ISO & exposure comp. -- aren't they redundant?
Charles Packer
and F-stop, had one other means of controlling how much
light reached the film: the ASA dial, which was
customarily set to the same "speed" as the film and left
there.
My first digital, a Sony Mavica, dispensed with the
ASA setting but had exposure compensation, called "EV",
from -2 to +2, easily accessible in two clicks of the
main button.
My next digital, an Olympus SP-350, had both the -2/+2
exposure compensation and "ISO", which seemed synonymous
with film speed. The former was immediately available
with up/down buttons; the latter was buried way the
hell down in the menu, which seemed similar to film
mentality.
My current digital, a Canon 20D, reverses the
accesibility of ISO and exposure compensation. The
former is a button-press and a wheel; the latter,
incredibily enough, is a power switch position,
a half-press of the shutter, a peek in the viewfinder,
and a wheel.
Where is the logic in all of this? In the digital world,
aren't ISO and exposure compensation redundant, anyway?
--
Charles Packer
http://cpacker.org/whatnews
mailboxATcpacker.org
Marvin
They are not redundant. If you are taking an action
picture, as one example, you don't want the shutter to stay
open long, so you let the camera alter only the f-stop or
ISO setting. If you want to improve your photo skills, buy
or borrow a book on photography basics. For a question like
this, it doesn't matter if the book is about film or digital
photography.
semoi
exposure.
Does one use manual exposure, a zen master of the Zone system driven by the
illusion of controlling all things photographic?
Is one slavishly devoted to programmed exposure, abandoning all
responsibility?
Is one unable to abandon an earthly desire for shutter/aperture control?
Does one comprehend the impact on the digital universe caused by altering
ISO settings?
Have you mastered the sacred rituals of Adobe Photoshop?
Marco Tedaldi
> My last film camera, a Minolta SLR, beyond shutter speed
> and F-stop, had one other means of controlling how much
> light reached the film: the ASA dial, which was
> customarily set to the same "speed" as the film and left
> there.
>
is inside, so it can calculate the right exposure.
> My first digital, a Sony Mavica, dispensed with the
> ASA setting but had exposure compensation, called "EV",
> from -2 to +2, easily accessible in two clicks of the
> main button.
Right, this way you can under or overexpose a picture when you think
your camera automatics are not doing it right.
>
> My next digital, an Olympus SP-350, had both the -2/+2
> exposure compensation and "ISO", which seemed synonymous
> with film speed. The former was immediately available
> with up/down buttons; the latter was buried way the
> hell down in the menu, which seemed similar to film
> mentality.
>
Thats wrong. the ISO-Setting on a digital camera is really like changing
the film and telling the camera the ISO-Setting of the new film. So a
picture taken at ISO400 should look the same as a picture taken at
ISO100 (except some more noise in an image with ISO400 in some cases)
> My current digital, a Canon 20D, reverses the
> accesibility of ISO and exposure compensation. The
> former is a button-press and a wheel; the latter,
> incredibily enough, is a power switch position,
> a half-press of the shutter, a peek in the viewfinder,
> and a wheel.
>
40D... the process sounds almost the same but i think it's quite convenient.
Half-Pressing the shutter button (releasing it, if I want) and turning
the thumb wheel on the back to change the EV-Correction. Shown on the
display on the top and in the Viewfinder. A no hassle process.
> Where is the logic in all of this? In the digital world,
> aren't ISO and exposure compensation redundant, anyway?
Nope, not at all.
The EV-correction over the ISO setting in earlier days where a way
around a missing feature. You had to lie to your camera about the film
speed if you wanted it to behave like you wanted. Now you can tell your
camera, what you want and it should do it.
greets
Marco
--
Agfa isolette, EOS 40D
http://flickr.com/photos/kruemi
And a cool timekiller: http://www.starpirates.net/register.php?referer=9708
Floyd L. Davidson
>My last film camera, a Minolta SLR, beyond shutter speed
>and F-stop, had one other means of controlling how much
>light reached the film: the ASA dial, which was
>customarily set to the same "speed" as the film and left
>there.
