I am passionate about Macro Photography, and capturing images of some of the incredible (but tiny) little creatures that wander this earth. Whilst there are way to many creatures to outline, and I only ever see a tiny fraction of them, some of my personal favorites are Jumping Spiders. With that in mind there are some issues around depth of field which can be encountered when working with Macro Photography so I wanted to write a quick peice about it overall.
What is Macro Photography?
Whilst a full description about Macro Photography is outside of the scope of this post, an image is a macro image when the item you are photographing is at or greater than life-size, so for example a 10mm spider is represented as 10mm on the camera sensor. This means that very often you can create incredibly large and/or detailed photos of insects or small creatures. A phrase “Reproduction Ratio” is often used to represent the size of an image on the image sensor to the actual size of the subject, macro photography most commonly has a reproduction ratio of 1:1.
Depth of Field in Macro Photography?
One of the side effects of increased magnification (0r reproduction ratio), is that the greater the magnification, the smaller the depth of field. The depth of field can be described as the distance between the nearest and furtherist items in a scene that appear acceptably sharp.
Figure 1: A ruler showing examples of depth of field of the Sigma 150mm Macro Lens @ f/5.0
Consider the image (above), in this case we can say that the depth of field is very shallow as only the three (3) is acceptably sharp. I could increase the aperture which may help increase the depth of field (i.e. make more in focus) however, the depth of field will still not be enough to bring all of the image into focus. This is a very common issue in macro photography which is typically solved by the use of a technique called “Focus Stacking”.
What is Focus Stacking?
Focus stacking (or Focal plane merging, z-stacking or focus blending) is a technique which uses specialised software to combine multiple images taken at different focal points, so that different areas of the overall image are in focus. The software then analyses the images to extract the most sharp aspects of each of the images, tries to align the images and then blends them into one image which has a greater depth of field (i.e. is more sharp).
There are lot of different peices of software that can be used to conduct Focus Stacking which varies from Affinity Photo & Photoshop through to more specialised software like Zerene Stacker and Helicon Focus. The one I have most experience with is the software called Helicon Focus which offers software for Windows and Mac OS X.
Here's a brief explaination of each method:
Method A computes the weight for each pixel based on its contrast, after which all the pixels from all the source images are averaged according to their weights.
Method B finds the source image where the sharpest pixel is located and creates a “depth map” from this information. This method requires that the images be shot in consecutive order from front to back or vice versa.
Method C uses a pyramid approach to image representation. It gives good results in complex cases (intersecting objects, edges, deep stacks) but increases contrast and glare.
Whilst the different modes suit different subjects, i wanted to show the example of the same image fed into each mode to overall show how focus stacking can improve overall depth of field, but also some of the issues that can occur.
What are some of the limitations of Focus Stacking?
Focus stacking is a very useful technique to bring more of an overall image into focus or an acceptable level of sharpeness however, because it needs to align the images it tends to work best when an item is not moving, this can often mean that it is not always possible to get images of live moving animals, or it can be very difficuilt. Furthermore, the sucess of focus stacking relies on how many images you can capture (that each have a different point of focus), and also how consistently you can move the point of focus.
In the above images, I have taken about 12 photos however, as I have not changed the point of focus evenly throughout these photos you can see that some points of the image are more in focus than others. By move consistently moving the point of focus, and also capturing more images I would have been able to bring move of the overall image into focus. Sometimes people can try and overcome these by using a tool called a Macro Rail which allows you to motorise the movement of the lens (or use Helicon Remote which allows you to move the focus point using the lens motor).
I hope this has been of some interest to you, Macro photography is a great tool however it does often need some additional software to bring the best out of images, I would suggest to have a play with some of your images, and see how a Focus Stacking tool like Helicon Focus, or Zerene Stacker might be able to increase the depth of field in your images. In the meanwhile take a look at my YouTube channel as you should fine some interesting videos on there.
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