 Carolina K. Smith |
Upping the EV and Noise Hi, I know that increasing the ISO will increase the noise. What about increasing the EV? If increasing the EV increases 'noise' also, is there a lesser of the two evils?
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Jon Close |
If by "increasing the EV" you mean using the exposure compensation control, no, these are not equivalent. If your exposure at ISO 100 is f/4 and 1/15, then increasing the ISO to 400 allows 2 stops higher shutter speed: f/4 and 1/60. The total exposure remains the same, though. The loss of light due to the high shutter speed is offset by the higher sensitivity of the sensor at ISO 400. If you keep the ISO at 100, and dial in -2 EV of exposure compensation, you'll get f/4 and 1/60, but you'll be 2 stops underexposed.
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Carolina K. Smith |
Thanks for the explanation. Then why not increase the EV, rather than the ISO - for example, a low-light situation where you were trying to keep shutter speeds as fast as possible to reduce blur?
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Pamela K |
The problem is that your photo is then underexposed. You won't be able to see dark areas at all. I increase or decrease the EV when I'm trying to make lighting changes. For example, if I'm photographing a large white expanse, like a snowscape, I'll dial in +.7 so that the snow actually looks white. If I'm taking a shot of a sunset, on the other hand, I'll underexpose (-1.0) to capture the reds. However, if you use this trick under regular lighting conditions, your pictures will come out underexposed or overexposed. This means that darker areas will be invisible or lighter areas will be completely blown out. A little noise is probably preferable to this. If you wanted a picture with normal lighting but faster shutter speed, you would increase the ISO rather than using exposure compensation.
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
In layman's terms, EV is the amount of light there is. Midday has higher EV than dusk, like 8 is to 2. Camera meters see all white things in midday as very bright, thinking very high EV (like 10) and see all black things in midday as very dark EV (like 6). Light levels (EV Value) doesn't change, regardless if the meter thinks it does. EV compensation fixes the meter being fooled, but can't do anything about how much light there is. You change ISO for low light, because if it's dark, then it's dark.
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Robert Bridges |
Funny, I always thought that increasing or decreasing the exposure compensation was basically the equivalent of increasing or decreasing the ISO. Did I miss something somewhere along the line?
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Pamela K |
On my camera, exposure compensation seems to affect the shutter speed rather than the ISO. Maybe it's camera specific. It definitely causes the picture to be under or over-exposed relative to a picture shot without the compensation in automatic. Pam
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Robert Bridges |
Same difference - faster or slower shutter speed ... larger or smaller F/stop. Either way it's equivalent to increasing or decreasing the relative ISO ... I think.
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Jon Close |
If you are shooting with film, then changing the EV (or EC - Exposure Compensation) is the same as changing the ISO. If I load ISO 100 film, but set the ISO for 200, that is the same as -1 stop EC. The film's sensitivity has not changed, so exposures based on ISO 200 effectively give the film 1 less stop of exposure. If you are shooting digital they are not the same. When you change the ISO setting you are changing the sensitivity of the digital sensor. Changing the ISO on a digital camera from 100 to 200 is equivalent to taking out the ISO 100 film and replacing it with 200. It does not result in a -1 stop exposure compensation.
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Pamela K |
If you do this with film, isn't it called pushing the film rather than exposure compensation? Don't you have to get it developed differently so you have to keep it pushed for the whole roll? Is there a way to change the ISO just for one picture with film? Pam
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- Gregory LaGrange Contact Gregory LaGrange Gregory LaGrange's Gallery |
Pushing involves changing the development time with changing the exposure. That's why it's full name is push processing. You can't push a single frame on a roll. You can try printing lighter, or b/w with higher contrast filters. Exposure compensation is for when a camera meter gives incorrect exposures for certain situations. If it reads 250 at f/8 but the correct exposure needs to be 125 at f/8, setting a +1 exposure comp is what you do. For film, if you had 100 film in the camera, it would be the same if you change the ISO to 50. For digital, if you had the camera on manual, the same thing would happen with changing the ISO from 100 to 50 as long as aperture and shutter speed stayed the same on manual. Wouldn't work on auto modes.
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Pamela K |
Thanks, Gregory. That makes sense. Pam
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Robert Bridges |
Jon, Thanks. I don't shoot digital (obviously), and I did not know that but now that you mention it, yes ... makes perfect sense. Rob
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Steven Chaitoff |
Well, listen, I shot a roll in the evening (with street lamps) so it was adequate light. Anyway, I used 200 speed film and shot some shots at ISO 200, some at ISO 400 and some at ISO 800. I developed the roll like any other. No special processing. So it would seem like the shots at ISO 400 would be fine, just one stop underexposed. And 2 stops under for ISO 800. They are darker, but they are unfathomably grainy. Why is that?
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