It also had the potential of changing to a film with a
different speed. (Which in some cameras, with some types
of film, could automatically set the ASA of the camera to
match that of the film.)
And indeed, some film cameras had Exposure Compensation
too, if they had a built in light meter. All that EC
does is change where the meter reads 0. If EC is set to
+1, it will take 1 fstop more light to zero the meter.
Note that for our purposes ASA values and ISO values are
the same thing. It is a measure of the light
sensitivity of the film/sensor. ASA was from the
American Standards Association and ISO is from the
International Standards Organization. The difference
between the two values is highly technical and isn't
enough to be of concern in this discussion.
Given the above, each of your different cameras can be
compared in a useful way.
>My first digital, a Sony Mavica, dispensed with the
>ASA setting but had exposure compensation, called "EV",
>from -2 to +2, easily accessible in two clicks of the
>main button.
No difference, except the Mavica could not use "film" that
had a different ASA value, it had only one type of film.
>My next digital, an Olympus SP-350, had both the -2/+2
>exposure compensation and "ISO", which seemed synonymous
>with film speed. The former was immediately available
>with up/down buttons; the latter was buried way the
>hell down in the menu, which seemed similar to film
>mentality.
That statement hits a nail right on the head!
As you say, this camera is no different than were film
cameras, except for the means of presenting the
functionality. With cameras manufactured before silicon
based electronics, everything was necessarily a
mechanical user interface. And as first transistor and
then computer technology became sufficiently developed,
that has allowed a much more complex camera design which
can include automation not available previously, and
user interface options that are different. (Which of
course is true whether the camera has an electronic
sensor or whether it uses film; hence this is not a
matter of "film vs. digital".)
The point your paragraph above makes is that there are
different approaches to the user interface. Mechanical
buttons on the camera (the face, the back, the top, and
which ones are visible in the viewfinder or on various
LCD displays???), or via a menu system? (And how are
menus presented? Via rotary dials, clicky buttons, or
whatever?)
Every manufacturer did their own studies to determine
what they thought their customer base would find most
comfortable.
>My current digital, a Canon 20D, reverses the
>accesibility of ISO and exposure compensation. The
>former is a button-press and a wheel; the latter,
>incredibily enough, is a power switch position,
>a half-press of the shutter, a peek in the viewfinder,
>and a wheel.
>
>Where is the logic in all of this? In the digital world,
>aren't ISO and exposure compensation redundant, anyway?
Obviously it is indeed logical, but also targets different
types of people who may or may not be logical themselves.
And no, ISO and EC are not the same. However,
effectively you now have an ISO setting instead of
changing film, and you have EC rather than adjusting the
camera's ASA setting. Hence the old ASA setting is much
the same as todays EC setting.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) fl...@apaflo.com
Dudley Hanks
"Floyd L. Davidson" <fl...@apaflo.com> wrote in message
news:87y6vfy...@apaflo.com...
I'm not sure how true this is from a technical standpoint, but, the way I've
always looked at ISO vs. EC is that ISO changes base sensitivity of the
sensor while EC reduces (or increases) the amount of light admitted through
the aperture / shutter mechanism.
By changing the ISO setting, the change adjusts what the camera's circuitry
does with the data collected -- changing the EC adjusts the actual amount of
light that strikes the recording medium.
Hence, quite different results can be obtained.
Take Care,
Dudley
Doug Jewell
> My last film camera, a Minolta SLR, beyond shutter speed
> and F-stop, had one other means of controlling how much
> light reached the film: the ASA dial, which was
> customarily set to the same "speed" as the film and left
> there.
the emulsion on the film and to a lesser extent the
processing. It was then up to the camera to put the correct
amount of light onto the film. The ISO setting on the camera
was selected to match the film so that it exposed correctly.
