Note the warning at the start of this book, and do not attempt any solar observation until you have assimilated all the details in this and other chapters.

To repeat: smoked glass and exposed film cannot be relied upon to act as safe filters for looking directly at the Sun; neither can you depend on CDs, space blankets, aiuminised helium balloons, potato crisp packets, floppy disks, smoked plastic, crossed Polaroid filters, sunglasses, mirrors, medical X-rays or almost any other of the items that may be suggested from time to time as a substitute for the filters discussed below, to act as a reliable filter.

Remember that you may have more than one telescope. Most main telescopes have a small telescope attached to their side to act as a finder, and in some cases there may be more than one. The objective of the finder must be blanked off (covered completely with an opaque screen), or equipped with a full-aperture filter before any soiar observing procedure is attempted with the main telescope┬╗ The sunlight passing through a finder if it is not blanked off may be sufficient to cause burns or to damage parts of the telescope. Note also that most finders have cross-wire eyepieces to enable them to be used for aligning the main telescope onto an object. The focused image of the Sun is likely to melt or burn these cross-wires, so the finder should not be used for eyepiece projection unless a non-cross-wire eyepiece is put in place of the normal finder eyepiece (see the section on projection below for further details).

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