Focus on Bluebells, Tehidy Country Park - Photography Week 16 (2016)

I read an article about preparing for summer and photographing wildflower meadows. Unfortunately I can't find the original source, but the recommended technique included using a long lens to condense the perspective combined with focus stacking to ensure front to back sharpness.

Focus stacking is often used in macro photography to combat a lack of depth of field. It uses software to combine exposures with different focus points. I was interested in trying out the technique with some bluebell shots in Tehidy Country Park.

I used a 100-400mm telephoto lens with a tripod. My first shot was a standard f5.6 exposure focusing on the closest tree in the composition. The bluebells around the tree are sharp but the ones in the foreground and background are out of focus. As a stand alone photograph the lack of focus in the foreground and the sharp tree on the right are distracting elements in this composition.

To see if image stacking could resolve this, I combined eleven separately focused images. This was achieved by manually focusing on the closest flowers, taking the shot, then focusing a little further into the scene and taking another ...and so on. All eleven images were opened as layers, aligned and then blended automatically in Adobe Photoshop (as they say, other image stacking applications are available!).

The result shows more definition in the bluebells from front to back. Zooming in I can see patches where the bluebells have moved between shots and the software has been unable to reconcile this. I also stopped the refocusing at the end of bluebells so the far background is still out of focus. This is an error and I probably should have continued the process to the furthest point.

I also tried, in a separate composition, extending the depth of field by changing the aperture (f18) to see how this would impact on overall sharpness. Unsurprisingly there are more bluebells with definition both before and after the point of focus (the first tree). Flowers in near foreground and the far background are out of focus but the transition from sharp to non sharp does look natural. Perhaps my concern with image stacking is the potential for the results to look hyper-real with some elements looking unnaturally sharp.

For my final experimental shot I focused on one element in the composition and used a narrow depth of field as a creative tool. This was my preferred shot of the afternoon.

Every now and then I think it is important to experiment and practice techniques. I can see how focus stacking may avoid an unwanted fading of focus due to an insufficient depth of field. The trip to Tehidy was useful in this respect. The next step is to recognise when the technique is required and then to execute it properly.