Meaning of yaw

[Leonard Evens]

I think I finally understand what yaw is about. I must admit having been confused about it in the past and even giving some misleading, incomplete advice. I will try to explain what I now think and see if anyone thinks I'm right.

Yaw, pitch and roll refer to terms used to describe the change of attitude of a rigid body such as a ship or an airplane, and in view camera photography, we use tilt, swing, and yaw to describe what happens to a standard. (Identifying which corresponds to which depends on how you set up the reference system.)

As we use the term yaw, it refers to rotation of the standard about an axis perpendicular to it, e.g., the lens axis for the front standard. Yaw may result from performing a tilt followed by a swing, or, vice versa. Exactly what happens depends on on how the axes for tilt an swing are attached to the camera frame.

Yaw could clearly be a problem for the rear standard because it would change the orientation of the film frame with respect to the horizontal and vertical. But I never saw why yaw would be a problem for the front standard. After all, the image is symmetrical about the lens axis, so you you can rotate the front standard about that axis to your heart's content without seeing any difference.

What I've finally figured out is the following. It is not yaw itself that is the problem for the front standard. It is what caused the yaw in the first place. Let me elaborate.

Suppose you apply a tilt. If you have axial tilt, this will be a rotation about a horizontal axis through the lens. But even if you have base tilt, you can adjust the position of the standard by rise/fall or movement along the rail to accomplish the same thing, rotation about a horizontal axis through the lens center. So let's assume that is the case. The question then is what happened to the swing axis. For some cameras it may remain vertical where it was. That will generally be the case for cameras with axial tilt, but it is not generally the case for cameras with base tilt. For the latter, the swing axis stays fixed in the standard and hence is tilted with it. This is usually phrased by saying that in the good case the "point of attachment" for tilts is "above" that for swings, but I've never understood exactly what that is supposed to mean, so I just try a tilt and see where the swing axis goes to be sure.

What happens next is a bit subtle. You do get yaw in the bad case where the swing axis has moved, but something else happens that is more complicated. Consider what happens to the hinge line. You hope you can move it through tilt followed by swing so it coincides with where it should be in the desired subject plane. After the tilt, the hinge line is horizontal. In the good case, as you swing, the hinge line rotates in the vertical plane parallel to the image plane about a fixed point---that is harder to see than you might think, but it is right. If you got the tilt right, which turns out to be feasible, you can rotate the hinge line to where it should be by a swing. The amount it rotates is related to both the tilt angle and the swing angle by a complicated formula, but the important thing is that for fixed tilt angle, the swing angle and the hinge line rotation angle determine one another, and you don't need to know what that formula is.

In the bad case, whatever tilt angle you choose, the hinge line will move in its entirety, no point in it remaining fixed. I don't see in that case how you can possibly predict in advance just how much to tilt in the first place, without doing elaborate calculations. You would have had to have overshot or undershot the tilt by exactly the right amount, and thaat would require knowing the formulas. So you end up having to go back, adjust the tilt, readjust the swing, etc. Of course, since in practice, you never get anything exactly right, you may have to do that anyway. But if you go about it right, fewer adjustments should be necessary.

I'm sure someone will say that the effect I'm talking about is an obvious effect of yaw, but it wasn't at all obvious to me. I had to look exactly at what happened before I saw the importance of the hinge line for this, and the geometry was not that simple. It only occurred to me when I was thinking about something else entirely. It seems more enlightening to me to say that both yaw and the effect on the hinge line result from the same basic cause. In any case, I think it is well worth understanding the importance of the hinge line in all of this. Of course, if you already have a yaw free camera, you will know from experience that something is better, in which case you may not care why, but if you don't have such a camera, which was true for me, it may take a while to figure it out. Anyway, I think I now understand the reason why many experienced view camera users extol the advantages of being yaw free.

Let me mention as an aside that usually base tilt cameras will work just fine in this regard if you just do the swing first. At least for all I've looked at, including my Toho FC-45X, the tilt axis doesn't change when you swing, so the good case becomes the bad case, and vice versa. I didn't know this because no one seemed to mention it anywhere, so it wasn't until now that I realized that I should swing first and then tilt. For the axial tilt cameras I've looked at, you run into the same problem if you reverse the roles of tilt and swing. I haven't looked closely at any cameras purported to be yaw free, but for that to be really true, the swing and tilt axes would have to be entirely independent of one another. I'm sure that can be managed by an appropriate mechanism, but as far as I can see few view camera manufacturers bother.

Any comments would be appreciated.

[Jan Pedersen]

Yaw means rotating something horizontal (Perhaps not the scientific expression) If you have your camera set up on your tripod and you rotate the camera from let's say south to west, then you are yawing CW.
Hope that makes sense.

[Leonard Evens]

P.S. I've now gone back and looked at some explanations of yaw, and now that I understand what is going on, they make sense. One explanation even highlighted the crucial point: that in order to avoid difficulties, you want to be sure the axis for the second operation is not moved by the first operation. But most of the explanations seem to be saying that the difficulty in focusing is caused by the yaw, which I still think is misleading. Also, the explanations say that in the presence of yaw you have to go back and forth continually readjusting the tilt and the swing. My mathematical intuition and knowledge told me this statement is false. If you know the formulas, then both the tilt angle and the swing angle, no matter how they are done are completely determined by the final position of the subject plane, even just by the hinge line lying in it. What is true is that you can't easily determine those angles without doing elaborate calculations. I guess this amounts to the same thing, but I misinterpreted the statement to mean it was literally true.

In addition, some of the implications implied that being yaw free meant it didn't matter which order the operations were done, and then went on to describe mechanisms whereby tilt followed by swing was yaw free, but not vice versa. I agree that a truly yaw free camera would work that way, but not the arrangements they described.

I'm sure there is an explanation somewhere which explains it correctly, probably in a much better way than I did, but if so it is hard to find among the many misleading or incomplete explanations.

