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Meter accuracy
Meter accuracy
This really isn't a darkroom question but since most who read these
posts are competent photographers I will ask.....how do I calibrate or
check the accuracy of a handheld light meter? I use it in the ambient
light mode.
This really isn't a darkroom question but since most who read these
posts are competent photographers I will ask.....how do I calibrate or
check the accuracy of a handheld light meter? I use it in the ambient
light mode.
Re: Meter accuracy
On 9/19/2007 5:53 PM Terry Davis spake thus:
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
Well, the Really Obvious answer is the one you no doubt thought of:
check it against a known good meter. If you can find one, that's really
all you need to do. (And if it turns out to be off, you can find out how
far off it is and adjust your settings to compensate.)
On 9/19/2007 5:53 PM Terry Davis spake thus:
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
Well, the Really Obvious answer is the one you no doubt thought of:
check it against a known good meter. If you can find one, that's really
all you need to do. (And if it turns out to be off, you can find out how
far off it is and adjust your settings to compensate.)
Re: Meter accuracy
Take it outside on a sunny day, set for ASA 125, should indicate
f11-f16 at 1/125th
The other method is to compare it to _two_ other light meters.
If you only compare it to one, and they don't agree, you
don't know which is wrong.
--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http :// www .darkroomautomation,com /index.htm
n o lindan at ix dot netcom dot com
Take it outside on a sunny day, set for ASA 125, should indicate
f11-f16 at 1/125th
The other method is to compare it to _two_ other light meters.
If you only compare it to one, and they don't agree, you
don't know which is wrong.
--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http :// www .darkroomautomation,com /index.htm
n o lindan at ix dot netcom dot com
Re: Meter accuracy
On Sep 19, 11:52 pm, "Nicholas O. Lindan" <s...@sig,com > wrote:
> Take it outside on a sunny day, set for ASA 125, should indicate
> f11-f16 at 1/125th
On a really clear day, when the sun is high enough
that your shadow isn't much longer than you
are tall, a grey card shouldn't be more than
a third stop off f/16. I have checked this many
times and it is remarkably repeatable.
> The other method is to compare it to _two_ other light meters.
> If you only compare it to one, and they don't agree, you
> don't know which is wrong.
If it is an old selenium meter it may have gone
non-linear. Check it under low light and sunny
f/16 conditions. If it has two ranges then find
some light which is at the top of the lower
range and the bottom of the upper range and
see if it agrees with itself.
I have a 50 year old GE meter which is actually
pretty accurate, but many old selenium meters
have not fared as well.
Old CDS meters which were meant to take mercury
cells may be non-linear if the meter has been
inexpertly adjusted to cope with a different voltage.
Peter.
--
pirwin@ktb,net
On Sep 19, 11:52 pm, "Nicholas O. Lindan" <s...@sig,com > wrote:
> Take it outside on a sunny day, set for ASA 125, should indicate
> f11-f16 at 1/125th
On a really clear day, when the sun is high enough
that your shadow isn't much longer than you
are tall, a grey card shouldn't be more than
a third stop off f/16. I have checked this many
times and it is remarkably repeatable.
> The other method is to compare it to _two_ other light meters.
> If you only compare it to one, and they don't agree, you
> don't know which is wrong.
If it is an old selenium meter it may have gone
non-linear. Check it under low light and sunny
f/16 conditions. If it has two ranges then find
some light which is at the top of the lower
range and the bottom of the upper range and
see if it agrees with itself.
I have a 50 year old GE meter which is actually
pretty accurate, but many old selenium meters
have not fared as well.
Old CDS meters which were meant to take mercury
cells may be non-linear if the meter has been
inexpertly adjusted to cope with a different voltage.
Peter.
--
pirwin@ktb,net
Re: Meter accuracy
Terry Davis wrote:
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
If it does seem to be off, check it in reflected light mode. If it's
correct in reflected and off in ambient, look around to make sure there
is not a problem with the switch.
