Spencer’s Explanations & Interpretations


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21 April 2015


Why eye protection is essential>

Are normal spectacles suitable?>

Why visual correction may be needed

Occluders: the use and abuse of…>

Adjustable Irises; the use and abuse of…>

Coloured filters; the use and abuse of…>


Why eye protection is essential


a)      There is a lot of high velocity particulate matter flying around the firing line at a shooting venue.  While each individual particle might seem small, due to its velocity it can inflict permanent damage on an eye!


b)      Any burning powder that contacts your eye can inflict permanent eye damage!


c)       Air Pistol pellets that hit a wall outside the pellet trap are notorious for ‘bouncing back’: with sufficient velocity to inflict permanent eye damage!


d)      Mandatory for


Are normal spectacles suitable?


a)      Unless you have an abnormal shooting position (not unheard of, but rare) your head will not line up the optical centre of the lens with your sights – for ISSF-style events the short answer is NO!


b)      The best optical effect is achieved when you are looking through, and perpendicular to, the optical centre of a lens.  The adjustments on specialist shooting glasses enable you to look through, and perpendicular to, the optical centre of a lens.


Why visual correction may be needed


a)      You should be focussing on, and at, the front sight (see sights and sighting>>)


b)      Unless you are short-sighted (myopic) and your natural focus exactly coincides with the distance to the front sight, you will need some level of visual correction to bring your natural focus to the front sight distance.


c)       While you might be able to focus at/on the front sight without a visual correcting lens, the eye muscles will tire.



Occluders: the use and abuse of…


There are a few people who can effectively shoot pistol with both eyes wide open (I am not one of them), but for most of us the sight picture becomes impossibly confused with both eyes open and looking at the target.


On the other hand, simply closing the non-aiming eye is not a good ‘solution’: this leads to excessive strain on the eye muscles.


The ‘solution’ is to use an occluder over the non-aiming eye:

•To reduce eye strain, the amount of light entering the eyes should be the same for both eyes.  Numerous shooters use an opaque (even black) occluder – this is not a good procedure, translucent is best!

•The area that needs ‘occluding’ is only that which obscures the target width.  The ISSF rules limit the width of an occluder to a maximum of 30mm (not enforced at PA competitions) – in fact, a 10mm wide strip of ‘clear’ stick tape will do the job.


Adjustable Irises; the use and abuse of…


‘Stopping down’ the light reaching the eye increases the depth of field (basic optics) – “WHACKY DOO” I hear you saying: I can focus on the target, front sight and rear sight all at the same time!  Well, not quite; if you stopped down an iris to achieve this there would be so little light getting through that you would not be able to make out any of these components of the sight picture.


Do not use an iris in front of the shooting eye:

• To correct for incorrect focal length of the lens – get the correct lens, and or

• To enable you to focus on more than one element of the sight picture (that element being the front sight).


Adjustable irises have their use, and that is, for those that need it,  to adjust the amount of light reaching the eye


Coloured filters; the use and abuse of…




© 2015, Spencer C Tweedie