[steve simmons]

If you level the camera left to right and front to rear you will never have yaw.

steve simmons

[Gordon Moat]

I am reminded of some Arca Swiss and Linhof cameras, which claim yaw free design. What I see is a large section of a circle, about which the lensboard/standard can move at angles. However, if the effective focal distance is not the same as the flange to film plain distance, wouldn't that mean there is always a focus shift, even with these cameras?

Also, in Swing or Tilt, using the front standard, I have seen where the focus moves to either the left or right, or higher or lower, on the ground glass. Is this an example of focus shift, or just an aspect of lenses when using movements?

At least in the Arca Swiss brochures, they mention focusing once, then doing movements without needing to refocus. Would that essentially be yaw free movements, because of that capability?

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

[Sheldon N]

For me, the simplest way to understand what a Yaw free camera does is this:

If you use indirect rise/fall (meaning point the camera up/down then relevel both standards to vertical to create effective rise/fall) and THEN attempt use swing on either the front or rear standard....

1) A "Yaw Free" camera will have the swing work normally, i.e. on a flat horizontal plane.

2) A camera that is not "Yaw Free" will do strange things with the image/focus plane because the swing axis of rotation is not horizontal, but rather arcing on the plane aligned with where you originally pointed the camera (up/down).


If your camera is not "Yaw Free" you have to do what Steve said - keep the camera oriented on a perfectly horizontal plane in order for swing to function normally.

[Bob Salomon]

I am reminded of some Arca Swiss and Linhof cameras, which claim yaw free design. What I see is a large section of a circle, about which the lensboard/standard can move at angles. However, if the effective focal distance is not the same as the flange to film plain distance, wouldn't that mean there is always a focus shift, even with these cameras?"

A yaw free camera is one that has a tilt point below the swing point. On Linhof and Sinar yaw free cameras that means that there are two tilt points. The bottom one used for moving the standards to the proper point for leveling and the second for doing the camera movements.

"Also, in Swing or Tilt, using the front standard, I have seen where the focus moves to either the left or right, or higher or lower, on the ground glass. Is this an example of focus shift, or just an aspect of lenses when using movements?"

Those are the lines that you focus far and near on when the camera has assymetrical axis movements. That is an additional feature to being yaw free and are not part of making a camera yaw free.


Any camera that is yaw prone when used upright become yaw free when swung 90 degrees and used on its side. That puts the swing below the tilt point by making the tilt point into the swing point and the swing point into the tilt point.

You only get yaw when the tilt point is below the swing point and the camera has only the one tilt point.

Gordon Moat Photography (http://www.gordonmoat.com)

[Gordon Moat]

So if I understand what Bob is stating, if a camera has the swing and tilt rotation axis intersecting at the same plain, then the design is yaw free? Please feel free to correct my terminology, and I hope that question makes sense to someone. Also, it seems that some of the Silvestri designs are yaw free, but I don't recall them making that claim/statement.

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

[Sheldon N]

I'm not sure if that's the best way to put it...

It's more like if you can use tilt (usually base tilt) to relevel the swing axis back to a horizontal plane, then the camera is yaw free.

As Bob pointed out, you really need two tilt points to make a camera yaw free and fully functional. One tilt point to relevel the swing axis, and one tilt point for any additional tilts that may be needed.

For example, my Arca 4x5 w/orbix is yaw free. I can use base tilt to bring the front/rear standard back to vertical. When the standard is vertical, the swing movement pans around on a purely horizontal plane. I can then use the orbix tilt movement (axial tilt above the base tilt and swing movements) to dial in additional front tilt to go with the swing.

If I didn't have orbix, I could not use any front base tilt movements that deviated from vertical and still keep the camera "yaw free" for swing movements.

I don't think that the problem of yaw comes up very often in real shooting situations, maybe more for product shooters.

[Bob Salomon]

If I didn't have orbix, I could not use any front base tilt movements that deviated from vertical and still keep the camera "yaw free" for swing movements.

Yes you could. Just rotate the camera on the rail 90 degrees so that the swing is now the tilt point and you are yaw free.

All yaw prone cameras become yaw free when mounted on the side and all yaw free cameras become yaw prone when mounted on their sides.

All you need is a tripod and head strong enough to hold and support the camera when it is rotated 90 degrees.

This is also why the Linhof TK systems have an extra spirit level for when the camera is rotated 90 degrees to be yaw free. Hardly anyone ever does that though.

[Sheldon N]

If you used an Arca Swiss camera on its side, I'm not sure that the movements would work the way you wanted them to, yaw free or not.

The base tilt would become a strange sort of "hinge" swing where you'd need to do a focuing routine of "focus right, swing for the left" approach similar to the "focus near, tilt far" approach. And like you pointed out, not too many people want to put the camera sideways, and not many tripod heads can handle that.

Out of curiosity, does anyone know of a common situation when the "yaw free" design actually helps out? The only situation I can think of is if you needed more rise than the front standard allowed (forcing you to use indirect rise), and then also needed to use swing - like an architectural photograph of a tall building receding in the frame left/right. Most cameras have plenty of front rise, so you could usually just leave the camera level and not worry about yaw.

[John O'Connell]

I ran into yaw issues frequently when doing tabletop work requiring front fall greater than the camera permitted. I worked around it because of budgetary issues, but it would have been nice to use a yaw-free camera for that purpose.

[Bob Salomon]

Out of curiosity, does anyone know of a common situation when the "yaw free" design actually helps out?

Many studio shots benefited from yaw free movements but it is impossible to tell from a photograph if the camera that made it was or was not yaw free. The yaw free camera may have been quicker for some people to use but by the time the shot was set up, the shot made, the film processed and the art director wrote off on the shot the time savings was not a major point.

