Below is another entry in a series of periodic discussions that look at the intersection of art / artist vision with the technical aspects of photography. This post is more reading than images, consider grabbing a fresh cup of coffee.
In this discussion, two specific issues will be examined using real-life images from ZooTampa at Lowry Park in Tampa, Florida.
The issues:
1. Where to focus on wildlife / animals close-ups? (That is, portraits in general)
2. How much / how little depth of field is afforded by a wide aperture setting?
The equipment involved is a Canon EOS 5DIII with an EF 135mm f/2L. Other than the wide f/2 aperture options of this 135mm Canon lens, the issues presented are relevant to all photographers working on portrait-style images at relatively wide apertures and relatively close distances such as you might create in your portrait studio setting.
Consider the details of this first image. The edited full-image shows a very narrow depth of field (DOF) covering maybe just the distance between the beak and the eyes. I say 'maybe' because this full-screen version doesn't reveal the actual pixel-level details.
Sunbittern by
Paul Sager, on Flickr
The annotated version below is a 1:1 crop of just that in-focus section of the image. With these details revealed, we can begin to ask some critical questions:
1. Where is the focus?
2. Are the details actually in focus?
3. Is the image focused on the correct details? That is, are the features between the eyes more important for 'success' than the eyes?
Somewhat unrelated to these three analysis questions, is this image a keeper? If 'no' or 'maybe', what aspects of the capture technique are candidates to adjust?
Depth of field is the distance between the closest and farthest objects in a photo that
appear acceptably sharp.
As noted in the crop above, the DOF is probably about 1.4-inches (35-mm) of the bird's head between the end of the beak and the middle of the eyes. I'm assuming I was about 6-feet from the bird in this aviary. The use of the 1.4x Canon extender, as well as a guesstimate of the distance, makes the use of an online DOF calculator somewhat confusing. I get calculations between 1- and 2-inches as I vary the focal length between 135mm and 190mm and the shooting distance between 5-feet and 8-feet. Anyway, knowing the equipment and seeing the details of a result, we can see for this focal length (135mm/extended 189mm), the f/5 aperture and the 5- to 8-foot shooting distance, we have a DOF clearly between 1- and 2-inches.
To return to the questions above, are the details 'in focus' for that narrow 1-ish inch strip between the beak and eyes? To me, yes. When I reviewed the image in Canon DPP, a single AF point was positioned directly on the bird 'forehead', between the two red lines of the annotated image above.
For the second question, is the image focused on the correct details, here I say maybe, leaning toward no. I want that eye on our left, the eye nearest the camera, to be in sharper focus. Because of the bird's slight head angle relative to the camera, the DOF might actually pass through the nearest eye. But, it still could be better.
The necessary change is to use a smaller aperture, say f/5.6 to f/6.3. I know this aperture change from experience, as well as, I can plug-in the new aperture value to a DOF calculator and see the measure of the DOF increase. Also from the EXIF details, we see the shutter speed was 1/800 sec against the 189mm effective focal length, meaning we have 'room' to go slower on the shutterspeed for the same ISO-200 while closing the aperture to f/5.6 or smaller.
Consider this next image. It's almost the same image, but with some of the exact changes made to the parameters as discussed above.
Sunbittern by
Paul Sager, on Flickr
Given the same camera with the same lens and extender combo, we can judge from the wider view, I was a bit further back from the bird, but still so close that the bird doesn't fit within the frame.
The image is extremely sharp, where in focus, with a depth of field that covers the entire head, but not both the head and the beak. The DOF seems to cover the entire breast / front of the bird, see details above. The image is so sharp, we can see an insect (lice?) below the bird's eye, as well as all the feather details around the eye, see the cropped and annotated version, below.
In the EXIF data, we see the changes discussed earlier being implemented for this image, specifically: aperture now f/5.6 (from f/5), the shutter at 1/400 sec (down from 1/800 sec), and the ISO jumped way up to ISO-2000 (from ISO-200, the first image was very sharp, but grossly underexposed, it was 'saved' in post from the RAW). Being probably 1-foot further away, I gained maybe 2-inches of overall DOF using the smaller aperture and longer shooting distance.
ConclusionIs one image better than the other? Who knows. The second has more distractions in the background. The first is more 'artistic', but my own style is to have more DOF to capture the entire face / head in sharp focus, especially including the eyes.
(The first image has grown on me over the course of editing and writing, especially when I look closer at the nearer eye and consider it to be in better focus than I initially thought.)
Both images have options for cropping into the details, as used for these annotated discussion versions and for using on IG and similar, where extreme close-ups are more useful. I haven't finished editing all the images from the zoo visit. I'm not sure either of these are even my single favorite image of this session with the sunbittern.
Hopefully, a few other items are useful from this discussion, specifically:
Replace the bird with a human face, would you want to see just the bridge of the nose in focus similar to the first image, or the entire face in focus, similar to the second image?
When people ask about portrait lenses, here is a 135mm 'traditional' portrait lens focal length in real-life action on a full-frame body. The subject is close enough to the camera to fill the frame. A human face would require you to be a bit further back, but you can see f/5.6 or smaller might be needed for a DOF that accomplishes the entire face in focus, even with a larger subject at a greater shooting distance. Probably all of us own lenses covering 100mm to 200mm that look great around f/5.6 to f/8 that can function as a 'portrait lens', especially for a close-cropped headshot.
Consider too the importance of focusing on the nearest eye to the camera. If you miss that critically sharp focus at the 1:1 details, the portrait isn't going to work. As I've said in other posts on where and how to focus, you should be using a single AF point (or small group), set specifically on where you want the sharpest focus. Selective focus is needed when working at these wide(r) apertures, longer focal lengths, and very close distances.
Finally, note the impact of a slight angle of the subject relative to the camera / sensor. If your subject is facing directly into the camera, you need to consider a DOF that covers the tip of the nose through maybe their ears, with the focus set on an eye, or possibly an eye brow or maybe the bridge of their nose. Your own artistic style for aperture / depth of field will determine where exactly to focus. Take images from all these AF point positions to determine your own preferred location. If you adjust the subject to be slightly angled relative to the camera, you might need less DOF to cover the tip of their nose through just the one ear that can be seen in the image.
In the links below, you see some of the same issues being presented, especially in the cat portraits where maybe a bit too narrow a DOF was used for an overall successful 'portrait' in some of the examples.
Links to prior posts on Depth of FieldLooking at Depth of Field w/ cat portraits -
https://www.uglyhedgehog.com/t-685940-1.htmlA discussion of Depth of Field w/ lilac blossoms -
https://www.uglyhedgehog.com/t-694277-1.html