Most meters need some adjustment in ambient light mode. Usually this is
done by a small switch which is pressed by putting on or moving in place
the ambient light sensor. It may be dirty or broken.
Keep in mind that in ambient light mode it has to be pointed at the light
source. If you are in the shade, pointing it up may not work.
It may also be your camera. Still cameras with built in meters are calibrated
so that they expose properly, not meter accurately. Lenses are calibrated
in "F" stops which are not always 100% consistent between lenses.
Movie cameras are calibrated in "T" (transmission) stops which are.
Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson,com N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http :// geoffstechno.livejournal,com /
Terry Davis wrote:
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
If it does seem to be off, check it in reflected light mode. If it's
correct in reflected and off in ambient, look around to make sure there
is not a problem with the switch.
Most meters need some adjustment in ambient light mode. Usually this is
done by a small switch which is pressed by putting on or moving in place
the ambient light sensor. It may be dirty or broken.
Keep in mind that in ambient light mode it has to be pointed at the light
source. If you are in the shade, pointing it up may not work.
It may also be your camera. Still cameras with built in meters are calibrated
so that they expose properly, not meter accurately. Lenses are calibrated
in "F" stops which are not always 100% consistent between lenses.
Movie cameras are calibrated in "T" (transmission) stops which are.
Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel gsm@mendelson,com N3OWJ/4X1GM
IL Voice: (07)-7424-1667 U.S. Voice: 1-215-821-1838
Visit my 'blog at http :// geoffstechno.livejournal,com /
Re: Meter accuracy
Dnia Wed, 19 Sep 2007 20:53:24 -0400, Terry Davis napisal(a):
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
Correct measure is the one which gives you correct photos - not the
one which is the same as for other light meters.
Buy roll of Velvia, put it in camera and make a few photos using
your light meter and bracketing. Develop and look at results.
This is a base - later make test for your favorite process and film (BW?)
and tune it up - details you find in google ("Zone System" +calibrating).
Greeting from EU,
Henry
Dnia Wed, 19 Sep 2007 20:53:24 -0400, Terry Davis napisal(a):
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
Correct measure is the one which gives you correct photos - not the
one which is the same as for other light meters.
Buy roll of Velvia, put it in camera and make a few photos using
your light meter and bracketing. Develop and look at results.
This is a base - later make test for your favorite process and film (BW?)
and tune it up - details you find in google ("Zone System" +calibrating).
Greeting from EU,
Henry
Re: Meter accuracy
In article <3nwxntuoouqf$.9wg8sxec29kw.dlg@40tude,net >, Henry (k)
moj adres to henrykg@na serwerze gazeta.pl says...
> Correct measure is the one which gives you correct photos - not the
> one which is the same as for other light meters.
>
But it's handy if the setting on the meter is the one that works on the
camera, without having to apply some form of compensation. If a meter
is linearly off relative to a camera you just have to tweak the film
speed, but if the discrepancy isn't linear it's a pain to translate the
readings.
In article <3nwxntuoouqf$.9wg8sxec29kw.dlg@40tude,net >, Henry (k)
moj adres to henrykg@na serwerze gazeta.pl says...
> Correct measure is the one which gives you correct photos - not the
> one which is the same as for other light meters.
>
But it's handy if the setting on the meter is the one that works on the
camera, without having to apply some form of compensation. If a meter
is linearly off relative to a camera you just have to tweak the film
speed, but if the discrepancy isn't linear it's a pain to translate the
readings.
Re: Meter accuracy
Dnia Thu, 20 Sep 2007 11:48:22 +0100, Rob Morley napisal(a):
> But it's handy if the setting on the meter is the one that works on the
> camera, without having to apply some form of compensation. If a meter
> is linearly off relative to a camera you just have to tweak the film
> speed, but if the discrepancy isn't linear it's a pain to translate the
> readings.
Of course - I assumed that light meter has some calibration screw
and keeps linearity. If not then I suggest give it to children as
a toy ;-)
Some old light meters have only EV range - then it's easier
to print table/draw graph with translation.
