Panoramas (1): shooting

OK, it is time to move on to another subject. I think this one will take a good 3 entries and I am looking forward to covering it.

Panoramas are nice. Indeed they very much fit into our “natural vision” by embracing a wide view. So many times, a mountain chain, the see or a cityline is much wider than high: it is time for a panorama. Of course, you could simply use an wide-angle and crop, but sometimes no wide angle is wide enough; plus you end up with a relatively low definition picture (because of the crop). The other way, which we will talk about here, is to join (stitch) several pictures together.

How to shoot for panoramas?

In the same way that no amount of post-processing will turn a bad snapshot into a masterpiece, you can’t just expect “garbage-in, panorama masterpiece-out” from whatever panorama tool you use. So when you are shooting with panorama in mind, there are several points you need to take care of in order to be able to fit your pictures in a panorama later.

Axis of rotation

Theoretically, in order to have perfectly fitting photos, you should rotate the camera around the lense’s “entrance pupil”(wiki) which is situated somewhere between the sensor-plan and the end of the lens. The problem is that this entrance pupil changes with each focal length and focus position… so basically all the time 😦

And if you don’t respect it, the perspective between the close and remote subjects will change from one picture to the other (parallax), so you won’t be able to fit your pictures to make a panorama.

Now instinctively, we rotate around the axis of our head, not the lense’s entrance pupil. That is fairly standard for a human being standing on its feet, as illustrated by this highly technical “view from above of a photographer shooting a panorama the wrong way” (patent pending):

The perfect world solution would be to have a tripod with a sliding tray on it, so you can spend time finding your entrance pupil before you shoot your pictures. If you’re like me, you don’t bring along a tripod on your everyday shooting and probably don’t have the patience to fiddle around with a sliding tray. Since we don’t live in a perfect world, here is trick that (even if not perfect) gives good enough results in most case: rotate the camera on the axis of your (left) hand that supports it, while you (the photographer) somehow contortionates around it. Another (patent pending) view-from-above:

Even if this only approximates the correct rotation axis, it is good enough in most case because panoramas usually are only remote subjects (a mountain chain far away, a cityline) so the problem of parallax is not too crucial.

But if you have a subject that spreads from your feet to the horizon, then a tripod and sliding tray are your friends. Check this for a user-friendly method to determine the entrance pupil of a DSLR camera – at that stage, you probably want to write a table with focal length / entrance pupil pairs (assuming the focus is on infinity).

Keeping the same exposure and white balance settings

The second thing is that we need to have the camera delivering pictures that are as close as possible to each others in color and intensity.

So you need to keep the same exposure between the panorama pictures: switch your camera to M (Manual) and chose a pair diaphragm / exposure time that gives acceptable results on the whole panorama. It is not always easy since the variations can be very important from one side of the panorama to the other and digital photography doesn’t cope well with over-exposition. So generally, a variation from under-exposition to a tad of over-exposition is your best pick (something like -0.7 to +0.3) with a “white spot” (like the sun or a white cloud) if unavoidable. So chose the best diaphragm / exposure time couple for your panorama and make sure you shoot all your pictures with the same settings.

The same applies for color balance (if you shoot in JPEG): you don’t want your camera’s automatic settings to change in the middle of your series and end up with color variation within your panorama. So pick the manual white balance that is most appropriate (sunny or shade for landscape) and keep it while shooting all your panorama pictures. Or shoot in RAW…

Make sure you have plenty of overlap

Obviously, if you have a hole between two pictures, your panorama is ruined. But if you have too little overlap, you may not be able to properly stitch your pictures. I would say you need 25% to 30% of overlap on each side of your picture – and yes, that leaves only 40% to 50% “uniqueness” for each picture. At the digital age, however, each click doesn’t rime with “processing cost” anymore, so don’t hesitate to have large overlaps.

The right foundation

With that, you put yourself in the best possible position to create your panorama. So you have “technically good pictures-in” and can expect “technically good panorama-out”. The masterpiece bit, however, depends on the artistic skills of the guy who holds the camera 🙂