The lowdown on lens and tint quality

Bicycles.net.au interviews Associate Professor Colin Hall about the best sunglasses for cyclists

 

Jeff Banks glasses interview

 

It is a common complaint among cyclists to express dismay at the prices of some riding glasses; sunnies are too easily dropped, damaged or lost and hence are a risk to the high investment. But pricing can reflect the differences in quality, and certainly does with the Jeff Banks RX07 sunnies.

To explore optics further, I spoke with Dr. Colin Hall, an Industry Associate Professor at the Future Industries Institute (UniSA) who leads a research team focused on developing robust coating systems for aerospace, mining, automotive and energy applications. Dr Hall kindly shared insights into lenses and coatings.

 

Michael Bachmann: What are the key attributes of a good lens?

Dr Colin Hall: One component of a good lens is the optics, if it’s a prescription lens then there are all sorts of things that can be “optimised” to make a good lens. Material – that determines refractive index (how much it bends the light) and how thick/curved the lens needs to be to do its job, impact resistance, abbe number. This are important for normal “plano” (unpowered) sunglasses too – you don’t want distortions.

 

Michael Bachmann: What kind of quality differences will you see between lenses in a mid-range priced specs ($100 – $200) and the upper end ($250 +) and is it noticeable for most people?

Dr Colin Hall: Most often it is just the name – people buy a brand. All lenses have to pass standards; impact resistance, UV blocking, colour etc. The quality of the frame is where people will notice a difference, probably not the lens – unless the lenses scratch-up quickly and that comes down to the coating

 

Michael Bachmann: What colour lenses do you feel are best for cycling?

Dr Colin Hall: I think the best colour is neutral – grey / brown. There are standards for certain colours to ensure that they don’t interfere with traffic light signals. There are minimum transmission levels too, they can’t be too dark. Driving lenses would be designed to consider the wearer is sitting behind the windscreen and that will cut light levels by circa 10%, this would be different for a cyclist so the darker tint maybe more appropriate. And I’d recommend polarised as it cuts glare from the road.

 

Michael Bachmann: how important is the coating quality? Is the tint in the coating or the actual lens?

Dr Colin Hall: Most lenses are tinted in the lens material. A coating can be made to tint a lens, or alter an existing tint. But mainly the coating on the front is for fashion, a coating on the back (anti-reflection) can reduce ghost reflections or annoying side reflections.

All plastic lenses have a hard coating to protect the plastic from scratching, any additional coatings will further improve the scratch resistance and be used to add a colour. A poor coating here will scratch easily and be noticed. A good coating will extend the life of the lenses, a poor coating will shorten them.

 

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