I think many people have heard of shift lenses, but probably wonder exactly what they do, how to use one, and why one might need a shift lens to begin with.

Shift lenses are generally used for landscapes, interior and exterior architectural photography, and sometimes for food and product photography.

A shift lens has one basic purpose though and that is to shift your field of view (perspective) up or down to allow you to see more of either what’s above or below the current field of view of your camera, but without having to tilt the camera itself either up or down.

Now why wouldn’t we simply want to tilt the camera up or down? That is because the pointing of the camera up or down (as opposed to leveling the camera on the tripod and shifting the field of view) is that it results in something called barrel distortion, which basically looks like curving at the edges of the frame. The graphic below shows you the optical effect of what barrel distortion more or less looks like.

So the key to avoiding barrel distortion in photography, which normally occurs at wider angles below 35mm, is to keep your camera level. With a shift lens it allows you to do just that. You level the camera first and then use the axis of the shift lens to shift the lens elements themselves either up or down on the camera’s body in order to see more or less either above or below the camera.

To level your camera, the best method is to use a spirit level, which is a small level that fits into the hot-shoe on the camera. Many tripods come with a level built into them as well, but the level built into a tripod only indicates that the tripod is level and not the camera itself.

Unfortunately a good quality spirit level, such as the ones made by Manfrotto, cost around US$40, but from my experience the only ones that are reliable are the high quality ones like the Manfotto model. In the past I have purchased inexpensive spirit level copies and always found that they were not accurate and/or reliable at all.

To answer the question about how do you actually use a shift lens once you have leveled your camera, the answer is quite simple. In the image below you have a Canon 24mm shift and tilt lens mounted to a DSLR body.

This lens is actually capable of performing two very different and unique functions. One is the shift function which I have been discussing and the other is a tilt function which selectively allows you to play with the depth of field on a photo for some cool optical effects.

I am not going to get into the tilt function here, but you can go here on wikipedia to read more about tilt.

Now if you look at the lower adjustment knob on the left side of the lens you will see it is shifted all the way to the top. This is the knob on a shift lens that you use to actually shift the perspective either up or down on your camera. In the above photo the shift axis of the lens is set for shooting in the vertical position, but good shift lenses like this one made by Canon will be able to rotate the lens mount in order to allow you to shift the lens up and down, depending on whether you are shooting either horizontally or vertically on the camera.

So the first thing you do once you have mounted your camera on a tripod (best to use a tripod when shooting with a shift lens otherwise it is difficult to level the camera) is to level your camera using a spirit level. Then look through the viewfinder and see what you have within the frame of your camera in terms of framing.

If for example you were shooting a landscape, and wanted more sky, you could shift the lens up to add more sky into the frame by reducing the amount of area at the bottom of the frame. If you wanted to see more ocean then you could shift the lens down towards the ocean in the same way. And with the shift lens all the while the camera remains level so your horizon and the edges of your photo will come out looking level and squared and not distorted.

Does a shift lens always completely resolve and avoid all barrel distortion issues? Unfortunately not. When you are shooting at a wide angle and are standing very close to your subject then you might find you still get some barrel distortion, even if the camera is level. Unfortunately it can’t always be avoided in extreme close-up shooting situations. But not using a shift lens at all, and having to tilt the camera up or down will result in even more barrel distortion than if the camera itself is at least level.

There are also limits as to how far the lens can actually shift the perspective. So, for example, if you were standing below a tall high-rise building, and wanted to get the top of the building into the photo, then the shift lens may only be able to shift the perspective to a point. Then, unavoidably, you may have to tilt your camera upwards in order to get the rest of the top of the building into the photo too thus, resulting in some barrel distortion anyway.

So the further you are able to position the camera away from the subject you are shooting, then the better your chances of avoiding any barrel distortion all together with a shift lens.

It is also worth nothing that as you shift the axis of a shift lens you also start to lose some of the light coming into the camera. So as a result you may need to increase your exposure time to compensate for the loss of light that occurs as you shift your perspective away from the center axis point on the shift lens.

You also don’t want to shift the lens all the way to the absolute top or bottom of the lenses’ shift axis as the sharpness of the picture can start to degrade at extreme levels of shift since the light starts to bend a lot as it comes through the lens and into the camera.

The next question is can you shoot without a shift lens? The answer is yes, absolutely. If you shoot with a regular wide angle lens and keep your camera level on a tripod then you also won’t get much, if any barrel distortion at all. The problem though is that you won’t be able to control the field of view and thus, how much sky or sea you are seeing in your viewfinder for example. But the simple solution is you can crop off part of either the top or the bottom of your photo later that you don’t want (during post processing) in order to give you more of the final framing that you had wanted.

There are also perspective corrections you can make to a photo in post processing on a photo which has some barrel distortion in it. Photoshop for example offers a very good perspective correction tool to fix curving edges on a wide angle photo, but unfortunately the downside to using software to fix these optical issues in post is that after the perspective correction is made you will have to crop off a portion of your final photo. In many cases you may have to crop off as much as 25% of the image. So if you prefer to have the whole wide angle shot as you shot it with the camera, then the method of using software to correct the perspective may not be a good solution for you.

So the best solution to avoid having to crop off a portion of your photo later to remove part of it that you don’t want, or when performing perspective correction in post processing, is to simply to shoot with a shift lens.

I hope this covers the basic ins and outs of shift lenses for you and if you have more questions on the use of shift lenses please feel free to post them below and I will be sure to answer them.