In article <55tqn0$9t8@enterprise.netserv.chula.ac.th>, u3618352@student.chula.edu says...

> I'm almost new for photography .
> That I ever known about color reversal films , generally +2 and -3
>for them . Are these values exp. range or latitude ?
> Someone told me that ( for slide ) when spot to choose something
>to be middle. If you expose more than +2 stops from that values it cannot
>show details in that chosen part ( IMHO it must be in highlight ). And
>if expose lower than -3 stops from that ( mid ) it cannot show details
>( I think it must be in shadow ). Is it right ( I'm misunderstand ) ?
> If it's right , do color reversal films generally have exposure
>range 5 stops ?
> And what about negative and B&W ?
>
> Please let me know , thank you very much .

You have it right on the color reversal film range - and the result is
that it has virtually NO "latitude" (exposure must be very nearly exact
[+/- 1/4 stop, MAYBE!]). Things are slightly better with B & W negatives,
but for best results, there is also very little latitude (MAYBE one stop
over, 1/3rd under - but that's stretching it). With color negatives things
are easier, with about 2 stops over, 1/2 under still producing top quality results, and that can be stretched, with some quality loss.
Hope This Helps