Greetings,
Henry
Dnia Thu, 20 Sep 2007 11:48:22 +0100, Rob Morley napisal(a):
> But it's handy if the setting on the meter is the one that works on the
> camera, without having to apply some form of compensation. If a meter
> is linearly off relative to a camera you just have to tweak the film
> speed, but if the discrepancy isn't linear it's a pain to translate the
> readings.
Of course - I assumed that light meter has some calibration screw
and keeps linearity. If not then I suggest give it to children as
a toy ;-)
Some old light meters have only EV range - then it's easier
to print table/draw graph with translation.
Greetings,
Henry
Re: Meter accuracy
Bracket some exposures in a particular scene, then when you determined the
correct exposure turn the adjusting screw to indicate that exposure. Forget
about "zeroing it in" covering the cell and turning it to "zero".
Ray
"Terry Davis" <knight-dancer@webtv,net > wrote in message
news:25626-46F1C484-1440@storefull-3136.bay.webtv,net ...
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
>
Bracket some exposures in a particular scene, then when you determined the
correct exposure turn the adjusting screw to indicate that exposure. Forget
about "zeroing it in" covering the cell and turning it to "zero".
Ray
"Terry Davis" <knight-dancer@webtv,net > wrote in message
news:25626-46F1C484-1440@storefull-3136.bay.webtv,net ...
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
>
Re: Meter accuracy
Terry Davis wrote:
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
>
Dr. Richard J. Henry in the second edition of his book, "Controls in Black
and White Photography" gives a procedure for calibrating a light meter. It
is on pages 176-179 and are intended for a spot meter.
Calibrating a light meter by comparing it with others is fraught with
difficulties. At one time, I had four different light meters and they all
worked well. On a clear day, I put a grey card on my front lawn facing up. I
metered the card with each light meter and got readings from two stops over
to two stops under the middle value. Now I was surely not getting 4 stop
errors in my exposures. It turns out that each light meter had a different
color sensitivity. One was a cadmium sulfide meter, one was "silicon blue",
one was whatever is in Fred Picker's modified and color corrected spot meter
(the digital model), and one is a Luna-Pro F. I tried the experiment indoors
with 3400 degree incandescent light bulbs, and the meters were off in
different amounts.
In practical work, I notice that colors in nature are not usually very
saturated, so the color differences make less difference to the film than to
the light meters.
--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http :// counter.li.org
^^-^^ 08:35:02 up 6 days, 1:02, 2 users, load average: 4.91, 4.52, 4.27
Terry Davis wrote:
> This really isn't a darkroom question but since most who read these
> posts are competent photographers I will ask.....how do I calibrate or
> check the accuracy of a handheld light meter? I use it in the ambient
> light mode.
>
Dr. Richard J. Henry in the second edition of his book, "Controls in Black
and White Photography" gives a procedure for calibrating a light meter. It
is on pages 176-179 and are intended for a spot meter.
Calibrating a light meter by comparing it with others is fraught with
difficulties. At one time, I had four different light meters and they all
worked well. On a clear day, I put a grey card on my front lawn facing up. I
metered the card with each light meter and got readings from two stops over
to two stops under the middle value. Now I was surely not getting 4 stop
errors in my exposures. It turns out that each light meter had a different
color sensitivity. One was a cadmium sulfide meter, one was "silicon blue",
one was whatever is in Fred Picker's modified and color corrected spot meter
(the digital model), and one is a Luna-Pro F. I tried the experiment indoors
with 3400 degree incandescent light bulbs, and the meters were off in
different amounts.
In practical work, I notice that colors in nature are not usually very
saturated, so the color differences make less difference to the film than to
the light meters.
--
.~. Jean-David Beyer Registered Linux User 85642.
/V\ PGP-Key: 9A2FC99A Registered Machine 241939.
/( )\ Shrewsbury, New Jersey http :// counter.li.org
^^-^^ 08:35:02 up 6 days, 1:02, 2 users, load average: 4.91, 4.52, 4.27
