On Monday, 28 September 2015 14:57:17 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
On Friday, 25 September 2015 22:49:23 UTC+1, NY wrote:
"dennis@home" wrote in message
eb.com...
On 25/09/2015 16:27, whisky-dave wrote:
Why call it a stop one have such strange stop
numbers....... why does f5.6 let in twice that of f8

f number is a measure of aperture *diameter* relative to lens focal
length.



Its the same as a film camera, where do you think it differs?
Why do you even think it might differ?

My thoughts exactly. I can't work out whether he really doesn't know or
is
winding us all up. Film and digital cameras have more in common that
maybe
he realises.

They sure do, but there are some important differncies.

OK. So what do you think these important differences are? Do you use the
aperture and shutter speed controls differently for digital compared with
for film?

To some extent yes. You need to understand them more than you do with digital.

Do the optics of lenses behave differently?

No that I know of.

Does the reciprocity
law (halve shutter speed so double aperture etc) behave differently?

Yes significantly.

Actually that last one is a trick question because it is one case where film
*does* behave differently because the reciprocity law stops working for very
short (eg 1/5000 second) or very long (eg 60 seconds) shutter speeds

reciprocity depends on the film speed too and it can have an effect even at 10 seconds or less. The last tiume I encounted this was when a friend asked me what the R failure would be at 8 seconds I said about a gnats bollock worth.
She was using 120 roll film in a mamyai I think with long exposures.
I was right as she phoned here boyfriend who looked at the data sheet and it was about .2 secopnd on 8 seconds or so.


you need to correct the exposure using characteristics that change from one
make of film to another;

yuo don;t get that with digital, you don't even have to think about it.

you also need coloured filters to correct colour
cast because the three different emulsions have different non-linear
characteristics at extreme exposures; thankfully digital sensors don't
suffer from this.

So when studying photogrphy like my friend was who won a pjhopt comp in spain.
She works at a uni teaching photography and is an adobe registered certified to teach.


Yes if you set the camera on aperture priority and look at EXIF data of
the
resulting photos taken in various lighting conditions, you'll see a
variety
of unusual shutter speeds - whatever the meter judges is correct;

yes the meter is judging this isn't good if you're teaching the subject.


Right, so you'd prefer people to use manual metering (or even an external
meter)

external meeting is better but not always practical, but when teaching photography you should also teach reflective and incident meter reading.
Not sure how you'd do this with a digital camera.

while learning about exposure. Fair enough. You can insist that the
pupil uses manual mode on the digital camera *in exactly the same way as you
would insist that they did for a film camera*.

Cabn insist all you like, yuo can insist they don't chew gum, but part of teaching is outsmarting the students.

You might be making life more
difficult for him if you make him avoid using P or Av/Tv mode, but it will
make it easier to learn initially.

They have to know what those terms mean and why you use them.


Now let's have an example of something where a digital camera with the same
auto and manual settings as a film camera,

difficult to imagine, but carry on.

and the same rules about which
settings are forbidden whilst learning, makes it more difficult to learn
than on the equivalent film camera.

You give a kid a digital camera that is **** compared to their mobile phone
they get board unintrested and disruptive.
Now you have 20 kids around you not concentrating they'd rather use their phone to get a far better picture than they could ever get with the digital camera you've supplied.



Why does the image on my LCD look the same irrespected of the
aperature and shutter speed I set.

Because you have a cr@p camera

wrong answer .

So what's your answer? Is it that the image on an LCD screen (either when
used as a viewfinder or when examining the pictures after taking) is too
small to be able to distinguish clearly between in-focus and out-of focus
parts of the scene?

No because when you lok at the screen you see what you might end up with.


If so, you may have a valid point, although I can usually tell reasonably
well.

you are going to take a p[icture of usain bolt in teh 100 meters on the left is the start on the right is the finish.
Are yuo saying they'll be no differnce whether the exposure is
1/1000 or 1 second. the aperature will take care of itself, but will what you see on the screen be the same as the images yuo take.
NO.



So maybe for learning you need an SLR which has features such as:

- ability to turn off automatic-only settings (although most compact digital
cameras allow this as well; may well be true for compact film cameras)
- optical through the lens viewfinder (as opposed to rangefinder viewfinder
for film or LCD viewfinder for digital)
- ability to preview the image with the lens stopped down to judge DoF

Now assuming that we exclude cameras in mobile phones because they are
auto-everything and usually have poor sensors, lenses and too much
post-processing, and that we exclude compact cameras because they don't have
optical TTL viewfinder and ability to preview DoF...

If we insist on an SLR for learning on, is there anything that makes it
harder to learn on a digital than a film camera?



I presume to begin with we are just teaching about using a camera, and that
we leave manipulation of the pictures in the darkroom or using Photoshop as
a separate exercise, so we just get the slides developed or the negs printed
at default settings, and that we examine the un-modified digital photos on a
PC screen. Then for the next lesson we go on to how we can modify what the
camera has taken to improve it:

- cropping the picture to exclude unwanted sections that don't fit a
standard film/digital frame
- correcting colour cast
- altering brightness and contrast to correct for minor exposure errors or
to emphasise certain parts of the subject
- retouching blemishes, unwanted parts of the subject etc
- correcting parallelogram errors due to not being able to take picture
square-on
- arty things like cutting out parts of the subject and placing it on a
different background
- merging photos to create a panorama or to simulate a wide angle lens when
you only have a telephoto with you (*)


(*) Yes, this can be done with film: I remember seeing a book about press
photographs and how they could be manipulated, either to tell lies or to
correct for not having the right equipment. And there was an example of the
interior of a church where the photographer only had an 80 mm lens instead
of the 28 mm that he would have liked, so he took a series of photos all at
the same exposure and from the same viewpoint; he then printed them all
using identical settings and cut them along various boundaries in the
subject to disguise the cutting lines, and stuck them all together and
re-photographed the result. If you looked closely you could see
discontinuities here and there but he'd done a fantastic job and the fact
that it was a paste-up probably wouldn't have been noticeable with normal
coarse-screen newspaper printing. The same process can be carried out
digitally far more easily and sometimes so well that you'd have trouble
seeing the joins, but it's not impossible with film, given a bit of
patience.