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12/17/2004 11:41:13 PM · #1 |
I've been reading some books lately on photography - especially "Understanding Exposure" by Bryan Peterson, which has been a great book so far.
My question regarding metering is that, since you can essentially use a gray card to provide your camera with information on a proper exposure when conditions are tricky - does this mean that if you simply used a gray card for your metering everytime, everything would come out okay? It seems like this wouldn't always be the case - especially in extreme conditions such as sunsets or sunrises. When is the best time to use a gray card, as opposed to simply metering off of something else (ie: the sand in a beach sunset photo, the sky in a silhouette sunset photo)?
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12/18/2004 12:16:52 AM · #2 |
Originally posted by brianlh:
I've been reading some books lately on photography - especially "Understanding Exposure" by Bryan Peterson, which has been a great book so far.
My question regarding metering is that, since you can essentially use a gray card to provide your camera with information on a proper exposure when conditions are tricky - does this mean that if you simply used a gray card for your metering everytime, everything would come out okay? It seems like this wouldn't always be the case - especially in extreme conditions such as sunsets or sunrises. When is the best time to use a gray card, as opposed to simply metering off of something else (ie: the sand in a beach sunset photo, the sky in a silhouette sunset photo)? |
scnd try
Brian
u must realize u just do meter the light where it hits the greycard
so its prob not of much use in cases for example landscapes
or u have to carrie a greycard scale 100 yards/100yards
not very practical though
hope its a little helpfull to u this short explanation
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12/18/2004 12:57:59 AM · #3 |
Originally posted by brianlh:
I've been reading some books lately on photography - especially "Understanding Exposure" by Bryan Peterson, which has been a great book so far.
My question regarding metering is that, since you can essentially use a gray card to provide your camera with information on a proper exposure when conditions are tricky - does this mean that if you simply used a gray card for your metering everytime, everything would come out okay? It seems like this wouldn't always be the case - especially in extreme conditions such as sunsets or sunrises. When is the best time to use a gray card, as opposed to simply metering off of something else (ie: the sand in a beach sunset photo, the sky in a silhouette sunset photo)? |
for example if i take ur picture 'anticipition' wich is a lovely capture , these hopefull expressions on their faces is a rather unique capture
so if u had used a greycard at the spot u made this pic from u wld have measured the lightsituation at about the same where the boys where standing
soo the faces and bodys of the boys would have been far more bright (as it is underexposed now because of the strong influence of the watereflection i guess)
wich would prob not benefit this exposure at all in this case
soo that means u are bothering to have the most (average) proper lightmetering and in the end it means ure ruining a perfect capture
aint that confusing! |
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12/18/2004 04:13:02 AM · #4 |
Brian,
I have used test charts in the past for video purposes. So, I decided to pursued the same idea for my still imagery calibration requirements.
First of all, it is important to get the white balance correct. So, a proper white card would be needed to correctly balance your camera to the existing light colour temperature conditions.
Next, might be a colour chip chart. This is an image stabilized colour index chart that you can photograph and then use to compare to images of the same subject matter under different lighting conditions. By comparing the colourimetry of the same chip chart in two different lighting conditions, you should be able to match colour from one image to the other.
Finally, is the grey chart. Often, it can be a flat ASA 61 grey as is commonly used in film photography or it might be one of the newer graduated or staircase grey scale chip charts that identified a range of f-stops. This staircase is useful for a determining dynamic or exposure range of your shot. Artistically, you may want to adjust the exposure for effect while staying within the identified exposure range.
A company called, DSC Labs is creating a new set of digital camera test charts that will be available early in the New Year. DSC Labs are world-famous for making test charts for major motion pictures and television production.
DSC Labs are expected to soon release a combination test chart for digital still cameras that will be called CametteDigi. It is two-sided front-lit, reflective chart with simple colour bar / grey scale on one side with a true white on back.
You can check out DSC Labs' web site at DSC Labs
Does this help?
Cheers, Michael
Message edited by author 2004-12-18 09:13:27.
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12/18/2004 04:47:03 AM · #5 |
This is something I wanted to know about. I think a grey card is a 18% grey color, kind in the between of white and black colors. You have to remember human eye does not see intensity in linear fashion but rather in logarithmic(?) space. Thus gamma correction curves for devices displaying digital images ;D.
White balance is set using grey cards, since camera assumes gray card is an equal mixture of primary colors. White balance adjustment on gray card then just calculates the factors for each primary color channel to produce balanced exposure, in other words, which is white light in current light conditions. For example, in sunset the light is very warm and varies constantly over the time. Gray card would be ideal for these situations to adjust white balance precisely.
The information can be used for shutter speed also, but it's not so straight forward. Camera light meters work this way. If we know what intensity is in the middle of intensity range we can extrapolate the minimum and maximum value for sensor to record and adjust shutter speed based on this. But the problem is that there is only one reference point for scene brightness.
Imagine a situation where you want to photograph a black object in a black room. The only bright object is gray card and if you set shutter speed according to this information you will get underexposed image. This is because camera assumes your gray card is in the middle of scene brightness which is not true since your scene is black color only. This is why many cameras have a "multi meter mode", gathering intensity information all over the frame and thus archieving better results than "sigle point" exposure metering mode.
Message edited by author 2004-12-18 09:50:22.
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12/18/2004 04:55:31 AM · #6 |
Originally posted by brianlh:
I've been reading some books lately on photography - especially "Understanding Exposure" by Bryan Peterson, which has been a great book so far.
