Re: large format ortho

Hi:

By providing a longer range and shorter exposure times, preflashing the
film allows ortho to record shadow details much more effecctively.

I use an enlarger, and an exposure timer to do this. Its just about the
only thing I use an enlarger for now :)

I set the enlarger so that it will expose an area larger than the film I
use. I stop it down.

To determine the flash duration I did a series of test exposures until I
found the longest exposure that would NOT fog the film once it was
developed.

With my setup and developer its around 12 seconds.

If you don't have an enlarger you may be able to do something like turn on
a very dim light - a 7 watt nightlight or something like that for a few
seconds.

You essentially have to be able to illuminate the film under a very low
light level for an accurate amount of time.

The amount of time is determined by finding the longest exposure the film
can tolerate without fogging.

If you don't have a really accurate timer, you would have to use a dimmer
light source and expose it longer.

I could probably get away without using my timer, and use my wrist watch,
or count to 10 etc. (all of this can be done under safelight)

The film acts like it has a threshold of exposure. No latent image will
be formed until the exposure level has surpassed this theshold.

For pinhole this means that while taking the picture, some time is spent
simply getting past the threshold without recording any image information.
If this theshold is surpassed prior to exposure (by pre-flashing) the
exposure times will be shorter - resulting in a "faster" film.

On Sat, 2 Nov 2002, Ricardo Wildberger Lisboa wrote:

> Hi Gord,
>
> Just to clarify it, how do you pre flash these filmes ? I mean, what light
> source, how long exposure, etc. Thanks,
>
> Ric.
>
>
> ----- Original Message -----
> From: "Gordon J. Holtslander" <holtsg@duke.usask.ca>
> To: <pinhole-discussion@pinhole.com>
> Sent: Friday, November 01, 2002 3:32 PM
> Subject: Re: [pinhole-discussion] large format ortho
>
>
> > Hi:
> >
> > I use 8x10 ortho to make big negatives. I mostly print cyanotype though.
> > The key is using a very low contrast developer.
> >
> > People have had success using a highly diluted print developer - such as
> > dektol, selectol sprint etc. diluted (10:1 to 30:1).
> >
> > The ASA of the film is around 6 with these developers.
> >
> > I find these are still too contrasty with the ortho film I use (kpgraphics
> > CGP)
> >
> > A very good low contrast developer formulated specifically for producing
> > low contrast negatives from ortho film is Dave Soemarko's LC-1 developer
> >
> > http://members.aol.com/fotodave/Articles/LC-1.html
> >
> > This developer is not commerically made - you must mix it yourself.
> >
> > By varying the dilution and mix its possible to control the contrast
> > effectively.
> >
> > LC-1 does result in a significant speed loss though - film processed in
> > LC-1 has an ASA of 1.
> >
> > This does become an issue with very large format cameras, if your pinhole
> > is small, the f stop is so small that the expsosure time can stretch to
> > hours.
> >
> > You might try seeing how large of a pinhole you can tolerate (and its
> > fuzziness) before you start shooting 16 x 20
> >
> > I think an XTOL ascorbic acid based developer at a low pH seems to work
> > better
> >
> > See Mytol http://www.jackspcs.com/mytol.htm
> >
> > Chemical Amount Units
> >
> >
> > Distilled Water 750 ml
> > Sodium Sulfite 60 g
> > Sodium Metaborate 4 g
> > Sodium Ascorbate 13 g
> > Phenidone 0.15 g
> > Sodium Metabisulfite 3 g
> > Distilled water to make 1000 ml
> >
> > This formula mixed without the alkali agent (Sodium Metaborate) may work
> better.
> >
> > I also find that pre-flashing the film at an exposure just less than
> > something that would fog the film extends the range and sensitivity of
> > the film.
> >
> > Testing with a Stouffer step tablet I'm able to get an 18 step negative.
> > Using a similar developer to Mytol and preflashing the film.
> >
> > Gord
> >
> > On Fri, 1 Nov 2002, Tim Midkiff wrote:
> >
> > > Hello all,
> > >
> > > Does anyone have firsthand experience using large format ortho film,
> > > 16x20, in camera for gum prints? I've been doing a few the hard way,
> > > making the first exposure, then making a high density neg then making
> > > the gum prints. any ideas or suggestions, etc would be greatly
> > > welcomed!!!
> > >
> > > thanks, tim
> > >
> > >
> > >
> > >
> > > _______________________________________________
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> > >
> >
> > ---------------------------------------------------------
> > Gordon J. Holtslander Dept. of Biology
> > holtsg@duke.usask.ca 112 Science Place
> > http://duke.usask.ca/~holtsg University of Saskatchewan
> > Tel (306) 966-4433 Saskatoon, Saskatchewan
> > Fax (306) 966-4461 Canada S7N 5E2
> > ---------------------------------------------------------
> >
> >
> > _______________________________________________
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> >
>
>
>
> _______________________________________________
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>

---------------------------------------------------------
Gordon J. Holtslander Dept. of Biology
holtsg@duke.usask.ca 112 Science Place
http://duke.usask.ca/~holtsg University of Saskatchewan
Tel (306) 966-4433 Saskatoon, Saskatchewan
Fax (306) 966-4461 Canada S7N 5E2
---------------------------------------------------------
Received on Mon Nov 4 11:16:31 2002