digital camera as exposure meter

On Aug 8, 12:48 am, viewerofrecphoto wrote:

I'm most interested in a dynamic range check. For exposure,
I usually use a gray card or my hand, with the built-in full frame
meter. I'd like to see how far out the sky is, without pulling out
my spot meter and taking several readings.

If that's what you want, a digital camera isn't that good at it.
Histograms aren't marked in stops and, even by loading special white
balance settings and tone curves into my D200 (*), the histogram isn't
anywhere near being reliable except to judge distance from highlights
clipping. That is: I could not calibrate the lower end of the
histogram to be able to read off the distance from the darkest to the
brightest points.

A spotmeter is better for this. Personally I use my camera's spotmeter
and take 2 readings in aperture priority (the digital scales appearing
in manual mode only show up to 3 stops + or minus, so it takes less
wheel-turning to switch to aperture priority, do this, and switch back
to manual) to estimate DR. I don't think it's slower than snapping a
shot and looking at the histogram, even if that worked.

(*) Note that in-camera histograms are produced from a jpeg, not the
raw data, and so is affected by white balance, tone-mapping and other
settings; so you need to calibrate for a particular set of those if
you want to use it as an accurate lightmeter, as I sometimes do.

If you are thinking about buying a digital camera for this purpose I would
not waste the money. However experimenting with what you have is another
matter.

You will get more accurate results with a high end exposure meter properly.
This is true whether shooting film or digitally.

The incamera histogram tells you absolutely nothing about whether you have
captured the details you are looking for in the shadows and highlights.
Ditto for the LCD screens built into dSLRs as they cannot resolve enough
detail and brightness levels to tell you anything of value. Because of their
small size the screens are often misleading about whether you even had
proper focus for the shot. This is a major drawback of EVF cameras with
which it can be difficult to even achieve critical manual focus on a tripod.

Film, negative in particular, has more latitude than digital. Hence I
suspect the results of a digital histogram will not be worth the waste of
battery power as the results will not translate into information captured on
film.

Recently, viewerofrecphoto posted:

On Aug 7, 1:22 am, Noons wrote:

now, this baffles me. the histogram is really not mandatory
for exposure metering. it is useful mostly for dynamic range
and colour balance checking, particularly the rgb histogram
variety. Are you absolutely sure you are not after a colour
temperature meter?

I'm most interested in a dynamic range check. For exposure,
I usually use a gray card or my hand, with the built-in full frame
meter. I'd like to see how far out the sky is, without pulling out
my spot meter and taking several readings.

Since you have a Minolta spot meter, I'm also puzzled as to why you don't
just use it? As has been mentioned, the response of digital sensors
differs from film. So, "...how far out the sky is..." is likely to be
misleading. Of course, you might be able to learn how to read the response
differences, and in that case "any old" digital camera would probably
suffice.

Neil

viewerofrecphoto wrote:
On Aug 7, 1:22 am, Noons wrote:
now, this baffles me. the histogram is really not mandatory
for exposure metering. it is useful mostly for dynamic range
and colour balance checking, particularly the rgb histogram
variety. Are you absolutely sure you are not after a colour
temperature meter?

I'm most interested in a dynamic range check. For exposure,
I usually use a gray card or my hand, with the built-in full frame
meter. I'd like to see how far out the sky is, without pulling out
my spot meter and taking several readings.

If you're shooting film, esp. slide, the spotmeter is _the_ way to go.

--
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-- e-meil: Remove FreeLunch.

"gowanoh" wrote:
If you are thinking about buying a digital camera for this purpose I would
not waste the money. However experimenting with what you have is another
matter.

You will get more accurate results with a high end exposure meter properly.
This is true whether shooting film or digitally.

An external exposure meter is almost totally worthless
in conjunction with a decent DSLR. (For that matter,
the in camera light metering isn't all that necessary
either.)

The incamera histogram tells you absolutely nothing about whether you have
captured the details you are looking for in the shadows and highlights.

