Filters and eyepieces
Though small, these can end up being your most expensive pieces of kit
glass needed for filters and eyepieces means they can be expensive. They are, however, easy to post so if the seller can confirm (via photos) that they come with dust-free covers and a hard case, these should be fine for delivery.
Filters are delicate and need to be handled with care, so they can be susceptible to damage which you’ll need to check for. Obvious blemishes due to misuse can be highlighted in photos; it’s perfectly acceptable to ask for close-up images of a filter held up to a light, to check for obvious signs of damage.
If you’re buying filters for astrophotography, it’s always good to see images the seller has taken using them, and know what type of camera has been used. If it’s a clip-in filter, check in the photo that both tabs are intact and symmetrical – one hasn’t been bent or warped. This could affect how well the filter fixes to the camera. For screw-in filters check that the threads are clear and not worn or damaged.
Solar filters should only be purchased from a trusted astronomy vendor; the slightest damage to these could cause irreparable damage to eyesight or imaging equipment, so avoid second-hand items.
For eyepieces, check the ‘eye relief’ on the manufacturer’s website – for people wearing glasses this needs to be long enough to view through at a distance. Once again, ask for images of the glass in the eyepiece’s lens elements to check for scratches.
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