>
> My first digital, a Sony Mavica, dispensed with the
> ASA setting but had exposure compensation, called "EV",
> from -2 to +2, easily accessible in two clicks of the
> main button.
or only had fully automatic ISO controls. ISO on a digital
camera is a completely different beast to ISO on a film
camera. The exposure compensation function is used if you
think the inbuilt meter is getting it wrong - the inbuilt
meter will look at the scene, assume it is average grey and
set the shutter/aperture accordingly. If the scene isn't
average grey (eg lots of white from snow, or lots of black
from a black dog), or if you want to deliberately over/under
expose for mood, then the exposure compensation is used to
adjust it up/down accordingly.
>
> My next digital, an Olympus SP-350, had both the -2/+2
> exposure compensation and "ISO", which seemed synonymous
> with film speed. The former was immediately available
> with up/down buttons; the latter was buried way the
> hell down in the menu, which seemed similar to film
> mentality.
Remember with film the ISO is fixed by the emulsion. With
digital though the ISO is dynamic and is determined by the
amount of amplification done to the signal from the sensor.
So if you loaded 100ISO film and set your camera to ISO 400,
it would under-expose because the camera would put 1/4 the
amount of light onto the film. However with a digital
camera, the resulting image should be basically the same
(other than noise). At 100 ISO it lets more light onto the
sensor and does less amplification. At 400 ISO it lets less
light onto the sensor, but then amplifies the signal so that
it gets the same overall brightness in the image.
>
> My current digital, a Canon 20D, reverses the
> accesibility of ISO and exposure compensation. The
> former is a button-press and a wheel; the latter,
> incredibily enough, is a power switch position,
> a half-press of the shutter, a peek in the viewfinder,
> and a wheel.
screwed. Try a Pentax K10 for a far better implementation.
>
> Where is the logic in all of this? In the digital world,
> aren't ISO and exposure compensation redundant, anyway?
same thing because both controlled whether you put more or
less light onto the film than what it's ISO said you should.
Setting the camera to ISO 100 with -2 EC would let the same
amount of light to the film as ISO 400 would. A lot of
film cameras didn't have an EC setting, so if you wanted to
temporarily over/under expose you could temporarily change
the ISO setting. Alternatively some cameras didn't have ISO
setting, so if you wanted to expose a roll of film different
to the standard, you could change the EC setting. Therefore
on a film camera the 2 settings were kind of redundant - so
long as you had 1 or the other you could do the same thing.
On digital however, because the ISO controls the sensor
amplification, you need both an ISO and an EC function. With
ISO only, it will always expose at what the meter says is
correct, so you wouldn't have the ability to force
over/under exposure. With EC only, you wouldn't have the
ability to alter the ISO - Lower ISO has the advantage of
low noise, but requires longer exposures. High ISO has the
advantage of faster exposures, but at the expense of higher
noise.
Thus on a digital camera, both settings are required.
Pat
It is interesting but I read your question completely differently than
all of the previous posters because of 1 very important word in there:
ASA.
If you owned a camera with an ASA setting, then you are "older" and it
is likely that you think in a completely different manner than a all-
digital person does. The all-digital person might not even comprehend
the question.
On film, you are exactly correct. ASA/ISO is exactly the same as
exposure compensation and they are redundant. No one though of it
that way "back in the day" but it is true. If you were shooting and
you thought your auto-exposure was off, say you were shooting
something bright, you might override the meter by lowering your ASA
setting. That let in more light and compensated for the shortcoming
of metering. That's how it was done. It worked because you didn't
change the film. The film is a constant. You just outsmarted the
meter. It was exposure compensation before exposure compensation was
cool.
Now just to the digital age. When you change the ISO it isn't the
same thing because it, in effect, changes the "film" to the new ISO
number. The constant of the film is gone. So now you pick your ISO
and use your exposure compensation to give the image more or less
light than the meter wants.
