Canon T 90 - Manual (Page 126)

Please see p, 114 on the exposure warning
displays and the countermeasure for this
case.
1) Set the display panel to any one of “Av", “P",
or “Program”.
2) When using an FD lens, remove the aperture
ring from the “A” mark
3) Set the desired aperture value todhe lens
manually.
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