Many of the photographs shown on my website have been made from 2 or more photographs.  There are lots of reasons for doing this,  but for me the two main ones are; to extend the focus in macro shots and to extend the dynamic range in landscape shots and at other times where an image goes from really dark to really bright.  I'll expand a little bit on these ideas.

Macro. With close up photography,  the higher the magnification and the closer you get to the subject the narrower the band of focus ( referred to as depth of field DOF ) becomes. To overcome this and maiintain sharp detail across the subject, multiple imges are carefully taken with a tripod mounted camera at different focus points through the area where you want to show optimal detail.  With something like a single fungi only 2 shots might be required. The 2 shots can be processed manually in software like photoshop where you place the 2 shots into aligned layers ove each other, then use masks to simply reveal the the bits of detail you want. For some insect and other  shots where multiple shots are taken I use 'stacking software'. The one I use is called Zerene Stacker, very clever software with excellent scaling and aligning ability to even align handheld shots. Zerene Stacker can be purchased from the developer - Zerene Systems. There is a free trial period to check it out, there are also tutorials on the web.  I have also used focus stacking with some landscape shots to get sharp focus from the front to the back of the image.  I'll post a few examples of different subjects below taken using focus stacking. 



This photo of the fungi Entoloma hochsteteri was taken with a 180mm Macro lens. 6 images were 'stacked' to get detail across the parts of the subject where I wanted it.



This is a dead wasp that I photographed with a MPE-65mm Macro lens at around 3X lifesize. Depth of field with this set up is very thin, focus stacking of 35 images has allowed more of the subject to be shown at optimal detail.


This scene is taken in a fairly remote part of Dorrigo National Park - we walked some klms that day. Focus stacking 3 images from memory allows sharp detail from foreground to background.

Extending Dynamic Range.  Even the best camera sensors can't capture detail across a scene as well as our eyes. A good example of a scene that benefits from using this technique would be a shot at sunset where the sky is still relatively bright, but some foreground elements are quite dull. If you were trying to capture the scene in one shot you would have to make a choice whether to keep detail in the shadows or the highlights. The answer is to take 2 or more photos using tripod mounted equipment, expose one shot for the highlights and one for the shadows and then blend them together in photoshop using layers and masks or some special software.


                    This photo taken at sunset would have much less foreground detail, or too bright a sky with no detail if the scene had been captured with a single photegraph.



                                                                    A single exposure would not have shown detail in the darkest parts of this chasm and the sky.

I think the techniques I use give fairly natural looking results. The techniques can be pushed much further utilising techniques known as high dynamic range HDR for short. Some cameras also include the ability to use some of these techniques 'in camera' automatically.  Another area where multiple frames can be used is in night sky photography. I have done this a bit experimenting with minmising digital noise, but now don't use it as I don't find noise too big an issue if photos are taken well.  Full on astro photgraphers take literally hundreds of images and blend them in designated software to get the single frame they are after.

So once again digital photography can allow us to use techniques that would only been dreamed about in the days of film and darkroom processing. I hope I've given you some ideas to have a play with.