Category: Photography

Depth of Field

When reading about photography, most of the articles are focused on either gears or the “exposure triangle” to get clear and sharp photos. Plenty talks about “razor-sharp” images or “scene compression”. Many spoke about wide-aperture for a creamy background (bokeh). So, I’ve dreaded my lens and thought there was something wrong because my photos were out-of-focus.

I upgraded to a 50mm lens with settings for ISO 100, f/2.8 and 1/125 sec. The portrait came out unsatisfactory. Either it was sharp around the eyes (or just one eye), nose, ear, forehead – seldom do I get good sharpness for the whole face.

The image on left was taken at f/2.80 and it misfocused on the ear and blurry around the eyes. The image on the right was taken at f/3.50 and focussed on the eye and the ear almost quite clear, showing the facial features quite clearly.

I have been following the exposure triangle: setting the ISO, aperture and shutter speed. But something was still missing. So, I go back to my root and put on the mathematician hat. There is definitely a missing equation (or less talked about).

Depth-of-field. This is another factor that affects the sharpness around the focus area. It varies based on the distance between the face and the camera. To put it simply, in my understanding, depth-of-field is a buffer area on the focus object perpendicular to the lens. Toggling the aperture changes (compressing or widening) the depth of the buffer area. For a given aperture, the depth-of-field is also different based on the distance of the object to the lens.

If the aperture is fixed, putting the object farther away makes the depth-of-field wider.

Two examples of the effect of “depth-of-field” and the distance between the object and the camera. Assuming the aperture is fixed, and the focus is on the eye. On top, the buffer region between A and B is where the objects are going to look sharp perpendicular to the lens. Keeping the aperture similar and moving the object farther away from the camera, the buffer region, C and D expanded. The distance from A-to-B or C-to-D is directly related to the aperture size and the distance between the object and the camera. Narrower the aperture, the wider the region is. (Note: The buffer regions are not exactly scaled).

Using this understanding, I revisit the technique used to collect facial images for my experiment. The settings of the parameters are laid out below.

Parameters

ISO: 100
Speed: 1/125 sec.
Light source: Flash + bouncer
Distance: 1.5 meters
Focus: Wide (AF-C) + Eye AF
Camera: Sony A7R iii on a tripod
Lens: Sony FE 50mm F1.8

Using a DOF calculator, if I want the subject’s face to be overall sharp, the aperture has to be f/4.0 or narrower.

DOF Calculator downloaded from Google Play. For the selected settings, the buffer for depth-of-field around the focus area is 20.98cm (9 cm to the front and 11 on the back from the focus spot).

The distance was quite close because my study room on the campus is quite limited in terms of space.

Result

The overall facial features are clearly sharp from the top-point of the nose and back to the ear at f/6.30

Take-away

  • ISO-Aperture-speed is not the only factor for sharpness.
  • Knowing the distance between the object and the camera is also important as it affect the depth of field around the focus region on the object.
  • If the object has a depth perpendicular to the lens and is relatively close to the camera, use a narrow aperture so that the front and the back of the object is in focus.
I found a good explanation on depth-of-field by Kellan Reck.

Sony FE 24-70mm F2.8 GM

It pulls the duty for being sharp but the weight and size are bulky for a daily walk-around

This lens (SEL2470GM) is a Premium G Master Series Mid-range telephoto prime wide-angle to a short telephoto lens with a constant f/2.8 maximum aperture. It is claimed to have Sony Nano AR Coating to eliminate flare and ghosting.

It was acquired primarily to help with data collection for my experiments. Especially when it comes to seeing the movement of facial muscles. It works well with ɑ7R III as this camera captures at 42.4 megapixels, allowing zooming and cropping. The settings for data collection are set as a “distance between the camera and a volunteer is 1.5 meters, 1/80 – 1/125 sec, f/5.60 at 50mm”.

A nice clear and sharp portrait, with a flash, fired from on top of the camera.
49mm ISO 100 f/3.50 1/80 sec.

I think it is a great general-purpose travelling lens as covered by the focal length range. But because of travel restrictions, it will be some time before I can take this lens for my next holiday trip.

It also works well for videography! Due to the weight, I could not use the word excellent. I used Røde VideoMicro when recording and there was no noticeable noise from the lens’ focus adjustment.

It produces a barrel distortion on wide (24mm) and pin-cushion as it gets tele (70mm). It is said 1Sony FE 24-70mm F2.8 GM Lens Review to have the lowest distortion focal length at around 28-30mm. Of course, these can be corrected in Lightroom very easily.

Forest photography at Hareskov-Værløse (on mini-tripod and remote clicker).
24mm ISO 100 f/9.0 1/13 sec.

