Teleconverters and lens tilt
Lens tilt and extenders/teleconverters
How extenders affect lens tilt
This article follows on from Keith’s look at using teleconverters and extenders on shift lenses.
It’s one of our many articles about the use and capabilities of lenses that offer tilt/shift movements.
If you’re new to tilt/shift lenses then there is a more general introduction in the article What do tilt and shift lenses do?
Teleconverters, such as the Canon Extender 1.4x III used here are commonly used to give a longer reach for telephoto lenses, and typically include their magnification factor in the neame. Thus, the Extender 1.4x III gives an effective 1.4 times multiplier to a lens focal length, so a 200mm lens gets the field of view of a 280mm lens.
However this magnification comes at a cost, in that the maximum aperture of the lens is reduced. For a 1.4x extender, this is one stop, so my EF70-200mm F2.8L IS lens becomes equivalent to a 98-280mm F4 lens. For a 2x extender it’s 2x the original focal length and two stops reduction in aperture. There is also a drop in image quality, due to the extra glass in the extender and magnification, but with the latest versions of extenders, this can be quite small.
Although not formally supported, the Canon extenders work with Canon TS-E lenses, and as I’ve shown in the shift article, the magnification affects both the effective focal length and shift. So, for the 1.4x a TS-E24mm with ±12mm of shift becomes equivalent to a ~34mm shift lens with ~17mm of shift. This it turns out is quite useful, since the next TS-E lens in focal length is the 1991 vintage TS-E 45mm or the more recent TS-E 50mm
So, an extended 24mm lens works as a 34mm lens for shift, but does it work as a 24mm or 34mm for setting tilt?
What about tilt?
When using lens tilt to place the plane of focus at an angle, one simple way of setting tilt requires just one measured distance (‘J’) and the focal length of the lens. As I’ll show in some examples running the plane of focus along the top of my desk, this distance is just the height of the lens from the desktop. [Click on images to enlarge]
This method works really well at larger scales. For example with the level camera on a tripod I might want to use tilt to run the plane of focus along the ground, or a wall, or a ceiling. All I need is the distance, the focal length and a table of tilt settings. This is described in a lot more detail in my article about Focusing the tilted lens.
At closer working distances it can be difficult to set the tilt precisely this way, so I use an iterative method of focus for tilted lenses. The measured distance is still good for estimating whether your lens has enough physical tilt and setting an initial tilt estimate for the iterative method.
Tilt on my desktop
First a quick example of how tilting the lens changes the plane of focus. I’m using the TS-E24mm F3.5L II on my EOS 5Ds, which is connected via USB to the Mac Pro under the desk.
Note I’m using the term tilt, along with a direction, to describe any ‘bending’ movement of the lens. Left/right tilt as in this first example is sometimes known as swing, with tilt sometimes just referring to up/down tilting movements.
Three shots show the lens focused at its closest, a bit farther and then a bit farther still.
Exactly as you’d expect when focusing a normal lens. The shots are at f/3.5 so as to show where the focus plane is.
All fine, but let’s tilt the lens to the left.
The plane of focus runs diagonally, near left to far right.
One thing that I’ve found can confuse some photographers starting out using tilt, is that the result depends on the combination of tilt and focus settings, whereas with shift you can set focus normally and then add shift.
Setting the lens focus to the infinity setting, now runs the plane along the edge of the desk.
Tilting the lens to the right lets me run the plane of focus from near right to far left.
As before, changing the focus setting changes how much the plane is tilted – the distance settings on the lens only refer to focusing the lens with no tilt.
Near, with an extender
I’ll start with looking at how the extender affects close focus.
This is how close you can focus with the TS-E24
The lens shows a bit of barrel distortion at its close focus point, then again, I didn’t buy it for macro use.
Adding the extender gives the narrower field of view I’d expect.
Two overhead shots show how the closest focus at full tilt varies with the extender
The views from the camera once again reflect the reduced field of view.
Marking some lines on the paper show that both planes of focus are tilted at about the same angle, but the extender has moved the plane further away from the camera (which was in the same position).
This suggests that the extender is just expanding the tilted image from the lens onto the sensor. So whilst we may think of an effective increase of focal length to ~34mm for the field of view, for the purposes of setting lens tilt you would use the original (24mm) focal length of the lens.
Using a TS-E90mm
The test was repeated with the TS-E90mm F2.8 at full tilt and closest focus distance.
As you can see, the plane of focus is moved by a similar amount with the extender. The field of view is reduced to that of the equivalent longer focal length.
Although the results show the plane of focus tilted by about the same amount, I decided to check with the camera at a constant height above the desk and the lens tilted downwards to run the plane along the desktop.
The flat plane of focus
Mounting the camera (with its Rogeti L bracket) directly onto a tripod arm lets me level the camera and position it a certain height off the desk. The lens is the TS-E17mm F4L. [Click to see larger images]
The monitor behind the pile of assorted lenses is showing a live view feed from the camera, using the free Canon EOS Utility software.
The monitors have a blue cast because they are calibrated to a much higher colour temperature than the halogen lighting I use in the in the office when needing shots like these. The desk lamp has a warm white LED lamp.
The lens is 23cm (9″) from the desk
Here are the resulting photos, along with 100% zooms. They have had slight sharpening using Topaz Sharpen AI, my current go-to for sharpening of tilted/shifted images.
Moving to f/8 gives much better image quality than f/4, and thickens the depth of field of the plane of focus (a wedge, thinner nearer to the camera).
A look at the lens settings shows that only a slight adjustment in the focus setting was needed when adding the extender. The amount of tilt was the same for each shot.
The initial setup (no extender) was set up using the iterative focus technique, requiring slightly more physical lens tilt than initially suggested using just the height of the lens above the desk. This is why I have the two methods – one gets used outdoors and the other more in the studio.
That seems to answer the question I had about extenders and tilt…
Extenders don’t change the focal length for tilt
The extender magnifies the image cast onto the sensor by the lens. This magnification gives a reduced field of view that is equivalent to a longer focal length. The light is more spread out, making it fainter, resulting in the reduced aperture. It also magnifies some lens aberrations by making them bigger on the sensor.
The tilted part of the lens is in front of the extender, so it’s no surprise that the movement of the plane of focus is just given by the lens tilt and focus settings for the lens focal length.
Just one more thing…
What about tilt -after- the extender, such as here with this Mamiya Teleconverter?
The Mamiya Sekor 80mm F2.8 medium format lens and 2x teleconverter is fitted onto the Fotodiox TLT-ROKR tilt/shift M645->RF adapter I recently tested.
Here the lens/TC combination can be thought of as 160mm f/5.6 lens with 10 degrees of tilt and ±15mm of shift. Without the teleconverter it’s an 80mm f/2.8 with 10 degrees of tilt and ±15mm of shift.
The one setup I’ve not tested outdoors yet is the Mamiya 210mm f/4 with the 2x TC, giving me a 420mm f/8 tilt/shift lens with 10º of tilt…
There are lots more articles/reviews about using tilt and shift on this site, see them all by looking at the Tilt/Shift category for articles.
Questions? Email me or use the comments below?
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