Ergonomic Analysis of Mode Dependent Scroll Wheels

Introduction  I have spent substantial time over the last two years making camera mockups with the aim of improving the ergonomics of  hand held cameras. One strategy I have used is to explore options for the position and design of User Interface Modules (UIM).  I do this by physically moving buttons and dials to different places on the mockup. This article deals with the Mode Dependent Scroll Wheel.

Definition   There are two main types of control wheels or dials commonly found on cameras.  One is the "Set and See" type. Set and See levers are also popular, often incorporated into a dial type control module. Set and See dials have a single function at each set point although some cameras allow user configuration of the details.

A Mode Dependent Scroll Wheel [MDSW]  has no markings. It's function is dependent on the current operating mode.  It is particularly well suited to Capture Phase tasks.  Thus in Aperture Priority Mode the Scroll Wheel will change Aperture. In Shutter Priority Mode it will change Shutter Speed.

Rationale of the MDSW   Modern electronic cameras suitable for Level 3 users  (Expert/Controller, occasional use) or Level 4 (Expert/Controller, frequent use)  users, are very complex, requiring the operator to make many adjustments very quickly. In the Capture Phase, these adjustments need to occur while the operator is holding the camera firmly with both hands and looking at the subject through the viewfinder. The mode Dependent Scroll Wheel can, if optimally positioned and designed, meet the requirements of that situation.

Job Description for a MDSW  In the Capture Phase, a well designed and located Scroll Wheel should be able, if optimally supported by other User Interface Modules (UIM's) to  adjust Aperture, Shutter Speed, ISO, Program Shift and Exposure Compensation. In addition it provides  scrolling functions in Setup, Prepare and Review Phases. It should not be prone to unintended activation. It should be easily located and operated by feel, while the user is framing the subject with the eye level viewfinder. It must be fully operational without the user having to shift grip on the camera with either hand.

Current Practice  A review of current camera designs shows that some cameras have none, some have one, others two. Some cameras have three. There is no agreement about location. Some cameras have them on the top plate. Some of those rotate on a horizontal axis others on a vertical axis. Some are on the back but there is no common practice as to where precisely they should be located on the back. Some cameras put a Scroll Wheel on the front.

Compare this to the location and operation of shutter release buttons on cameras about which there does appear to be substantial consensus.

Scroll Wheels are in a state of design flux, with no agreement about the optimum number, position or function having yet been reached.

By way of further comparison we can consider the motor car.  Convergent evolution in cars has reached the point where  the main controls are located in the same place and operate the same way in all makes and models.

The same kind of convergent evolution has not yet occurred in cameras.

Functional Anatomy of the Human Hand  Camera design is subject to multiple interpretations but the hands which use those cameras do not change at all. They have had the same morphological and functional anatomy for many thousands of years.  I have discussed this in detail in my article "Functional Anatomy of the Hand" on this blog in March 2012.

Briefly, the right index finger is the only digit which has no "gripper" role. It only has "controller" functions. It is the only digit which can operate UIM's  (provided they are correctly designed and positioned)  without affecting the user's grip on the camera.

The Problem with Likes and Preferences  It might be thought that a useful way to discover the optimum arrangement of Scroll Wheels would be to ask camera owners about their likes and preferences. But there are serious problems with this approach. Likes and preferences are idiosyncratic, transient and sometimes unformulated.   They can only arise out of prior experience and as such may give no useful guide to the way forward. The conclusions reached from that experience may be misconstrued.

Here is an example from personal experience.  I bought and used a Pansonic G1 with a Scroll Wheel located upper front on the handle.  This was unsatisfactory as the right middle finger lay right across the Control Wheel in normal holding position. So, in order to operate the wheel I had to release the camera with  my right hand to allow access to the wheel with my index finger. Thus I could not hold and operate the camera at the same time. Subsequently I bought a Panasonic GH2. This camera has the Scroll Wheel located on the back, upper right where it is operated by the thumb. The GH2 wheel is easier to reach and operate. I might have concluded  incorrectly from this experience that rear/thumb operated Scroll Wheels are "better" than front/index finger operated ones.  However a full ergonomic task, time and motion analysis revealed that although one is easier to use than the other, neither solution is optimal. The way forward lies in a direction different from either of these arrangements.

Another example: I sometimes read on user forums the idea that a camera operator would "like" or "prefer"  to have his or her right index finger resting on the shutter release button "ready-to-make-the-exposure" while the right thumb makes adjustments using various UIM's.  A task, time and motion study shows that typical adjustments in the Capture Phase (AF Area position, Exposure Compensation ISO, Aperture, etc) are made sequentially prior to shutter release. The actions do not occur simultaneously. If these tasks are allocated to the thumb then a better ergonomic description of the index finger's role in the process would be "Sitting-idly-doing-nothing-when-it-could-have-been-adjusting-exposure-parameters".

