St. Valentine's day is again around the corner and so everyone is doing last moment flower shots for cards.
It is good excuse to talk about photography technique that became rather popular lately (in fact so popular that Adobe included it automation into latest Photoshop CS4, as they done to panorama stiching and HDR functions before).
Image harvesting is well described in Welcome to Oz and there is pretty much best place where one can get full description and ideas on it, but basic concept is fairly trivial.
Imagine situation when you dont have enough light to use small apperture (i.e f32 / f64) or even smallest apperture wont give you desired sharpness (example - if you trying to shoot wasp in 1:1 and fit it entirely into DOF. Most of times its impossible with single shot). Another scenario is when you shooting landscape and like to create few sharp zones, or make impression of focal plane going under funky angle.
Solution to that - image harvesting.
All you do - is shooting from same point few frames, trying to move camera as little as possible, changing only focusing points or even using manual focus and sliding it through some range.
This will give you few frame with great sharpness in different "layers". So now we simply load those frames into your favorite editor (Photoshop, PaintShopPro, GIMP, whatever you use), move layers a bit to merge details exactly (changing opacity to 30-50% helps a lot), and then either using masks, or eraser tool (if you comfortable with destroying pixels) - you playing game of making portions of final image sharp or out of focus as you please.For example coloured image at the beginning of this entry was made of 4 composite frames (on the right - click on it to see larger size but beware - it is rather big). Focusing points were on iron, on closest flower, on farthest flower. Of course - i could've use more light and close apperture to f16 and fit whole thing into single shot, but then i would have to worry about background far more, and also it will make more hotspots and lightspills..
In general image harvesting is brilliant technique when you got to shoot complex landscapes and wildlife (you can make few fishing bears standing far from each other appear in focus even though it wont be possible with single shot, eg), macro and, sometime, architecture.
To certain extend image harvesting is half-camera/half-software tiltshift lens, that allow you to bend quite a number of rules and tailor focus plane to follow path that is physically impossible but quite catchy for eye.
