The Altair Solar Wedge has been fully tested with the sun remaining in the centre of the field of view for 4 hours of continual use centred on the sun with a 175mm aperture refractor telescope in mid-summer from 11:00 – 14:00, cloudless sky.
At no point did the outer prism housing become too hot to touch, a problem common with solar wedges.
Whilst we cannot recommend use with telescopes of larger than 175mm aperture for longer or shorter duration, if your telescope is larger, then we suggest trying the wedge for a short time initially, to assess the heat build-up and make your own informed decision.