My point is that user's likes and preferences do not reliably lead us to optimal ergonomic solutions to problems at the Human Machine Interface (HMI).

1. Rear of camera, thumb operated.  Many cameras have these and they get the job done  in most cases. However if the Scroll Wheel is located directly under the ball of the thumb in basic hold position it will be constantly at risk of accidental activation. If  it  is located to the left , right or below the ball of the thumb in rest position then the user must shift grip with the right hand in order to operate the Wheel. The amount of shift may not be great but it still adds two steps to the process which is suboptimal.

2. Front of camera, below the level of the Shutter Release Button.  The worst of these require the right hand to shift downwards in order to allow the right index finger access to the Wheel. Better ones allow the grip to remain but require the index finger to move a substantial distance to reach the Wheel. 

Best Practice Derived from Ergonomic Study and Mockups  An analysis of task, time and motion shows that the best place for a Scroll Wheel is close to, on the same level as and just in front of or behind the shutter release button.  If optimally designed this location meets all the requirements of the job description.

My experiments indicate the  optimum distance between the center of the shutter button and the center of the Scroll Wheel is 13 mm.  The best ergonomic result is given by a cluster of four UIM's all operated by the right index finger. These are Shutter Release Button, Mode Dependent Scroll Wheel, ISO button and Exposure Compensation button. Both these buttons should permit user selectable function from a substantial list of options.

The optimum distance betweeen the center of the Shutter Release Button or Scroll Wheel and the Exposure Compensation or ISO buttons, is 17 mm.  Each of those UIM's has to have a precisely calibrated physical profile to ensure swift  operation without unintended activation.

How Many Scroll Wheels ?  My work indicates that IFthe UIM cluster described above is in place and IF there  is a JOG lever correctly positioned for thumb activation then only one Scroll Wheel is required.   The Scroll Wheel changes both Aperture and Shutter Speed in Manual Exposure mode.  In Manual Mode the function of the Exposure Compensation Button automatically switches to  toggle Scroll Wheel action between Aperture and Shutter Speed.  If the UIM's are all correctly positioned in three dimensions the process of adjusting Aperture and Shutter Speed  is quick and becomes almost instinctive.

Photo 1, Optimum MDSW Layout.  This photo shows one of my mockups. The Shutter Release Button and Scroll Wheel are optimally angled and positioned on top of the parallel type handle. ISO and Exposure Compensation buttons (both with user selectable function) are optimally located.  It is very easy to locate and operate these four UIM's by feel without shifting grip with either hand. All primary and secondary exposure parameters can be quickly adjusted by the right index finger using this UIM layout.

Photo 2, Good MDSW Location.  This a Samsung NX11, showing good Shutter Release Button position, with the Scroll Wheel 13 mm behind and on the same level, where it is easy to find and operate by feel.  Unfortunately some of the other buttons are not so well located.

Photo 3, Poor Front Location.  The Scroll Wheel on this Canon  G12 is obstructed by the third finger of the right hand in normal hold position. Therefore the right hand grip on the camera has to be released in order to get the index finger onto the Scroll Wheel.  Good idea, poor implementation.

Photo 4, Difficult Rear Location.  The Scroll Wheel on this Panasonic G3 extends from it's housing only about 1 mm. Therefore it must be operated by the very tip of the thumb, just below the nail. You can see the cramped, awkward  hand position which results from this constraint. You can also see the right hand has barely any grip on the camera while operating the Scroll Wheel.  

Photo 5, Poor Rear Location.  The scroll wheel of this Fuji X10 is located right where the thumb wants to be in basic grip position.  In this photo the thumb is pressing on the small thumbrest right at the edge of the camera body. This position is cramped and awkward as you can see in the photo.  There is a brisk trade in after market thumb rests for this and other cameras with the same problem from the same maker.

Photo 6, Canon DSLR Style.  This is a Canon EOS 60D which has a comfortable, well designed grip and mostly well designed UIM layout. However it could easily have been much better. The Scroll Wheel is not on the same level as the Shutter Release Button and is a little further away than optimal. The ISO button is one of four identically sized buttons behind the Scroll Wheel, identified only by a tiny nipple on top, so it is difficult to find by feel.   There is plenty of room on this camera for a more ergonomically productive arrangement of UIM's near the Shutter Release Button. I would describe this camera as a missed opportunity to achieve excellence.