Re: Transit of the sun. RE: SAFE SOLAR VIEWING

From: Ed Davies (
Date: Mon Apr 22 2002 - 09:56:18 EDT

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    "MALEY, PAUL D. (JSC-DO511) (USA)" wrote:
    > 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." 
    R. Chou's advice (
    mentions one reason for not using eyepiece filters - that the filter can
    overheat or crack without warning.
    Do you think that another reason for this advice could be that any tiny hole 
    in a filter behind the eyepiece could cause damage to points or lines across 
    the retina whereas similar sized holes in a filter in front of the objective 
    will a) be a much smaller proportion of the area of the filter (just because 
    the objective is bigger) and b) have their effect "diluted" across the whole 
    field of view (because the hole would be more out of focus)?
    R. Chou's advice also mentions use of a particular shade of welder's glass.
    Anybody know for sure whether welding masks in general are safe to use for 
    solar observation?  I've seen people use them for eclipse observation but 
    don't know if they have sufficient IR or UV filtering effect.
    > 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.
    Why are these methods not applicable?  I can imagine that a pinhole would
    have to be pretty carefully set up to get the resolution to see a small
    dot like a satellite but use of a small lens could work, couldn't it?
    Perhaps a camera obscura with a CCD camera set for macro focus inside?
    Maybe even a tiny pinhole "focused" directly onto a CCD - e.g., a 
    Philips web-cam with the lens removed.
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