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A Homemade 50mm Eyepiece

A 50 mm eyepiece is a great wide field accessory for a telescope, especially short focus refractors where the field of view will be close to that of binoculars. This is a very simple project, but the results will leave people looking through your telescope saying Wow!

Old 50mm SLR lenses are as-cheap-as-chips but have great colour correction, huge eye relief and flat fields so make great multi-element eyepiece's that would normally cost hundreds of pounds (2010) to buy.

I made this 50mm eyepiece from parts I had lying around, the optics are from an old Canon 50mm F2.8 ‘standard’ lens and the 1 ¼” barrel is from an unknown astronomical accessory I must have dismantled in the past!


The 50mm lens has to be fitted the right way round to work correctly, that is your eye will replace the film, this poses a small problem in that the lens probably has leavers sticking out of it to control the aperture, set the aperture to its widest, cut a suitable sized hole in the ‘back cover’ that came with the lens and place back on the lens this will cover any leavers sticking out and leave a professional finish to your new eyepiece, then attach a suitable mounting to connect it to your telescope – I glued mine using epoxy resin.

Stats: (on an F6 ED80)
Power 9.6 times
Exit pupil 8.3 ( a little large )
Eye relief ~25mm

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