Sometimes even the widest wide angle lens is not enough. In those cases you have to shoot multiple images and stitch it together into one extreme wide angle shot. You can go as far as 360° around, if you want. But you have to avoid parallax errors.
Shooting wide angle is fun. Almost every smartphone has the ability to make panoramic shots. But have you seen the stitch errors, often visible at the bottom of the image when there is something close to the camera? Those errors are caused by parallax errors. These errors also occur if normal cameras are used for panoramas.
Everyone has experienced parallax at some time. Even those people who don’t take any pictures. Just look at something close by and hold your hand against one eye. Watch how the orientation against the background changes if you hold your hand against the other eye. Suddenly the object has moved a bit against the background. The closer the object is, the more extreme the change will be. If the object is far away, closer to the background, the effect won’t be that obvious, or even invisible at some point.
This is similar to what happens with panorama photography. If you use your smartphone or camera to make a panorama with everything in the distance, there will be no stitching errors. There is no parallax error visible. This is one solution to avoid parallax; just make sure you don’t have any objects that are significant closer compared to the background.
The other solution makes use of the entrance pupil of the lens, and how the light rays find their way through the lens. By choosing the rotation axis at the right location, parallax will be eliminated. This point is known as the entrance pupil, but we commonly use the term nodal point or no-parallax point.
The Parallax Error
When the relative position of a subject changes while rotating a camera, it is called parallax error. This can be best explained with some examples. I have placed a camera on a tripod, just like we always do. The tripod is underneath the camera, with the lens sticking out. The rotation point when shooting panoramas will be approximately at the sensor location. This can be seen with the animation I made.
I have placed two objects in line with the lens, and took a three shots with different angles, as seen in the animation. As you can see in the example, the two objects are aligned in the shot straight ahead, but not when the camera is rotated.
If you would try to align these three images, there would be a stitch error. The objects are not at the same place relative to each other, between each shot. This is a parallax error.
How to Avoid Parallax Error
The parallax error has occurred because the rotation point is at the sensor location of the camera. The effect is the same as the experiment when holding your hand against each eye. The solution for this, is to rotate the camera at the entrance pupil location, or nodal point in common tongue. I will use the term nodal point from now on.
By rotating the camera this way, we avoid the parallax. I have done the experiment with the camera on the tripod again, but now the camera is rotating over the nodal point. This way we don’t change the lens position, and thus changing the orientation of the lens relative to the subject, but we rotate the sensor itself.
As you can see, the foreground and background have the same location relative to each other. There is no parallax error. Stitching software will have a much easier job, and stitching errors will be less likely to occur.
What Do You Need for Parallax Error Free Panoramas?
You already can guess by looking at the images. You need a way to change the position of the camera on the tripod. For this you need to buy a nodal slide. Or you can build your own, of course. It is a very simple and lightweight piece of metal, that can easily find a place in your camera bag. You only need to know where the nodal point of your lens is located.
You can search the internet to find out the exact position of the nodal point of your lens, or you can find out yourself by doing the same experiment as I did. Just change the offset of your camera on the tripod, and find the distance where two objects stay in line. Write the numbers down, and put the note in your bag. I made one myself, with every bit of information I need when I am going to shoot panoramas.
One Step Further
A nodal slide is perfect for horizontal panoramas up to full circle. But what if you want to shoot in multiple rows? The parallax error not only occurs with horizontal panoramas, but also when changing the vertical angle.
If you want to shoot multiple row panoramas, or even 360°/180° panoramas, you will also need a nodal slide for the vertical rotation. I once bought the Really Right Stuff, the PG-01 Compact Pano-Gimbal Head, which allows me to avoid parallax errors with vertical and horizontal rotation. It can be quite a challenge to set up the system, but it makes stitching a lot easier. Now I can also make vertical panoramas without the risk of parallax errors.
How About You?
Do you have a nodal slide for panoramic shots, or do you avoid close objects? I would love to see your setup for shooting panoramas, so feel free to share an image of your setup and tell me about the good things, and if present, also the downsides. I'm looking forward to your comments.