Sharpness

It has to be said that not all photographs have to be sharp. I have a friend who shoots most of her photographs using a technique called ICM, or Intentional Camera Movement. She produces images that are totally blurry but are also very beautiful and have a very distinctive aesthetic. See them on Flickr.

When I take photographs of flowers, I want all of the flower in the shot to be sharp, front to back. This is impossible just taking a one off shot, regardless of the lens or aperture used. If you take a shot of a flower using a 100mm lens at an aperture of f11 and 500mm from the subject, just less than 10mm of the flower will be in acceptable focus. If you have a subject that is 80mm across front to back, it follows that most of the flower will not be in focus. For many photographers that is not a problem as some make a virtue of having large areas of soft focus in their images. In the end it’s an aesthetic judgement. As far as I’m concerned I want all my subject to be in focus.

To achieve front to back focus in a shot of a flower, you need to use a technique called focus stacking. This is when multiple images of a subject are taken with the point of focus moving from the front to the rear of the subject in very small increments. Special focus stacking software that uses clever algorithms for detecting sharpness assembles all of the images, taking only those areas that are sharp and creating a single image that is sharp front to back.

For an example I shot a dried plant head which was 170mm in diameter from a distance of 500mm. I shot the first image (shown below) using a 90mm f2.8 Sony macro lens. The camera, a Sony A7R3, was mounted on a tripod and triggered using a wireless remote to minimise any camera camera shake. It was also set to a two second delay.

Dried Flower – first image

It can be seen from the first image only a small part of the plant head is in focus.

To create an image that was sharp front to back I shot 23 images altering the focus point a small amount for each shot. I started with the focus point at the front of the plant head and then worked toward the rear a small amount at a time until I had covered the whole of the plant head. I use manual focus with focus peaking enabled that lets me see exactly what is in focus for each shot.

I imported all 23 images into Lightroom where I performed a basic edit for exposure. I then sent all 23 images to HeliconFocus, the image stacking software. The short movie shows how HeliconFocus creates the single front to back sharp image by incorporating all the sharp portions from each image into the final single image.

When you compare the two images below – the single shot with the focus stacked shot – you can clearly see what a difference focus stacking makes. For the final image I added a texture in Photoshop to make it look less stark.

Dried Flower – slide right for single shot, slide left for focus stacked shot

Dried Flower – final image with background

I use this technique not only for flowers, like the Iris, but for all the still life images I shoot.