Bear in mind that the very first yaw free view camera was the prototype Linhof Kardan which was made in extremely small numbers. It was introduced in 1952 and had a "universal joint" or knuckle design which let the swing and the tilt take place at the same point. In later models Linhof went away from this rather complicated design and decided that as lenses were getting greater covering power the easiest and best way to do indirect displacements was by using direct displacements. So their later cameras, starting with the B and the original Super Color had 3.5" of shift left and right and up to 6.6" of rise. These numbers were on both the front and rear standards. When the camera was mounted level and the the lens was dropped and the back raised and the front shifted towards and the back away from the subject then three point perspective was easily done with no tilts or swings and thus was yaw free. Tilt or swing was then added to control the plane of focus.

[David A. Goldfarb]

Out of curiosity, does anyone know of a common situation when the "yaw free" design actually helps out?

I've been doing some food photography in 8x10" with my Sinar P, and the yaw free design does mean one less potentially frustrating thing to worry about. It's a pretty common situation to have the camera pointed down to look into a cup or a glass or a bowl or a pot, and then use short DOF requiring both tilt and swing to put the plane of focus in just the right place, and usually a little shift and rise/fall to adjust the composition, and it helps not to have the whole composition leaning or rotating on the groundglass during the setup.

For landscapes and architecture and portraits, though, I seem to manage fine with my other non-yaw-free cameras.

[steve simmons]

I only experienced yaw once when I had a camera with yaw. As a rule I always leveled my camera left to right and front to rear but I was photographing a model once, an architectural one:), and had to tilt the camera down. I tried to use some tilt and swing and realized after a few minutes I was chasing my tail. Once I realized the problem I came up with a work around and got the shot I wanted anyway.


steve simmons

[Ken Lee]

Yaw is what linguists call the radix, or root, of the term Y'all.

For example: "Yaw come back now, hear ?"

[Ralph Barker]

Ken, that was yawful. ;)

[Leonard Evens]

I am reminded of some Arca Swiss and Linhof cameras, which claim yaw free design. What I see is a large section of a circle, about which the lensboard/standard can move at angles. However, if the effective focal distance is not the same as the flange to film plain distance, wouldn't that mean there is always a focus shift, even with these cameras?

Also, in Swing or Tilt, using the front standard, I have seen where the focus moves to either the left or right, or higher or lower, on the ground glass. Is this an example of focus shift, or just an aspect of lenses when using movements?

At least in the Arca Swiss brochures, they mention focusing once, then doing movements without needing to refocus. Would that essentially be yaw free movements, because of that capability?

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

I saw an Arca Swiss camera in a store many years ago before I understood much of anything, but I've never examined one carefully, and I don't think I've ever seen one with the Orbix system. The basic cameras seem to be base tilt with the swing axis moving, which is the more difficult configuration for tilt followed by swing, but should be all right for swing followed by tilt. But I' only going now by pictures. The Orbix system, which you refer to, appears to shift the tilt axis to provide a second tilt mechanism by gearing on a track at the bottom. That in effect provides axial tilt in addition to the base tilt and if I understand correctly, you can adjust the mechanism so the tilt axis passed through the center of perspective for your lens and in addition, that point doesn't move as you tilt. So it should be possible to do tilt followed by swing or vice versa without yaw. As I noted originally, it also makes focusing easier in either case..

I was at Calumet Photo in Chiciago the other day and I played with the few remaining view cameras they have on display. The Cambo Ultima, which is a marevouls mechanism, has similar gearing on a circular tracks for tilts for both standards.

I've tried to analyze the issue of focus shift you raise before, and I'm not sure I completely understand it yet. If you tilt, you get a focus shift even if the center of perspective remains fixed, but it is very small. In a real lens you of course have two principal points and when you take circles of confusion into account, it turns out that you need to consider the exit and/or the entrance pupils in deciding what to take as the center of perspective. In principle, you want the center of perspective to stay fixed, but since it is not entirely clear just where it is, it seems unlikely that any method of tilt or swing can avoid the necessity for refocusing.

In principle, if everything were exactly where it should be, there should be a line on the gg which stays fixed as you tilt (similarly swing). But if the center of perspective moves, that won't be the case. Different lens will have different centers of perspective, but for most normal lenses it should be close to the front of the lens board.

[Leonard Evens]

I'm not sure if that's the best way to put it...

It's more like if you can use tilt (usually base tilt) to relevel the swing axis back to a horizontal plane, then the camera is yaw free.

.

Several people have used terminology like this, and I must say I don't understand what it means. Its hard for me to imagine a circumstance in which the swing axis is horizontal. It would happen if you started with the standards in standard position and you pointed it straight down or if you started with the camera vertical and you moved the swing axis through a tilt by 90 degrees, neither of which is a very likely scenario.

I presume you guys are making meaningful statements, but I'm not sure what they are. The axis of any rotation is by definition the line which stays fixed when you apply the rotation. Perhaps you mean to say the swing axis is situated so that the plane perpendicular to it is horizontal. That would make sense.

[Leonard Evens]

If you level the camera left to right and front to rear you will never have yaw.

steve simmons

I don't know what this means. With my Toho FC-45X, which has fairly standard base tilt and (close to axial swing), if I do a tilt followed by a swing, there is no question that I have yaw. The same thing happened with several cameras I played with at Calumet. Of course, I don't get yaw if I do either just a tilt or just a swing. From past experience, I believe you are saying something useful to know, but I think we are somehow talking at cross purposes, and I don't know what it is.

[Leonard Evens]

Yes you could. Just rotate the camera on the rail 90 degrees so that the swing is now the tilt point and you are yaw free.

All yaw prone cameras become yaw free when mounted on the side and all yaw free cameras become yaw prone when mounted on their sides.

All you need is a tripod and head strong enough to hold and support the camera when it is rotated 90 degrees.

This is also why the Linhof TK systems have an extra spirit level for when the camera is rotated 90 degrees to be yaw free. Hardly anyone ever does that though.


