Fixing converging verticals without a shift lens
Fix converging verticals without a shift lens
Eliminating leaning verticals
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The classic way of dealing with converging vertical lines is to take your photo with a shift lens, but if you don’t have one with you, what can be done and what things do you need to consider.
A simple editing fix may be all you need, especially if the image is just for web use.
Buildings falling over
With a level camera, the sides of a building will be straight, point the camera upwards and vertical lines converge.
Here’s a shot taken with a 24-70mm zoom lens on a (35mm) full frame camera (Canon 5Ds) looking slightly upwards.
[click on images to enlarge]
You could use a much wider angle lens, keeping the camera level and just crop out what you don’t need.
Using the Canon EF11-24mm F4L and cropping gives me a square shot – fine if I wanted a square shot and the camera had enough resolution for what I needed.
My own solution to the problem is to use a lens with shift, such as the TS-E24mm F3.5L II, which was used from the same location as the first photo.
The camera is level, whilst the lens is shifted upwards. I’ve a lot more about using lens shift and what it does in another detailed article.
I’ve seen it suggested that a simple perspective stretch in Photoshop can fix things.
This would be: Select All | Edit > Transform > Perspective.
The top of the image is stretched to align the vertical lines (a grid can help)
The problem here is that the image gets vertically compressed.
There is a lens correction tool in Photoshop that compresses the bottom of the image and vertically/horizontally stretches the top. This alleviates some of the crushed look that a simple perspective stretch can produce.
The amount of correction needed for this image is relatively small. With a lens much wider than the 27mm, the amount of image lost to cropping is significant.
One other way of using the original perspective transform is to shrink the bottom of the image, whilst making the top wider. A point part way from the bottom of the frame (corresponding to the sight line/height of the level camera) is neither stretched nor squeezed.
This gives a more pleasing correction.
I’ve left in the chopped-off corners to show where you’d either need to do a bit of ‘fill work’ or crop.
Where I need to correct image geometry, my normal choice is to use DxO Viewpoint. This offers very precise adjustment of verticals (and/or horizontals if needed) and can correct for minor camera levelling issues. I quite often shoot hand held, so it’s excellent for slight ‘fixes’. I’ve a full review of DxO Viewpoint if you’re curious. [DxO shop]
You don’t have to crop the image, but as yet, few clients have expressed much interest in trapezoidal photos.
As I mentioned, wider lenses need a lot more cropping – here’s a shot at 14mm just to show the effect.
If you look at the one below, you can see how my name was stretched in the process.
I use the Canon TS-E17mm quite a lot for my work [See my TS-E17 review] Using just a normal wide angle lens, I’d need to shoot wider and not have a good feel for the final composition of the image if I was correcting in software.
It’s knowing what the final image will contain that is a powerful reason for ny using shift. Add to that a stack of unpaid editing work that would be needed and commercially it makes sense.
However, such lenses are not cheap and knowing how to fix things in software is useful for when you want true verticals.
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