Need dig. photography help.

[BillyRay]

Big thread that got a little off topic. The quickest way I've found to manage this "dark snow" phenomenon is to use the flash. It's no guarantee your shots will be perfect, but it goes a long way to trick the camera into (or out of) compensating for snow scenes. My experience has been mostly with a Kodak EasyShare, but my Nikon D70 also seems to behave similarly. IMHO, unless you're focused on infinity, you should always use the flash anyway.

 

[DougPaul]

The quickest way I've found to manage this "dark snow" phenomenon is to use the flash. It's no guarantee your shots will be perfect, but it goes a long way to trick the camera into (or out of) compensating for snow scenes.

The flash can only help for close-by subjects.

Increasing the exposure by up to 2.5 stops is the basic cure.
(1 stop = 50%, 2 stops = 25%, 2.5 stops = 18%. Thus an exposure taken off a 100% reflectivity card plus 2.5 stops will be the same as an exposure taken off an 18% reflectivity card.)

IMHO, unless you're focused on infinity, you should always use the flash anyway.

Some of us will disagree with this--I only use mine occasionally.

Doug

 

[Neil]

Can someone please explain, in light of the previous post by DougPaul, the principle behind the reflectivity card and the 18% number?

 

[jwind]

Can someone please explain, in light of the previous post by DougPaul, the principle behind the reflectivity card and the 18% number?

Simple (sort of) 18% gray is what your light meter is calibrated to per sey. It's often refereed to as photo gray or a reflectance card b/c photographers (like myslef) use it for various technical photo application I won't bore you with.

Like I said before, your camera light meter calibrated to expose your photographs to the same density of 18% grey. Consequently, if the vast majority of your photograph is bright ( say 8% grey) the camera doesn't know that and exposes incorrectly resulting in a darker image. the same is true for the opposite. Snow is particularly difficult.

I'd check and see what your metering mode is set to. You can often set light metering to encompass the whole scene (which is easier but results fluctuate inevitably) or to spot metering (which is more pinpoint). Spot meter will allow you to meter of something you KNOW is close to 18% grey.

It's kinda a tough concept to describe without the technical jargon...

 

[Grumpy]

Can someone please explain, in light of the previous post by DougPaul, the principle behind the reflectivity card and the 18% number?

I used to explain the 18% gray card to photojournalism students, very non-scientifically, this way:

If you took all the gray scale tonal values (from black to white) in a typical scene and ran them through a blender together, what you’d come up with is 18% gray. That is, it reflects 18% of the light that strikes it. So that blended “average” becomes the standard for a light meter’s aperture vs shutter speed scale. In other words, the meter is calibrated to give an exposure that will produce the 18% gray tone in a finished black & white print.

Trouble is, when the scene is predominantly white, the meter only “sees” it as 18% gray. So you wind up underexposing. The white values then will fall in a darker part of the gray scale continuum from black to white than where they should be.

Likewise, if the scene is predominantly dark -- say a hillside of dark spruces -- the meter will see it as 18% gray. Using the meter reading directly will cause overexposure, pushing the darker tones up toward the 18% range, and the lightest tones will tend to “block up” with no tonal separation or detail.

In either case, you have to compensate. The best trick is to take the exposure reading off a standard 18% gray test card, or equivalent, lit like the scene.

One improvised method is to take a meter reading off the palm of your hand, tilted so the light that strikes it is comparable to the light that hits the part of the scene you want rendered as 18% gray (which is somewhat lighter than you might guess -- a little lighter tone than a mid gray flannel business suit). The typical hand palm has about 18% reflectance. Old trick, that works well, especially with hand held light meters.

Luckily, most modern light meters built in to cameras use very good analogs to get us around these problems, within limits. But in extreme cases (as in snow or over water, as common examples) even the best of them can get fooled. The best way to get around these things is to experiment with controls and see what works. The instant preview feature on digital cameras can be very useful for this, with a little practice.

G.

 

[jwind]

Some of us will disagree with this--I only use mine occasionally.

Doug

And I only use it when I ABSOLUTELY need it. If there is one sure way to screw up a photograph it's to use the built in flash. At anyrate, point and shoot flashes are good for a distance of 15-20 anyway and if your too close they'll blast your forehead to pure white

 

[DougPaul]

One improvised method is to take a meter reading off the palm of your hand, tilted so the light that strikes it is comparable to the light that hits the part of the scene you want rendered as 18% gray (which is somewhat lighter than you might guess -- a little lighter tone than a mid gray flannel business suit). The typical hand palm has about 18% reflectance. Old trick, that works well, especially with hand held light meters.

I thought one's palm reflected about twice 18%, so one metered off one's palm and increased the exposure 1 stop. (I'm remembering back about 30yrs here...)

The reflectance card or palm trick also assumes that it has the same lighting as the photo subject.