Actually it does tell pretty much what you've caught in
the highlights. Shadows analysis takes a bit more, but
not much. (Use the histogram or the
blink-on-over-exposure LCD display to set highlights;
then use the camera's spotmeter to measure the shadows.
That technique does require experimenting to know
exactly how far down from the actual exposure the
shadows can be for whatever level of detail is
acceptable to the photographer.)

Ditto for the LCD screens built into dSLRs as they cannot resolve enough
detail and brightness levels to tell you anything of value. Because of their
small size the screens are often misleading about whether you even had
proper focus for the shot.

With a good DSLR the LCD image can be magnified several
times, allowing analysis of focus. (That is cumbersome,
and I have never bothered to actually do it, but for
photographing static scenes it should work just fine.)

This is a major drawback of EVF cameras with
which it can be difficult to even achieve critical manual focus on a tripod.

Film, negative in particular, has more latitude than digital. Hence I

That isn't true for current DSLRs.

suspect the results of a digital histogram will not be worth the waste of
battery power as the results will not translate into information captured on
film.

That might be the case. On the other hand if the
photographer understands the technology it can be of
significant value. I'm not sure the significance equals
the price of a good DSLR for a person who wants to shoot
film though... But certainly one instance would be for
medium or large format film users. A DSLR would stomp
all over using a Polaroid.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd L. Davidson wrote:
"gowanoh" wrote:

If you are thinking about buying a digital camera for this purpose I would
not waste the money. However experimenting with what you have is another
matter.

You will get more accurate results with a high end exposure meter properly.
This is true whether shooting film or digitally.

An external exposure meter is almost totally worthless
in conjunction with a decent DSLR. (For that matter,
the in camera light metering isn't all that necessary
either.)

The incamera histogram tells you absolutely nothing about whether you have
captured the details you are looking for in the shadows and highlights.

Actually it does tell pretty much what you've caught in
the highlights. Shadows analysis takes a bit more, but
not much. (Use the histogram or the
blink-on-over-exposure LCD display to set highlights;
then use the camera's spotmeter to measure the shadows.
That technique does require experimenting to know
exactly how far down from the actual exposure the
shadows can be for whatever level of detail is
acceptable to the photographer.)

Ditto for the LCD screens built into dSLRs as they cannot resolve enough
detail and brightness levels to tell you anything of value. Because of their
small size the screens are often misleading about whether you even had
proper focus for the shot.

With a good DSLR the LCD image can be magnified several
times, allowing analysis of focus. (That is cumbersome,
and I have never bothered to actually do it, but for
photographing static scenes it should work just fine.)

The D200 is easy to zoom in to more than 100% magnification to check
focus with one click, if you set it up right. It has a spot meter too
but to check the histogram on spot area results, you'll need to load the
image into a laptop & make a selection on the area of interest. The
metering systems on modern DSLRs are too clever, making all sorts of
assumptions, not like a manual meter. I have no idea how this translates
to film exposure but I suspect the simplest digital histogram would be
about as useful as the most advanced for translating to film exposure.
Simply looking at the LCD image is sort of useless given the variation
in visibility & contrast in different lighting conditions so for
exposure, zooming doesn't help without a laptop. Some digital's allow
cropping the image in-camera where you could then see the cropped
histogram but that's an awful lot of bother.

This is a major drawback of EVF cameras with
which it can be difficult to even achieve critical manual focus on a tripod.

Film, negative in particular, has more latitude than digital. Hence I

That isn't true for current DSLRs.

Agreed.

suspect the results of a digital histogram will not be worth the waste of
battery power as the results will not translate into information captured on
film.

That might be the case. On the other hand if the
photographer understands the technology it can be of
significant value. I'm not sure the significance equals
the price of a good DSLR for a person who wants to shoot
film though... But certainly one instance would be for
medium or large format film users. A DSLR would stomp
all over using a Polaroid.

