How to measure ISO

On 2015-11-03 16:59, Alfred Molon wrote:
In article , Mort says...

A similar situation existed years ago with mechanical shutters, which
oftentimes did not deliver their higher speeds with any degree of
accuracy.

Ehhpp... exposure times are inaccurate? Even nowadays with digital
cameras? Is there any place where I can read more about this?

In a mechanical shutter camera (like both of mine) it's a certainty that
there is some error in exposure period.

OTOH, I have a feel for both and I meter appropriately for both and when
there's time to look at some shots and histos to be sure I'm not off the
reservation too much. That said, I'd rather underexpose by half a stop
than overexpose by a stop.

In article ,
Whisky-dave wrote:

I very much doubt shutter speeds were measured in stops.

yes they were and still are. 1/250th is a stop less exposure than
1/125th.

In article ,
Whisky-dave wrote:

Yes in other words you as a manufacter can chosee any 1 of 5 stanbdards to
follow.

which means there's no standard.

No it means there's more than one standard.

which makes all of them useless, thus no standard.

Womens dress sizes are another 'standard' differnt in the UK from the US.
In the UK we have two standard measurements imperial or metric.

that's not the same thing. unlike iso, there is a conversion between
those measurements. they even have different names. a meter is not a
foot.

for iso, there is no conversion. it's all called iso and you have no
way to know which way they measured it so you can't convert it yourself
even if you wanted to, making it only a rough guide.

In article , Alfred
Molon wrote:

A similar situation existed years ago with mechanical shutters, which
oftentimes did not deliver their higher speeds with any degree of
accuracy.

Ehhpp... exposure times are inaccurate? Even nowadays with digital
cameras? Is there any place where I can read more about this?

no to all three.

In article ,
Whisky-dave wrote:

I very much doubt shutter speeds were measured in stops.

yes they were and still are. 1/250th is a stop less exposure than
1/125th.

It's NOT a stop is it, it's half the exposure time.

that's what a stop is.

When I measured my prakticas 1/1000th it came out at about 1/700th.

then it was off by quite a bit.

F Stops have NOTHING to do with shutter speeds they are independant of each other.

i didn't say f/stops.

a stop is a unit of exposure. one stop more exposure is twice as much
light. that can be a larger f/stop on the lens, a slower shutter speed
or an increase in iso.

exposure meters are also measured in stops. i have one that's about a
half-stop off.

In article ,
Whisky-dave wrote:

I very much doubt shutter speeds were measured in stops.

yes they were and still are. 1/250th is a stop less exposure than
1/125th.

It's NOT a stop is it, it's half the exposure time.

that's what a stop is.

No a stop reducese the incoming light by 50%

a stop can either reduce or increase the incoming light by a factor of
two.

and it changes the DoF
and other optical effect

only if it's changed on the lens.

the shutter speed has NO effect on DoF.

nobody said it did.

F Stops have NOTHING to do with shutter speeds they are independant of
each other.

i didn't say f/stops.

then what stop was you talking about a bus stop ?

photographic stops.

as usual, you're thoroughly confused.

a stop is a unit of exposure. one stop more exposure is twice as much
light. that can be a larger f/stop on the lens, a slower shutter speed
or an increase in iso.
but it also hads an efect on the image which is quite differnt from that of
giving twice or half the exposure time.

twice or half the exposure time does have an effect on the image.

exposure meters are also measured in stops. i have one that's about a
half-stop off.

I have a few an old selienium one seiko I think that has a little cream shutter.

meters don't have shutters and this isn't a selenium meter either.

In article ,
Whisky-dave wrote:

A similar situation existed years ago with mechanical shutters, which
oftentimes did not deliver their higher speeds with any degree of
accuracy.

Ehhpp... exposure times are inaccurate? Even nowadays with digital
cameras? Is there any place where I can read more about this?

no to all three.

yuo can test things yuorself.

http://photo.net/large-format-photography-forum/00Uajj

refering to a D700
" I just tried this on my "new" Schneider Symar 135mm f/5.6 and found it was
dead on at all shutter speeds except 1/500 sec. which is actually exposing at
1/400 sec. "

it's highly unlikely that a mechanical shutter would be accurate at all
shutter speeds except for just one, especially an old one.

Of course some people believe that the word digital means perfect in that whatever
shutter speed you set will be exact.

while nothing is perfect, they are correct.

electronic shutters (on both film and digital cameras) are *far* more
accurate than mechanical shutters ever will be.

On Wed, 04 Nov 2015 09:10:21 -0500, nospam
wrote:

In article ,
Whisky-dave wrote:

I very much doubt shutter speeds were measured in stops.

yes they were and still are. 1/250th is a stop less exposure than
1/125th.

It's NOT a stop is it, it's half the exposure time.

that's what a stop is.

When I measured my prakticas 1/1000th it came out at about 1/700th.

then it was off by quite a bit.

F Stops have NOTHING to do with shutter speeds they are independant of each other.

i didn't say f/stops.

a stop is a unit of exposure. one stop more exposure is twice as much
light. that can be a larger f/stop on the lens, a slower shutter speed
or an increase in iso.

There are no standards for 'stops'.

f/... stops are a different matter.

exposure meters are also measured in stops. i have one that's about a
half-stop off.

I bet that's f/... stops.
--

Regards,

Eric Stevens

In article , Eric Stevens
wrote:

a stop is a unit of exposure. one stop more exposure is twice as much
light. that can be a larger f/stop on the lens, a slower shutter speed
or an increase in iso.

There are no standards for 'stops'.

yes there is. one stop more exposure is twice the amount of light.

f/... stops are a different matter.

yes. that's the whole point.

exposure meters are also measured in stops. i have one that's about a
half-stop off.

I bet that's f/... stops.

you'll lose.

In article , Alan Browne
says...
That said, I'd rather underexpose by half a stop
than overexpose by a stop.

Well, there is a general recommendation to expose to the right, to
minimise noise (also taking into account that cameras nowadays tolerate
some overexposure).
--
Alfred Molon

Olympus E-series DSLRs and micro 4/3 forum at
http://tech.groups.yahoo.com/group/MyOlympus/
http://myolympus.org/ photo sharing site