Which is better for scanning film? A dedicated film scanner or a flat-bed? Well, I have two film scanners, neither of which is the latest or greatest kit, but one of each type. One is a dedicated 35mm film scanner, the other a flat-bed with transparency adaptor.
The older of the two I've had since about '01, a trade-in against a Pentax ME Super, back when film cameras were still worth money! It's an Acer Scanwit 2720S dedicated 35mm film scanner, SCSI interface, scans at 2700ppi. I use this for 35mm negs and mounted slides.
The newer addition is a Microtek ScanMaker 6100 flat-bed which scans film up to 5"x4" at resolutions up to 3200x6400 ppi. I bought this one for 120 film and my 5"x4" pinhole negs. I've also used it to scan darkroom 'wet' prints.
I regularly have fights with them fight both, attempting to get the best possible scans. Scanning is always frustrating! So, I was wondering how the higher resolution of the Microtek flat-bed compared to the ancient but dedicated 35mm Acer. I took an old test slide of a resolution/colour chart and scanned it with both scanners at maximum resolution.
It was clear straight away that the Acer was better, but also I found that the Microtek wasn't providing any more detail above 2400ppi. Also, I found that it produced better scans if I placed the slide directly on the glass instead of in the plastic carrier. The results really speak for themselves. Here are the 100% crops of the scans, Acer dedicated above, Microtek flat-bed below (the latter re-sized to 2700ppi for comparison):
I wish I had something of the quality of the Acer for medium format...!