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Message: <blockquote data-quote="Binastro" data-source="post: 3184145" data-attributes="member: 111403">.Dear Dr Owl,I am well aware of the 10 stop modern neutral density filters, some which you can vary in density.And one might think that stacking two and a bit of these would equal a welders glass 13.Unfortunately, I very much doubt whether these neutral density filters are approved or have been tested for ultraviolet and infrared radiation. This also applies to any other neutral density filters or polarising filters.The fellow who was selling the plastic filters refused to believe that his filters were unsafe, even though laboratory tests at a top university showed that they were transmitting up to 28% in the infrared. People using these awful things were reporting their eyes were getting hot, even though I don't know if we have pain receptors in our eyes. Maybe we do in the front part of the eye? Although not in the retina.If you could get one of these 10 stop neutral density filters tested throughout the wavelength from far ultraviolet to far infrared I would be interested. But this test would only apply to one particular filter or type and name of filter.When I was talking to my neighbour, and I said the neutral density filter may reduce the light intensity 10 times he didn't comment. He is a very bright fellow, but I think he has somewhat fixed ideas. And in his innocence is quite unfamiliar with direct solar observation.My neighbour was talking of using the neutral density filter for visual use when I gave him the welders glass 13 to see the sunspot. With the Cirrus clouds this was about the correct density.For photographic use, there are special filters, which are less dense than for visual use. These filters should definitely not be used visually.Also, digital cameras are sensitive in the infrared, and the special photographic filters take into account the sensitivity.Unfortunately, very few people understand direct observation of the Sun. Every report that I have read in the media has glaring mistakes, except for the ones in the astronomical press, or from astronomical societies.In a way I would be quite happy if next week's eclipse had never been publicised, but it has been and will be, and unfortunately there are going to be many cases of permanent eye damage where the weather is clear.We just try to give safety advice for those who want to observe the Eclipse and are prepared to listen.In a way we are lucky in Britain, as the timing is such that schoolchildren will be in their classrooms and can be controlled somewhat by adults.This is not the case in Europe, either with their time one hour ahead or two hours ahead, where they will have real problems keeping the kids safe.And for those not wishing to watch the eclipse, that is absolutely fine by me.</blockquote>

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