mpgxsvcd: In order to believe this article you have to accept that shot noise is a significant factor in short exposure photography. That fact is stated in the article. However, it really isn’t demonstrated. I think that is where some people are getting hung up. They can’t accept that fact without seeing it.
It would be really cool if you showed how much noise is contributed from shot noise vs. read noise in each review. You could stack out the read noise with Dark Frames leaving only the shot noise from a very dark scene.
Very good information there Mike. Thanks for that.
mpgxsvcd: This is the first time that I have seen shot noise factored into the argument that the larger the sensor the better the noise characteristics are. That is why I was finding it so difficult to accept this as fact before.
@Felix E Klee
Actually that isn’t true. Your mistake is that you assumed that the smaller sensor uses all of the light that the aperture can provide. If the lens illuminates the entire full frame sensor then the smaller sensor will literally discard a portion of that light because the light falls outside of its area. That will also decrease your signal to noise ratio because you are discarding some of the light and the shot noise and absolute aperture haven’t changed.
I made the same mistake in one of my questions as well.
In order to believe this article you have to accept that shot noise is a significant factor in short exposure photography. That fact is stated in the article. However, it really isn’t demonstrated. I think that is where some people are getting hung up. They can’t accept that fact without seeing it.
mpgxsvcd: “There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor.”
I am confused about the statement above. The aperture diameter determines how much light is available to your sensor, right? The focal ratio just determines how concentrated that light is. The focal ratio does not affect the total amount of light that is available at all. The aperture diameter does that.
The focal ratio only affects the light per unit area. However, your statement refers to total light available. Or am I reading that wrong?
I see where my mistake is now. You were implying that the lens was identical in both situations so the total light and the shot noise through the lens was equal in both situations. However, the smaller sensor literally discards a portion of that light because that light falls outside of its area.
When looking at it like that then yes the sensor size is what causes the light loss and therefore would decrease the signal to noise ratio.
“when you shoot two different sized sensors with the same shutter speed, f-number and ISO, the camera with the smaller sensor has to produce the same final image brightness (which the ISO standard demands) from less total light.”
I guess where I was getting confused was that you didn’t specify that the focal lengths were the same in the above statement. The shutter speed, f-number, and ISO could all be the same but if the focal length for the m43 sensor was half that of the full frame sensor then both would be seeing the same total light because the aperture diameters would be the same.
Should the statement above also say that the focal lengths or aperture diameters are the same as well? If either one of those is different then the sensors could see the same amount of light despite their size difference.
“There are three factors that affect how much light is available for your sensor to capture: your shutter speed, f-number and the size of your sensor.”
mpgxsvcd: I agree with everything you said for short exposure photography but what about long exposure photography like astrophotography(Several minutes or more)? There longer exposures increases the electrical read noise and decreases the shot noise because the signal is more consistent over the longer period of time.
It would be interesting to find the shutter duration at which shot noise is surpassed by electrical read noise in particular cameras.
In addition stacking light exposures along with dark frames can reduce the shot and read noise by using some form of averaging with multiple frames. Since the noise is random the difference between each frame is the “unwanted signal”.
It might be really interesting to add a new section to your reviews for long exposure photography. It would be great to not only know what ISO is best to use but also what shutter speed is most desirable. If you have a stationary scene then it could be possible that using a longer exposure than you normally would use might improve the shot noise even at the same ISO value.
I think there are really two categories of long exposure astrophotography. There is the amateur component where we are typically focused on the Messier objects and the like. Those objects(M42, M31, M27, M16, M8, …etc) are fairly bright. From my experience with those objects shot noise is really not as big an issue as read noise once the exposures pass a few minutes.
Then there is semi-Pro and Pro astrophotography where they are trying to get the stuff that is extremely dark. There every single photon counts and those cameras are typically super cooled with extremely low read noise characteristics. I doubt there are many people using an off the shelf DSLR for this type of work. Usually this doesn’t involve pretty pictures. It just involves gathering and analyzing very specific data to the nth degree.
Have you ever done any astrophotography Rishi? I think you would really enjoy it if you haven't. You can get a great setup for about $1500 if you choose the components with a budget in mind.
This is the first time that I have seen shot noise factored into the argument that the larger the sensor the better the noise characteristics are. That is why I was finding it so difficult to accept this as fact before.
A requirement for registering for this site should be that you have to read this article first.
Photato: About Sensor Size.Strictly speaking Sensor Size should not be a factor in Noise, because lenses can concentrate the same light (photons) in a large or small area.So much so that you can start a fire concentrating Photons with a magnifying glass in a small area.
What happens is that normally smaller sensors have a higher Density of pixels making it less efficient in photon collection.
For instance. A Small Sensor filled with 8 Micron Pixels should be able to collect the same amount of Photons than a Bigger Sensor filled with 8 Micron pixels. The difference is that the Bigger Sensor would have higher resolution.
The speed booster would change the focal ratio though. Thus the images would no longer be equivalent.
stevevelvia50: If you want to take the exact same image, same DOF using the same shutter speed. Full Frame: F 22, 1/500 sec (ISO set to 3200)Dx: F 16 1/500 sec (ISO set to 1600)Micro 4/3 F 11 1/500 sec (ISO set to 800)
F11 is never good for any native Micro Four Thirds lens.
I wonder how aperture affects shot noise. Shot noise must be very high for extremely small apertures and then decrease parabolically as aperture is increased. At some point shot noise would become inconsequential even at very short exposure durations if your aperture were large enough. That number is probably huge though.
Typically astronomers simply say “Bigger is better in reference to the aperture of a telescope”. However, at some point increasing the aperture should have little shot noise gain especially if you factor in the cost increase for that larger aperture. Now it will always give you a resolution advantage no matter what.
The Hubble telescope has a 7.9 foot diameter while the upcoming James Webb Space telescope has a diameter of 21 feet. That makes even telescopic full frame lenses look like tooth picks.
Thanks. Stacking has always been something that puzzled and intrigued me at the same time.
Does the size of the sensor become less and less important as the shutter duration becomes longer? The shot noise should become more consistent with longer durations but the electrical noise should increase. If the sensors are made from equal technologies then the contribution of read noise should be consistent per unit area between both sensors.
If Dpreview gave awards for articles like they do in camera reviews this one would get a unanimous Gold star.
Do our eyes see noise? Let your eyes adjust to a dark moonless night sky one night. Then look up and gaze into the starlit blackness. I swear you can see what looks like noise in the sky. It is probably fluctuations due to transparency and seeing conditions but it resembles shot noise that we see in short exposure night time images.
I agree with everything you said for short exposure photography but what about long exposure photography like astrophotography(Several minutes or more)? There longer exposures increases the electrical read noise and decreases the shot noise because the signal is more consistent over the longer period of time.
Thank you. Simply, Thank you. That was a brilliant article. More like this please if you can find the time.
Did the camera choose f11 or did the photographer choose that focal ratio?