Discovering Camera Ergonomics Part 6 Functional anatomy of hands and fingers

Bones of the human wrist and hand

Most cameras are hand held devices so it makes sense to begin a study of camera ergonomics with an exploration of the range of movements and capabilities of the hand and fingers. 

I take it as self evident that a camera should be designed to fit the hand, not the other way around.

Size    Wikipedia gives 189 x 84 mm as the average size for an adult male hand and 172 x 74 mm as the average for an adult female. Hands vary in length, width and finger thickness. However reasonably healthy hands all function the same way. 

I have found that with thoughtful design is readily possible to make a camera which can accommodate most of the hand size/shape variation in the general population from children aged about 10 to adults.

The skeleton of the hand and wrist has 27 bones.   There are 8 carpal bones in the wrist giving it flexibility in all directions without which operating a camera would be almost impossible.  Next come the 5  metacarpal bones, then the phalanges, of which the thumb has 2, the other fingers 3 each.

Sensory capability    To operate a camera the fingers must detect touch and position to a high level of sensitivity.  This is particularly the case with modern electronic cameras with many controls. My reading of research on this subject would indicate that sensitivity increases towards the fingertips, being greatest just below the nail bed. It would also appear that the thumb is less sensitive to touch discrimination than the other fingers. These characteristics are important to the design of physical controls.

Natural half closed relaxed hand posture. All human hands (assuming freedom from deformity or disease) find this posture natural, relaxed and a good gripping/holding position providing freedom to move the index finger and thumb in limited ways as described in the text.

Basic Hand Posture        This is the ‘half closed relaxed’ posture which is a natural  position for the hand to adopt.  Muscle force is required to clench the fingers further,  straighten them, or move them into a different alignment.  A properly designed camera will be sized and shaped to fit easily into the relaxed hand, which can then grip the camera securely with minimal stress.

Movements    Each finger has a range of possible movements which are critically important to the design of the shape, layout and controls of a camera. I find it useful to categorise fingers as "grippers" or "controllers".

Right Index finger  This is a controller. It has good position and touch sense. It can curl and  straighten in the line of the finger. It can also angle from side to side at the metacarpophalangeal joint over a small but vitally useful range.  These movements can take place without the slightest change in the position of the hand or any other finger. You can demonstrate all this for yourself. These characteristics make the index finger the best choice for actions required to be made during the capture phase of photography, that is,  while one is actually in the process of making photos.

Right middle, ring and little fingers.  These are grippers, usually operating together as essentially one gripping unit. They will function  best if the camera is designed so all three can get a proper hold on the camera's handle.

Opposition of the thumb. This is essential to holding a camera.

Right thumb  The role of the thumb in holding and operating a camera is complex. In most cases it has to perform both gripping and controlling functions. It requires good design to achieve both at once. 

The thumb has three main movements: Opposition, Flexion / Extension and side to side movement.

Opposition is rotation of the metacarpal bone at the carpometacarpal joint. This allows the tip of the thumb to simultaneously touch the tips of the other fingers. Opposition is essential to holding and operating a camera.

Flexion / extension can occur at the metacarpophalangeal joint and the interphalangeal joint.

Side to side movement occurs at the carpometacarpal joint. Note this is quite different from the index finger which uses the metacarpophalangeal joint for side to side movement. 

So what ?? do I hear you asking ?? Well, so quite a lot as it happens. 

You need to have the thumb metacarpal in opposition to be able to hold onto the camera with the right hand.

There are lots of buttons and dials on the back of modern cameras. Some can be pressed / operated with the thumb held straight or almost so. This is desirable because with the thumb in this position opposition at the metacarpal bone is present and the user's grip on the camera can be maintained. 

But other cameras have controls which require you to flex the thumb in order to operate them. Sometimes the controls are inaccessible to a  straight thumb, sometimes a semi submerged or high/forward dial can only be operated with the tip of the thumb.  In either case, flexing the thumb forces the metacarpal to derotate and opposition is lost. In this case you cannot hold the camera with the right hand  and operate the thumb controls at the same time. You must support the camera with  the left hand while the right thumb is operating the controls. During this process the index finger is sitting idle, when it could have been operating controls with no disruption to the right hand grip at all.

Many modern cameras have a ‘4-Way controller’ module in the lower part of the control panel.  

Operation of this module requires the thumb to drop down from its capture position. This disrupts opposition and forces the left hand to support the mass of the camera and lens while the 4-Way controller is being operated. This is not the end of the world and users get accustomed to it but there is a better way.

Wrist tilt forward. Some cameras with a non anatomical handle force the wrist into this position when eye level viewing. Young flexible beings don't mind. Those of more mature years appreciate a better designed handle which allows the wrist to be held straight.

Why does all this matter ?? 

There are four phases of camera operation; Setup, Prepare, Capture and Review. In the Setup, Prepare and Review phases, it is perfectly satisfactory to fully support the camera and lens with the left hand while operating buttons, dials or even touch screen controls with the right thumb. But in the Capture phase that is not acceptable. While actually in the process of taking photos the operator needs to be able to adjust all primary and secondary exposure and focussing parameters while continuously viewing the subject  with both  hands firmly supporting the camera.

Many modern cameras require derotation of the thumb metacarpal or in some cases complete removal of the base of the thumb from the camera in order to access the controls required during Capture phase operation.  Many also require the user to look at the controls in order to hit the right one. This destabilises the right hand grip, jiggles the camera, takes the user's eye off  the subject and disrupts the flow of taking photos.  Many of these camera work just fine in one of the fully automatic, snapshot settings, where the camera makes all the key exposure and focussing decisions. But they are  frustrating to operate in one of the user control modes, for instance one of the P,A,S,M shooting settings.

Lateral dominance    I should raise the issue of dominance.  Most humans are right side dominant. This means they perform better  at writing and operating devices with the right hand.  Most also are right eye dominant.  These people have a left side dominant brain. About 10% of people are left handed, although about half of these also have left side brain dominance. Crossed and/ or mixed dominance is not uncommon.

Cameras are designed to be operated by right handed people. Those who are left handed are not catered for. In this case the user has to adapt to the camera which is ergonomically suboptimal. However, most manage to train their non dominant side to do the job. They have little choice, until someone comes up with a right/left inverted camera shape.

Left hand  

Like the right hand, the left hand has to carry out holding, supporting and operating duties. However while the position of the right hand on the camera is usually fixed by the handle and principal controls, the left hand has a more roving type of assignment. The same wrist/finger movements allow freedoms and impose restraints on the types of actions which the left hand can perform.

Next I will explore further the application of an understanding of functional anatomy to the design of a camera and its controls.