So the answer to your question is "yes and no". On film they are the
same but in digital they are not.
I hope that clarifies it for you.
Toby
"Charles Packer" <mai...@cpacker.org> schrieb im Newsbeitrag
news:0711d544-581b-400a...@e15g2000vbe.googlegroups.com...
No one ever accused Canon of having good ergonomics...
In a word, yes they are redundant in terms of function, but there are good
reasons to have both. You want to have your base ISO as a given, and not
have to worry about math in the field. Much easier to set ISO 320 and go +/-
1 EV than to sit and have to think about switching from 640 to 160. Also,
when you adjust exposure compensation you get a warning in the viewfinder so
that you know that your effective ISO has been changed from your base
setting. Beyond that, you have the exposure compensation information
included in the EXIF data, which gives you valuable information about the
behavior of your meter.
Toby
Floyd L. Davidson
>> Where is the logic in all of this? In the digital world,
>> aren't ISO and exposure compensation redundant, anyway?
>
>No one ever accused Canon of having good ergonomics...
>
>In a word, yes they are redundant in terms of function, but there are good
>reasons to have both.
The good reasons are that they are *not* redundant.
/Each/ /control/ /provides/ /a/ /distinctly/ /separate/ /function/.
The *ISO* *value* selects the gain of the amplifiers between
the sensor and the Analog-to-Digital-Converter (ADC).
For all practical purposes that sets "sensitivity" of
the camera to light, and more specifically it *determines*
*what* *scene* *brightness* *level* *will* *be* *recorded* *as* *the*
*maximum* *digital* *brightness* *level* *in* *the* *image*.
*Exposure* *Compensation* is an adjustment to the
camera's light metering system. It sets the light level
at which the meter reads "0". That is, it *determines* *where*
*scene's* *middle* *gray* *will* *be* in relation to the maximum
digital brightness level that is set by the ISO value.
ISO and EC each perform a very different function. If a
scene is metered, and exposure is adjusted (either
automatically or manually) for the meter to read 0, a
given level of scene brightness will produce a specific
digital brightness value that is recorded in the image
produced by the camera.
Changing the ISO value changes the sensitivity of the
camera's sensor. If the ISO is made 1 fstop more
sensitive, the same scene will read +1 on the meter.
That will cause automatic exposure modes to reduce
exposure to get a reading of 0 on the meter, and the
effect will be to have *exactly* *the* *same* digital
brightness values recorded by the camera. The same image
will be recorded!
If instead the EC value is changed to -1, the meter will
then read +1, and again in automatic exposure modes the
camera will adjust exposure to get a meter reading of 0,
which will reduce the digital brightness values that the
camera records by 1 fstop across the entire recorded
image. At different image will be recorded!
If the shutter is fired only when the meter reads 0,
then ISO will set the maximum digital value recorded,
and EC will set which value middle grey is recorded at.
Again, the ISO value sets the sensitivity of the sensor
to determine brightness levels that are recorded as
image data. It sets the absolute maximum light value
that can be recorded as part of an image will be.
The EC value sets the sensitivity of the metering
system. It sets the light value that will be recorded
as middle grey in an image when the meter reads 0.
The rest of these comments are based on a misunderstanding
of ISO and EC:
>You want to have your base ISO as a given, and not
>have to worry about math in the field. Much easier to set ISO 320 and go +/-
>1 EV than to sit and have to think about switching from 640 to 160. Also,
>when you adjust exposure compensation you get a warning in the viewfinder so
>that you know that your effective ISO has been changed from your base
>setting. Beyond that, you have the exposure compensation information
>included in the EXIF data, which gives you valuable information about the
>behavior of your meter.
Charles Packer
> So the answer to your question is "yes and no". On film they are
the
> same but in digital they are not.
>
> I hope that clarifies it for you.