I think this is only the case if you do the tilt first and then the swing. I believe you can also turn yaw prone to yaw free simply by reversing the order of the operations.

[Leonard Evens]

I ran into yaw issues frequently when doing tabletop work requiring front fall greater than the camera permitted. I worked around it because of budgetary issues, but it would have been nice to use a yaw-free camera for that purpose.

I was just experimenting with my camera and a table top scene to see how the theory worked out in practice. I must say it was pretty painful getting the table in focusl. Since my talble was flat, I had to simulate a slanted plane on which to focus by tillting the camera down and to one side. I didn't want to bother setting up lighting, so everything was pretty dim, particularly at the edges of the scene. The bizarre angles and the lighting made everything much harder.

I have to think some more about it to see if there are any flaws in my reasoning, but I think the problems I had were mainly because of shifts in the center of perspective as I tilted or swung. Such a shift might be insignificant relative to a distant scene, but it could become a problem for relatively close scenes as in table top work. So I think you are right that something like an Orbix mechanism would be a great help for such work, particularly if you were working under time constraints. It would also be a help to have fine focusing of the front standard as well as for the rear. I have it for the rear, but for the front I have to slide it along the rail.

[Gordon Moat]

. . . . . .

In principle, if everything were exactly where it should be, there should be a line on the gg which stays fixed as you tilt (similarly swing). But if the center of perspective moves, that won't be the case. Different lens will have different centers of perspective, but for most normal lenses it should be close to the front of the lens board.

Hello Leonard,

It seems the point you are describing corresponds to the Nodal point. I checked numerous Rodenstock and Schneider lens data sheets, and the Nodal point is very close to the flange, often within 6 mm. This is shorter than the effective focal length, but slightly longer than the flange to focal distance.

So if movement axis was around the nodal point, the in focus area of the ground glass would seem to not move left and right (during swing) nor up and down (during tilt). Perhaps this is a better way to describe this.

I stumbled upon this when doing selective wedge focus shots. I would choose where I wanted focus, then use lots of swing to throw the left and right side of the shot out of focus. Unfortunately, the line I wanted through the composition to be in focus tended to move left or right. I corrected composition by shifting the rear of the camera. I don't know if there is any camera that makes this easier or faster, but it would make this much easier. Same problem applies to tilt for a similar effect, and using rear standard rise to alter the composition and focus placement.

Ciao!

Gordon Moat Photography (http://www.gordonmoat.com)

[steve simmons]

Here is what I said

if you keep the camera level front to rear and left to right you will not have yaw, regardless of the camera's maker or style.

You are way over complicating this.

Yaw occurs when the swing platform is not level and using the swing rocks the standard and prevents a perfect Scheimpflug relationship between the three planes - film, subject and lensboard.

Nothing more, nothing less


steve simmons

[Leonard Evens]

In pretty much all the responses, yaw seems to refer to the difficulty in focusing when applying first a tilt and then a swing. Let me reiterate again that by definition, yaw means a rotation about an axis perpendicular to the standard, such as the lens axis for the front standard. My point was that it is not the yaw that creates the difficulty, but rather what happens to the swing axis when you tilt (or vice versa). One can envision a mechanism such that you could correct for yaw by rotating the standard to compensate, but the same problem of focusing would arise because tilting moved the swing axis.

In principle, the ideal situation is a set up under which you only have only one rotation of the standard about an axis, but you can move that axis to any desired orientation. If you put it horizontal, you have a tilt, and if you put it vertical, you have a swing. More generally, you could move the axis so it was parallel to the desired subject plane and then swivel the standard about the axis to get the subject plane in focus. You could call the motion tilting (swinging?) about an arbitrary axis or anything else that sounded right.

Looking at the orbix mechanism, I wonder if something similar could be rigged up to do what I want. I've thought of several approaches, but they all have problems with how to attach the bellows. Otherwise, it wouldn't be difficult to do.

[Ken Lee]

Sinar gives their explanation with illustrations, here (http://www.sinar.ch/site/index__gast-e-1832-52-1959.html). They provide an animated GIF image as well, which I have taken the liberty of attaching, below.

In a nutshell: "Yaw" is defined as the sideways tipping of a standard when swung round its vertical axis during a sharpness adjustment of an oblique plane. Although this "minor" error can easily be corrected by changing the camera position to bring the verticals back to vertical, the sharpness adjustment already made then needs repeating. Focusing turns into a time consuming process of trial and error, until the photographer finally accepts a compromise. Since 1972 Sinar has therefore been designing its cameras for absolutely yaw-free.


http://www.kenleegallery.com/images/tech/yawfree.gif

[Leonard Evens]

Hello Leonard,

It seems the point you are describing corresponds to the Nodal point. I checked numerous Rodenstock and Schneider lens data sheets, and the Nodal point is very close to the flange,

Gordon Moat Photography (http://www.gordonmoat.com)

Thanks for elaborating on the problem. I think you've highlighted an important point. I've looked at it some more, and I must say it can be confusing, and I am still confused. Let me share with you some of my thoughts. ( I apologize in advance for being so long winded . I often think people ignore two thirds of what I say because it takes to long to wade through it.)

First, there is a distinction between the nodal points and the principal points, which are where the principal planes intersect the lens axis. I've never understood the exact significance of that difference, but I'm pretty sure it is the principal planes and the principal points that are relevant to image formation in geometric optics. Fortunately, it seems that the nodal points. are usually the same as the principal points.

