The tilt of a tilt-shift lens explained

Monday 15 March 2021, 20:20 by Nando Harmsen | 8,003 views | 4 comments

This article was translated from Dutch with the help of AI. Read the original.

I recently wrote about the shift function of a tilt-shift lens. But these lenses have a second special feature, which is tilting the lens. In this article, I explain how the tilt function of a tilt-shift works and what it is useful for.

I have already shown how impressive a tilt-shift lens can look when you set both the shift and the tilt. You may wonder whether a good photo can come out of it at all.

The possibilities of a tilt-shift are clearly visible in this photo. Tilting and shifting make the view look slightly surreal
I have already explained the use of the shift function in this article, including how you can use it to prevent converging lines. Although you might expect tilting a lens to do this, it creates a completely different effect.

The focusing plane of a lens

To understand what happens, it is important to realise that a lens has a focusing plane. This is a plane in two directions, from top to bottom and from left to right, that is in focus. Focusing determines how far this plane is from the sensor, the focusing distance.

Everything in front of and behind this plane is out of focus. The greater the distance from the focusing plane, the more blurred objects there are.

You can influence this blur with your aperture. With a large depth of field, the area in front of and behind that focusing plane is also in focus. A shallow depth of field leaves only a very small area in front of and behind this focusing plane in focus.

It is a little more complicated than this, but for now this is an acceptable representation of the situation for explaining how tilt works. What matters is that you understand that this focusing plane always runs parallel to the sensor.

Tilting a focusing plane

The special thing about the tilt function of a tilt-shift lens is that it allows you to tilt the focusing plane. This means that the focusing plane is no longer parallel to the sensor, but is at an angle to it.

How the angle changes when you tilt your lens is determined by the Scheimpflug principle. Going into detail would take us too far, but the drawings I made make it somewhat clear how it works.

An experiment

I built a setup to show the effect of tilt, together with a schematic representation of how the focusing plane changes. This schematic representation is only a general illustration and is absolutely not to scale or drawn with exact angles. It is about understanding the principle.

Learning to use and understand a tilt function. This was my setup
I focused on the middle book. The focusing plane lies at that distance, with everything at that distance appearing sharp. Anything in front of or behind it is out of focus because I used the shallowest possible depth of field.

The result without tilt, with a shallow depth of field.
Tilting the lens down also tilts the focusing plane down. This means that everything is no longer in focus at the same distance, but the focusing plane runs from the bottom up towards an angle at the top.

The result of the change in focus with a tilted lens. Compare this with the normal photo above.
If you can tilt the lens far enough, the focusing plane can even become parallel to the table. This is not possible with an ordinary tilt-shift lens, though. For that, you need a completely different kind of camera.

Creative use of tilt

You can position the focusing plane almost entirely as you wish by choosing the direction of the tilt and the camera angle. This allows you to get subjects completely sharp with a minimal depth of field, while the surroundings are out of focus.

Four examples in which I have shown the focusing plane in the image.

What happens with a large depth of field?

If you introduce depth of field by stopping down your lens, the effect of an ordinary lens is easy to imagine. An area in front of and behind the focusing plane will also appear sharp. We make a lot of use of this in our photography.

Stopping down the aperture gives you a greater depth of field. Part of the area in front of and behind the focusing plane is also in focus. This example diagram is not drawn to scale, by the way.
The depth of field is parallel to the sensor, just like the focusing plane. But when you tilt the lens, the area of depth of field tilts along with the focusing plane.

Something unusual happens, though. Your depth of field no longer runs from front to back, but from diagonally below to diagonally above. It has become a triangle that runs backwards from a point close to the lens.

The way the area of depth of field changes when tilting the lens. It runs backwards from a point like a triangle.
This means that tall objects can extend above the area of depth of field, especially when they are close by. This creates a very unusual effect that you can once again use to give a photo a distinctive look.

A large depth of field no longer controls sharpness in depth, but from bottom to top.

Tilting the focusing plane in the other direction

In this example, I tilted the focusing plane so that it is almost parallel to the subjects I want to include in the image. This allows you to get an extremely large depth of field, even with a wide aperture.

You can also tilt the focusing plane in the other direction, giving you an extremely shallow depth of field instead. This makes the subject you are photographing look like a miniature.

In effect, you are simulating the shallow depth of field of a macro photo and applying it to the real world. This is naturally a playful effect that can sometimes produce very fun results. It usually works best with slightly longer focal lengths.

I do not have a good example of a miniature photo taken with a tilt-shift lens, but you can simulate this effect with Photoshop. This is roughly what you can achieve by tilting a tilt-shift lens.

Very specialised use

Using the tilt function of a tilt-shift lens is highly specialised work. It can produce special results, especially when used for photographing landscapes with an extreme depth of field or for product photography, results that cannot be achieved in any other way.

The minimal depth of field has been made even smaller by tilting the focusing plane. This made it possible to get only the front bluebells in focus, even with this 17mm wide-angle lens.
It takes a lot of time to work with the tilt function, and it does not always produce the results you would expect. Especially because the amount a tilt-shift lens can tilt is limited.

If you want to use this to its full potential, you soon end up with large-format cameras, where not only the lens can be tilted, but the photographic plate as well.

These specialist cameras are expensive and are not suitable or necessary for everyone. A tilt-shift lens at least gives you the ability to control the position of your focusing plane to a certain extent.

Would you have a use for the tilt function of a tilt-shift lens? Or is this kind of photography too much for you? Share your opinion in a comment below this post.

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