Wide Angle Distortion

Morning all,

Just after a bit of advice please

I have a Canon 16-35mm f/4L which I love to use but on occassions, I get a lot of distortion in the images and i'm wondering why.

I just assume that what I see is what i'm going to get, but apparently not.

First image is the one from the camera, just edited to black and white etc but no adjustment to the distortion, the second is more or less how it looked when I was in the field taking the images (had to amend this in lightroom to get it straight).

IMAGE LINK: https://flic.kr/p/27R5​gaf

IMAGE LINK: https://flic.kr/p/2awA​ojN

In this case the distortion is, in the main, due to the sensor. What you are seeing is called keystoning; where lines that should be parallel instead converge. The wide angle lens isn't exactly causing it but it is contributing because, as you get closer to the building you have a tendency to start tilting the camera upwards (in order to keep the top of the building in frame). This results in the sensor not being perpendicular to the uprights.

Solutions
The only way to prevent this is to ensure that the sensor remains perpendicular to the uprights but this may mean that the top of the building is cut off and that there is too much empty space at the bottom of the frame. This means you have to shoot from further away (so you get the whole building in frame) and then crop off the excess empty space at the bottom of the frame. Alternatively use a tilt-shift lens or do what you did with this shot - fix in post.

^^^ yup

It has nothing to do with the lens, but the angle of the camera/sensor to the subject. Your brain "corrects" this when in a 3D world but not on a 2D screen.

Yes either get a 17mm TS or allow a bit of room around the edges, and compensate in post. You actually get keystoning in every image you take where the back of the camera isn't vertical. It's just that it is often not nearly so pronounced. At least it is a lot easier to fix today with often a single click of the "auto" button in Lr. I remember that in the darkroom you needed to tilt the masking frame in the opposite direction, and hope you could stop down enough on the enlarger to build a little depth of field to cover that tilt.

Alan

Thanks very much everyone, for your replies.

Makes sense now you've pointed it out to me.

I'll have move back a little more when taking the shots. I'll just need to make sure I use a tripod and keep things steady to keep the details being further away.

The one I did correct just had enough space either side to be able to correct and crop so I think I got lucky there as I don't want to be going back to a 'private no trespassing' field again full of cattle