But there is almost always going to be a difference between the front and rear principal planes and the corresponding principal points. If you tilt or swing about an axis passing through the rear principal point, you rotate the rear principal plane but you both translate and rotate the front principal plane. A ray entering the front principal point at some angle to it emerges from the rear principal point in a parallel ray at the same angle. If you follow the image formation in detail that means that the rotation will shift the image on the gg, issues of focus aside. Thus an image point which was centered on the lens axis before the rotation will shift slightly. Other points may move more than that because of magnification and focusing issues associated with the swing or tilt The amount of the shift is proportional to the distance between the two principal planes. It is also roughly proportional to the swing or tilt angle, as least for small to moderate rotations. Even if there is a significant distance between the two principal planes, there shift will be too small to notice for angles of a few degrees but may become noticeable for angles of 10 degrees or more. If you tilt or swing instead about an axis through the front principal point, some thing similar happens, but the shift is in the other direction.

At least that is what I think theory says should happen. I haven't yet checked it carefully with my lenses. That is difficult to do because I have base tilt and I would be surprised if the swing axis, which is nominally axial, goes through either principal point for any of my lenses. I would have to rig up an optical bench to do it right. I may be able to arrange something along those lines, but I haven't figured out how. I should be able to look up the nominal locations of the principal planes for my lenses and then determine their position relative to my camera's swing axis. From that I should be able to predict the shift on the gg, and check it.

Another difficulty in all of this is the issue of parallax, which refers to what appears behind what in the image when you have subject elements at different distances from the center of perspective. This depends on circles of confusion, which in turn depend on the aperture, its size and location. But the aperture appears from the back of the lens to be at the exit pupil and from the front at the entrance pupil. If you want to avoid a parallax shift, you need to swing about the center of the entrance pupil---or it might be the exit pupil??. That point is usually close to or the same as the corresponding principal point, but that is not always the case. It depends on the pupil magnification.

[Leonard Evens]

Here is what I said

if you keep the camera level front to rear and left to right you will not have yaw, regardless of the camera's maker or style.

You are way over complicating this.

Yaw occurs when the swing platform is not level and using the swing rocks the standard and prevents a perfect Scheimpflug relationship between the three planes - film, subject and lensboard.

Nothing more, nothing less


steve simmons

I guess what I was saying is that with my camera, the only way I could keep the standard level after a tilt followed by a swing would be to rotate the entire camera. I guess I could do that without ill effects if we are talking about the rear standard. But if I did it for the front standard, I would end up rotating the rear standard and the film frame.

But even if I did it, it would not eliminate the basic focusing problem; indeed, it would complicate it.

So I still think I don't understand what you are saying.

[Leonard Evens]

Sinar gives their explanation with illustrations, here (http://www.sinar.ch/site/index__gast-e-1832-52-1959.html). They provide an animated GIF image as well, which I have taken the liberty of attaching, below.

In a nutshell: "Yaw" is defined as the sideways tipping of a standard when swung round its vertical axis during a sharpness adjustment of an oblique plane. Although this "minor" error can easily be corrected by changing the camera position to bring the verticals back to vertical, the sharpness adjustment already made then needs repeating. Focusing turns into a time consuming process of trial and error, until the photographer finally accepts a compromise. Since 1972 Sinar has therefore been designing its cameras for absolutely yaw-free.


http://www.kenleegallery.com/images/tech/yawfree.gif

Ken,

Thanks for the explanation. I had looked at the web page you referenced, but I hadn't seen the animation. As a result I didn't understand how the mechanism works. In addition, I think a Sinar I looked at recently at Calumet just had simple base tilt, and it definitely had yaw if you tilted first and then swung.

I think I now see what is going on. In the animation, because of the geared track below the standard, the tilt axis is shifted upward, presumably at or close to the center of perspective for the lens. The Cambo Ultima I looked at at Calumet has a similar mechaism on both standards.

But the diagram doesn't make it clear to me how the swing is done. From the animation, it looks like the swing axis is being tilted with the standard. If that is the case, I can assure you that you get yaw. Just try it with a rectangular piece of cardboard. Tilt it with respect to a horizontal axis lying in the cardboard, and then swing it with respect to the perpendicular axis, originally vertical, but now tilted with respect to the vertical. You can see one top corner rise and the other fall. The standard does not remain level in any direction. The whole rectangle has been rotated about its center, and that is what we mean by yaw.


If you swing first, the Sinar mechanism in your animation appears to work properly. The joint where the swing mechanism attaches is above the track which performs the tilt, so the tilt axis stays fixed under the swing, which is the crucial point. When you tilt, the top and bottom of the standard stay horizontal, i.e., no yaw. Essentially the same thing happens for my base tilt Toho FC-45X, but in my case, the center of perspective moves when I tilt. In order to get it back where it was, I would have to use a rise and also move the standard back on the rail. With the Sinar mechanism, which in effect produces axial tilt, that is not necessary.

The discussion on the Sinar web page about where the joints should be only makes sense if you assume that you are going to swing first and then tilt. A mechanism which would avoid yaw if you tilt first and then could work as follows. Suppose you have an outer frame which is attached to the rail at its base and swings at that join. Suppose also the standard is attached at two points on opposite vertical sides of the frame and can tilt within the frame. In that case, if you tilted the standard within the frame, you wouldn't affect the position of the frame, and so the swing axis would remain vertical. Indded, there were one or two such cameras on display at Calumet and when I played with them, I found that there was no yaw if I tilted first and then swung.

Perhaps I have some really fundamental misconception. If so, I wish someone would explain it. to mean in terms I can understand. I've been playing with my camera and those at Calumet, drawing dagram after diagram, and applying relatively sophisticated mathematical techniques. No matter how I go about it, I always come up with the same answer.

as an aside, I explained to a salesman at Calumet why I was doing what I was doing and mentioned that I had recently begun to really understand the point. For cameras of a certain design, which were sitting right there in front of us, you need to do swing first and then tilt to avoid yaw. He nodded as though this was something that every large format photographer knew. Perhaps that is so, but, in discussions I've seen, it seemed as if the assumption was that one tilted first and then swung.

[Sheldon N]

Are you assuming that the camera is level? Most of the benefit of a yaw free camera is that you can shoot with the camera pointed up or down and then use tilt to bring the swing mechanism back to a level plane.

