[rollei_list] Re: Rollei R3 film review
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Mon, 9 May 2005 15:54:17 -0700
----- Original Message -----
From: "Aaron Reece" <oboeaaron@xxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Monday, May 09, 2005 2:58 PM
Subject: [rollei_list] Re: Rollei R3 film review
> Richard,
>
> I had the same concerns when I first heard the claims that
> this film
> could be used anywhere from EI 25 to EI 6400. They claim
> it has three
> photosensitive layers, each with a different sensitivity.
> That is why
> you have to use the special developer to "unlock" the
> multi-speed
> capabilities (layers). With ordinary developers it has a
> nominal speed
> of ISO 400. At least, that's what they claim. I have not
> used this film
> myself.
>
> Cheers,
> -Aaron
This makes no sense. Depth developers are those that can
reach the latent image sensitivity specs below the surface
of the silver grain. Developers with relatively high amounts
of sulfite or other halide solvents do this. For instance
D-76 is a depth developer to some extent. There are also
surface developers which limit development to the
sensitivity specs on the surfaces of the crystals.
Developers which strip away the surface of the halide
crystals do increase speed somewhat but not by a lot. The
terms depth and surface developer are sometimes used in
another sense. That is whether they develop crystals near
the surface of the emulsion or those deeper. In this respect
surface developers were used to some degree in developing
motion picture sound negatives because they tended to
increase resolution by not developing the somewhat blurred
image deeper in the emulsion. This sort of thing is obviated
by thin emulsions and good anti-halation layers. Motion
picture sound recorders also employed ultra-violet sources
for a time in the late 1930's to early 1940's for the same
reasons.
Multiple layer emulsions are the standard practice.
Modern emulsion technology has allowed a single, thin, layer
to have enough latitude to cover the range of brightness
required by pictorial photograpy. This is the kind of
emulsion found on T-Max and other tabular grain films. The
square crystal emulsion mentioned in the R3 data is the
conventional type of emulsion that has been in use for a
century. Many conventional films have two or even three
layers of emulsion, each of a different sensitivity and of a
different contrast, to control the shape of the D-LogE curve
and to extend latitude.
Anti-halation layers coated under the emulsion are common
in color films and are used by Agfa in its black and white
films. It is a good way to prevent halation and eliminates
the need for a pigmented support for 35mm film where one end
may be exposed to bright light. Such a layer may have an
improving effect on resolution by eliminating the reflection
between the emulsion and the top of the support although
this does not seem to be an important factor in other films.
All film, except special purpose films, has a top coating
for anti-abrasion purposes, it has nothing to do with the
ability of the film to withstand reversal processing as is
stated in the data sheet. Reversal processes require rather
high pH developers which tend to cause emulsion swelling and
the bleach baths also can cause swelling. Color films are
hardened in manufacture to withstand 100F processing and
reversal films are hardened to withstand any additional
softing by the processing solutions. The surface coating
must also be hard or it will slough off.
The statement about color sensitivity is laughable:
apochromatic film; oh dear. This is mixing optical terms
with film terms. From the published curve the film has
extended red sensitivity suggesting it was originally
designed for some purpose requiring near-IR sensitivity such
as traffic monitoring cameras. Technical Pan has similar
extended red sensitivity although not as far extended. This
may actually be a disadvantage for pictorial use as it can
result in odd tonal rendering if a green filter is not used.
The D-logE curve looks pretty normal.
I was able to download the data sheet for the 35mm film
and for the chemicals but the others are corrupted and will
ont open in Adobe Acrobat 7 reader.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
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