Any digital with reasonable manual control would be super-useful
tethered to a laptop as a mega-polaroid. The LCD displays are not bad
(newer ones are much better) but are a far cry from a polaroid or a laptop.

--
Paul Furman Photography
http://edgehill.net
Bay Natives Nursery
http://www.baynatives.com

viewerofrecphoto wrote:
looking for a digital camera to use as an exposure meter and histogram
display for my film camera.
preferred features:
- small size
- low price
- accurate histogram
- iso range 100-1600
- zoom range 24-200 (35mm equiv)
- manual aperture & shutter speed
- ease of use to look at histograms

resolution/noise are not important.


But a good (£300) meter is a lot cheaper than a digital camera and 24-200 lens.

Another thing: many digital sensors do not respond exactly as a film would at
the named ISO rating. Canon, in particular, seem to claim a quite different
ISO to the actual response. The built-in meters compensate but this will not
help you metering for film.

The histogram is of almost no use whatsoever with respect to film, at least
unless you recalibrate it for your film.

What have you got against buying a decent meter?

Just out of interest why do you need a zoom meter? Take multi-spot readings of
the bits you're interested in and the meter will average them. Or
alternatively, something you can't do with a camera is incident light
metering, measuring the light falling on a subject rather than that reflected.

Just one other thought, if you still find a £300 meter too expensive, you can
spend half that on a Canon T90 and lens which is one of the finest meters ever
made. Hell, you can even get one with a stuck shutter for peanuts as you don't
want to take photos with it.

Rich

Paul Furman wrote:
Floyd L. Davidson wrote:
"gowanoh" wrote:
Ditto for the LCD screens built into dSLRs as they cannot resolve enough
detail and brightness levels to tell you anything of value. Because of their
small size the screens are often misleading about whether you even had
proper focus for the shot.
With a good DSLR the LCD image can be magnified several
times, allowing analysis of focus. (That is cumbersome,
and I have never bothered to actually do it, but for
photographing static scenes it should work just fine.)

The D200 is easy to zoom in to more than 100%
magnification to check focus with one click, if you set
it up right.

It isn't something I have an interest in, but I'm sure
that for those who need to know if the last image was or
was not in focus it certainly is easy enough to do. In
my case, 99% of the time it is of no significance
because the scene can never be recreated, so what I got
already is all I'll get.

It has a spot meter too but to check the
histogram on spot area results, you'll need to load the
image into a laptop & make a selection on the area of
interest.

Off hand I can't think of a circumstance where a
histogram, or any type of spectoral analysis, of the
area metered would be of any value.

The metering systems on modern DSLRs are too
clever, making all sorts of assumptions, not like a
manual meter.

Very true for "matrix metering" and that sort of thing.
But spot metering doesn't do that cute stuff.

However your point is well taken in that for the
purposes we were discussing it would be very wise to
carefully understand which metering modes are making
unknown assumptions and which are not, and avoid the
ones where it isn't possible to know which assumptions
are being used (things like matrix metering where there
is a table of 40,000 different combinations stored in
the firmware!).

I have no idea how this translates to film
exposure but I suspect the simplest digital histogram
would be about as useful as the most advanced for
translating to film exposure. Simply looking at the LCD
image is sort of useless given the variation in
visibility & contrast in different lighting conditions
so for exposure, zooming doesn't help without a
laptop.

It would indeed help, but it has to be done right. Here's
an example of what I'm thinking of:

If the entire scene is framed in the DSLR viewfinder
(with ISO and exposure compensation settings that match
the lenses and film being used by the other camera), the
"correct" exposure can be determined very precisely by
making a few exposures and observing the blink on over
exposure display. Once exposure is set at 1/3 of an
fstop below an exposure that causes any desired
highlight to blink, the fstop and shutter speed are
noted. It is perhaps interesting to take a "whole
screen" exposure reading to see what the average
reflectance of the entire scene is by comparison, but
frankly that is not really important.