I don't think it really matters what order you do the operations in.

If your camera is not yaw free, you can never bring the swing axis back to level if the camera is pointed up or down.

[David A. Goldfarb]

On a Sinar P or P2, there are two tilt mechanisms.

One is the asymmetrical tilt, which you see in the animation, and this isn't the function that makes a Sinar yaw-free. The axis isn't in the center of the frame, but about an inch and a half from the edge of the frame, marked by a dotted line on the groundglass. The swing is similarly positioned with respect to the right edge of the groundglass. To use the tilt, you focus at the dotted line, tilt, and watch the groundglass until the plane you want is in focus. If you want the tilt on the front standard rather than the rear standard, you read the tilt angle off the rear scale and then apply the corresponding tilt on the front standard and restore the rear standard to plumb. The swing works the same way.

See the lever and the scale behind those two lower knobs? That's the base tilt. The idea is that if you have to point the rail up or down, you can use the base tilt and the levels on the camera to restore the standards to plumb, so that if you swing, the film plane stays perpendicular to the ground (which we'll call a plane for the sake of demonstration), rather than perpendicular to the horizontal plane of the rail.

When the rail is not level with respect to the ground and the film plane is perpendicular to the horizontal plane of the rail, rather than to the ground, and you swing the rear standard causing the image to rotate, that's what we usually call "yaw."

You've been describing it as a focus problem, which I suppose it is, if you look at it that way, but I usually think of it as a composition problem, in that you're trying to keep everything straight, but it's moving when you don't want it to. Of course it's both, because you want everything both straight and in focus, and adjusting for one upsets the other.

[Leonard Evens]

Are you assuming that the camera is level? Most of the benefit of a yaw free camera is that you can shoot with the camera pointed up or down and then use tilt to bring the swing mechanism back to a level plane.

I don't think it really matters what order you do the operations in.

If your camera is not yaw free, you can never bring the swing axis back to level if the camera is pointed up or down.

Thanks Sheldon. You raised a point I hadn't considered. If you point the camera up and then tilt to bring the standard back to plumb, and then swing, you won't get yaw. But, for me, that maneuver is just a complicated way to raise the front standard. You generally use it when you can't get the desired rise the normal way. A rise will alter the center of perspective, but it will leave the subject plane parallel to the standard. So you are in effect just performing a swing with no tilt. If you needed a skew subject plane, you would still need to tilt and swing, and it might very well matter which you did first.

Consider instead what would happen if you pointed the camera upward, but didn't tilt to bring the standard plumb. Then, with the swing axis no longer vertical, you would get yaw.

[Leonard Evens]

David,

Thank you for pointing out the existence of the second tilt mechanism. I hadn't abosrbed that.

I'm not sure I follow everything you said,, but I do see that you could use the track mechanism to tilt front standard with respect to the vertical, then negate that tilt by using the base mechanism to bring the standard back to vertical. With the tilt axis now vertical, a swing would not produce yaw.

Is that what you meant?

But, I still don't see what that would accomplish if you are trying to get the subject plane in a skew position, i.e., so that the hinge line and Scheimplfug line are neither horizontal nor vertical.

Perhaps I should explain more clearly what i envision the purpose to be. For the front standard, I don't really care whether the top and bottom of the standard are horizontal or not, since that doesn't matter for image formation. I want to be able to get the subject plane where I want it, and when the desired subject plane is skew, you need both a tilt and a swing. For all the cameras I've looked at, it appears to matter which you do first. If I now understand the Sinars, that appears to apply to those also.

Let me also add that the orientation of the rail is not relevant. The only things that count are the orientations of the front and back standards with respect to one another and with respect to to the desired subject plane. If you tilt the front standard so it is no longer parallel to the rear standard and in the process also tilt the swing axis with it, then, when you swing, you will get yaw in the sense that the standard will rotate about the lens axis. But, what is more important is whether you can get to the desired subject plane, at least in principle, by one tilt and one swing or whether you have to go back and forth and get there by a series of iterations. You want the axis for the second operation you perform to remain parallel to the rear standard while you apply the first operation in order to minimize the number of adjustments needed to get to the desired subject plane. Yaw is not the cause of the problem, but a symptom that it exists.

[Jorge Gasteazoro]

Let me also add that the orientation of the rail is not relevant

Yes it is Leonard, here is an example that as a LF user I am sure has happened to you. Have you ever run out of shift in the camera and decided to pan with the tripod head? If you do this and look in the GG you then see that things don't look right, specially if you are photographing buildings or things with straight lines. I beleived this is what SS was alluding to, that for you to avoid yaw, is important that you have the planes of focus perpendicular and this includes camera position.

Look, all a yaw free camera does is mantain the vertical and horizontal plane perpendicular to each other in ALL positions. Notice that this can only be acheived with mechanisms like the SInar and AS Orbix, or as Bob pointed out by turning the camera on the side. A lot of the claims of yaw free makers are BS including AS's with exception of their orbix carrier. AS cameras are yaw free if the rail is perpendicular to the subject and the floor, the moment you tilt the rail and apply tilt and swing on the standard you will have yaw unless you are using an orbix carrier.

I don't know if you have it, but it is very well explained in the Leslie Stroebel book.

Is yaw really a problem, not for me, I fiddle with the camera until things look right in the GG.. :)

[steve simmons]

You are all making this much too complicated. It does not have anything to do with nodel points, etc.

Take your camera, any camera. Level it front to rear and left to right. Now use the swing and tilt on either standard. You will notice that the edges of the gg, or the lens board, do not rock up on one top corner and down on the other top corner. When level, all cameras are yaw free.

