I need to build on my previous explanations of angle of view and perspective but before I do that (in future posts), I'm going to write about something else: Photostitches. If you follow my photostream, you will have probably noticed that I've become particularly fascinated with photostitches of panoramas over the past year or so. By no means have I become good at them, but at least I seem to have picked up a few tips and tricks along the way which seem to help me get some results. So I thought I'd jot them here in case anyone else finds them useful or in case I forget them over time :-). In point form:
- Use a relatively small aperture/large depth of field: When doing a photostitch, the number of possibly interesting things/subjects in the resulting photo (nearly) multiplies with each photo added as part of the stitch. As a result, it's considerably more likely that you'll have something of interest in the foreground as well as in the distance. Having a shallow depth of field here is therefore not desirable as it will likely result in either the foreground subject or the distant subject being out of focus. I therefore typically pick an aperture of around F/11 (maybe even smaller if lighting permits it). F/8 is the least I think one could get by with...
- Wide angle: In relation to the above, keeping a wide angle helps in allowing for a greater depth of field. Depth of Field after all is a function of aperture, distance from the subject and zoom. Besides, keeping a wider angle should help keep the number of individual photos you need to make a stitch of a given panorama to a minimum. The trade off here is that you'll lose some detail but at least you won't spend hours waiting for the software to stitch the result! In practice, nearly all of my stitches are shot under 25mm focal length on a crop sensor (37.5mm full frame) and in practice most are around the 18mm mark (27mm full frame) if not lower.
- Low ISO: Desirable for any photo really; photostitches are no exception. There is an added consideration though that extremely high noise (e.g. ISO 3200 or higher) can throw the stitching software off course when comparing two images to be stitched...
- Shutter speed: All the above already hints at various settings that you'd need to set manually. If truth be said, it's probably best to set shutter speed manually as well. Setting shutter speed manually ensures that you get a panorama that's more representative of the actual scene being photographed. For example, if one side of the panorama is brightly lit (e.g. due to sunlight) whilst the other one is darker (e.g. shadowed by a building), then you probably want this difference showing in your final photostitch. If the camera were to decide shutter speed for these two different ends of the scene, it might decide on a fast shutter speed for the brightly lit corner and a slower shutter speed for the darkly lit one. The camera does this to try and get a balanced exposure for each shot but in this case we probably want to represent the difference in lighting between one end of the panorama (i.e. one shot) and the other. It's therefore probably ok for one end to be slightly overexposed and the other to be slightly under exposed as these will probably balance each other out once the panorama is stitched. The trick is deciding on the correct shutter speed. To do this, I usually fire a few test shots of the scene before. In particular I concentrate on an area of particular interest in the whole scene to be photographed and decide the shutter speed based on that areas. This ensures that the area of particular interest will be correctly exposed whilst other areas may then be slightly under or over exposed.
- Manual Focus: Besides exposure, it's also a good idea to set focus manually to. Though we've opted for a small aperture (so a large DoF), if we leave the camera on auto focus, it might decide to focus on the foreground for one shot and at infinity/the horizon for another. You may therefore end up with two shots belonging to the same panorama, only one has the foreground in focus whilst the other is focused on the horizon. That's clearly undesirable as ideally the panorama should be in focus at the same distance from the camera throughout. Worse still, when shooting a panorama, it's quite likely that the camera might not be able to find automatic focus for a particular shot within the sequence. For example, this may happen if there's nothing interesting/of contrast in one particular shot (e.g. just sea and sky with no clouds). Manual focus overcomes all these issues so it's best to use it. Just one other note on this subject, if you're like me and find focusing the camera manually somewhat tricky (due to wearing glasses, squinting etc.), there's a trick I usually use: Use Auto focus to focus the camera on a particular shot/subject in the camera you want to be in focus and then simply flick the switch to manual focus without touching any of the lens focus rings. In this way, the camera should be focused on the subject that interests you in the panorama and should stay that way so long as you don't touch any of the focus rings or flick the switch back to auto focus.
- AE-L/AF-L Button: One other trick I usually use as a shortcut for all the above and when I'm not using a tripod is to hold down the Auto Exposure-Lock/Auto Focus-Lock button on the camera. If your camera has such a button, then I'd recommend getting acquainted with it :-). I typically set the aperture and ISO to what I want them to be (I use Aperture priority for this) and then focus/meter (press the shutter release button half way down) on a particular scene in the panorama. As a result, at this point, the camera decides focus and shutter speed. I then press the AE-L/AF-L button and, so long as I keep this button pressed down, all the settings (focus/shutter speed/iso/aperture) remain as is. This therefore serves as a quick way around having to set all the setting manually. All I do is keep the button pressed down and shoot all the pictures that make up the panorama with the button pressed down. Voila! Unfortunately, I can't really use this button when shooting on a tripod as I have to keep it pressed down and that could introduce shake/vibrations from my hand. Maybe your camera has some form of a lock for this button so you needn't keep it pressed. Best to check the manual as that would mean you could also make use of it on a tripod!
- Tripod: Some of the above constraints make for a low shutter speed so you'll want to shoot on a tripod whenever possible. Besides, keeping the camera on a tripod helps ensure that you keep the same perspective for each individual shot.
- Manual white balance: Set the white balance manually on the camera for all the shots. I know that when shooting RAW you can adjust white balance afterwards but I've found it's still not quite the same at times. I prefer to set it manually for all the shots and not worry about the camera's auto calculations. The reason for setting white balance is the lighting can change (at times drastically such as when shooting at dusk) whilst you're shooting the individual shots. The camera's auto calculations may therefore yield considerably different results between sucessive individual shots and I found this can be quite a problem...
- Get to know your photostitching software: Whist the automatic photostitch generation may work fine most of the times, I've faced a few problems with particular photostitches (e.g. when the lighting isn't great or there isn't high contrast in the shots). In a number of these cases, I've been able to 'manually' correct these problems using some of the manual/advanced features of the photostitching software. Options like adding control points manually, adjusting yaw/pitch/roll, adjusting colour balance across the stitch etc...
That's about it for now. I'll try to come up with a further post later on about this subject with some more tips about what to be careful of etc. I thought I'd start off with what I think are the ideal basic camera and setup settings. I'll try to jot down a few pointers on what to avoid/what to shoot/how to go about dealing with certain issues with regard to the scene being shot/stitched together in a future post.
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