ISO vs shutter speed

[bel0r]

I have a question re. noise performance of smaller sensors, i.e. 1/2.3 to 4/3.

It is true that iso 200 1’ is not iso 200 1/250 in terms of noise performance.

But what should be better: iso 200 4’ or iso 800 1’?
Do large sensors perform much better is this comparison?

 

[Tom Axford]

I have a question re. noise performance of smaller sensors, i.e. 1/2.3 to 4/3.

It is true that iso 200 1’ is not iso 200 1/250 in terms of noise performance.

But what should be better: iso 200 4’ or iso 800 1’?
Do large sensors perform much better is this comparison?

ISO does not directly affect noise. The important thing is exposure time. Four times the exposure will always give less noise, provided overexposure does not occur.

In practice, that means that you should use the lowest ISO (not below the camera's base ISO) and the longest exposure time that does not lead to overexposure.

All this, of course, assumes that other things remain the same: the aperture setting, the light level. etc.

 

[tony field]

I have a question re. noise performance of smaller sensors, i.e. 1/2.3 to 4/3.

It is true that iso 200 1’ is not iso 200 1/250 in terms of noise performance.

But what should be better: iso 200 4’ or iso 800 1’?
Do large sensors perform much better is this comparison?

Although sensor size can be important, there is something to be aware of: if you set your iso manually and use your camera light meter to determine exposure, the ISO you select fixes the Exposure to one value which should be identical for all cameras. The lower the iso, the higher the exposure and therefore the lower the image noise.

--
Charles Darwin: "ignorance more frequently begets confidence than does knowledge."
tony

 

[Jacques Cornell]

You need to understand that exposure is determined by the aperture and the shutter speed, and not by the ISO setting. The latter has no impact on the amount of light landing on the sensor, it simply magnifies the signal, much as a stereo amplifier does. If there's tape hiss or noise from dust on a vinyl record, that gets louder as you turn up the volume, and this is exactly what happens with image noise as you increase the ISO setting. Turning up the ISO brightens the image by increasing all values, including noise.

Thus, ISO 200 and 8 sec. will deliver 4x more photons to the sensor and yield 2 stops less noise than ISO 800 and 1 sec. even though both exposures will yield the same overall brightness.

 

[petrochemist]

I have a question re. noise performance of smaller sensors, i.e. 1/2.3 to 4/3.

It is true that iso 200 1’ is not iso 200 1/250 in terms of noise performance.

But what should be better: iso 200 4’ or iso 800 1’?
Do large sensors perform much better is this comparison?

My older APSC cameras will be worse than modern small sensor models, so it's not just down to sensor size. I'd rather use ISO 6400 on my Pentax Q (tiny sensor) than ISO 1600 on the K100d (APSC, but over 5 years older). I'd expect any modern phone to out perform either wrt noise at higher ISO.

ISO does not directly affect noise. The important thing is exposure time. Four times the exposure will always give less noise, provided overexposure does not occur.

In practice, that means that you should use the lowest ISO (not below the camera's base ISO) and the longest exposure time that does not lead to overexposure.

Quite often there'll be no significant noise at moderate ISO so there's no need to push things to the lowest, especially as long shutter speeds can introduce other issues.

With a static subject & a solid tripod your advise would be spot on, but in most shooting a compromise is needed between acceptable movement blur & noise. Getting this balance right is something you pick up with experience (both with your camera & the subject type).

All this, of course, assumes that other things remain the same: the aperture setting, the light level. etc.

Perhaps the degree of camera/subject movement could be included in 'other things' but sadly they won't remain the same.

 

[bel0r]

I understand the concept of exposure.

I mean that for every camera slower shutter speeds lead to increased noise. How does it compare to amplification via iso setting? Is there a limit causing slow SS noise to overcome amplification. Maybe amplification is always worse than long exposure noise.

 

[Jacques Cornell]

I understand the concept of exposure.

I mean that for every camera slower shutter speeds lead to increased noise.

Um, no. Slower shutter speeds = more light delivered to sensor = less noise.

How does it compare to amplification via iso setting? Is there a limit causing slow SS noise to overcome amplification. Maybe amplification is always worse than long exposure noise.

Are you talking about really long exposures like over 30 seconds? Some older cameras handled this badly. But, generally, longer exposures or larger apertures will deliver more light and thus less noise.

An ISO-invariant camera such as my a7RIII can deliver the same noise by shooting at ISO 25,600 or using ISO 800 with the same aperture and shutter speed to produce a much darker image and increasing image brightness via the Exposure slider by 5EV in my RAW processing app. This demonstrates that noise is almost entirely determined by the total amount of light falling on the sensor and has little or nothing to do with ISO setting, at least with modern cameras.

--
"I learned long ago, never to wrestle with a pig. You get dirty, and besides, the pig likes it." - George Bernard Shaw
http://jacquescornell.photography
http://happening.photos

 

[MarshallG]

The lower the iso, the higher the exposure and therefore the lower the image noise.

Simply stated:

The lower the ISO, the lower the noise.

 

[MarshallG]

Turning up the ISO brightens the image by increasing all values, including noise.