Now aim the camera up or down. Use the swing and tilt movements. If one top corner of the gg or the lens board rocks up and the other corner rocks down, you have yaw. In this type of situation, you can not get a perfect Scheimpflug relationship with the plane of the subject, the plane of the film, and the plane of the lensboard. One of them is cocked and will not line up with the other two.


steve simmons

[Leonard Evens]

Yes it is Leonard, here is an example that as a LF user I am sure has happened to you. Have you ever run out of shift in the camera and decided to pan with the tripod head? If you do this and look in the GG you then see that things don't look right, specially if you are photographing buildings or things with straight lines. I beleived this is what SS was alluding to, that for you to avoid yaw, is important that you have the planes of focus perpendicular and this includes camera position.

Look, all a yaw free camera does is mantain the vertical and horizontal plane perpendicular to each other in ALL positions. Notice that this can only be acheived with mechanisms like the SInar and AS Orbix, or as Bob pointed out by turning the camera on the side. A lot of the claims of yaw free makers are BS including AS's with exception of their orbix carrier. AS cameras are yaw free if the rail is perpendicular to the subject and the floor, the moment you tilt the rail and apply tilt and swing on the standard you will have yaw unless you are using an orbix carrier.

I don't know if you have it, but it is very well explained in the Leslie Stroebel book.

Is yaw really a problem, not for me, I fiddle with the camera until things look right in the GG.. :)

Part of my problem is that I use these terms as they are defined in mathematics, astronomy, and related subjects, so I often don't understand what others are saying, although they may be perfectly clear to other people.

Vertical and horizontal planes to me are always perpendicular by definition, so I don't know what you mean by the statement about keeping them perpendicular. I'm sure you mean something relevant; I just don't know what it is.

I am very familiar with what happens when you pan. I have a panoramic head, and I've used it with software to produce very wide angle images of building facades that are impossible with the shortest focal length lens I have. This requires my understanding things I had never worried about before.

Of course, if you are photographing such a facade, and you can't shift far enough to get what you want, you may be able to do it instead by rotating the rail horizontally and then swing the standards so that the rear standard is parallel to the building facade. Otherwise, horizontal lines in the building will converge to a vanishing point. So from a practical point of view, that is a useful technique, and the position of the rail certainly is part of it. That may be what you are talking about. But, from the point of view of image formation, that is really just a complicated way of shifting. As I said previously, it is the relative orientation of the standards with respect to one another and with respect to the scene that matters, not how you managed to get it.

A useful way to get to understand this is to take a flat white matte board and project an image on it with a lens. Then fiddle with the orientation of the board and see how the image changes.

[Ken Lee]

It seems to me that the Sinar (http://www.sinar.ch/site/index__gast-e-1832-52-1959.html) illustrations are illustrative... no ?


http://www.kenleegallery.com/images/forum/sinaryaw.jpg

[Jorge Gasteazoro]

Vertical and horizontal planes to me are always perpendicular by definition

Leonard, please read the entire sentence. The idea is to keep the planes perpendicular to each other even when you apply movements. Look at the illustrations Ken posted.

Look the exercise is very easy to visualize, and I tell you this because I also had problems understanding yaw. Hang a plomb line and put the front standard underneath the line so that is right at the center of the standard. This will be your vertical axis, now, if you have a base movements, tilt the standard forward (or backwards) and you will see your vertical axis does not pass throught the center of the lens board but passes (if you imagine a line projecting through the lensboard) underneath the center of the board.

Now if you have axis tilts, then this becomes a little bit more difficult to understand because we normally have the bed or rail of the camera parallel to the ground, so for axis tilts tilt the bed or rail a little bit, then apply both tilt and swing, you will see that the line from your vertical axis no longer passes through the center as well.

If you have a Sinar, or an AS with orbix and do the same exercise, you will see that no matter which movements you apply, the line always passes through the center of the board. YOu can also place a wire that points to the center of the board on the side and do the same exercise.

The yaw concept is a little difficult ot understand because we have to visualize circular movement in 3 dimensions, if you go through the exercise I explained to you, you then realize that all the yaw free cameras do is to keep the horozontal and vertical planes passing throught the center of the board regardless of movement.

Hope this helps, if it does not then I have reached the limit of my knowledge, I don't know how to explain it better.

[Bob Salomon]

If you have a Sinar, or an AS with orbix

Or a Linhof Master GTL or Master L or M679 or several other yaw free cameras as well.

[Leonard Evens]

You people must be getting sick and tired of this discussion. You are probably thinking I am just a doltish nerd who can't get it through his thick head what is obvious to everyone else.

But I have found this discussion very useful. I've learned a lot I didn't know about the different mechanisms that view camera manufacturers use. I just wish I had more at hand to play with.

In addition, trying to respond to the many asnwers, I realized that there was a fundamental point I had misunderstood, and I hope I've finally gotten it straight.. There are two problems here. One is yaw with respect to the horizontal, but the other, which was what interested me originally, was how to get the exact subject plane where I wanted it. It turns out the two are related but one does not cause the other. Whether or not you have horizontal yaw is not always an indication that you will have have focusing problems, and vice versa. I thought the two always went together, and sometimes they do and sometimes and sometimes they don't. Part of the problem is that yaw can mean different things at different times, and it hard to keep it all straight when the standard is being moved.

Let me explain how I got started with this. I started writing a discussion of geometric principles, as seen by a geometer, and how they might apply to view camera photography. It turns out that you can derive quite a lot from a few principles. I had a pretty good understanding of exactly what happens when you tilt or when you swing, but I've never really looked carefully at what happens when you combine the two.

In particular, the question I was interested in was whether it was possible to apply one tilt followed by one swing and thereby get the exact subject plane where I want it, assuming the standard is perpendicular to the rail, but can move on the rail, a fairly standard situation for me.
I can prove that is theoretically possible, but the calculations needed to determine the tilt and swing angles are horrendous and the process is not intuitive. The question was whether or not it was possible to do by seeing what happens on the gg. If you can't do it in two steps, you have to iterate repeated tilt, swing cycles, which can take quite a while.