What is important is to zoom in on a shadow area that
has detail of interest, and use a spot meter to measure
that area.

One has to know the dynamic range of the film/processing
system being used, and imperical knowledge is the only
way that a useful comparison can be made. If we know,
for example, that a we can get detail in shadows that
are 5 fstops below a "correct exposure", then the
difference between the correct exposure determined by
blinking highlights and the shadows determined by spot
metering tells us *exactly* how much detail is going to
be recorded in the shadow area measured. In that case,
with a 5 fstop range if it measured 6 fstops down *no*
detail is going to be recorded, while if it measured at
4 fstops then a significant amount of detail will be
there, but there certainly won't be any headroom!

(Keep in mind that the spot meter is telling us what
exposure would be necessary to get that area to record
as an average 18% grey. Recording 5 fstops below 18%
grey is a lot of dynamic range...)

Some digital's allow cropping the image
in-camera where you could then see the cropped histogram
but that's an awful lot of bother.

This is a major drawback of EVF cameras with
which it can be difficult to even achieve critical manual focus on a tripod.

Film, negative in particular, has more latitude than digital. Hence I
That isn't true for current DSLRs.

Agreed.

A persistent myth... :-)

suspect the results of a digital histogram will not be worth the waste of
battery power as the results will not translate into information captured on
film.
That might be the case. On the other hand if the
photographer understands the technology it can be of
significant value. I'm not sure the significance equals
the price of a good DSLR for a person who wants to shoot
film though... But certainly one instance would be for
medium or large format film users. A DSLR would stomp
all over using a Polaroid.

Any digital with reasonable manual control would be
super-useful tethered to a laptop as a
mega-polaroid. The LCD displays are not bad (newer ones
are much better) but are a far cry from a polaroid or a
laptop.

I don't agree that the LCD is a far cry from a Polaroid,
but I do agree that tethering to a laptop adds at least
an order of magnitude _more_ functionality.

Of course that works better in a studio than it does in
a swamp... (I spend more time in swamps.)

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Richard Polhill wrote:
viewerofrecphoto wrote:
looking for a digital camera to use as an exposure meter and histogram
display for my film camera.
preferred features:
- small size
- low price
- accurate histogram
- iso range 100-1600
- zoom range 24-200 (35mm equiv)
- manual aperture & shutter speed
- ease of use to look at histograms
resolution/noise are not important.


But a good (£300) meter is a lot cheaper than a digital camera and 24-200 lens.

A $600 camera (Nikon D40 with an 18-55mm kit lense) will
run circles around any $600 light meter. At $800 for a
DSLR the OP might nearly want to simply ditch shooting
with film at all, and use only the "meter"!

Another thing: many digital sensors do not respond
exactly as a film would at the named ISO rating. Canon,
in particular, seem to claim a quite different ISO to
the actual response. The built-in meters compensate but
this will not help you metering for film.

As with *any* meter, one would need to "calibrate" to
match the camera/film/lenses being used.

The histogram is of almost no use whatsoever with
respect to film, at least unless you recalibrate it for
your film.

What have you got against buying a decent meter?

Just out of interest why do you need a zoom meter? Take
multi-spot readings of the bits you're interested in and
the meter will average them. Or alternatively, something
you can't do with a camera is incident light metering,
measuring the light falling on a subject rather than
that reflected.

The camera and film will be responding to the reflected
light though, not to incident light. The usual problem
with use of a reflected light meter is the averaging of
an entire scene. The accuracy of the reading depends on
the *photographer's* (not the meter) ability to judge if
the scene is actualy 18% reflectance, and how much
brighter the highlights are than the average. Some
photographers do that quite well, most don't.

Use of an incident light meter eliminates the need to
adjust the average in relation to 18% reflectance, but
there is still the problem of relating the highlights to
the average.

