Focus stacking is a very useful 'tool' to create some otherwise impossible results.
Focus stacking (software) is predominently most useful for (and indeed designed for) extreme close-up photography, but it can also be used effectively for some areas of landscape photography.
Here I will explain using focus stacking software and also the less radical/more conventional (for landscape photography at least) manual stacking of just a few images to create the ultimate sharp image quality.
USING FOCUS STACKING SOFTWARE FOR LANDSCAPE PHOTOGRAPHY
As mentioned above, focus stacking software is/was predominently designed for close-up photography, but like many photographic techniques it can be 'crossed over' into other areas of photography as well.
I suppose the first question will be why?, if you look at the focus stacked Bluebell image below you may wonder why it has needed to be stacked at all?
The reason is purely because I have used a short telephoto lens (180mm) to create the super dense appearance of the bluebells. The problem this creates is that the telephoto compression (and it becomes more compressed the longer the lens is) results in a relatively shallow depth of field....again you may think why not just use a wide angle lens?, so that any 'lens compression' isn't a problem.
Check out this similar Bluebell photo, it's a single exposure shot with a wideangle lens (@29mm)
It appears that the Bluebells in the foreground are very sparse and the Bluebells in the distance are very dense, the reality is that those distant Bluebells are just as dense as the ones in the foreground, they just appear very dense because they are further away.
I have tried many times to stand in those super dense bluebells (and use a wideangle lens)......but it was a bit like trying to find the end of a rainbow!, it's just not going to happen! and this is where a telephoto lens comes into play.
Here's the same image to simply show the sort of angle of view a short telephoto could achieve (please note that the area within the red box is not showing the exact difference between 29mm and 180mm) .
And here's a crop of that same scene.
Now this dense 'sea' of blue was what I was after!, but of course it's a really large crop, what I wanted was a full frame scene like this, so I used the 180mm lens....but this was where the lens compression was a problem for the results I wanted, hence using the focus stack method!.
THE STACK AND SOFTWARE
For the (finished) stacked image at the beginning of this article I used the stacking software 'Helicon Focus', I needed 6 shots (@f8) to create the depth of field I desired, 6 shots (@f8) were all that was needed to have enough 'overlap' between shots for the software to create the sharp scene (the software can't create sharpness that isn't there, so with no decent 'overlaps' between shots there would have been undesirable/messy out of focus parts)
Here's a composite that will hopefully show the focus points (and overlaps?) of those 6 shots.
MANUALLY BLENDING IMAGES
All the above words and images were specifically about having to stack/blend multiple images to create a pleasing/desired scene with a telephoto lens.
This next part is about blending 2 or 3 sharp images for the more conventional wide-angle landscape.
For example 'blending' 2 exposures (i.e one exposed perfectly for a bright sky, the other perfectly exposed for a relatively much darker foreground/land) has pretty much been common practise in digital landscape photography for some time now.......but the same can be applied to depth of field as well!, even with extreme wide-angle landscape photography it' often not possible to get the ideal depth of field required (especially if there is a dominant foreground element that you are almost 'on top of')
Here's a few tips and examples on creating a super sharp landscape image without having to compromise your composition or aperture.
Article under construction, watch this space