My question regarding metering is that, since you can essentially use a gray card to provide your camera with information on a proper exposure when conditions are tricky - does this mean that if you simply used a gray card for your metering everytime, everything would come out okay? It seems like this wouldn't always be the case - especially in extreme conditions such as sunsets or sunrises. When is the best time to use a gray card, as opposed to simply metering off of something else (ie: the sand in a beach sunset photo, the sky in a silhouette sunset photo)? |
Let my try to answer one of your questions, which was âwhen is the best time to use a gray card?â First it helps to understand what goes wrong with light metering. The camera assumes that you are photographing a ânormalâ scene with a normal mix of bright and dark areas. For this normal scene it is assumed that the average brightness of the scene is 18% of the brightest areas of the scene, so the camera adjusts the exposure to give good whites at a brightness that is one over 18%. The problem comes in when the average of the scene is either higher or lower then 18% of full white. The best example is a scene that is mostly snow, the camera will take this as the 18% point and way underexpose the image. What the gray card does for you is give you a target to meter off of that will set the exposure correctly under these conditions, but only if you place the gray card in the same lighting as the scene is getting. And this will not work if there is a bright sky in the scene that you donât want blown out.
There are other ways, that are better, to get the same result. If you camera has a spot meter then use that to look at the brightest part of the scene and then increase your exposure by 2 stops. You have to be using the camera in manual mode for this to work. This will work for sunsets and other cases where there is something bright that you canât get too with a gray card. This also will work a lot better then you are say in a house and wishing to shoot a snow scene out a window. This assumes that you donât want any part of the photo overexposed, which may not be the case. This also assumes a digital camera, film is very different and the rule for setting exposure are not the same at all. For example with film it is better to over expose by a stop to two rather then under expose, digital is just the opposite.
For cameras that have a live histogram life is even easier, but that is another whole discussion.
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12/18/2004 05:02:54 AM · #7 |
Originally posted by lode:
This is something I wanted to know about. I think a grey card is a 18% grey color, kind in the between of white and black colors. You have to remember human eye does not see intensity in linear fashion but rather in logarithmic(?) space. Thus gamma correction curves for devices displaying digital images ;D.
White balance is set using grey cards, since camera assumes gray card is an equal mixture of primary colors. White balance adjustment on gray card then just calculates the factors for each primary color channel to produce balanced exposure, in other words, which is white light in current light conditions. For example, in sunset the light is very warm and varies constantly over the time. Gray card would be ideal for these situations to adjust white balance precisely.
The information can be used for shutter speed also, but it's not so straight forward. Camera light meters work this way. If we know what intensity is in the middle of intensity range we can extrapolate the minimum and maximum value for sensor to record and adjust shutter speed based on this. But the problem is that there is only one reference point for scene brightness.
Imagine a situation where you want to photograph a black object in a black room. The only bright object is gray card and if you set shutter speed according to this information you will get underexposed image. This is because camera assumes your gray card is in the middle of scene brightness which is not true since your scene is black color only. This is why many cameras have a "multi meter mode", gathering intensity information all over the frame and thus archieving better results than "sigle point" exposure metering mode. |
I do not believe that a grey card is the best choice to calibrate white balance settings on when using a digital camera. A proper white card that is calibrated neutral white is preferred.
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12/18/2004 05:06:57 AM · #8 |
all this theory soo true and its prob to the benefit if u know any of these things how a camera is thinking
but than again we should not ignore the punk dimension of hi tech cams as we all own by now
bracketing can get u quit far in moments of doubts
it should be punk in a way, if u know 3 chords u can play the damn thing
the same for a cam if u use the facilities on it u can make a whollota fantastic pics and let the cam do the thinking for its quite clever
and u can judge it in a sec when still in doubt
just some thought about the subjects
i mean one can face the most magnificent views for a capture but when u have a terrible headache its not likely it comes out well
i c E
Originally posted by lode:
This is something I wanted to know about. I think a grey card is a 18% grey color, kind in the between of white and black colors. You have to remember human eye does not see intensity in linear fashion but rather in logarithmic(?) space. Thus gamma correction curves for devices displaying digital images ;D.
White balance is set using grey cards, since camera assumes gray card is an equal mixture of primary colors. White balance adjustment on gray card then just calculates the factors for each primary color channel to produce balanced exposure, in other words, which is white light in current light conditions. For example, in sunset the light is very warm and varies constantly over the time. Gray card would be ideal for these situations to adjust white balance precisely.
The information can be used for shutter speed also, but it's not so straight forward. Camera light meters work this way. If we know what intensity is in the middle of intensity range we can extrapolate the minimum and maximum value for sensor to record and adjust shutter speed based on this. But the problem is that there is only one reference point for scene brightness.
Imagine a situation where you want to photograph a black object in a black room. The only bright object is gray card and if you set shutter speed according to this information you will get underexposed image. This is because camera assumes your gray card is in the middle of scene brightness which is not true since your scene is black color only. This is why many cameras have a "multi meter mode", gathering intensity information all over the frame and thus archieving better results than "sigle point" exposure metering mode. |
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12/18/2004 10:20:21 AM · #9 |
| wow, thanks for all of the replies - went to sleep not expecting much and woke up to all these detailed responses. i guess i had never considered the fact that scenes aren't always shed in uniform lighting, or thought about the creative implications of always making a "correct" exposure. i think i have a better idea about what's available and what's necessary - thanks! |
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