Simply stated:

The higher the ISO, the higher the noise.

 

[D Cox]

I understand the concept of exposure.

I mean that for every camera slower shutter speeds lead to increased noise.

Um, no. Slower shutter speeds = more light delivered to sensor = less noise.

How does it compare to amplification via iso setting? Is there a limit causing slow SS noise to overcome amplification. Maybe amplification is always worse than long exposure noise.

Are you talking about really long exposures like over 30 seconds? Some older cameras handled this badly. But, generally, longer exposures or larger apertures will deliver more light and thus less noise.

An ISO-invariant camera such as my a7RIII can deliver the same noise by shooting at ISO 25,600 or using ISO 800 with the same aperture and shutter speed to produce a much darker image and increasing image brightness via the Exposure slider by 5EV in my RAW processing app. This demonstrates that noise is almost entirely determined by the total amount of light falling on the sensor and has little or nothing to do with ISO setting, at least with modern cameras.

True for raw files. JPGs often have stronger noise reduction applied in the camera at higher ISO settings.

 

[bel0r]

Jacques Cornell wrote

Are you talking about really long exposures like over 30 seconds? Some older cameras handled this badly. But, generally, longer exposures or larger apertures will deliver more light and thus less noise.

No, longer than standard handheld SS range 1/mm + 4 stops of IBIS/OIS. Around 4 seconds.

 

[PhotoTeach2]

Jacques Cornell wrote

Are you talking about really long exposures like over 30 seconds? Some older cameras handled this badly. But, generally, longer exposures or larger apertures will deliver more light and thus less noise.

No, longer than standard handheld SS range 1/mm + 4 stops of IBIS/OIS. Around 4 seconds.

That would not then be an issue for noise.

Cameras do have a "Long-Exposure Noise Reduction" feature, but again that is usually for 10-seconds or (much) longer exposures.

 

[alcelc]

Compared to what?

Longer exposure time (slower shutter speed) is to allow more light reaching onto the sensor. More light = lower noise.

Therefore, if you use longer exposure time and lower ISO to produce an image having similar lightness output by using a shorter exposure time and higher ISO, the output from the earlier setup would have less noise.

The smaller the size of sensor, would require more light to keep noise low.

It is that simple. Nothing related to what particular shutter speed used (e.g. 1/focal length + effect of stabilization). Whenever you are free to use any shutter speed (not over expose the shot), use 4" & lower ISO is always cleaner than using 1" and higher ISO. It is the true for other shutter speed, says 1/60" vs 1/250" etc.

So whenever possible, push on f/stop and Shutter speed for the lightness of output. Raise ISO only when you have reached the max of your gear on f/stop and Shutter speed if you wish to keep noise low.

 

[Bill Ferris]

I understand the concept of exposure.

I mean that for every camera slower shutter speeds lead to increased noise.

I wonder, are you associating slower shutter speeds with increased noise because you often use 1-second or longer shutter speeds in dark environments and often with higher ISOs? For example, do you use those settings when doing night sky photograhy, nighttime street photograhy, or when traveling and photographing the dark interiors of historic buildings?

How does it compare to amplification via iso setting? Is there a limit causing slow SS noise to overcome amplification. Maybe amplification is always worse than long exposure noise.

Let's go back to the concept of exposure. If you collect all the light passing through the lens to the sensor and spread that evenly across the entire sensor, that's exposure. It's determined by the available light in the scene, the lens aperture and the length of time the sensor is exposured to light.

The more light delivered to a sensor, the greater the exposure - think about it as spreading one or two dollops of peanut butter across a slice of bread. Two dollops is more peanut butter, which means it spreads thicker across the bread. The thicker you can spread light across a sensor, the greater the exposure.

Now, if we're out at night or in a naturally dark environment, there isn't much light in the scene to work with. Even if we use the fastest f-stop available or a really slow shutter speed, there's so little light available in the scene that not much gets to the sensor.

Here's where noise comes into play. The more total light used to make a photo, the less visible shot noise will be. Suppose we spread peanut butter across a slice of bread and a cracker so the peanut butter coats both to the same thickness. If the peanut butter were light, and the bread and cracker were camera sensors, we could say both cameras are working with the same exposure (the peanut butter spread to the same thickness) but that the camera built around the larger sensor is working with more total light. If we scrape all the peanut butter off the bread slice and the cracker, and compare how much PB was spread across both, the slice of bread will have more.

Can you tell I've got a thing for peanut butter?

Anyway, exposure is about the light delivered to the sensor. Noise is about the total light used to make the photo.

ISO has no direct affect either on exposure or the total light used to make the photo. ISO's used to manage the lightness of a photo. If you're making a night sky photo, you might shoot with the lens wide open at f/2.8 and a slow shutter speed of 4-seconds. There may not be much available light in the scene but you're squeezing as much of it as possible onto the sensor.

Even at f/2.8, 4-seconds the test photo may look dark at ISO 200. So, you increase ISO to 800, 1600 or higher to get a lighter photo. But you also see a noisy mess. It wasn't the increase in ISO that introduced or created all the noise. The noise was there at ISO 200. In fact, since you used the same exposure settings (f-stop and shutter speed), the amount of light used to make both photos is the same. Since the amount of light is the same, the amount of noise is the same. The noise in the ISO 800 or 1600 photo is more prominent to the eye because it's a lighter image.

