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Manual iso
- Thread starter 4dampadac
- Start date
Sure, if shooting a lot in constant lighting, M is a great way to lock exposure. I don't run into that often.
From ice hockey in a rink where lighting is uneven to performances where the spot doesn't keep up, it seems pretty rare that I shoot a lot at a constant exposure and/or need to change exposure compensation frequently. (My use of exposure compensation is more typically with something like ice hockey, where the ice demands an exposure boost, but I set it and forget it; meanwhile, the lighting changes from one end of the rink to the other).
But I can imagine situations like you describe and I'm sure I've run into them on occasion. (Even a simple panoramic stitch shows how the meter reading can change and locking an exposure is a good thing to do).
- Dennis
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Gallery at http://kingofthebeasts.smugmug.com
sybersitizen
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Use of flash could be a good reason.
How did those film photographers ever take a photo? They had to decide which film ASA to put in the camera.
And there is a mirrorless camera on the market, a very expensive one (H---), that does not have an Auto ISO option when you put the camera in M mode.
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http://www.flickr.com/photos/41790885@N08/
And there is a mirrorless camera on the market, a very expensive one (H---), that does not have an Auto ISO option when you put the camera in M mode.
--
http://www.flickr.com/photos/41790885@N08/
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CameraCarl
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Let's say I am photographing birds in flight and there are trees in part of the background. I want a shutter speed of, say, 1/1250 and an aperture of f/11. I need to maintain a certain exposure value to ensure that there is detail in the feathers and under the wings. So I set a manual ISO to keep that proper exposure on the bird regardless of whether it is flying in a clear blue sky, against clouds or against a backdrop of dark trees. If I had auto ISO set, the ISO would keep changing so the exposure of the feathers would keep changing, sometimes way underexposed and sometimes way overexposed.
The Ghost of Caravaggio
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I have no idea whatsoever what illusion you refer to. Please explain.
John Sheehy
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For one thing, If the lighting is non-variable, and the subject matter switches from dark to light and visa versa, fixed manual everything will keep working to give you images that all need the same tonal level conversion tweaks, if any at all.
For example, with fixed everything, if you shoot a black horse and then it is replaced in the same light by a white horse, the same manual settings will work for both, instead of trying to fight the camera trying to make both horses middle grey.
The Ghost of Caravaggio
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Actually, automated ISO impacts image brightness after the shutter closes. The metering modes compute how much brightness to apply in-camera when the sensor happens to be underexposed when it is open.
Final image brightness depends on sensor exposure and post-acquisition applied brightness. Exposure determines the signal level. Increasing exposure also reduces the relative contribution of photon noise. Increasing the camera ISO setting can not increase the signal. It can not improve the signal.
Some cameras have electronic noise levels that are pseudo-ISO independent. The electronic noise does not vary with camera ISO setting to within +/- 1/3 stop. In this case camera ISO only affects image brightness. Some cameras rely on increasing signal gain to minimize electronic noise as camera Iso setting increases. In this case camera ISO setting can affect both image brightness and signal-to-noise ratios.
All cameras use digital multiplication at very high camera ISO settings to achieve the image brightness predicted by the meter.
More specifically, if the light is constant the shutter time and aperture that optimizes sensor exposure are constants.
Of course practical considerations (DOF, subject motion and camera motion) determine the practical shutter time and aperture. Often the result is unavoidable sensor underexposure. Sensor underexposure occurs when the number of photoelectrons generated in a pixel (photo-diode site) exceeds the photo-diodes' maximum electrical charge capacity.
So the goal is to optimize sensor exposure by using a shutter time and aperture that fully exposes highlight regions without causing sensor overexposure. When this happens underexposed shadow regions will have the highest possible signal-to-noise ratios.
Some highlight regions are not important to a photograph. These regions should be intentionally overexposed. Some examples are specular highlights from sunlight reflections, vehicle headlights and streetlights in night scenes.
FingerPainter
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How would it do that? I think the reverse is true - manual ISO could result in less exposure than optimal. If you manually set the ISO to a value higher than you need, you will get less exposure than you could have, and that means more noisiness than necessary. Auto ISO won't increase the ISO setting unless it cannot get the lightness targeted by the metering system with the exposure you chose with your aperture and shutter settings.
With Auto ISO in M you also have control over the real exposure., You set the aperture and shutter yourself. These two parameters, plus the amount of light in the scene, determine the exposure. So M modes lets you choose the exposure regardless of whether Auto-ISO is set.
FingerPainter
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In M mode with Auto-ISO, you control exposure with your A and S settings. You control lightness relative to the metering with the EC setting. What Is it you that you fear you are not controlling?
Why do you care what the ISO setting is as long as you get the exposure and image lightness you want?
I don't think my cameras work that way. Seems like you are saying that shutter speed and aperture alone control exposure for any specific amount of light in the scene. On my cameras if I have a setup that the available light requires 1/250 sec shutter speed at f8 and ISO 100 and I change the ISO to 800 and leave shutter speed and aperture the same, the camera will produce an image much brighter and overexposed than the one with the ISO set at 100.
FingerPainter
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If the light on the subject isn't changing, bu the lightness of the of the background changes as the subject moves, all you need to do to maintain a constant exposure is keep the aperture and shutter unchanged,. Easy to do in M mode.
Yes, the ISO will change but the exposure will not.
Nope, the lightness of the wings and the rest of the subject will change if eh meterign solution changes, but the exposure on the wings cannot change because the light, aperture and shutter did not change.
