What's the optimal number of shots to produce a high dynamic range
Does it vary from scene to scene? Do the capabilities or limitations of my camera factor in?
Are there different HDR techniques better suited to more or fewer individual frames?
What are the advantages and disadvantages of using a greater or smaller number?
I typically take three shots, 1 1/2 or 2 stops apart, and then process in photomatix pro followed by cleanup in Lightroom. That seems to work fine for most of what I do.
Recently, I've been exploring Exposure Fusion as an alternative to HDR. I've lost a lot of interest in HDR processing to improve photographs that can't be captured in a single photograph due to the amount of meticulous and very careful effort required to properly tone-map the extensive dynamic range of an HDR image into the far smaller dynamic range of a 16-bit or 8-bit image.
Exposure Fusion is an alternative way of merging multiple exposures into a single 8-bit image. In my experience, it produces far more pleasing output, and it requires far less effort than HDR does. It uses an intelligent algorithm to automatically identify the "best" outcome, and produce an "enfused" image for you. While the concept and basic approach have been around for a while in different ways, Exposure Fusion as a dynamic range tool is fairly new. There are not a lot of programs that support it, nor any plugins for Photoshop, however I think it has a lot of potential.
When I do it myself, I've done up to 5 shots, with 2 EV between shots. My camera has a built-in HDR function which takes 3 shots, at -2, 0 and +2 EV. It is really no use to use smaller steps because each shot would overlap too much as information. If your camera permits it or you're will to bracket manually, I would even go 3 or 4 EVs between frames.
What works best is when your scene exceeds the sensor's dynamic range by a few stops only, otherwise you have a huge dynamic range which you must then compress into a small one to view or print it (since nearly every display on the planet can't even show the range captured by most cameras). The result is an image which lacks punch has low local contrast.
Here the only that worked using the built-in HDR: http://www.neoluminance.com/slide.php?id=v028perubak70033
I've tried several others but find most results unsatisfying due to the low local contrast I mentioned or because of unwanted halos from blown-out lights. To get rid of those you have to use something more sophisticated than what's in the camera.
I always take 3-shots because I use my camera's bracketing exposure mode, which only allows for 3 shots. By default this mode is set to +/- 2EV,0.
There are some bodies that allow for 5 shot brackets, which is more ideal for creating HDR images.
My HDR technique is heavily influence by Trey Ratcliff from Stuck in Customs and I follow his HDR tutorial (http://www.stuckincustoms.com/hdr-tutorial/) to a large degree.
I don't have bracketing in my camera, so I have to either adjust my settings manually or use exposure compensation. I lock my camera down on a tripod, then take 5-7 photos, depending on the light in the scene (trying to get all the detail in either the sky / bright area or a particularly shadowy area will mean more exposures). I think use Photomatix Pro from my HDR processing (I've tried Photoshop's new HDR product and HDR Expose but they didn't seem to get the same quality processing of light that Photomatix does. I then do adjustments in Aperture, possibly do some masking in Photoshop if there are an artifacts on my image (see Trey's tutorial for how to do this), and then do any final edits using Nik Software's plugins. If I'm going for a really surreal look, then I almost always apply Tonal Contrast in Color Efex Pro, and I've been doing a lot of black and white HDR recently using Silver Efex pro.
I always take 3 shots that are 2 stops apart. I've tried just doing 1 stop, but typically find that it's not enough. Then, from within Lightroom, I run Photomatix and do the processing. You can see some at http://www.flickr.com/photos/seanbatten/sets/72157623769215732/
There's a guy I follow on Flickr called David Gn who takes some stunning HDR shops and always gives a description of how he's processed them. They're well worth a look.
It depends.
Most of my multi-exposure work in the film days were two shots (though i tried three and four at times), one exposed for the highlights and one exposed for the shadows, hand-merged in Photoshop. Required a stable tripod and patience.
When i moved to digital, but before HDR was all the rage, my process was similar, using whatever tools were available, mostly hand-merging two or three shots in Photoshop but trying various software tools.
Then lately, with the move to Photoshop CS3, and now to CS5, i merge one to nine bracketed shots (but usually two to five) from Lightroom to Photoshop's HDR Pro. If i only have one shot, i create two or three virtual copies in Lightroom before sending to HDR Pro, which will ask how i want them processed (a 2 EV spread usually works well).
I usually take 3 at 2 stops apart. Sometimes if I only want the effect I'll do it with a single RAW image which is OK if all you want is a trippy image.
Some lighting conditions will call for more than 3 shots (like shooting directly towards the sun). For most cases 3 RAW shots will give you plenty of detail to work with.
Usually the larger of shots you can take will enhance the range - so if your camera is possible in bracketing 7 shots with 1 stop exposure difference, go at it. Or you can always go manual.
But at least you will need 1 RAW shot or 3 JPEG shots. 1 RAW shot can be manipulated during pp to get +1 and -1 exposure.
Depending on the scene, I usually take from 5 to 9 shots, with jumps of +/- 1 EV.
Then, I process those photos in my Linux box, using hugin_hdrtools or Bracket to create an EXR high depth photo.
The tone-mapping is then done by Radiance HDR.
It depends on the subject.
Action scene... one raw exposed to the right (usually +2/3)
Still life or landscape or anything else that's not moving... 3 raws, exposed to the right. (ususally -2 1/3, +2/3, +3 2/3)
It depends on the subject and the scene. If you are going for an action shot, you won't be able to get multiple exposures of the subject. Normally I shoot HDRs for landscapes.. for those, I find the correct exposure for the brightest object and then I find the correct exposure to expose the darkest object.. and then take multiple exposures from dark exposure to light exposure at increments of 2/3. Most often, 3 bracketed shots are sufficient.. but it does vary with the scene.
Depends on the scene...
If you take 40 exposures on say a sunset, you are most likely wasting your time. If you try to capture the interior of a church and a stained glass window, around 40-60 exposures (including overlap) are a guarantee for success.
You first need to judge the dynamic range of the scene in stops. Next you decide whether you step up in 1/3, 1/2 or 2/3 stops or even full stops. Use AEB in whichever way you want to and shoot away. Having said that, it is better to take too many exposures and to throw some out rather than take too few. Exposure overlap also isn't an issue as far as I can tell.
Because you ask about advantages/disadvantages: More images = smaller differences = finer gradients. Obviously you can also cover a greater dynamic range.
On the downside, you need more space and quite possibly more processing time with more images.
Edit: One last thing to remember is how many stops does your sensor cover without much noise. Generally you can expect about 8 stops out of a digital camera. (Even if you can push the shadows more and pull the highlights more, the image quality suffers - why do that in an HDR?) - Hence you would ideally want to have some good exposures of the darker parts of the scene - BUT overexposing too severely can lead to halos. (But you can throw some images out later if you want to.)