I found the crucial point was the following. Call the plane through the the lens, parallel to the rear standard,, the reference plane. (It contains the hinge line.) If when you tilt, the swing axis remains in the reference plane, a tilt followed by a swing will work well. If when you swing, the tilt axis remains in the reference plane, then swing followed by tilt will work well.

On the other hand, I know of examples of camera design where there is no horizontal yaw, yet when you swing, the tilt axis doesn't stay in the reference plane. If you went by horizontal yaw, you might think you were okay, but you wouln't be, vis-vis focusing ease.

I think I will drop the subject now. Anyone interested can look at my analysis when I get around to making all the diagrams and put it up on my web site. I doubt if many people will be interested, but there may be a few.

[Leonard Evens]

Leonard, please read the entire sentence. The idea is to keep the planes perpendicular to each other even when you apply movements. Look at the illustrations Ken posted.

Look the exercise is very easy to visualize, and I tell you this because I also had problems understanding yaw. Hang a plomb line and put the front standard underneath the line so that is right at the center of the standard. This will be your vertical axis, now, if you have a base movements, tilt the standard forward (or backwards) and you will see your vertical axis does not pass throught the center of the lens board but passes (if you imagine a line projecting through the lensboard) underneath the center of the board.

Now if you have axis tilts, then this becomes a little bit more difficult to understand because we normally have the bed or rail of the camera parallel to the ground, so for axis tilts tilt the bed or rail a little bit, then apply both tilt and swing, you will see that the line from your vertical axis no longer passes through the center as well.

If you have a Sinar, or an AS with orbix and do the same exercise, you will see that no matter which movements you apply, the line always passes through the center of the board. YOu can also place a wire that points to the center of the board on the side and do the same exercise.

The yaw concept is a little difficult ot understand because we have to visualize circular movement in 3 dimensions, if you go through the exercise I explained to you, you then realize that all the yaw free cameras do is to keep the horizontal and vertical planes passing through the center of the board regardless of movement.

Hope this helps, if it does not then I have reached the limit of my knowledge, I don't know how to explain it better.

Okay. I am beginning to understand what you are saying. I think you are using the term "vertical" in a sense different than I use it.. There are two important axes in the standard through its center.. One is perpendicular to the top and bottom and one is perpendicular to the sides. I believe you are using the term "vertical axis" to refer to the one perpendicular to top and bottom, and perhaps "horizontal axis" for the one perpendicular to its sides. I use the term "vertical" to refer to the up-down direction. I use the term "horizontal" to refer to any plane such that if you put a ball on it, it won't roll. I also use the term "horizontal" to refer to any line in a horizontal plane.

So, note that when you start with the camera level and the standards plumb, then if you tilt the front standard about its base, what you call the "vertical axis" will no longer be vertical in the sense I mean that term. It will make an angle, i.e., the tilt angle, with respect to the vertical direction.

You are also using "yaw" differently than I do. If I understand you correctly, you seem to be referring to the fact that the center of perspective shifts when you tilt about an axis that doesn't pass through the center of perspective. I agree that the Sinar and Orbix mechanisms help you avoid that. I don't have an explicit name for that phenomenon. For me "yaw" is something entirely different. The technical meaning is a rotation of a plane about an axis perpendicular to it, such as the front standard about its axis. In practice, it often means rotation of the top and bottom of the standard with respect to the horizontal. If the manufacturers mean by yaw a shift in the center of perspective, I agree that is a problem that should be dealt with, but the issues I raised are different problems that often merit attention.

I don't claim that my PhD in mathematics and experience teaching geometry over some 50 years gives me any special expertise in the use of a view camera. But i really do understand three dimensional geometry very well. I generally assume when someone here says something that doesn't make sense to me that they are saying something sensible, but I don't understand what it is because we are talking at cross purposes. I hope you will consider that possibility when something I say doesn't make sense to you.

[Jorge Gasteazoro]

Okay. I am beginning to understand what you are saying. I think you are using the term "vertical" in a sense different than I use it.. There are two important axes in the standard through its center.. One is perpendicular to the top and bottom and one is perpendicular to the sides. I believe you are using the term "vertical axis" to refer to the one perpendicular to top and bottom, and perhaps "horizontal axis" for the one perpendicular to its sides. I use the term "vertical" to refer to the up-down direction. I use the term "horizontal" to refer to any plane such that if you put a ball on it, it won't roll. I also use the term "horizontal" to refer to any line in a horizontal plane.

So, note that when you start with the camera level and the standards plumb, then if you tilt the front standard about its base, what you call the "vertical axis" will no longer be vertical in the sense I mean that term. It will make an angle, i.e., the tilt angle, with respect to the vertical direction.

You are also using "yaw" differently than I do. If I understand you correctly, you seem to be referring to the fact that the center of perspective shifts when you tilt about an axis that doesn't pass through the center of perspective. I agree that the Sinar and Orbix mechanisms help you avoid that. I don't have an explicit name for that phenomenon. For me "yaw" is something entirely different. The technical meaning is a rotation of a plane about an axis perpendicular to it, such as the front standard about its axis. In practice, it often means rotation of the top and bottom of the standard with respect to the horizontal. If the manufacturers mean by yaw a shift in the center of perspective, I agree that is a problem that should be dealt with, but the issues I raised are different problems that often merit attention.

I don't claim that my PhD in mathematics and experience teaching geometry over some 50 years gives me any special expertise in the use of a view camera. But i really do understand three dimensional geometry very well. I generally assume when someone here says something that doesn't make sense to me that they are saying something sensible, but I don't understand what it is because we are talking at cross purposes. I hope you will consider that possibility when something I say doesn't make sense to you.

Well yes, if you pass a line through the center of the camera, tilt and then swing then the standard (the plane which is the standard) rotates about this axis, it does not when you have a yaw free camera.