Well, I am using the holders from Doug,
http://www.betterscanning.com which indeed can be calibrated in height. So you bring your negative in max. focus of the scanner.
The difference is slightly sharper and the whole negative is sharper in the corners with these holders.
When you're slightly out of focus the USM parameter can be adjusted by software but this is also sharpening the negative. But I am not a scanning specialist, I am printing via classical wet print, however I can tell you everything about film development.
1) By diluting a developer the negative will be sharper.
2) Fix time = 2x clear time for classical cubical films (like HP5+) and 3x clear time for Tgrain type films (Tmax, Delta).
3) Wash time = about 15 minutes. Then one minute a wetting agent to prevent stripes and drying marks.
A higher iso rate is more grain and less resolution. An ortho (pan) film has always a much higher resolution, same like micro films.
With a V500 you can get good scans for medium format around 2400dpi, for 35mm 3200dpi or more however a V500 over 4000dpi produces only more data not a better scan.
My question: How is a print from your (B&W) negative when you're going to scan it?
About selecting for films and developers: Rodinal, Beutler are high acutance developers so they give the impression of a very sharp negative. But they pronounce grain. Fine grain developers will give some speed loss but very fine grain, however here sharpness is a bit lacking.
So when you want the highest acutance and sharpness use Rodinal and HP5+ . When wanting fine grain use HP5+ (iso 200) and Perceptol. By diluting Perceptol you can control a bit the sharpness: More dilution is less Sodiumsulfite which means more sharpness but a bit more grain.
When using Rodinal, 1+25 will give less sharpness then the 1+50 dilution. Rodinal is a Para Amino Phenol developer in fact best suitable for slow and medium speed classical (cubical type) films. But in medium format you can use it for iso 400 films too.
It's a liquid concentrate and the stuff keeps remarkable well (>10 years is not a problem). It's a one shot developer.
But if you're not sure about your negatives, sent me one in, I will have a look to it and then we know it's a scan problem or a film problem.
Best regards,
Robert