I took this lens for forest photography, once. The focal range is good, but the size and weight are not very flexible, especially if you are mounting on a mini-tripod. Cityscape and street photography can benefit from the medium-range focal length but for these genres, I, however, prefer my 28mm prime.

Aperture range: f/2.8 to f/22
The angle of view: 84º (24mm) to 34º (70mm)
Minimum focus distance: 38 cm
Maximum magnification ratio: 1:4.2 (0.24×)
Filter size: 82 mm
Dimensions (⌀ × L): 87.6 × 136 mm
Weight: 886 g

Sony FE 28mm F2

Lightweight, compact and my best companion for the majority of the time

This 28mm (SEL28F20) is my second prime lens, which I use 99% of the time when going out. The price was in the lower range as the target market is entry-level photographers. The cheapest market price in 2021 is DKK2,550 (around ?340).

This lens is attached to my Sony A7Riii and has been the go-to lens for most of my photos. Sometimes, it is the sole lens that I took with me when I can’t pack a lot of gear.

I like this lens because it is lightweight and compact, hence the system works well on my hands and with my shooting style. It also locks focus rather quick. The wide aperture is helpful, especially in low light conditions and handled handheld. I like the wide-angle view as I can fit more scenes without the need to move too far back.

The Hermitage Hunting Lodge, Klampenborg.
ISO 100 f/3.50 1/640 sec.

It works really well with my landscape, architecture, cityscape and street photography with its wide perspective. It also works well for full-body portraits. I do actually feel a bit pleased with the portrait produced by this lens even for ? headshot. But for ? headshot seems awkward as I have to be quite close to the person. And yes, the face distortion is there when taking a close-up portrait!

Cityscape photography at Copenhagen Central Station.
ISO 1000 f/2.8 1/100 sec.

This lens is discreet and does not really attract attention when used in the public. Because of its wide-angle and close focus distance, I also use this for food photography.

Cantaloupe shrimp cocktail.
ISO 200 f/4.0 1/160 sec.

My sweet spot is between f/2.8 and f/5.6 depending on the situation. For food, I prefer f/4.0 and street photography at f/2.8 but sometimes I do go wide between f/2.0 to f/2.2. Somehow for landscape, I prefer something from f/3.50 and narrower.

However, it has a strong barrel distortion which of course can be corrected in Lightroom.

Aperture range: f/2 to f/22
The angle of view: 75?
Minimum focus distance: 29 cm (AF) / 25cm (MF)
Maximum magnification ratio: 1:7.7 (0.13?) (AF) / 1:6.25 (0.16?) MF
Filter size: 49 mm
Dimensions (? ? L): 64 ? 60 mm
Weight: 200 g

Sony FE 50mm F1.8

Prime for portrait, it does the job and probably that’s it!

My first prime lens. The cheapest I can afford as a student. At first, I thought I can use this lens for all occasions as an all-in-one. But after I tried street and landscape photography, I found this lens is quite tight in terms of viewing-angle, noisy focusing motor and also slow at that.

Receipt for the lens SEL50F18F, around ?175 (17-10-2021)

Noisy! You can hear the motor keeps on locking focus during a playback, definitely is not for videography (unless the sound is not needed or using a wireless audio unit). Also when it hunts to lock a proper focus when pressing the shutter button for photography.

At a platform sandwiched by trains (Copenhagen Central Station, 2021).
ISO 100 f/2.2 1/60 sec.

For me, this lens is probably not suitable for street photography because of its slow focusing. For landscape, the focus is sharper when using Manual Focus (MF) instead of Auto Focus (AF).

A landscape view from Viking Ship Museum towards the shore as it was covered with thick fog (Roskilde, 2022).
ISO 100 f/2.2 1/160 sec.

However, it works pretty well and I mostly use this lens for portraits. The results came out sharp. The good thing about this lens is the size. Petite and it doesn’t take much space. I carry this lens with me most of the time.

The aperture can be opened wide to f/1.8 but my sweet spot for this lens is between f/2.8 and f/5.6. The output has no barrel distortion but Lightroom seems to correct the darkened areas (vignetting) around the edges.

Prognosis: it’s a keeper! ?

Aperture range: f/1.8 to f/22
The angle of view: 47?
Minimum focus distance: 45 cm
Maximum magnification ratio: 1:7.1 (0.14?)
Filter size: 49 mm
Dimensions (? ? L): 68.6 ? 59.5 mm
Weight: 186 g

A commentary video on this lens by Chris Brockhurst (2022).
https://youtu.be/iO6wZUvDzC4
A review by Aron Andersen (2018).

UPDATE

May 2022: I sold the lens as I no longer use it after getting the Sony Sonnar T* FE 55 mm F1.8 ZA.