Hi;

This is a continuation of a tangential discussion from the "Pros and cons of field cameras" thread. In that thread, I wrote:

"Consider the simple manipulation of using front rise to prevent convergence. Convergence is a perspective effect, and front rise can be used to control convergence. This example therefore proves that camera movements CAN alter perspective. Obviously, there are some limitations: In particular, camera movements cannot alter the near/far size relationships of objects which are overlapped in the image (though you CAN alter the aparrent size relationships of objects which are separated in the image...)"

Larry Shearer then replied:

"Not that I am trying to cause more confusion for Alan then is already present,but Patrick how do you control convergence of a scene by raising the front standard? Alright I have to drop a name here e,ummm Ansel Adams states on more than once in "The Camera" that "True perspective depends only upon the camera-to-subject distance." (page 106)."

Depends on what you define as "perspective". When Ansel Adams says "perspective", he is defining it as the size relationship between near and far objects which overlap in the scene. He's right, but only within the narrow limits of his own definition. To see where that definition breaks down, consider the following example: You have a near object on the left side of the image, and a far object on the right. You want to change the relative sizes of those object without moving the camera. Though Adams' comment appears to suggest that you cannot accomplish this task, it is in reality a very simple matter of swinging the back standard such that the film plane moves away from the object you want rendered larger (you'll then probably need to swing the front standard as well to establish focus). The reason this works is because changing the relationship between the film plane and subject planes allows you to change the distance relationships between off-axis subjects, the lens, and the film plane without moving the camera. The key thing to note here is that for this trick to work, there has to be separation in the image between the objects whose relative sizes you are trying to alter. If they're overlapped, then you're hosed.

Whether you call what I've described above "altering perspective" or not is entirely a matter of semantics.

Just to be perversely confusing, I'll also throw out a case where camera movements truly cannot alter perspective: When photographing with a fisheye lens.

To understand the answer to your specific question about correcting convergence, you need to understand how rectilinear lenses work: A rectilinear lens renders parallel lines in the subject as parallel in the image if and only if those lines lie in a plane which is parallel to the film. To use movements to eliminate convergence, you simply set the back of the camera parallel to whatever it is you're photographing (for example, the side of a building) and then use rise/fall and shift to establish the composition you want. Note that what I've described above controls covergence on both the horizontal and vertical axes; If you're only worried about one or the other, then you only need to set the film plane parallel to the subject along that one axis. Adams definitely explains this to some degree in "The Camera".

You might want to check out the Stroebel and Simmons books (Stroebel is encyclopedic; Simmons is more readable) on large-format technique.

-- Patrick

-- Patrick Chase (patrick@sdd.hp.com), January 08, 2000

Answers

Another question: How important is it to have a yaw-free camera for outdoor work? My understanding is that unless you do macro or table- top photography, it isn't a big deal to have an axis-tilt camera...

-- Alan Cecil (pangaea7@yahoo.com), January 09, 2000.

I like you revised example much better Patrick, with mention of the back adjustments,changes in the angle of the film plane etc.I just couldn't understand how you could alter an images size or shape by merely raising the front standard. Larry

-- Larry Shearer (rlrajls@yahoo.com), January 09, 2000.

Alan: Yaw-free camera movements outdoors ain't a big deal. I cannot think of a normal photographic problem outdoors that requires axis tilts and swings. Actually, the easiest camera to use for this ancient photographer is base tilt on the back and center tilt and swing on the front. It is a lot easier to set up and much quicker. The back tilt is fastest if the back is moved forward slightly and tilted back to vertical when shooting down and opposite when shooting front. A front tilt around the axis doesn't require as much refocusing as base front tilts. The nice thing about the view camera is you can see on the ground glass what is happening. Once you get used to the ground glass image being upside down and start watching the edges of the ground glass it isn't too difficult to keep everything on the image as you want it. A grid on a couple of accurate lines on the ground glass helps keep everything straight. Incidentally, nothing helps composition like viewing the image upside down. Doug

-- Doug Paramore (dougmary@alanet.com), January 09, 2000.

