Tilt Shift Lenses?

Started Feb 7, 2013 | Discussions thread
kb2zuz
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Re: Tilt Shift Lenses?
In reply to hypercore360, Feb 7, 2013

They generally tend to fall under the "if you need to ask what it does you probably don't need it"

First you have to understand that a lens projects light in a circle over the sensor. To cover a full frame sensor the image circle it projects needs to be at least 44mm in diameter, to cover an APS-C sensor it needs to be at least 26mm in diameter. This is partly why full-frame lenses are larger and more expensive, they need more glass to project a larger image. This will be important later.

A tilt-shift lets you do 2 things:

Tilting the lens allows you to move the plane of focus. Normally focus is a flat plane (welll... often it's slightly curved, but I digress..) that is roughly parallel to the sensor in the camera. With a normal lens, you can expand the depth of that plane by stopping down the aperture, but that's is about it. There is a limit to how much you can stop down and it becomes difficult or impossible to have 2 objects at different distances from the camera in focus, especially if you want other things out of focus. Tilting the lens allows you to use a principle referred to as Scheimpflüg to tilt the plane of focus... this can be used to make the plane of focus in line with the ground which can make an entire long street be completely in focus or it can be used to make 2 objects that are not in line with each other to be in focus while a 3rd is out of focus.

Shifting lets you shift the lens so that a different area of view is projected onto the sensor. This is often used to correct for perspective distortion. Imagine you have a tall building in front of you, if you photograph just the entrance of the building point the camera straight forward (not up) the sides of the building would appear perfectly parallel, however if you pointed your camera up to get the top of the building, the sides of the building would lean inward: / \ and make converging lines. A tilt shift lens would let you point your camera straight forward at the entrance and then tilt the lens up, meaning allowing the sensor to see the top of the building but the sides would still be parallel.

These techniques can only work if the lens projects a much larger image circle...55 to 75mm. This means the lens must have a much larger higher quality optic. The mechanics that allow the movement also add to the size and cost.

Finally there are a lot of downsides to a tilt-shift lens. They generally are not autofocus and they often are a bit complex for people who are not familiar with them... these combined with the higher cost to make means fewer people are going to want to buy them, so Nikon or Canon won't make money if they did not make a decent profit on each lens they sold. Fortunately there are people who need them so they will pay an arm and a leg for one.

As far as perspective control, you can simulate that to a decent extent in software lens correction tools. The focus effects are not as easily reproduced.

In the past 5 years there have been a trend of "miniature" looking photographs using tilt-shift lenses with the camera pointed up slightly and shifted down, with a little bit of a tilt to narrow the plane of focus to make it look like you're viewing a tiny set of toys from above (a couple people made some very popular time-lapse videos using this technique). This has brought a little more attention to tilt-shift lenses, but traditionally the main people who uses them are often landscape or architectural photographers who are used to used large format cameras that have an even wider range of movements, but want something that is smaller/lighter/more portable.

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\~K

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