Any recommendations for a good reasonably priced reactive welding helmet. Lots for sale on Ebay from around £15 but how good are they?
|1) Optical Class (1 / X / X / X)|
This section could also be referred to as accuracy, as it rates the level of distortion the lens provides. As an example, looking through rippled water would provide a great deal of distortion, while a clear pane of glass would provide almost none. A rating of '1' would be earned if there is minimal distortion, resulting in a clear picture with crisp, accurate details.
2) Light Diffusion Class (X / 1 / X / x)
This section focuses on what many of us would see as the traditional definition of clarity: whether the image is blurry or not. While cheap glass will often feature impurities and cause extra light diffusion that will blur the image, quality glass will not, resulting in a better and clearer image. A '1' rating here would mean a clear and uniform image, with no blurring or extra light diffusion in certain areas.
3) Luminous Transmittance Variation Class (X / X / 1 / X)
This category is concerned with how consistently the lens' auto-darkening function works. The shade of your filter should darken uniformly across the surface of the lens, with no dark or light areas in comparison to the lens as a whole. A lens that is completely uniform with the same level of shade in all sections would garner a perfect score of '1'.
4) Luminous Transmittance Angle Dependence Class (X / X / X / 1)
The final spot in the EN 379 rating scale refers to the clarity of your filter when looking at an angle. A poor quality lens may distort the image you're looking at when you look down, up or to the side, making the image look dark, stretched, blurry or distorted. A perfect '1' quality lens would maintain a consistent shade and image quality, no matter what angle you're looking from.