Sheet processing apparatus and image forming system

An image forming system comprising:

• an image forming apparatus configured to form an image on a sheet;
• and
• a sheet processing apparatus configured to perform a post-process to the sheet, the sheet processing apparatus comprising:
• a conveyance unit configured to convey the sheet from the image forming apparatus along a conveyance path, the sheet being a first type of sheet or a second type of sheet that is higher in transmittance than the first type of sheet;
• an optical sensor provided on the conveyance path and configured to detect the sheet during conveyance;
• an alignment unit configured to align the sheet conveyed by the conveyance unit based on detection information about the sheet detected by the optical sensor;
• a post-process unit capable of performing a post-process to the sheet aligned by the alignment unit;
• an input unit configured to input post-process information indicating whether or not the post-process unit performs the post-process to the sheet;
• and
• a control unit configured to control, in a case where the optical sensor does not detect the sheet during conveyance within a predetermined time period and the sheet corresponds to the second type of sheet, the conveyance unit to stop conveyance of the sheet based on the post-process information input with the input unit,
• wherein the control unit is configured to control, in a case where the optical sensor does not detect the sheet during conveyance within the predetermined time period and the sheet corresponds to the first type of sheet, the conveyance unit to stop conveyance of the sheet regardless of the post-processing information input with the input unit.