3-D model as an aid in understanding the view camera settings

[Jos Segers]

Hello All,

Let me start with a brief introduction to my photographic past.
In 1976 I was introduced to analog photography, in black and white. Soon came the challenge of making my own color prints as well. At that time, I only had a 35mm enlarger built by my father himself. With simple AMALOCO color filters in three primary colors, I was still able to get started easily and relatively inexpensively. Since 1980 I have mainly focused on black and white photography.
About six years ago I purchased a Cambo 4x5 monorail camera. A few years later followed by a Wista 45SP field camera. The biggest challenge quickly became mastering the use of camera movements.

A lot of information can still be found on Photrio and the LF-Forum on how to position the plane of sharp focus and controlling depth of field. Merklinger's articles were a rewarding addition. His animated diagrams nicely show how Scheimpflug Rule and Hinge Rule work together. For me, more was needed to truly understand how it works and what was happening.

All this gave me the idea of making a three-dimensional model with which I could see that it works and how it works. It ended up being a rewarding project but also time-consuming and complicated too.
I will try to describe the characteristics and operation of the 3-D model as accurately as possible. The model is built to a scale of 1:10 and can be almost completely dismantled. Some of the parts can be seen in one of the photos.

When designing the right half of the 3-D model, I was guided by the images of Harold Merklinger. The movements of the five coloured planes are simulated by a rod mechanism.
The left part of the 3-D model is a supporting rod mechanism that functions according to the principle of an old-fashioned drawing machine (US patent from 1901). This makes it possible to move the yellow Film Plane accurately and without rotation in both the vertical and horizontal directions. The movement of the yellow film plane, which is actually the focusing on the subject, is towards or away from the green parallel-to-film Lens Plane. At the same time, the Scheimpflug Line moves over both the white Lens Plane and the red Plane of Sharp Focus. This left part of the 3-D model is, as it were, the motor that drives the mechanical rod mechanism and rotates the Plane of Sharp Focus around the Hinge Line.

A characteristic feature of the 3-D model is that Lens Tilt (Alpha) can be adjusted by allowing the white Lens Plane and the blue Front Focal Plane to tilt simultaneously around the axis of the lens (Lens Axis Tilt), thereby determining the position of the Hinge Line in space. Alpha can be read with an accuracy of plus or minus 0.2 degrees.

The distance J is variable and depends on the degree of Lens Tilt (Alpha). J can be easily read on a scale and is a minimum of 50 cm and a maximum of 300 cm in the 3-D model.

The fixed distance between the Lens Plane and Front Focal Plane (f) is determined by the selected focal length of the lens. In the model, f=150 mm has been chosen.

The degree of rotation of the red Plane of Sharp Focus can be read on a protractor, also with an accuracy of approximately plus or minus 0.2 degrees.

Finally, the distance from the yellow film plane to the green Parallel-to-Film Lens Plane is measured with a caliper.

The functioning of the 3D model more than meets my expectations. I have compared the readings for the individual variables such as α (°), J (cm), φ (°) and A (mm) with the calculated values from the official Merklinger table.

I hope I have been able to explain in short what my intention was with the conception and creation of this 3-D model. It has indeed given me a better insight into working with the view camera because it fills a gap in the information I could find.

I am very curious how you experienced the whole learning process of focusing.

 

[Doremus Scudder]

Let's separate "focusing" the view camera from positioning the plane of sharp focus (PoSF). The Scheimpflug principle and all of its derivations deal with how camera movements, primarily tilt and swing, interrelate with the position of the PoSF in the scene.

Focusing is also about positioning the PoSF, often aligned with things we want in sharp focus, but for many of us, it's the near-far depth of field limits that determine optimum position for the PoSF. Using movements to achieve that ends up being a different exercise using different reference points than the reference points used for focusing.

Complicating matters further is the use of swings and tilts together, something that really happens in 3D. Merklinger's illustration only applies to tilts. While swings are just tilts transposed 90°, when using both together, the PoSF ends up being obliquely positioned to both plumb and level (when just one of the two movements is used, the PoSF is always aligned with one or the other vertical or horizontal axes). This is something that would likely need 3D computer modeling to accurately reproduce.

I think your machine would be an excellent teaching tool, since it's hands-on, like the camera, and allows easy visualization of what happens when tilts are applied. I can't see from your photos if bellows draw (lens-to-film-distance) is a variable in your model. I would assume so. Maybe there's a way that base tilts can be represented as well, which would be a real help for those using field cameras with base tilts only.

Best,

Doremus

 

[Jos Segers]

Thank you, Doremus, for your detailed response. I realise that my explanation is flawed because it is incomplete, as English is not my native language. The fact that you have nevertheless taken the trouble to clarify a few points reinforces my belief that I am on the right track with the machine, as you rightly call it.
For practical reasons, when determining the specifications of the model, I limited myself to a few things that are most essential to me. Moving the film plane towards or away from the lens is indeed one of them. Furthermore, being able to accurately read the values of α, J, φ and the distance between the film plane and the lens on a scale was essential to me. The whole experiment was educational for me to do. And that was what I had hoped for.

