Sunday, October 17, 2010

Panoramic tripod head

Parallax errors are the enemy of seamless panoramic images and must be avoided.

A parallax error is a situation where you take a picture of, say, 2 trees from a point of view that the rear one is hidden by the front one. If you are taking a panoramic image then 2 of the images that comprise it will probably include those 2 trees. It’s likely that the view of them will be different in picture 1 than it will be in picture 2 as the view point changes slightly when the camera is rotated to take in the whole view.

There is a way to counter this, and whilst I don’t fully understand it, there are plenty of smart folks on the internet that do. Many of them have published guides on how to make your own apparatus that attaches to your tripod and takes this issue away. The principle is simple, just make sure the camera is rotated around a specific point known as the ‘entrance pupil’ of the lens, rather than the tripod mounting hole as it normally would when installed on a tripod.

This entrance pupil is usually a few mm or cm from the very front of the lens barrel. This is different on all lenses and bodies, but there are databases that can help work out where yours is such as this one. For my lens/camera, the correct point was 101mm from the centre of the tripod mounting hole.

The pano head can be any shape you like, but it’s worth creating it to hold the camera in the portrait rotation to take in as much as it can up and down. Left and right is taken care of by rotating the camera. The only important points are that the rotation point for left and right is exactly inline with the centre of the lens, and that the arm that holds the camera back be exactly 101mm (in this case)

The first prototype head I made as of chipboard and it was not good; It was wobbly as it fit into the tripod quick release, or not. And the angles were not square. It was also too big to be practical so I have made a new one out of 90 degree aluminium.

Once again, Doug’s tools saved me and I was able to make a reasonably neat job:



This is the head mounted to the tripod. The normal tripod head has to be removed to expose the central screw.









Camera mounted to the thing.







One the pictures are shot, you can use software to put them together. It’s meant as a way of capturing outdoor scenes, but a good test is inside as parallax errors are more likely the closer the subject is to the camera.

I did a test of the inside of the ice cream shop. There are a couple of holes because I didn’t shoot as much of the ceiling as I should have, but you get the idea:


Now I need to go try it somewhere pretty!

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