Getting back to your original question about noise visibility in photos made with smaller sensor cameras, it's entirely possible to get clean, noise-free photos with crop sensor cameras given a bright enough scene. The challenge comes when doing photograhy in inherently dark settings, or when doing photograhy that requires very fast shutter speeds or very small lens apertures.

In a dark setting, there just isn't much light to work with. Similarly, a very fast shutter speed (very short exposure time) or a small lens aperture will work to limit how much light gets to the sensor even in bright conditions. These aren't necessarily situations in which it's impossible to make a clean image. But you will need to be conscious of using the other exposure setting (f-stop or shutter speed) to compensate.

Good luck.

--
Bill Ferris Photography
Flagstaff, AZ
http://www.billferris.photoshelter.com

 

[FingerPainter]

The lower the iso, the higher the exposure and therefore the lower the image noise.

Simply stated:

The lower the ISO, the lower the noise.

True only if you or the camera is zeroing the meter on all compared shots.

On most cameras, increasing the ISO but leaving the exposure unchanged will actually make the image a little less noisy.

 

[FingerPainter]

...

Thus, ISO 200 and 8 sec. will deliver 4x more photons to the sensor and yield 2 stops less noise than ISO 800 and 1 sec. even though both exposures will yield the same overall brightness.

Check your math, Jacques (or if you are like me, your typing).

Assuming same scene luminance, same f-stop and same sensor surface area, ISO 200 and 8 sec will deliver 8 times as many photons as ISO 800 and 1 sec, and the former will also be one stop lighter.

 

[FingerPainter]

I understand the concept of exposure.

Perhaps.

I mean that for every camera slower shutter speeds lead to increased noise.

That is generally untrue. It is never true WRT shot noise. With certain cameras and very long exposure times it may be true of certain forms of heat-generated noise. These will only become problematic if the exposure is low, so the magnitude of the heat-generated noise is large relative to shot noise, as it may be for long exposure of night skies.

In general, a slower shutter allows more photons to fall on the sensor. An increased number of photons reduces the noisiness (increases the Signal to Noise Ratio (SNR)) of shot noise.

How does it compare to amplification via iso setting?

Increased amplification tends to improve the SNR because the amplification is applied to all the signal but only some of the noise. It is applied to the shot noise, and those elements of camera-added noise that are added before the gain stage. Noise added during or after the gain stage is not amplified.

Most of the noise that some people associate with increased amplification, is actually caused by the accompanying decrease in exposure that occurs in a auto-exposure mode without Auto-ISO.

Is there a limit causing slow SS noise to overcome amplification.

Noise that is caused by heat buildup from long exposures probably occurs at different thresholds on different cameras.

Maybe amplification is always worse than long exposure noise.

Amplification is never worse because amplification never causes the SNR to decrease.

 

[bel0r]

Thank you very much for the detailed explanation.

Now i understand the following:

1. If i change lighting conditions or aperture to keep brightness of the photo the same, there is no visible long exposure noise on a modern camera for any realistic exposure below 30s, and in-camera noise reduction using another shot with closed shutter works pretty well.

2. Higher iso means more noise in any situation, and i should let in max amount of light and use the lowest f-stop and the longest SS for properly exposed photo, given DOF and motion blur limitations.

 

[bel0r]

Jacques Cornell wrote

Are you talking about really long exposures like over 30 seconds? Some older cameras handled this badly. But, generally, longer exposures or larger apertures will deliver more light and thus less noise.

No, longer than standard handheld SS range 1/mm + 4 stops of IBIS/OIS. Around 4 seconds.

That would not then be an issue for noise.

Cameras do have a "Long-Exposure Noise Reduction" feature, but again that is usually for 10-seconds or (much) longer exposures.

For Panasonic TZ80 with 1/2.3’ sensor long exposure noise reduction is applied for SS of 1 second.

 

[Bill Ferris]

Thank you very much for the detailed explanation.

Now i understand the following:

1. If i change lighting conditions or aperture to keep brightness of the photo the same, there is no visible long exposure noise on a modern camera for any realistic exposure below 30s, and in-camera noise reduction using another shot with closed shutter works pretty well.

There is no such thing as "long exposure noise". There is shot noise, which is determined by the total light used to make the photo and there is electronic read noise, which is a product of in-camera processing, minimal at low ISOs and even lower at higher ISOs.

2. Higher iso means more noise in any situation,

No.

and i should let in max amount of light and use the lowest f-stop and the longest SS for properly exposed photo, given DOF and motion blur limitations.

That's a good general rule to live by in low light situations: use the smallest f-number that delivers an acceptable depth of field and the slowest shutter speed that acceptably renders movement in the frame. If you do those two things, you'll optimize exposure for the shot you're trying to make.

In brightly-lit environments, there's often more latitude to use a faster shutter speed or larger f-number than needed for your creative goals, maximize depth of field and freeze even very fast movement, and still deliver a high exposure to the sensor.