Hi there,
There's a couple reasons those lenses would not work as well as we would hope on the EOS 90D. The first is that those lenses are designed for a much much smaller imaging sensor than the EOS 90D's APS-C sensor, so the lens would only make an image on the very center of the image sensor, what you would see would look like you're peeking through a keyhole rather than a complete image. After that there is also the flange distance of the lens, this is the appropriate distance from the lens's focusing element to the image sensor. On the XL1 camcorders this distance is very short, just a few millimeters while the EOS 90D needs 44mm of space to accommodate the shutter assembly and mirror box. This additional distance added to the XL lenses would mean that they could not focus properly on the sensor plane because it is much too far from the image sensor. This is why for a short time there were adapters which could allow for the use of EF lenses on the XL camcorders but not in the reverse, an EF lens can function because it has a larger image circle than the XL1 needs and can be adapted outward from the camera to reach that 44mm flange distance while the XL lenses need less distance and produce a much smaller image circle.