Best regards,
Jos.

 

[grahamp]

One of the beauties of this device is that it makes it clear (by providing a physical object) where all the planes lie. A lot of novices (I was one once) put in more movement than needed, and get confused. It is hard to visualise imaginary planes at first, but much easier when you understand the basic example. With this device one can start with what one wants, and work back to how to get it.

 

[koraks]

I am very curious how you experienced the whole learning process of focusing.

As fairly intuitive. The only thing I felt I ever needed is that picture of the three planes (film, lens, subject) and how they are either parallel, or they intersect. As soon as tilt or swing is applied, the planes intersect and I can visually imagine this intersection; with large movements and/or when working in a close-up configuration I sometimes step back from the camera and look at it from the top or from the side to 'see' where the intersect is. But most of the time when working in the field, the movements are slight and they are easily made by simply adjusting swing/tilt while simultaneously moving the front standard (depending on camera construction).

The device you built certainly looks very neat, but referring to the first photo, that would have confused me much more than it would have solved anything for me, personally. I can imagine how building the device might have made you intimately familiar with the Scheimpflug principle. Then again, looking at my own photography, only a pragmatic and basic understanding seems to be perfectly adequate to get me through the day.

 

[Jos Segers]

Thank you for your candid answer. It shows once again that there is no universally applicable method. I think it's impressive how you have developed a method that is not only intuitive but also effective and efficient for your photography.

I myself fell into the trap of trying to meticulously understand all the information I could find and eliminate any contradictions. I quickly discovered that there are not only many good tips but also many inaccuracies regarding the technique of focusing with a technical camera.

You indicate that the Scheimpflug rule gives you sufficient guidance. That is very special for me to hear. I will therefore briefly explain how I view it, without claiming that my method of working is better.

Without even looking at the ground glass, I visualise at a location whether the subject is worth taking out the camera and putting it on the tripod.
This means that I first look for my point of view. I need this to assess the perspective and image section. From the lenses I have with me, I then choose the one that best suits the image section I have in mind. This is followed by a critical step, which is to visualise the position of the hinge line and the slope of the plane of sharp focus. The aperture is usually f/22. I can see afterwards on the ground glass whether the depth of field is sufficient. The Hinge Line plays a crucial role in my understanding of how things works.

The Scheimpflug rule only tells me that the plane of sharp focus rotates around the hinge line during focusing.

I can well imagine that in your case the first photo does not immediately lead to acceptance or recognition. This may be different if you are familiar with Merklinger's image, bottom left, and compare it with the device.

 

[Jos Segers]

One of the beauties of this device is that it makes it clear (by providing a physical object) where all the planes lie. A lot of novices (I was one once) put in more movement than needed, and get confused. It is hard to visualise imaginary planes at first, but much easier when you understand the basic example. With this device one can start with what one wants, and work back to how to get it.

Thank you for your feedback. I can only confirm what you say.

The difficult thing about Merklinger's illustrations for me was that the settings and movements are clear in themselves, but they are not to scale, which means that the proportions are incorrect.

 

[koraks]

to visualise the position of the hinge line and the slope of the plane of sharp focus

That's pretty much exactly what I do as well. The only bit that I can imagine people may find tricky is the concept that the hinge line can run underground or someplace high up in the sky, which will be the case if the movements applied are only very slight. But I'm now trying to imagine how this could be non-intuitive for someone, which is of course very hard to do if you experience something as intuitive. It's a bit like trying to explain how you don't fall over when riding a bike. You just feel the balance, and the act of balancing is pretty much automatic. For me, camera movements are the same way. And it helps that you have a ground glass that shows you exactly what's going on.

 

[BrianShaw]

An exceedingly cool tool!

 

[Jos Segers]

Koraks: The only bit that I can imagine people may find tricky is the concept that the hinge line can run underground or someplace high up in the sky, which will be the case if the movements applied are only very slight.

That's how I see it too. I was initially misled because in many examples the location of the hinge line is the same as the location of the tripod.

But I'm now trying to imagine how this could be non-intuitive for someone, which is of course very hard to do if you experience something as intuitive.

It depends on how you want to explain the concept of intuition. I would refer to it as the necessary experience, knowledge and skills that someone has acquired over time, enabling them to perform actions smoothly and efficiently without much effort and without thinking. I have no problem with calling this intuition for the sake of convenience and in this context. When it comes to the example of cycling, which also appeals to me as a Dutch person, I can follow your reasoning. Insofar as cycling is also an acquired and lasting skill. One that you don't have to think about once you've learned it.

But skill does not come out of nowhere. In addition, skill is a relative concept. When I see on Photrio how many discussions have been held over time about the technique of focusing the camera, I get the impression that for most people it is quite a challenge to understand and master. Some have thrown in the towel prematurely. It doesn't help when a whole lot of mathematics and trigonometry is thrown into the mix.

 

[Jos Segers]

An exceedingly cool tool!

Hi Brian, nice to hear this