This has been very enlightening. First, I never knew that
film cameras had exposure compensation controls as well
as the ASA dial. My Minolta wasn't that fancy, I guess,
and I got into advanced cameras only as the film era
was pretty much over.
So...it's interesting that the electronic designers
mapped the analogy of film speed onto sensor amplification
to the extent that they kept the same numbering scheme
as film speed. Does this mean that there's an industry
standard for that? Will a setting of ISO 100 at a given
shutter speed, F-stop, and default exposure compensation
give similar results on any brand of camera with a
similar number of megapixels?
bugbear
> Where is the logic in all of this? In the digital world,
> aren't ISO and exposure compensation redundant, anyway?
ISO - in effect a choice between speed and noise
exposure comp - the ability to intervene when the automatic
exposure algorithm does not serve well enough.
In what way are these redundant?
BugBear
bugbear
> Will a setting of ISO 100 at a given
> shutter speed, F-stop, and default exposure compensation
> give similar results on any brand of camera with a
> similar number of megapixels?
Exposure compensation is applied to the automatically
generated exposure.
If you've set aperture and shutter speed,
exposure compensation is disabled (or meaningless)
BugBear
Floyd L. Davidson
>So...it's interesting that the electronic designers
>mapped the analogy of film speed onto sensor amplification
>to the extent that they kept the same numbering scheme
>as film speed. Does this mean that there's an industry
>standard for that? Will a setting of ISO 100 at a given
>shutter speed, F-stop, and default exposure compensation
>give similar results on any brand of camera with a
>similar number of megapixels?
"ISO" stands for International Standards Organization,
which actually is the International Organization for
Standardization.
ISO film speed is indeed a standardized measure,
technically known as ISO 5800:1987. Of course, as with
many such terms there are never pairs of an engineer and
a marketeer who see it the same as another pair who work
for a different company. (See ISO 9000, regarding
quality standards for management... :-) Hence there can
be some significant differences between various camera
models.
Incidentally, "ASA" is "American Standards Association"
which eventually became ANSI (in 1969), the American
National Standards Institute. ANSI is the US
representative to the ISO. (At one time ISO simply
adopted many ANSI standards with little change, but
today ANSI generally adopts ISO standards without
change.)
Marco Tedaldi
>
> So...it's interesting that the electronic designers
> mapped the analogy of film speed onto sensor amplification
> to the extent that they kept the same numbering scheme
> as film speed.
Yeah. Luckily they did not reinvent the wheel on this one. Within some
tolerances a digital camera at 100ISO should have the same sensitivity
as a film camera. In a compact camera you can't check if this is true
anyway. They could just make the sensor less sensitive and make it show
another aperture to compensate for this...
> Does this mean that there's an industry
> standard for that? Will a setting of ISO 100 at a given
> shutter speed, F-stop, and default exposure compensation
> give similar results on any brand of camera with a
> similar number of megapixels?
>
Yes. I used this fact to get my pictures of my Isolette exposed
correctly. I have no light meter, but a digital camera. So I used the
camera to tell me, what exposure it would take and just took this
settings to my Isolette. Worked great!
This way you don't have to learn from new about aperture and time. You
just have to remember, that the DOF at a given aperture changes with the
size of the sensor.
Hope this helps
kruemi
Marco Tedaldi
camera about the speed of the film to make it under or overexpose. In
digital days this is not the case anymore :-)
Pat
Yeah, ISO is standard and in theory all cameras/films should have
about the same sensitivity. If they didn't, then light meters, flash
meters, etc. wouldn't work right. If you're shooting Tri-X 400 and
someone is standing next to you shooting a digital set to ISO 400;
then you should have more or less the same exposure. It might be off
a little but it shouldn't be off too much.
There is some differences in color though. Just like Kodacrome and
Ektracrome had very different looks to them, different manufactures
also have different looks to them. It isn't as much as the different
films, but there's a difference. So if you own 2 cameras and shoot
them both at the same time/event, it's probably a good idea to have
them the same brand (if not model).
