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M4/3 System                                        
(16th December 2016)

Practical Checks for Lenses + Camera
for potential problems when using long ‘pro’ lenses ‘in the field’.
(Test procedures devised by and article © Adrian Harris)

Frequently when photographers acquire their first ‘pro’ ultra-long telephoto zoom lens, their initial results can often be disappointing, and with some the immediate next response is to ‘rubbish’ the lens and manufacturer.

As sensors have got smaller and lenses have got much longer and faster, critical alignment and stabilisation demands are pushing design and manufacturing to new extremes.

Slow lenses which operate at f5.6 or above are far less critical of any optical or sensor misalignment than fast ‘Pro’ lenses which often operate at f2.8 or below. Which is why when a camera user has been happy with a camera for a while and then ‘upgrades’ to a fast lens, a nasty little problem may well show its head for the first time. But is it the lens or the camera at fault!

Of course sometimes it may well be a poor lens that has sneaked through the system, but often there are other factors that come into play. Speaking from personal experience, disappointment turns to dismay when after returning the suspect item for checking it is sent back saying there is nothing wrong with it. Which if true means that either the camera is the problem – possibly faulty in some way, a bad match for that particular lens, or just not set up correctly, - or the photographers technique needs to be looked at.

But how does a normal person who has no test equipment at all go about checking their equipment in a simple, repeatable, and easily accessible way? … which has been the dilemma facing me for some time as I have tried my utmost to get the results I would expect from my ‘flagship’ M43 equipment.

TESTING  TESTING:  

Photographing flat charts on a wall with a tripod mounted camera is not a great way to test equipment which will be used possibly handheld in a 3D real world environment. The following series of three tests were devised to try and eliminate factors which could possibly be degrading images when using ultra-long zoom lenses in practical situations and I would advise for the checks to be carried out in the following sequence:

1. Off-Centre Lens & Sensor Alignment Testing.
(tests for lens optics and camera sensor alignment faults).

2. Lens and Stabilisation - Sharpness Testing.
(tests for lens sharpness and image stabilisation issues).

3. Front Focus & Back Focus Testing.
(tests for focus alignment setup accuracy between the camera and lens.)


Important Note:
Regarding ‘depth of focus’, the term ‘fast lens’ is relative. For example a 50mm f2.8 is not a particularly fast lens, but a 600mm f4 certainly is. (If you would like to know more about Depth of Focus, please Google ‘Optical Circle of Confusion’.)      



    

EXAMPLE  FAULTS
 

 1. Misaligned Optics or Sensor.
   
 1. Lens Optics or Stabilisation Issue.
   
 1. Back-Focus Error.
   

Article © Adrian Harris