Setting the tilt axis for tilt-shift lenses
Setting arbitrary tilt for tilted lenses
Finding the tilt axis to match your subject
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Tilt-shift lenses can be rotated on their mounts so as to tilt the lens up or down or side to side.
This limits the tilted plane of focus to vertical or horizontal.
The lenses can usually be set to tilt the plane of focus at any arbitrary angle, but there is no simple way to know if this will match up to your desired plane of focus for a particular subject.
Looking at photographing a flat object, leaning at an angle, Keith Cooper explores ways of ensuring optimum focus for all of your subject.
This is quite a specific article for a particular use of a tilt-shift lens and assumes you are familiar with their basic functions.
The plane of focus
One of the key reasons to use lens tilt is that the plane of focus, in front of your camera, can be moved away from its normal position square on to your camera.
This overhead view of a test setup from my review of the Canon TS-E17 lens shows how the plane of focus tilts and moves as you add tilt to a lens.
The position of the tilted plane is set by a combination of lens focus and tilt, so that focusing a tilted lens is not as straightforward as normal. Adjusting just the focus, in the example above, alters the angle of the tilted plane as well as where it runs.
For outdoor use I have a simple set of tilt tables that allow me to quickly run the plane of focus along the ground or along a wall, from knowing just a single distance measurement. I’ve covered this in my detailed introduction to focusing a tilted lens article.
The technique outlined there becomes a little more cumbersome if you try and use it for close-up work, such as product photography. In those cases I use an iterative focus technique for tilted lenses, which works very well if you’ve good live-view, or the camera working tethered to a computer.
In the example I’m going to show here, I use the iterative technique, after I’ve set the focus plane tilt axis.
The plane of focus problem
I’m going to use an old Mac graphics card as an example.
I’ve set it up on a small product photo table, that I keep for photos of small stuff and some of our macro work.
It’s propped up with a paper roll – normally I go to some trouble to hide such supports, but it’s not important in this example. [click to enlarge]
A photo taken using my TS-E90mm F2.8 at f/2.8 shows how only a thin strip of the board passes through the plane of focus and is sharp.
The photo’s taken from my 5Ds, on a studio stand, with the camera tethered to my nearby Mac.
What I need to do is tilt the lens so as to run the plane of focus along the plane of the card.
The problem is that the plane is leaning at an angle, so neither up/down or side to side tilt will run it along the card.
This is where I need to know what angle to set the lens tilt axis to, in order to match the plane of focus to the card.
Initially I have no need to know how much tilt to use, just the angle to rotate the lens.
The focus target
I have a very fine resolution print that I use for focus adjustment. It’s a simple 8×10 print of this pattern, glued to a flat piece of card.
If you want to print one – click on this image to see the full size version, and save it.
The print pattern is fine enough that it will show up distinct moire fringing when sharply in focus.
The card is placed in front of the camera, occupying the same plane that I want for my eventual plane of focus.
Not the bit of blu-tac stopping the card from sliding – this sticky stuff is an integral part of many small product photo setups.
I’ve the 5Ds connected to my computer, and am using Kuuvik capture to control it. You could use any tethering live-view software, but Kuuvik has a few features that make it easier to set tilt (and show it here).
Here’s the live view screen with the lens focused as it was for the shot earlier (no tilt or shift set).
I’ve turned on focus peaking (the red bits) showing where the image is sharp.
Here’s the live view of the focus card in the same place. I’ve not turned on the peaking, but if you look carefully (click to enlarge) you can see some colour fringing in a band running across the card.
Taking a photo and bumping up the saturation for the image makes it very obvious.
It isn’t the position of this band that’s important, but the angle at which it tilts.
This angle is how much we need to rotate the tilt axis of the lens.
Another example shows using an iPad asr the focal plane target to create the band. This is from my TS-E135mm F4L Macro review.
Setting the lens tilt axis
You use the angle of the coloured line to set the tilt axis of the lens. Just remember that facing the camera, the angle is reversed. Here’s the lens set up for this shot.
Now, I’ve set the tilt axis, I need to decide how much lens tilt and the focus setting required for running the plane of focus along that card.
If it’s not clear, here’s a side view showing how the lens tilt axis was rotated.
I just do the rotation by eye, looking at the coloured band on my screen. It’s not a precision angular setting and setting like this is likely accurate to a few degrees.
Setting lens tilt and focus
One of the Kuuivk features that helps me in setting tilt/focus is the split screen. In this screen shot I’ve picked 100% views at the furthest and nearest points of the focus target.
I’ve focused at the far point, and you can see that the near point is very out of focus. This is at f/2.8 without any tilt.
The tilt/focus technique I use is fully described in my iterative focus technique for tilted lenses article.
The essential element involves starting at an estimated tilt, checking near/far focus and making an adjustment
The process for focusing is:
- Pick an arbitrary value for tilt
- Focus on the far point
- Look at the near point (zoom to 100% to see clearly, if using liveview)
- Decrease the lens focus distance slightly and look what happens to the near point
- If the near point becomes sharper, then you need more tilt (select a higher value for tilt and go to step 2)
- If the near point becomes softer, then you need less tilt (select a lower value for tilt and go to step 2)
- Both sharp? – you’re done.
- If the change in focus of the near point is difficult to see, then try the alternative at step 9
- Focus on the near point
- Look at the far point
- Increase the focus distance slightly and look what happens to the far point
- If the far point becomes sharper, you need more tilt (select a higher value for tilt and go to step 9)
- If the focus point becomes softer, you need less tilt (select a lower value for tilt and go to step 9)
Within a few iterations of this process (starting with the near point or the far point), you should end up with a combination of focus and tilt that has both near and far points at optimal sharpness.
If you find the lens doesn’t tilt enough then you need to move a bit further back, since maximum tilt of the plane of focus is given by focus distance and tilt.
After a few steps I’ve both focus and tilt set, and the live-view shot with focus peaking is looking very different.
Here’s a photo, taken at f/2.8 [click to enlarge images]
If I now put the graphics card back in position, the focus peaking screen shot shows our new plane of focus.
I’ve left the focus card in the background to show how the plane carries on to the rear.
Two photos taken at f/4 and f/8 remind me that the plane of focus has a thickness that depends on aperture. [Click images to enlarge]
It’s thinner near to the camera and should be thought of as a wedge of focus. This means that at wider apertures it may not be deep enough to get parts of your subject in focus.
The end plate is more in focus when I move to f/8 (view is cropped from the full shot)
Using different TS-E lenses
One problem I didn’t mention earlier is that when applying the iterative focus technique you may find you’ve run out of tilt. If this happens then you need to go back and change your setup, so that the subject is not tilted away from you by so much, or you could just move backwards a foot or two.
The new TS-E lenses (50/90/135) have an increased tilt range and much better performance at wider apertures. They also have smaller minimum apertures, which may be of use as well (see my reviews for more about this).
Tilt and shift
I hope this somewhat detailed note has been of use for potential users of tilt/shift lenses.
If it’s whetted your appetite then I’ve a lot more tilt/shift articles and reviews that cover the many fascinating benefits of using my favourite lenses…
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