Re: [photo-3d] Provia !!

[Paul Talbot <ptww@xxxxxxxxx>]

"Hans A.J. Middendorp" wrote:
> 
> Yes, I did try Sensia 200 as well, but I found it much more grainy compared
> to Provia 100 and not worth the extra f-stop. This seems to be in
> contradiction with the Table posted below, were the RMS value is only about
> 10% different between Provia and Sensia? How should one understand these
> values?
> 
> >Paul Talbot wrote:
> 
> Film                    Code     ISO     RMS   Resolving Power*
> ----                    ----     ---     ---   ---------------
> Provia F                RDPIII   100       8      60 ;  140
> Velvia                  RVP       50       9      80 ;  160
> Provia                  RDPII    100      10      60 ;  140
> Astia                   RAP      100      10      55 ;  135
> SensiaII                RA       100      10      55 ;  135
> Provia 400/SensiaII 400 RHP/RH   400      15      40 ;  125

I'm puzzled where you got an RMS value for Sensia 200, as that
film was not in the table.  The only ISO 200 listing was for
Fuji's multi-speed film.  Sensia II (ISO 100) and Provia rate
the same RMS granularity; Provia has higher resolving power,
and looks much better to me in stereo.

As far as the numbers, first note that RMS ("root mean square")
is a mechanical measure, and other factors affect perceived
graininess.  And now a word on terminology.  I had always
thought in terms of high visibility grain ==> "very grainy;" ==>
"a lot of grain."  But I'm told I had things backwards.  When
a film has more grain the grain is less visible because the
particles are smaller (other things being equal).  Thus, more
grain is better (less visible).

Expressing it in those terms, I'm further told that RMS
is analogous to exposure values: each unit represents a
doubling.  So Provia F at RMS 8 has twice as many grains
as Velvia at RMS 9, which in turn has twice as many grains
as Provia at RMS 10.

Disclaimer: I have no idea whether what I was told was in
fact a true interpretation of RMS values for grain.  Perhaps
an engineer can help us out.

Paul Talbot