I suspect the reflectance of one's palm would also be a function of the skin pigmentation.

Doug

 

[DougPaul]

Like I said before, your camera light meter calibrated to expose your photographs to the same density of 18% grey. Consequently, if the vast majority of your photograph is bright ( say 8% grey) the camera doesn't know that and exposes incorrectly resulting in a darker image. the same is true for the opposite. Snow is particularly difficult.

Just a nit: the percentage is the percentage of the incident light that is reflected. So a bright scene would reflect >18%.

Scenes with a large range, such as both sunlit snow and shaded objects are particularly difficult to expose correctly. In fact, such scenes can exceed the range of film or the sensor in your camera. Backlit objects are also very difficult. (As mentioned previously, generally best delt with by taking the picture at a range of exposures and choosing the best later.)

I've also been disappointed by the supposedly intellegent exposure (and focus) systems in automated cameras. I do much better with my fully manual SLR with through-the-lens metering.

Doug

 

[Neil]

Does pointing the camera at the snow and taking a "white reading" off of it have anything to do with this?

Am I correct in my understanding:

The light meter says, "I want the finished photo to have an average refectivity of 18%. Therefore, given the current amount of light hitting me right now I need to set aperture and shutter values to x and Y in order to get that 18%.

Bright snow and faces get averaged into that 18% so neither are exposed properly.

My most recent crop of pics turned out a lot better thanks to this thread BTW. Thanks everybody for their input. They are here.and I invite criticism.

 

[DougPaul]

Am I correct in my understanding:

The light meter says, "I want the finished photo to have an average refectivity of 18%. Therefore, given the current amount of light hitting me right now I need to set aperture and shutter values to x and Y in order to get that 18%.

Bright snow and faces get averaged into that 18% so neither are exposed properly.

Generally correct--if you simply do what an averaging meter says. You compensate one way if you want the best reproduction of the face or the other way if you want to show the detail of the snow.

But of course, the reflectivity of real snow ranges from ~90% (very clean) to much less (very dirty).

--- Warning! Tutorial follows. ---

The theory is that the "average" scene returns an average of ~18% of the amount of light returned from a perfect white (100% reflective) scene. Any individual scene returns a range of intensities, say 1% to 90%. (These numbers are just examples pulled out of my imagination.) You want your camera to record the entire range--if the exposure is too large, the bright parts of the scene will saturate; if too small the dim parts will be lost in a general black. So the camera meters are calibrated so that the indicated exposure of an 18% reflective object will fall somewhere near the middle of the useful range of the sensor (or film).

In practice, many scenes have a distribution of intensities that differ significantly from the ideal, an average reflectivity different from 18%, and an (averaging) automatic light meter will choose an inappropriate exposure.

Types of meters:
* average: averages the intensity of the reflected light over the entire frame
* spot: measures the intensity of the reflected light of a small part of the frame (the spot)
* incident: An external meter that you hold by the subject to measure the incident light.

How to use:
* average: works ok for an average scene, but you have to compensate for atypical scenes.
* spot: place on a part of the scene that you want to come out at ~18% (a slightly darkish gray). Good for measuring exposures of atypical scenes.
* incident: hold right in front of subject. Requires that you can place it where the primary subject is (or in a spot with the same illumination). Typically used in studios.

Pragmatics:
* bracketing an exposure: take 3 images: 1 at the indicated exposure, 1 at less than the indicated, and 1 at more than the indicated. (-1, +0, and +1 stop are reasonable values.)
* If you think the meter will err in one direction, take 1 pic at that exposure and 2 more at +1 and +2 (or -1 and -2) stops.

Some cameras (or computer programs) can plot a graph of the number of pixels at each intensity--ideally all should be between the extremes.

Definition: stop: a factor of two in exposure. Obvious for time--a factor of 2 or .5. Or a factor of 1.4 (or .7) in aperture (f-stop). (A factor of 2 or .5 in aperture is 2 stops.)

Definition: f-stop: a measure of the light gathering power of a lens--smaller f-stop numbers gather more light. Equals focal_length/lens_diameter. The amount of light is proportional to (1/f-stop)**2.

Doug

 

[nartreb]

Does pointing the camera at the snow and taking a "white reading" off of it have anything to do with this?

No. That's for color, not brightness. Look up "white balance", and also "color temperature" in your favorite search engine.

 

[MichaelJ]

Look up "white balance"

Especially if you find that all your winter pictures in the woods look to have a bluish tint to them, especially on cloudy days. Generally, a setting of Daylight will put some warmth back into the image, a setting of Cloudy or Shade even more.

Experiment with the different modes to see what you get. It doesn't even require snow; you can even improve the colors of pictures taken, say, in the woods in the "green canopy" shade, again to take out the bluish or pinkish tinges.