Most of the time you can point a camera at a flower, focus in the middle, take the picture and get something acceptable. A wider aperture will blur out the background and the fact that the nearest and furthest points of the flower are slightly blurred won’t matter at all.
A typical single flower where you can focus on the centre of the flower, the point where you eye is drawn naturally, works just fine. There are times though, when for one reason or another, you want the whole subject in sharp focus. It may be that there is no obvious centre, perhaps in a fully double flower, or the floral bits, the stigma and stamens, are too big to be acceptably sharp, or perhaps the flower is somewhat globular and you either have the centre sharp and the perimeter blurred or vice versa, neither of which is satisfactory.
A very small aperture will increase depth of field but increase diffraction blur, more of the image is in focus but none of it is as sharp. Also, using a small aperture will mean using a faster ISO setting, which in turn increases noise in the image. Both can be corrected using software and I have seen an article about using this technique for fast moving insects which won’t stay still for long. The same might be true of flowers of course, they seldom stay dead still outdoors.
When I can take the subject inside out of any wind, I use focus stacking to get very sharp images. This involves taking a series of images, the first focussed at the front of the subject, the last at the back of the subject, with a set of intermediate in focus ‘slices’ between them. With a wide aperture setting, the depth of field is very shallow but the bit that is in focus is very sharp. The stack of images means that all of the subject is in sharp focus in at least one of the set of images.
All you then need is to combine the sharp bits of each image and discard the rest, producing a picture that is sharp from front to back. That’s a job for a computer program and the one I use is Zerene Stacker. You can download this for a 30 day trial. I started out using CombineZP, which was mostly adequate for what I wanted and was free.
I just did a stack of a camellia I have in flower. It is a seedling, something completely new, flowering for the first time and I am tentatively
quite very excited about it. That’s all I’m going to say for now. Obviously I need a picture record of it and I need the greatest possible detail. I did a series of 35 images at f4. This first sequence shows the first, middle and last of them.
The 35 images were then processed to produce two versions of a finished product, sometimes one is preferable, sometimes the other. Even in the version I chose, it had done some slightly weird stuff to the background. The program allows me to edit these artifacts out. Here then are the unedited version, the edited version and a single image taken at f10, a small enough aperture to get the whole flower in focus. That it is, but it is less sharp and the background is in sharper focus and more distracting. I could have sharpened it using software but don’t have a program that will produce as good a result as stacking. I could select just the flower, sharpen that and blur the background but the edge between the two would probably be a mess.
My camera (Canon EOS 800D) comes with software that allows me to take pictures remotely from the computer, with the camera connected to USB. I can make tiny incremental steps to the focus much more accurately than I could do by hand.
It’s all good fun, gives me something to do on a rainy day. It’s how the pros do those stunning images of insects and pollen grains and so on. It does occasionally bring me up short when I notice some detail of a flower that had completely passed me by.
Here are a few more that I did several years ago, using CombineZP. It’s worth mentioning that phone cameras generally have wide angle lenses which bring a great deal into focus anyway.