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Using a shift lens – why not just fix verticals in software

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Using a shift lens – why not just fix in software?

Some of the issues if you correct image geometry such as converging verticals in software


Keith regularly uses Canon’s TS-E 24mm and 17mm tilt/shift lenses as an important part of our architectural and interior photography services (Ely Cathedral right – 17mm shift lens)

At the time of writing, Keith had a Samyang 24mm T/S lens for a review. We’re often asked though, why bother with an expensive manual focus tilt/shift lens when you can fix everything in Photoshop?

This short article shows some of the issues faced if you don’t have a lens that shifts…

If you are completely new to tilt/shift lenses you might first want to read the article about using tilt/shift lenses that Keith wrote after getting the original Mk1 version of the Canon 24mm lens.

Interior of Ely cathedral

Problems with verticals

When you look upwards at a building it doesn’t appear to be falling over backwards. Our visual system and perception handles the shift of viewpoint of the head pretty well.

This view of our house is taken using a 24mm lens on a ‘full frame’ body, my Canon 1Ds Mk3.
square on shot, shows no converging verticals

The camera is level, so vertical lines are parallel.

However, when you take photos looking upwards, many of the perceptual cues are missing. If you add to this the fact that viewing angles for prints and screens rarely match up with the field of view of the camera/lens you used, then we perceive a distinct distortion.

Here’s the same view, but looking upwards to show more of the building.

I’ve opened the image in DxO’s Viewpoint plugin, which (amongst other things) allows me to correct for the converging verticals

correcting verticals

No problem – a few clicks and my house is no longer falling over…

Move your mouse over the image below to see the ‘fixed’ version.

However, from my own point of view, where I produce photos for paying clients, I’ve found that not many really want trapezoidal shaped images, so I have to crop.
cropped image after corrections

As you can see, I’ve lost some of the edges of the full image. With a tall thin shot like that, it’s perhaps not such an issue.

Using shift

The 24mm lens I used for the shot above, was the Samyang (aka Rokinon) EF mount 24mm F3.5 ED AS UMC tilt/shift lens. Which BTW is also available in Nikon, Sony and Pentax mounts.

Keeping the camera level and shifting the lens upwards produces an image without convergence (all the shots here are hand held, just for my convenience in the street. This is one time I’d usually use a tripod)

Here’s the image from a shifted lens.
photo taken with 24mm shift lens
One immediate advantage of this approach is that I don’t lose any of the image from cropping. I also get to compose just the view I want, since the required crop from a software ‘fix’ is almost impossible to predict at the time.

At 24mm, the loss from cropping is modest. If I didn’t need the full camera resolution, then why not just use a wider lens?

This is indeed a reasonable approach if you are not supplying high resolution images professionally for the likes of brochures and magazines.

However, as you go wider, the effects of convergence get more noticeable…

17mm

With a wider lens, I’m moving closer to the house, since one of the reasons I typically use a wider lens is that I can’t move back far enough. The shots in this article are intended to be similar to what I’d actually use the lens for, rather than a direct comparison of fields of view.

Here’s a view taken with a 17mm lens – move your mouse over the image to see a version corrected in Viewpoint

Compare that with a shifted version (the lens was the Canon TS-E17mm f/4L )

shifted image - tse17
Quite a difference if composition was critical. Note how the shot looks similar to the shifted 24mm one – I’m closer, so the perspective is exagerated. The point is that with the shift lens I’ve been able to compose the image close to the frame edge.

14mm

What about going wider still?

At 14mm (Canon EF14mm 2.8L Mk2), this is the view.

How much do you think will be lost upon correction and cropping?
wide angle view with 14mm lens

Move your mouse over the corrected image below to see the crop.

Conclusions

There are two main reasons I like using shift lenses.

The main one is predictability – what I see in the viewfinder is the image I’m going to end up with. If I want to crop then at least I have a choice. If I’ve waited for the weather and travelled several hundred miles for a job, then this is even more important…

The second is that I’m making use of the whole sensor, important if the image is for a large print or magazine. I’m looking for as much detail as possible, without having to go for multi-shot solutions.

Unfortunately such lenses are not cheap. Even the Samyang 24mm is going to set you back £800-£900 and the Canon 17mm ~£1900 and 24mm ~£1700. My excuse is that I do this sort of stuff for a living ;-)

Tools such as Viewpoint (or even the correction available in Lightroom/Photoshop) make it relatively easy to ‘fix’ perspective, and, with care, produce results good enough for many uses, just watch out for that unpredictable crop…

Other features

If you keep the camera fixed, and shift the lens up and down (or side to side) for two shots, you will get two images that stitch together very well, giving an even higher resolution image at a wider angle (across the diagonal of the resultant image)

Take for example this view inside the church at Staunton Harold, taken (hand held) with the Samyang 24mm

Interior of Staunton Harold church - two stitched images taken with shift lens

Hand-held shift lenses – surely not! A minor heresy…
I’m of the belief that with practice, it’s actually quite straighforward to use shift lenses hand-held. I rarely have a tripod with me if I’m not on a paid job, but regard the 17mm and 24mm Canon lenses as two of my favourites to have in the bag when out and about. I too read all that stuff about how vital tripods are for landscape work – nope, never really believed it. Useful in low light or at night, but otherwise I don’t bother, unless I’m ‘working’ ;-)

I even have a special tripod mounting bracket for my Canon lenses, for just this shift and stitch type of shot (with a tripod).

Note that I’ve not mentioned the use of tilt with these lenses.

In general I use it quite rarely, mainly to place the plain of sharp focus along a wall, ceiling or the floor in tight confines, where I can’t get far enough back to get a square on view.

I’ve written up some details about tilt in the original tilt/shift article, and special one describing how to focus a tilted lens.

If I’ve piqued your interest, then there are lots of other articles on this site about related issues…

More Information

Keith also provides bespoke personal photography tuition to private individuals in the Leicester area (UK) – this is in addition to Northlight’s corporate training services, and is aimed at at photographers looking to learn more about particular aspects of photography, such as architecture and landscape. It includes using various tilt/shift lenses, which are available (with a FF DSLR) to use during sessions.

Other areas of our site that may be of interest...

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Categories include Colour management and Keith's camera hacks - there are over 800 articles/reviews here...

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