guys, wen shooting with slides, is it better to be underexposed abit?
Slides have very limited latitude. For Zones (levels of light and dark), we use the slide film at this levels:
Zone II = -3 stops (very black)
Zone III = -2 stops
Zone IV = -1 stop (dark middle tone)
Zone V = +- 0 stops (middle tone from grey card)
Zone VI = +1 stop
Zone VII = +2 stops (already burnt out! totally white)
Usually real life is very complex. Readings from an average meter (zone V) , assuming the meter is accurate, and -1 stop to zone IV, may give a general good exposure for slides. I would say its 70-80% success rate.
If you want 100% success rate, identify all the zones and make sure your subject of interest is right between zone IV and zone V.
Use a spot meter from a DSLR or a dedicated light meter. The DSLR sometimes give -1 stop off because of the lens or whatever reason.
Note that Fuji velvia 100, Kodak E100VS and Fuji velvia 50 all behave differently.
However, for print film (negatives), modern versions are so good it allows a lot of errors.
-0.5 stop to +4 stops may not tell any difference.
For print film, I always expose +1 stop to get better contrast.