On 30/09/2015 19:16, NY wrote:
"dennis@home" wrote in message
web.com...

See as far as teaching goes there are no differences between film
and digital unless you decide to use them.

So I'm right there sis a differnce even more significant when you
teach the subject.

Whisky Dave has given several things that you need to be aware of when
using
film, such as

- reciprocity failure at extreme shutter speeds
- need to choose the film type (eg speed, manufacturer, B&W/colour,
slide/neg) before shooting

And the colour temperature of the continuum light source. All bets are
off with film in narrowband or emission line based illumination.

It is mainly of historical interest CCDs get it right. It so happens
that panchromatic and colour emulsions have a safelight wavelength
sensitivity gap that exactly matches the bright green OIII nebula line
in many astronomical nebulae. This meant that until about the mid 1970's
when a special emulsion sensitive to this line was created all the
Palomar deep sky slides showed nebulae to be red, pink and powder blue
with no hint of green, yellow or turquoise.

It always seemed a bit odd that something that visually looked dirty
oily grey green photographed as mostly pink and blue.

This raises an interesting philosophical question: do you need to know
about
film (and the limitations and issues that only affect film and not digital)
in order to know about photography nowadays?

I would never go so far as to say that film is an obsolete photographic
medium (in the same way that I wouldn't describe vinyl as an obsolete
sound-recording medium), but it's becoming more of a niche product.

An interesting quirk of colour film is that to get flesh tones exactly
right in different parts of the world different makers bias their colour
films slightly differently (and so do digital cameras). The residual
errors are hidden along the line of purples which makes a few rare plant
flowers with just the wrong peak wavelength reflected look very strange
indeed when using film. Notocactus Ubelmannianus (purple form) is one
such plant that photographs badly on most colour films.

Digital images can easily have their white balance and flesh tones
tweaked afterwards if necessary and the residual colour errors are also
considerably less than film on decent kit.

Is there anything about photography (the creation of pictures using light)
which you would lose if you didn't teach about film-specific issues like
reciprocity, different light curves of different makes of film, the need to
choose the speed of film before you start shooting, given that these are
not relevant to digital.

Choosing the speed can still be relevant in digital if you want to
deliberately create a motion blur or freeze fast action. You are always
trading signal to noise for shorter exposures (courser grain in film and
more intrusive thermal noise/less resolution on a digital camera).

One thing a one shot colour camera struggles with is monochromatic
images at certain wavelengths. Some sensors really don't like red
H-alpha and leaks in the other filtered channels gives a weird effect.

Choice of colour v black and white is an after-shooting post-processing
issue with digital (indeed the photographer who took digital photos of my
wedding presented a few shots both in colour and monochrome, with
contrast-enhancement to emulate a B&W negative as opposed to straight
colour-to-monochrome conversion).

Choice of emulsion can be controlled after the event using programs that
alter the gamma curve to emulate different brands of colour slide and
negative film - again, deferring that decision until after shooting.

You could do some of these things by scanning slides or negatives back
when film was the only high resolution game in town.

Choice of ISO speed can be made from shot to shot. When I used film I used
to wish I could do this. As a photographer you need to know why you don't
shoot everything at 3200 ASA (greatly increased noise, maybe different
tonal
and colour representation though I can't detect any with my cameras), but
you don't need to decide on a fixed ASA for all shots.

You could in the old days push process film or bake it in a dry N2/H2
gas mix for a day or two before use to trade shelf life for sensitivity.
You didn't have to develop it exactly by the book.

In extremis uranium intensifier could sometimes rescue faint under
exposed silver based images to printable negatives.

It is not a deficiency of digital that some of these issues do not exist.
Some might even see it as a bonus that you have fewer restrictions like
this.

The main advantage of digital especially in hard to repeat situations is
that you have instant feedback and know almost immediately whether or
not you have a decent quality record of the event.

We used to carry a Polaroid instant camera around with negative capable
film stock as an insurance policy when taking important images.

Polaroid was doomed the moment that Mpixel digicams became affordable.

--
Regards,
Martin Brown