I want to add my concurrence to Dave's warning as someone who has been to 25 solar eclipses as well as attempted to view satellites transiting the sun. I always construct an eclipse safety briefing with strong words of caution to eclipse observers in order to minimize any possibility that someone could suffer eye damage as a result of not having correct advice. The human eye can tolerate a lot before experiencing injury and since the cornea has no pain sensors, a person would not be aware of anything until long after the damage is done. Making a homemade solar filter is not a wise thing to do. Since ISS transits of the sun are perhaps going to be more widely publicized as ISS grows larger in size structurally, SEESAT should be diligent in providing the best eye safety advice in connection with this level of hobbyist interest. Use of any "sunglasses material" in any part of the optical chain is potentially dangerous to anyone attempting to view satellites during the day. Note also that the problem with mylar when bought in the form of solar blanket or thin film available in rolls is that you cannot always be sure you have the correct density, hence the bright field of view that often results when viewing after the material (one or two layers) is placed IN FRONT OF the telescope objective. I capitalize "IN FRONT OF" because some people have actually used mylar between the eye and eyepiece--an inherently dangerous practice also. The mylar itself normally provides good protection assuming 1) it is used correctly in the optical chain, 2) it has no pinholes, 3) it is of the correct density. However, when the observer can easily detect that the field is 'bright', the thickness of the mylar is not high enough or there is light leaking somewhere around the mylar and being scattered inside the telescope. I don't think it was intentioned to say that sunglasses were OK to use, and that Ralph was just trying to dim the background after already using mylar to get it to a comfortable level. But the mere mention of using sunglass material may give some novice readers the erroneous impression that it is a safe practice. I propose that there should be a standard rule in daytime satellite observation that states: "Warning: Observing satellites transiting the sun SHOULD NEVER BE ATTEMPTED unless the observer utilizes a neutral density 5.0 filter placed IN FRONT OF the telescope objective." Perhaps such a warning ought to be placed on the SEESAT web page. As R.Chou points out in his advice to eclipse observers, there are a variety of bizarre materials that people have used to view the sun durign eclipses such as black and white/color exposed photographic film, CD's, smoked glass, the small green sun filters that often come with cheap telescopes that are screwed onto the back of an eyepiece (extreme danger here!), sunglasses, aluminum foil, clouds, reflections from a pail of water, etc. All of these are potentially dangerous and must never be used even if there is a marginal possibility that eye damage might be incurred. There are two other similar safe sun viewing methods that are not applicable for satellite viewing: 1) pinhole camera; 2) eyepiece projection onto a white screen. Paul Paul D. Maley Tel. 281.244.0208, Fax. 281.244.1140 Lat. 29.6049N, Lon. 95.1069W, Alt. 6m -----Original Message----- From: DJLaszlo@aol.com [mailto:DJLaszlo@aol.com] Sent: Sunday, April 21, 2002 1:25 PM To: rmcconahy@earthlink.net; SeeSat-L@satobs.org Subject: Was: Transit of the sun. RE: SAFE SOLAR VIEWING In a message dated 4/20/02 1:52:22 PM Mountain Daylight Time, rmcconahy@earthlink.net writes: << About 30 minutes before the transit I set off with a Meade ETX-90 telescope with a doubled-over piece of silverized Mylar over the front for a solar filter . . . One other problem was that the sun was still a little too bright in the scope, but I solved that problem by making a poor-man's neutral density filter by holding a pair of clip-on sunglasses between my eye and the ocular. >> Ralph -- I got chills reading this. I hope no one else attempts to watch a solar transit with a homebrew Mylar filter like this. Your eye is telling you something, I think, if there is too much light to view in comfort. Even if you are comfortable with a homemade filter, you can damage your eye and feel no pain, if IR and UV are excessive, as they easily could have been. Eyepiece mounted solar filters, exposed photographic film, smoked glass, pieces of compact disk, foil-coated wrappers: all are inappropriate in a solar telescope. Please spend the nominal $ to obtain a safe solar filter with a securely attached cell, and spare yourself the risk of of a scotoma in the middle of your visual field. Baader Astro-Solar film is inexpensive, available in sheets or mounted, and gives a solar image markedly superior to typical glass and Mylar filters. My view of sunspot detail and solar granulation markedly improved when I switched to the Baader film from a US-made glass unit. The sharpness and contrast are much better, and the color is neutral. In the US, it can be obtained from Astro-Physics; Jim Kendrick in Canada supplies it in cells. Perhaps Markus Ludes carries it Germany, or can recommend a source. Dan Laszlo Fort Collins CO ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www.satellite.eu.org/seesat/seesatindex.html
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