As someone wrote above, a yaw free design is most useful when you are making a photo that requires a combination of swing and tilt (plus possibly other) movements. I find that a yawfree camera is faster to work with, but if I am making only simple movements (straight forward rise/fall or lateral shift or a simple tilt or swing) it doesn't make a difference.

-- Ellis Vener (evphoto@insync.net), January 10, 2000.

Pardon me if my obtusity is showing, but I don't understand why we are seeing this relative flood of "yaw-free" i.e. base tilt only, cameras of late, the ones from Calumet/Cambo and the Toyo with the super-duper green bellows. Are there others as well?

I assume they are designed with the tilt and swing points in the appropriate yaw-free position, but if so, why delete axis tilt & swing? Why not offer it as an additional cost option?

Is there that much of a market out there for these cameras after the Linhoff Technikardan?

-- Sean yates (yatescats@yahoo.com), January 10, 2000.

A comment to Sean Yates: I'm not sure I see why the existence of the Technikardan in particular should have any effect on the market for yaw-free, base-tilt only cameras like the VX-125 or the Cambo. The Technikardan is a non-yaw-free, center-tilt camera, just like many others on the market (though it's arguably far better built than most...). People who like center tilts will buy the Technikardan and cameras like it, just like they always have. People who like yaw-free base tilts will buy yaw-free base-tilting cameras, just like they always have.

The cheapest way to get a camera that does both yaw-free base tilts and center tilts is either the Linhof Kardan GT45, or the Arca-Swiss F-line with the optional Orbix (both of which run in the low $3000s, though I'm not positive about the price of the Orbix).

-- Patrick

-- Patrick

-- Patrick Chase (patrick@sdd.hp.com), January 11, 2000.

Two things:

1.) Not all base tilt cameras are yaw free! The tilt axis must be below the swing mechanism for a yaw free camera. I admit to being biased but but I still think the most technically elegant solution for this is found on the Arca Swiss F-line camerasand on the Sinar X/C2/ & P2 cameras. lasdt time I checked, btw, the Arca Swiss F-line camera was somewhere between US$2200> 2500, depending on the configuration you want (F-line classic, FC, with or withoutthe Orbix, and or the F-Metric version.

2.) Two of my cameras are base tilt, one (the Arca) is yaw free; the other (a Canham DLC) is not. I have a third camera, the V-Pan 617 which is an axis tilt camera. My training with large forge format and then my first nine years of work were with a Sinar P and then a Sinar C. I thing I have had to learn with all of the other cameras I have used (and you name it, I've probably auditioned it) is how to get things equally out of focus around the swing axis. With the V- Pan and all other axis tilt cameras the complication is to get things equally out of focus around the tilt axis as well.

With a well designed base tilt and yaw free camera that has the rise in the focal plane my methodology is this: focus on the top of the scene (in other words at the base of the ground glass and then tilt the front or the back to bring the bottom of the scene to sharp focus. having rise in the focal plane means that if I need to I can use rise on either the front or rear standard to bring the top of the scene to the base of the ground glass, do my tilt and then adjust my riseor fall as need be to reestablish my composition and I do not need to refocus. it is that simple. This is my primary bias towards the Arca Swiss F-line as a general purpose, do everything well, large format camera. This procedure also works well with the DLC, like most field cameras, alas, it has no rear rise or fall.

I don't want to turn this into an Arca vs. Toyo VX thread, but if you look carefully at the VX you will see it is nothing more than a limited capability clone of the Arca F-line metric camera, albeit one with a better distribution system and a higher price tag.

As far as the argument about "altering perspective" goes, any camera that lets you move the lens (i.e., the Point of View) vertically or horizontally or a combination of the two, will let you alter the spatial relationship between any two objects in your image. The change maybe be profound (in the case of a really strong near/ far composition) or too subtle to see (both objects are a long way from the camera and are close to each other) but it is there.

-- Ellis Vener (evphoto@insync.net), January 11, 2000.