Measured scanner resolutions

Unashamedly from my original DPR posts, these are some scanner resolutions I measured using a USAF 1951 target

Olympus EM1ii with sensor shift, Olympus 60mm f/2.8 macro at f/4.
Expect 8230ppi
Actual 3962ppi

Plustek 8200i
Expected 7200
Actual 3505

Canon FS4000US
Expected 4000
Actual 3150

Plustek 8200i
Expected 3600
Actual 2794

Nikon D610 + f/2.8 50mm AF-D + ES2
Expected 4233 (based on 4000 pixels per 24mm)
Actual 2794

Epson V550
Expected 3600
Actual 1575

Veho VFS-008 (all in one cheap scanner)
Expected 1828ppi (based on final 5MP image size)
Actually 762 ppi

Hm, I really should start to investigate how to improve my 120 scanning, using my xt-3 and a macro lens instead of my V550...

You might find it’s not that much higher a resolution - 6cm would be ~3700 pixels on a V550, which is pretty close to the short side resolution on the XT3.

I am a little lost with dpi /ppi etc.. I scan at 2400 dpi and my 120 images are around 5200x5200 pixels after scanning and small border crop corrections. Does that seem reasonable? Maybe I am wasting space.

For those tests I scanned the 35mm USAF target at 3600 dpi, and then looked for the highest resolution block I could find, which then gives a measure of the real resolution of the scanner (1575ish), but if you scan lat 2400 you might get a slightly lower resolution - I’ve not tried that. I suppose what the target measurement is saying is that you could scan at 3600 and then half scale the final image and you wouldn’t be losing any information, plus it would be sharper too.

So is there a (simple enough for me) explanation of why scanners deliver so much less resolution than they claim?

My understanding is that the quoted figures are the resolution which the head can be moved by. The actual resolution is dependent on things like the lens, focussing etc. I’ve found the same when using a camera, the Nikon D610 should have given a 24MP image, but in reality it was closer to 11MP (because of loses in the lens, focus (possibly), sensor etc.

Glad you are sharing this here…just in case it is lost forever on the old forums. I was always a bit surprised by the D610 performance. I sold my Epson V700 recently and will look to a dedicated 35mm scanner or going the DSLR scanning menthod.

Some additional measurements

Reflecta ProScan 10T
Expected 5000
Actual 3962

Nikon CoolScan V
Expected 4000
Actual 3962 (possibly 3505 horizontal - i.e. one group less)

Further details of the target are here www.film4ever.info/vtt