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04/12/2008 12:23:46 AM · #1 |
| i was reading an article about using the in camera meter. In it, it mentioned to get a proper exposure reading set your camera to automatic, take a reading of the subject, then set your camera to manual and set the aperture, and shutterspped to the reading you took. I guess my question is, why would you need to set it in manual if you are using the the same reading from auto mode? Wouldn't both exposures be the same? What woud be the advantage to using manual mode? |
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04/12/2008 12:32:01 AM · #2 |
The main benefit is that you have a little more precise control over your metering in Manual mode.
Automode uses evaluative metering, that is, it examines the entire area and gives a meter for the average amount of light. In manual mode, it is reduced to 9% of the view finder, which means, the metering is more spot on. Higher end cameras actually have spot metering mode, which reduces it even more.
The main advantage, is that you can get creative over what you want, or don't want exposed. Don't assume an average exposure is the best, often it is not. Many times, you will want a region underexposed just to have the brightest region balanced properly.
This is the most basic explanation. Sometimes, you need certain priority over your exposure settings. Sometimes you need shutter priority Tv (where you set the shutter speed, and let the aperature balance) and sometimes you need aperture priority Av.
What article said that? I'd be very weary about that, or perhaps the interpretation was for something else?
Message edited by author 2008-04-12 00:34:35. |
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04/12/2008 12:36:52 AM · #3 |
| thanks that makes total sense to me...i just didnt understand what the artilce was saying. I never really use manual mode, but I assume in manual mode you take a reading, and then dial in to the proper exposure. I just didn't get the point of "copy and pasteing" the meter reading from auto mode to manual. Am i still missing something? |
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04/12/2008 12:50:32 AM · #4 |
Originally posted by brimac:
thanks that makes total sense to me...i just didnt understand what the artilce was saying. I never really use manual mode, but I assume in manual mode you take a reading, and then dial in to the proper exposure. I just didn't get the point of "copy and pasteing" the meter reading from auto mode to manual. Am i still missing something? |
If that's actually what the article said, the article is wrong. You may have misunderstood what the article was saying. The article may have said "Look at the suggested exposure in auto mode, then switch to manual mode and set the 'correct' exposure based on your evaluation of the automatic exposure." That would be the right way to do it, more or less. Here's why:
When the camera's meter evaluates a scene, it assumes that the average "luminance" of the scene it is metering is a middle gray, what we call a "zone 5 gray", 18% reflectance, halfway between white and black. It delivers an exposure which will render the scene based on that assumption. It works pretty well for the average landscape, say, but it can be fooled. Examples:
1. Frame up a white wall and use the suggested exposure. This will be an underexposure, since the camera assumes the wall is 18% gray.
2. Frame up a black wall and use th suggested exposure. This will be an overexposure, since the camera assumes the wall is 18% gray.
Straight from the camera, these two exposures will be basically identical to each other; they will both look gray. No black, no white.
3. Frame up a shot that is 50% white wall and 50% black wall, then use the suggested exposure. This should be spot-on, with both true black and true white showing, since the average between the two different areas is a middle gray.
So, in the real world, if you're shooting a scene in the snow you need to give more than the suggested exposure, or you will be underexposed. If you are shooting a scene from within a forest glen, with an opening and a view of distant mountains through it, you need to give less than the suggested exposure or the scene will be overexposed, with the mountain view totally blown out.
Hope this helps,
R.
Message edited by author 2008-04-12 00:50:52. |
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04/12/2008 01:00:38 AM · #5 |
If the overall scene is very light or very dark, then the metering in the camera can be fooled, as it is set up to shoot an average scene at neutral grey.
Try shooting a piece of white paper on auto, and you will see that the photo is much darker than you would expect it to be. With manual settings, you can override the meter readings and adjust exposure (EV) to add exposure and make the photo turn out with the paper looking white.
I am not sure that you understood what the article meant, as you explained it to us. I think that they were saying that if you shoot manual using the settings that "auto" would select, then you can adjust from that test shot using manual settings to get what you want in the shot. I was shooting a white bird today, and was shooting at about double the shutter speed that the camera would have selected in order to not "blow out" the details of the birds feathers.
Shoot away, and enjoy doing it.
I think that Bear just posted this same stuff better than I can articulate it.
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04/12/2008 01:04:00 AM · #6 |
| ok, i understand...i may have misunderstood the article...i must have. thanks Bear. So let me ask another question...lets say you are shooting a pic of a couple, one in a white outfit, the other in a black outfit.. would the camera read the correct expsore, or would you have to correct the exposure. Wouldthis be similar to your 50% balck wall / 50 % white wall? |
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04/12/2008 03:28:26 AM · #7 |
Originally posted by brimac:
ok, i understand...i may have misunderstood the article...i must have. thanks Bear. So let me ask another question...lets say you are shooting a pic of a couple, one in a white outfit, the other in a black outfit.. would the camera read the correct expsore, or would you have to correct the exposure. Wouldthis be similar to your 50% balck wall / 50 % white wall? |
It depends on what metering mode your camera is set on and the relative percentages of the white and black in the image. On our 20D's we have several metering modes to choose from: Evaluative, Partial, and Center-Weighted Average.
1. Evaluative averages the whole scene with extra emphasis on what is under the center autofocus spot.
2. Partial is a wannabe "spot meter" that takes its data from a smallish circle that fits into the middle of the autofocus grid.
3. Center-Weighted Average emphasizes the center strongly but considers the entire scene.
By default the camera uses Evaluative metering, and in basic modes that's all it will use.
Now, in your hypothetical situation, if you are using evaluative metering, if the subjects are posed against a white wall you will probably underexpose, and if they are posed against a dark wall you will probably overexpose. If they are posed in a normal landscape setting in normal lighting conditions (i.e. not backlit) the exposure will probably be about right.
If you use partial metering and the white dress is centered and the black dress is to one side, you'll underexpose. If the black dress is centered, that will cause overexposure.
Center weighted average metering is probably most likely to get this scenario right. But basically, you need to bracket exposures and study them to see the differences, and learn from that how to override the camera's choices with your own adjustments, using wither full manual mode or "EV Compensation" to add/subtract exposure as needed.
R. |
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