Yes, you can use it and you CAN have Auto Exposure Flash as well. I have a Canon 199A and also a Canon 299T. Both of these flashes are old enough to use Auto Thyristor flash which can still give you auto exposure flash with today's digital cameras. This is because the auto sensor is in the flash itself and needs no communication with the camera in order to get an auto exposure.

Later film flashes like the 300TL, 300EZ, 420EZ etc. Used TTL or ATTL flash metering which read the exposure off the film plane. Drag And Drop File Conversion. These will only fire at full power on a Digital camera since there is no film plane to read the exposure from.

The 199A when used with your AE-1 was very automated. You could just leave the lens set to 'A'and the camera would do everything else for you. With today's cameras you need to set the shutter speed, aperture and ISO on the camera, and then the flash will be able to match those settings and give you Auto flash exposure. Serial To Parallel Converter I2c.