Good luck, old guy ;-)
bugbear
> bugbear schrieb:
>> Charles Packer wrote:
>>> Where is the logic in all of this? In the digital world,
>>> aren't ISO and exposure compensation redundant, anyway?
>>
>> ISO - in effect a choice between speed and noise
>>
>> exposure comp - the ability to intervene when the automatic
>> exposure algorithm does not serve well enough.
>>
>> In what way are these redundant?
>>
> Back in analog days they would have been. You could just lie to the
> camera about the speed of the film to make it under or overexpose. In
> digital days this is not the case anymore :-)
If you set the shutter speed and aperture,
then alter the ISO on your digital camera,
you will indeed alter the exposure, at least in
JPEG output.
BugBear
Dave Cohen
make a meaningful post.
Dave Cohen
Marco Tedaldi
Sensitivity (iso)
Aperture
Exposure time
If we change one we have to change (at least) another one too the get
the same result. Thats nothing new.
The thing is, that if I change the ISO-setting on a digital camera, it
change two things in fact. I change the "sensitivity" of the sensor and
tell this to the camera so it's taken into account. So in the end
effect, nothing but noise-level should change.
If I change the setting on an analog camera (without changing the film),
the exposure is changed.
IF I set my camera to "manual" no automatics apply at all, so you have
to care for the exposure for yourself. With manual setting you don't
need EV-correction.
Marco
Tzortzakakis Dimitrios
? "Floyd L. Davidson" <fl...@apaflo.com> ?????? ??? ??????
news:87y6vfy...@apaflo.com...
> Charles Packer <mai...@cpacker.org> wrote:
>>My last film camera, a Minolta SLR, beyond shutter speed
>>and F-stop, had one other means of controlling how much
>>light reached the film: the ASA dial, which was
>>customarily set to the same "speed" as the film and left
>>there.
>
> It also had the potential of changing to a film with a
> different speed. (Which in some cameras, with some types
> of film, could automatically set the ASA of the camera to
> match that of the film.)
>
> And indeed, some film cameras had Exposure Compensation
> too, if they had a built in light meter. All that EC
> does is change where the meter reads 0. If EC is set to
> +1, it will take 1 fstop more light to zero the meter.
>
> Note that for our purposes ASA values and ISO values are
> the same thing. It is a measure of the light
> sensitivity of the film/sensor. ASA was from the
> American Standards Association and ISO is from the
> International Standards Organization. The difference
> between the two values is highly technical and isn't
> enough to be of concern in this discussion.
>
standard);I remember in the 80's film marked ASA 100, 21 DIN. There used
also to be Gost, the soviet standard, which of course became obsolete after
the disbanding of the Soviet Union.
--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr
dj_nme
That's if you have the camera set to auto expose.
Then it will compensate for you changing the ISO sensitivity by altering
the shutter speed or aperture or both to get the same mid-tone exposure.
The same happens with film cameras with full automatic control of both
aperture and shutter speed.
Most of the early AE film cameras only have "aperture priority" AE which
alters the shutter speed to meter for an ISO/ASA change, simply because
the camera body had no way of altering the aperture.
> If I change the setting on an analog camera (without changing the film),
> the exposure is changed.
That's only if your film camera isn't set to (or doesn't have an) AE mode.
The same thing will happen with most digital cameras set to manual exposure.
> IF I set my camera to "manual" no automatics apply at all, so you have
> to care for the exposure for yourself. With manual setting you don't
> need EV-correction.
That's because there's nothing the camera can do to change the exposure
settings without being in one of it's AE modes.
Pat
> On 2009-03-09 04:09:39 -0700, Charles Packer <mail...@cpacker.org> said:
>
> > On Mar 8, 8:39 pm, Pat <gro...@artisticphotography.us> wrote:
> > > So the answer to your question is "yes and no". On film they are
> > the
> >> same but in digital they are not.
