Slides and transparencies are scanned at least 2000 PPI (Pixels per Inch). Smaller slides, such as APS and 35mm slides are scanned at 4000 PPI, which is beyond what is necessary to capture all the detail.  4x5 transparencies are scanned at 2200 PPI+. 4x5 transparencies can be scanned at a higher resolution or up-sampled on request. Keep in mind that anything beyond 2500 PPI generally doesn't yield better results.