Shooting the pictures

How many pictures?

Each picture should overlap with the next by up to 50% (or at least somewhere between 30 and 50%). But please note that providing you overlap each picture with the next, it doesn't matter exactly how much overlap you use, and the amount of overlap can be different between each pair of pictures. So, you can just guess 50% overlap and that will be fine. If you think you will need 10 pictures but you take 9 or 11, it doesn't matter!

But if you want to work out how many pictures you need to take you can do so as follows: The first thing to do is to work out the horizontal field-of-view of your images, which depends on the orientation of the camera (whether you took your pictures portrait or landscape). If you are using a 35mm camera:

  • portrait HFOV = 2 * tan-1(12 / focal_length)
  • landscape HFOV = 2 * tan-1(18 / focal_length)
  • number of images to take = 36000 / ( 50 * HFOV )

This assumes a 50% overlap and 360 degree panorama. I use a 50% overlap for my images and for wide angle lenses this is probably advisable, especially if you are not using a pano-head (I am but so what?). For narrower lenses a 40% or less overlap may be sufficient. To generalise the equation, let's make 'P' the desired percentage overlap and 'A' the angle of view of the panorama. Putting everything together:

  • number of images to take = 100 * A / ( (100 - P) * HFOV )

Note: more overlap means it is easier to blend lighting/colour differences (if you make a mistake with exposure/colour temperature or the light changes anyway). A larger overlap also makes it generally easier to edit out moving subjects (vehicles, people, etc).

Depth of field

Generally panoramic pictures capture a scene rather than a moment. In other words most panoramic pictures are of places rather than of people or events as such, therefore you will probably want to aim for a crisp picture that captures the entire scene through to the horizon. To do this you want to set a very large depth of field so that everything in shot is in crisp focus, by focusing on the hyperfocal distance.

When determining the depth of field you need, remember that when shooting indoors you do not need to focus further than the walls of the room and therefore you are likely to be able to widen the aperture and consequently reduce the exposure time.

Avoid altering the depth of field because to do this you will need to alter focus, and when you alter focus you subtly change the field of view of your lens. Most software cannot cope with a mixture of lenses being used for a panoramic sequence - they assume the same lens was used throughout, or more specifically that the lens was used with exactly the same settings (including focus).

So in conclusion, you need to:

  • decide whether you want everything in focus (large depth of field)
  • make sure that if you use these settings that they are sufficient for every frame of the sequence. In other words, if one of the pictures features something very close to the camera, which you want in focus, then you should set up a large depth of field for all pictures.

Shooting panoramas hand-held without a tripod

To get good results without using a tripod, make sure you stand in one spot and as you turn to take each picture keep the camera close to your body, i.e. close to the point of rotation. Don't move from the spot you are standing on between shots. Don't learn forwards or backwards between shots, but try to stay still and steady.

What you are trying to do is to emulate the tripod - keep the camera steady and level, and rotate it around a single point. All of these things help you to produce a good set of pictures from which to create a panorama.

White balance (digital cameras only)

Some digital cameras can correct colour casts caused by lighting. (For example both incandescent and fluorescent lighting can cause a yellow cast across your photos.) Be careful when using the 'automatic' white balance setting if your digital camera has one.

The reason for this is that if the scene contains a mixture of lights, your camera may switch white balance setting half way through the shoot and you will then have problems stitching the pictures because the colours will look different. Instead, decide for yourself which is best and manually set the white balance. If you can't decide, shoot the scene several times using different settings for the whole set of images.

Contrast/Brightness: Exposure

That leaves just one thing to play with. Exposure. You might have a scene in which everything is well lit in which case you can probably set an exposure for every frame. However you will quite often come across situations where the lighting changes. Lighting problems can perhaps be generalised as:

  • areas of strong shadow in a scene where there is also strong light
  • light directly at the camera in part of the scene

The first of these is more likely. I find it useful to spin my camera around the scene while holding the shutter button halfway (which on my camera causes it to focus and meter the scene). I can then instantly see whether there is going to be a problem because the camera will show me in the viewfinder the exposure it thinks is appropriate for each image. If the exposure changes dramatically I will have a problem: if I let the camera judge exposure, it will ensure each picture is as good as it can be. But that means any two adjacent images could differ greatly in lighting conditions so that a shadow in one is barely visible in another. That will confuse the stitching application. Exactly this happened with the Finchampstead Ridges Woodland scene. The first 10 pictures from that set are shown below.