But if one actually uses a "spot" meter to determine the
an appropriate exposure level for the highlights, and
then confirms that the shadows are within the dynamic
range of the film (or the electronic sensor with a
digital camera), a "reflected meter" reading is by far
more acurrate.

Obviously a zoom meter is quite useful for that task.

Just one other thought, if you still find a £300 meter
too expensive, you can spend half that on a Canon T90
and lens which is one of the finest meters ever
made. Hell, you can even get one with a stuck shutter
for peanuts as you don't want to take photos with it.

That might well be just about as useful as a $600 meter.
But just like a light meter, it pales by comparison to
a DSLR.

--
Floyd L. Davidson http://www.apaflo.com/floyd_davidson
Ukpeagvik (Barrow, Alaska)

Floyd L. Davidson wrote:
Richard Polhill wrote:
viewerofrecphoto wrote:
looking for a digital camera to use as an exposure meter and histogram
display for my film camera.
preferred features:
- small size
- low price
- accurate histogram
- iso range 100-1600
- zoom range 24-200 (35mm equiv)
- manual aperture & shutter speed
- ease of use to look at histograms
resolution/noise are not important.

But a good (£300) meter is a lot cheaper than a digital camera and 24-200 lens.

A $600 camera (Nikon D40 with an 18-55mm kit lense) will
run circles around any $600 light meter. At $800 for a
DSLR the OP might nearly want to simply ditch shooting
with film at all, and use only the "meter"!

Thereby solving all his problems, bring world peace, banish poverty, hunger
and suffering. Of course.

How exactly will it "run rings around" a meter? It IS a meter.

And just what the **** is a "lense"?

Another thing: many digital sensors do not respond
exactly as a film would at the named ISO rating. Canon,
in particular, seem to claim a quite different ISO to
the actual response. The built-in meters compensate but
this will not help you metering for film.

As with *any* meter, one would need to "calibrate" to
match the camera/film/lenses being used.

Sure right. Perhaps with a DSLR...

The histogram is of almost no use whatsoever with
respect to film, at least unless you recalibrate it for
your film.

What have you got against buying a decent meter?

Just out of interest why do you need a zoom meter? Take
multi-spot readings of the bits you're interested in and
the meter will average them. Or alternatively, something
you can't do with a camera is incident light metering,
measuring the light falling on a subject rather than
that reflected.

The camera and film will be responding to the reflected
light though, not to incident light. The usual problem
with use of a reflected light meter is the averaging of
an entire scene. The accuracy of the reading depends on
the *photographer's* (not the meter) ability to judge if
the scene is actualy 18% reflectance, and how much
brighter the highlights are than the average. Some
photographers do that quite well, most don't.

Use of an incident light meter eliminates the need to
adjust the average in relation to 18% reflectance, but
there is still the problem of relating the highlights to
the average.

It doesn't occur to you that there will often be elements in a view that are
outside the exposure latitude of the chosen medium, then? You can only expose
correctly for the bit you want.

But if one actually uses a "spot" meter to determine the
an appropriate exposure level for the highlights, and
then confirms that the shadows are within the dynamic
range of the film (or the electronic sensor with a
digital camera), a "reflected meter" reading is by far
more acurrate.

********. Sorry, that's total, unmitigated bull****.

Unless you mean something different by the word "acurrate" than what I
assumed: "accurate".


Obviously a zoom meter is quite useful for that task.

Zoom? Why?


Just one other thought, if you still find a £300 meter
too expensive, you can spend half that on a Canon T90
and lens which is one of the finest meters ever
made. Hell, you can even get one with a stuck shutter
for peanuts as you don't want to take photos with it.

That might well be just about as useful as a $600 meter.
But just like a light meter, it pales by comparison to
a DSLR.


What? And how does a spot meter in one camera get blown away by the spot meter
in another? I guarantee the T90 meter is as accurate as any DSLR, so what else
do you think the guy will gain?

Oh yeah: world peace, etc...