You are using both the wrong metering mode and the wrong shooting mode if you want a constant exposure of the subject under constant light but the exposure changes as the background changes. In M mode the exposure cannot change due to a change in metering. Usually, if you spot meter the subject, the metering solution won't change as long as the light on the subject doesn't change.
There are three cases, though, where even spot metering will fail to keep a constant metering solution:
- When the subject is so small relative to the frame that the meter also measure part of the background.
- When the subject has multiple colours, but its movement makes it practically impossible to keep the spot meter on the particular colour you want to meter from
- When the subjects movement and small size relative to the frame make it practically impossible to keep the spot meter on the subject.
In M mode with AUo-ISO , a changing metering solution won't result in a change in exposure as the background changes, but it will result in a change of subject lightness which can be disconcerting if showing a sequence of shots of the same subject. If the subject is moving fast enough, it may not be practical to adjust EC for each shot.
So, when
- subject motion and relative size are such that it is not practical to spot meter, and
- rate of subject motion means it is not practical to adjust EC from shot to shot, and
- when the metering solution is likely to change from shot to shot even though the light on the subject is not changing
FingerPainter
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It's a pretty rare digital camera that doesn't work that way. More likely, you are mistaken about how they work.
Yes. That's correct.
I'm not sure what sort of "setup" requires any particular aperture or shutter.
... when displayed, yes.
No. It's exposure hasn't changed, so if it wasn't overexposed in the ISO 100 shot, it isn't overexposed in the ISO 800 shot. What it is is "too light", not overexposed. The problem with the image is not its exposure but its lightness.
With roll film, there was little practical reason to avoid conflating "lightness" with "exposure" With digital, there is: properly diagnosing the problem, and makiogn appropriate settings choices.
FingerPainter
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Exposure is how much light fell on the sensor per unit area during the time the shutter was open. It is not how light or dark a processed image looks.
Exposure affects two aspects of an image.
- For a given camera, it is the only significant factor in determining how noisy and image looks.
- In conjunction with the ISO setting, it determines how light or dark a SOOC JPEG looks.
So with your cameras you can just set the shutter speed and aperture to the settings you want, ignore ISO setting and everything will be fine (whether the iSO is set at 100 or 1000) and resulting images will all exhibit the same exposure and quality when viewed or printed? Maybe me and my wife need one of those cameras.
FingerPainter
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And sometime those choices made by the camera will be better than those made by the average user. E.g. Auto-ISO is less likely to set the ISO too high than is the average user.
And sometimes the camera can make those automatic adjustments much faster than a human operator can. Full manual control may require making more adjustments per shot than there is time for the average user to make in a rapidly changing scene.
True enough, but making a proper assessment of when manual ISO is actually the better choice requires a better understanding of what is actually going on than is displayed by some of the posters in this thread (not you of course).
FingerPainter
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We are talking about M mode with Auto-ISO. The exposure cannot change automatically in this mode - unless the light is changing automatically.
Not possible. If the light is not changing and the aperture and shutter are not changing, the exposure does not change. What might change as the meter reading changes is the image lightness.
Using M mode takes care of that.
Which you get from M mode and not manually adjusting A or S.
A variable ISO wouldn't change the exposure, just the lightness.
Then don't use matrix or centre-weighted metering when you don't want changes in background lightness to affect the metering solution.
What happens when the sun gets behind one of those puffy white clouds?
If you successfully spot meter the face, clothing or background won't result in a change of metering solution.
Which one? Your approach is just fine if the fixed ISO is the base ISO. with any other ISO selection, it might result in more noise than necessary in some shots.
But exposure doesn't change in M with Auto-ISO, unless light, aperture or shutter are changed.
What might change if the metering solution changes, despite the lack of change in light, is subject lightness. (If the background lightness is changing from shot to shot, you want the image lightness to change.) This change in subject lightness can only happen if you fail to meter for the subject alone. The usual way to avoid that is to use spot metering. Sometimes (like with distant or erratically moving BIF) it may not be practical to spot meter the subject.
It is in situations where
- the light on the subject is constant, and
- you want constant subject lightness over a sequence of shots, and
- unwanted metering solution changes cannot be avoided, and
- one cannot practically change EC between shots
FingerPainter
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IDK how you reached that conclusion.
Yes, but you seem to misunderstand what "exposure" means. It isn't how light or dark the image looks.
no
The ISO setting and exposure combine to determine image lightness. Anything about lightness can be wrong if you ignore the ISO setting.
Auto-ISO doesn't ignore the ISO setting however, so with it set, Image lightness will be correct, according to the Auto-ISO parameters, EC and metering solution you selected.
I use manual ISO. I usually have decided what ISO I want based on conditions and select it as one of the first settings adjustments I make.
If that doesn't give me the shutter speed I want it only takes a moment to change it.
Mark_A
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A thread of photos from SmartPhones ..
Without debating the nuances of exposure....
I use full manual, including manual ISO, when I'm shooting two things:
- a series of shots to be stitched into a panorama
- a series of shots using focus stacking.
In truth, I often forget in either case, which sometimes makes more work, since I then need to equalize the exposure of some of the individual shots. I shoot in raw, so it's extra work, but not harming my results.
I use full manual, including manual ISO, when I'm shooting two things:
- a series of shots to be stitched into a panorama
- a series of shots using focus stacking.
In truth, I often forget in either case, which sometimes makes more work, since I then need to equalize the exposure of some of the individual shots. I shoot in raw, so it's extra work, but not harming my results.
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