No 1 2 3 4 5 6 7 8 9 10

Note the dramatic change in contrast between frame numbers 2 and 3, and the slightly less dramatic change between numbers 4 and 5. Different stitching programs cope with contrast change in different ways: some will offer to automatically adjust colour and contrast between each of the pictures, others use a wide blend area to soften the transition.

I allow the exposure to change by no more than two increments between frames (e.g. if one shot was taken at 1/30sec then the next one should be no less than 1/60sec and no more than 1/15sec). If a scene contains a mixture of brighter areas and darker areas, I will meter correctly for an intermediate position, and then slightly over expose the dark areas (to make them lighter) and slightly under expose the light areas (to make them darker). You can see exactly this in the set of images used for Trinity Hall, shown below.

4
OK
6
under
4
over
4
OK
3
over
2
over
4
under
6
under
4
OK
3
over
3
over
3
over
Small exposure time changes in a pan sequence
aperture: f22; times shown in seconds together with camera metering information

Most cameras will tell you as you take a picture whether they think you are correctly focused and whether they think you are correctly exposing the scene. I have also shown above what the camera metering system made of each shot - whether it thought the shot was under or over exposed. Note that the shots that did not include windows were therefore darker and the camera thought they were under exposed. Those facing windows with light streaming in confused the camera so it throught they were over exposed. Had I gone with full automatic exposure there is a good change the pictures facing windows would become sillouettes.

You can alter the exposure if your camera has manual controls, or allows you to set the exposure manually. If it does not, you might be able to:

  • set the exposure on a mid-lightness frame and use AE-lock to lock the exposure, then all subsequent shots will use these same settings
  • adjust the exposure by under or over-exposing by adding f-stops, normally from -2 to +2 stops

Using flash or additional lighting

If the scene you are shooting is not very well lit, your camera may prompt you to use flash. My advice is that you avoid ever using a flash gun in or attached to you camera or tripod. There are a couple of reasons for this:

  • flash guns have a limited range and a limited field of coverage which is why if you use a wide angle lens the flash is normally disabled. Also in some cameras there is a risk that the built in flash will be partly blocked by the lens itself so you would end up with the shadow of the lens in the picture!
  • flash gives strong shadows, which then won't line up when you stitch images together because the light (from the flash) is moving as you rotate the camera

I recommend you either:

  • Use a large reflector and point the flash gun at the reflector - this will give more diffuse light and more even lighting
  • Alternatively, if you are shooting in a room with pale walls, use a wall as a reflector/diffuser, by pointing the flash at the wall behind you (but beware that you might end up with a faint shadow of the camera/tripod if you use a wide angle lens)
  • If you are shooting indoors, turn on all the lights to enhance the lighting (but beware that this might give uneven lighting, unwanted shadows and a yellow cast from tungsten bulbs)
  • Use additional freestanding lights (spots or flash guns with reflectors) and be careful about moving them about while shooting so as to avoid changing the direction of any shadows which would cause stitching problems later
  • Use a longer exposure and vary it if necessary (see above) - this is what I do most of the time!

If in doubt, shoot twice

An added complication is if there is a view through the window that you want to capture (let's assume there is). So, not only do you need to ensure you take a picture which properly captures the room, but you want to get a good view of what is outside too. The answer is to simply take two (or more) pictures of this part of the panoramic sequence. Force the camera to meter the scene based on the foreground only (most SLR's allow this, if you can't do this then point your camera at somewhere else in the room with similar lighting conditions but without light directly at the camera and meter there). Use that meter reading to take one picture of the window. Now take another and allow the camera to meter the scene to take account of the light.

So you have two images of the same part of the room. When it comes to stitching you should stitch the panorama twice, once with the dark images (which have the view out of the window) and once with the light ones (which do not because it the view is thrown into a haze of light). What you can then do is retouch the image afterwards by using parts of each image to create a wholly new image in which both the room and the view are visible.

See also

Books