>
> >> I hope that clarifies it for you.
>
> > This has been very enlightening. First, I never knew that
> > film cameras had exposure compensation controls as well
> > as the ASA dial. My Minolta wasn't that fancy, I guess,
> > and I got into advanced cameras only as the film era
> > was pretty much over.
>
> with ASA adjustment from 20-3200, shutter speed from bulb to 1000th.
The K1000 was fully manual and therefore did not have/need exposure
compensation.
>
> No auto special modes, use the TLM, adjust the f-stop, shutter speed
> and ASA for your need of the moment.http://homepage.mac.com/lco/filechute/K1000.jpg
>
>
>
> > So...it's interesting that the electronic designers
> > mapped the analogy of film speed onto sensor amplification
> > to the extent that they kept the same numbering scheme
> > as film speed. Does this mean that there's an industry
> > standard for that? Will a setting of ISO 100 at a given
> > shutter speed, F-stop, and default exposure compensation
> > give similar results on any brand of camera with a
> > similar number of megapixels?
>
> It should.
>
> --
> Regards,
> Savageduck
Toby
"Floyd L. Davidson" <fl...@apaflo.com> schrieb im Newsbeitrag
news:87ljrfv...@apaflo.com...
Yes that is indeed right, and thanks for the correction. You should think
about getting your keyboard fixed. The shift+8 seems to be stuck ;-)
Toby
Bob Larter
> This has been very enlightening. First, I never knew that
> film cameras had exposure compensation controls as well
> as the ASA dial.
They mostly don't - at least none of the basic 35mm film SLRs I've ever
used have had EC, so we used to either shoot with the meter off the zero
position, or change the ASA setting to give the same effect.
> My Minolta wasn't that fancy, I guess,
> and I got into advanced cameras only as the film era
> was pretty much over.
Ditto. I learnt on very basic SLRs in the late 70's, & switched to
digital when the EOS 10D came out.
> So...it's interesting that the electronic designers
> mapped the analogy of film speed onto sensor amplification
> to the extent that they kept the same numbering scheme
> as film speed.
Well, it would've been silly of them to create yet another new
sensitivity rating.
> Does this mean that there's an industry
> standard for that?
Yes, thank god. There was DIN & ASA, then ASA became ISO.
Will a setting of ISO 100 at a given
> shutter speed, F-stop, and default exposure compensation
> give similar results on any brand of camera with a
> similar number of megapixels?
It should do, roughly. (The number of megapixels is irrelevant, though.)
--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
Doug Jewell
> Charles Packer wrote:
>> This has been very enlightening. First, I never knew that
>> film cameras had exposure compensation controls as well
>> as the ASA dial.
>
> They mostly don't - at least none of the basic 35mm film SLRs I've ever
> used have had EC, so we used to either shoot with the meter off the zero
> position, or change the ASA setting to give the same effect.
attached to the ISO dial, so internally it did exactly the
same thing to the meter as changing ISO.
--
Have you ever noticed that all legal documents need to be
completed in black or blue pen, but we vote in pencil?
JoelH
> aren't ISO and exposure compensation redundant, anyway?
Not at all.
You have three ways of controlling the exposure of an image: ISO, F-
stop, and shutter speed. The right combination of those three will
result in an identically-exposed image. For example F/16, 1/125 and
ISO 100 is the same as F/16 1/500 and ISO 400 (or F/8, 1/500, ISO 100)
The two examples I just gave heppen to be the right exposure on a
sunny day, and most good metering systems will give you these
settings. By contrast, most metering systems will give you
underexposed scenes of snow. So if you're taking pictures of snow,
you will want to use exposure compensation to add more light.
I will say that most dSLRs offer convenient access to f-stop and
shutter speed, but not ISO. That's purely a remnant of how older SLRs
worked.
-Joel