

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    Re: Arca Swiss RM3D Tilt

    Front, or lens movements affect only focus. Rear movements affect focus and perspective.

    Kumar

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    Subscriber & Workshop Member GrahamWelland's Avatar
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    Re: Arca Swiss RM3D Tilt

    It's certainly true that there is a practical difference between base & axis tilt when focusing and also using wide angle lenses.

    With base tilt the whole front panel tilts forward on a tech camera which means that you have to refocus as you add or subtract tilt since the lens effectively not only tilts but moves back & forth at the same time. The problem that in theory can occur is that with very wide lenses you may end up with the lens too far away from the film/sensor plane and hence not be able to focus where you want. That's the theoretical downside although I've never had any lenses wide enough to run into this myself - maybe someone with a tech cam & super wide can comment on how much of an issue this is in reality (Personally, I've only ever used axis T/S with 4x5).

    With axis tilt & swing the centre of the lens stays put, although obviously you'll still have to refocus slightly depending upon where you want your plane of focus to lie.

    Kumar pretty summed up the front/rear differences. I can recommend the works of Harold Merklinger & Leslie Stroebel if you want a reference for this stuff - surprisingly expensive new but there are good used copies around too. Hmm, actually Jack's a bit of a LF guru here come to think of it ...
    Last edited by GrahamWelland; 2nd January 2011 at 19:48. Reason: Horrible iPad spull chocker ...

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    Re: Arca Swiss RM3D Tilt

    Thanks for the info. folks.

    I understand the principles of tilt/swing on the front and rear standards - I've shot 8x10 in the past, and my dog-eared copy of Steve Simmons 'View Camera' is always an invaluable reference.

    The thing that's interesting me is that if you look at how Cambo have implemented tilt/swing on the Wide DS and RS, you'll see that the centre of the lens never moves up/down or left/right - it tilts or swings about the same point. Thus the distance from the center of the lens to points on the digital sensor doesn't vary with the degree of tilt or swing - and hence the 'shape' of the subject doesn't vary with tilt/swing.

    Contrast this with Arca or Sinar where - from what I can tell - when you tilt the lens, the center of the lens is moved, and thus, from what I understand, the 'shape' of the subject will be altered, even if only by a fraction. Just wondering how big of a fraction.

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    Re: Arca Swiss RM3D Tilt

    Hi and welcome to the forum.

    I have a RM3D and like it very much. You are correct in that it does not tilt about the nodal point for all lenses, since the tilt axis is always fixed at the base of the lens inside the camera. For some wide lenses the tilt position is probably close enough. For long lenses, technically there will be some perspective distortion introduced but the limited amount of its tilt (5 degrees max deviation) will show up less as the focal length increases.

    I guess the best way to think about the RM3D is that its tilt mechanism is like having front standard lens tilt for wide lenses but becomes more like rear standard tilt when long lenses are used. I have rarely needed more than a degree of tilt in actual usage and do not use long lenses, so I cannot answer your question with more details. If you still have your view camera, you can estimate the effects of the RM3D with longer lenses by experimenting with rear tilt. If the images look good to you for tilts under 5 degrees, then you should not expect any worse from the RM3D.

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    Re: Arca Swiss RM3D Tilt

    Thanks for the explanation David - having not seen an RM3D in person I was intrigued as to how tilt was implemented. Would be nice if Arca had a website.

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