Although this is a safe technique, it is important that equipment is never left unattended, especially when children are around.<\/p>
For a similar project, you could also make a solar projection screen<\/a>.<\/p> The length of the cone for our solar funnel is calculated to suit small refracting telescopes with a focal length between 300mm and 1,000mm.<\/p> Because the aperture of such telescopes will be relatively small and they lack internal structures, heat build-up is not a problem.<\/p> However, if your scope\u2019s main lens is larger than 3 inches we recommend reducing the effective aperture by using a cardboard mask with a smaller hole (2 inches) cut in the centre and taped over the dew shield.\u00a0<\/p> Solar funnels are less suitable for use with Newtonian reflectors as these telescopes have large apertures and the secondary mirror can be damaged by heat.<\/p> The solar funnel displays the Sun in white light: in other words, all the visible wavelengths of light are seen.<\/p> The eyepiece determines the size of the image; we found that any eyepiece with a focal length between 12mm and 25mm produces acceptable results, so you may be lucky enough to have a suitable candidate in your accessory box already.<\/p> Using a solar funnel is straightforward.<\/p> After capping your main lens and any accessories \u2013 such as finderscopes<\/a> \u2013 and with your eyepiece fitted, position it in the focuser.<\/p> Ensure the eyepiece is firmly fixed in the funnel and gripped in the focuser.<\/p> Next, align the telescope with the Sun. Don’t look down the eyepiece to do this!<\/p> The easiest way is to watch the shadow the telescope tube casts on the ground.<\/p> Line up the scope so the shadow becomes small and round. When it is, you should be pointing towards the Sun.<\/p> Remove the lens cap (or uncover the opening of your aperture reducer, if you fitted one) and you should see a bright image of the Sun or solar eclipse somewhere on your screen.\u00a0<\/p> Finally, make small adjustments to the mount and focuser to centralise the image and bring out any fine details on the Sun\u2019s surface.<\/p> All being well, you should be treated to a display of sunspots, which appear dark against the bright surface.\u00a0<\/p> You could sketch these and keep a record or (as we did) photograph the screen using a camera or smartphone.<\/p> If you\u2019re feeling ambitious you could draw a circle on your tracing paper screen in advance and then mark sunspot positions in-situ with a felt-tipped pen.<\/p> Or you can download our solar observing form (PDF)<\/a> to help with this.<\/p> Replace this screen after each viewing session and keep them as a record of your observations.<\/p> You should also be able to see variations in tone across the solar surface.<\/p> A nice paint finish or sticky-backed plastic covering would increase the solar funnel\u2019s longevity; the logo is, of course, optional.<\/p> Whatever you choose to do, we know you\u2019ll get a lot of pleasure from making and using this simple device.<\/p> Three pieces of thin, A4 packaging card for the funnel. Tracing paper works really well for the screen although any translucent, thin material is worth trying.<\/p> Any low-cost eyepiece with a focal length in the 15-25mm range will suffice.\u00a0<\/p> For a non-reflecting internal finish, matt black spray paint works well. For the outside, you could use gloss paint or sticky-backed plastic.<\/p> Craft knife, steel ruler, hot-melt glue gun or strong craft glue, spray adhesive or glue stick, black duct tape or electrical tape, strong elastic bands.<\/p>Downloads<\/strong><\/h2>
Solar funnel measurements<\/strong><\/h2>
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<\/figure>How the solar funnel works<\/strong><\/h2>
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Tools and materials<\/strong><\/h2>
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<\/figure>Cardboard and tracing paper<\/strong><\/h3>
Eyepiece<\/strong><\/h3>
Finish<\/strong><\/h3>
Tools and sundries<\/strong><\/h3>
Step-by-step<\/strong><\/h2>
Step 1<\/strong><\/h3>
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