If there's a really grainy photo. Not much natural light here and a tripod was available. What should be changed in settings to decrease the noise in the photo?
Settings Focal length 12mm ISO 6400 Aperture 5.4 Shutter Speed 1/30
Increase ISO, aperture and shutter speed, Decrease shutter speed and ISO, increase ISO and aperture or increase shutter speed and aperture?
Primarily ISO. There can be a noise tradeoff if you end up having long exposures (depends on the camera and/or sensor), but the quick answer is always "lower the ISO". In your case, lowering the ISO to a more reasonable 200 would mean (at the f5.4 aperture- I don't know what lens you're using) lowering the shutter speed by 5 stops to 1 second. This speed is unlikely to result in much sensor noise and would almost certainly be a noise improvement.
The tripod allows you to lengthen the exposure, so motion will be rendered differently but there will be much less noise by going to the Native ISO of the camera. This is not necessarily the lowest ISO, but depending on the model it is usually ISO 100 or 200. Going lower will not introduce more noise but can lose dynamic-range. Many cameras now have the lowest ISO ad their native but on Micro Four-Thirds ones, most have a Native ISO of 200 and Expansion of 100.
Simply lowering the ISO produces a darker image, so you must compensate with the other exposure parameters. ISO 6400 is 5 stops above ISO 200, so you can use stops over 1/30s which is 1s or you can open the aperture as much as possible which and then add the remaining stops to shutter-speed. In your example of 12mm ISO 6400 Aperture 5.4 Shutter Speed 1/30, you can use F/2 and 1/8s that will give you almost the same result since I calculated in my head from F/5.6 instead of your F/5.4.
In order to have less noise, or more accurately, a higher signal-to-noise ratio, you need more signal, i.e., light. This can be done in three ways: wider aperture (lower f number), longer exposure, or more powerful lighting (or a combination thereof).
I wanted to explore how each answer would affect the photograph. Initial changes to the parameters will use a ⇧ arrow while parameter changes made due to the initial change will be noted with a ↑ arrow.
To avoid confusion, the arrow definitions are:
Given:
Increase ISO, aperture and shutter speed
Let's assume that we increased the ISO by two stops, and then adjusted the aperture and shutter accordingly. We'd have a shot taken at:
The repercussions of this change would be: Increased noise (due to higher ISO)*, increased depth of field (due to a smaller aperture), and decreased subject motion/motion blur (due to a faster shutter speed).
Decrease shutter speed and ISO
Keeping with the two stop change to the ISO, we'd now have:
This change would yield: decreased noise (due to a lower ISO)*, no change to depth of field, and [potentially] increased subject motion (due to a slower shutter speed).
increase ISO and aperture
Keeping with the two stop adjustment to ISO, we'd now have:
This would yield: Increased noise (due to increased ISO)*, increased depth of field (due to a smaller aperture), and no change in motion blur.
increase shutter speed and aperture?
This time, we'll change the shutter speed by two stops. This gives us:
The results of which would be: no change in noise, decreased depth of field (due to a larger aperture), and decreased subject motion (due to a faster shutter speed).
Even though you have a tripod handy and don't have to worry about you shaking the camera...depending on your subject, you may have to worry about them blurring in the photo.
Applying this question to a real-world photograph means striking a balance between acceptable noise (ISO), acceptable depth of field (aperture), and a shutter speed that will work for the subject. This could be as drastically different as photographing a city skyline at night, shooting a river in the shade, or photographing your friends at a club.
*The Photography 101 understanding of ISO and noise can be simplified into saying that: increasing ISO increases noise, and decreasing ISO decreases noise.
However, this is not the full picture. The reality is that increased noise is caused by a reduced signal-to-noise ratio. The more light you have hitting the sensor, the better. Increasing ISO generally means getting less light - but exposure also plays a roll here. For example, you would get less noise using a properly exposed shot at ISO 1600 than an under-exposed shot at ISO 200.
For more light reading, see these posts:
**A big Thank-You to Michael Clark for compiling this list for this answer.
Of the options, increasing the aperture and reducing the ISO is the best in terms of noise.
The primary issue causing the noise is photon shot noise due to a lack of ambient light (the randomness of light), the ISO amplification is only making it more apparent. Increasing the exposure time will increase the amount of light recorded, but it will still suffer more from shot noise (due to low light levels compounded by the restricted aperture), as well as possible other issues that can arise with long exposure times.
Conversely, aperture controls exposure by (essentially) stacking images on the sensor. By increasing the aperture you are stacking more images simultaneously, each with a different shot noise characteristic... effectively, the randomness is filled in increasing the ratio of signal. You are adding light and reducing noise very similarly to the method used in post production techniques.
What is your subject matter?
A running bull at night under a full moon and street lamps may need to be treated different than a sleeping baby lit by a full moon and a street lamp.
1.) A sleeping baby in that light you could just change the ISO (ASA speed) to a smaller number like 400 and change the shutter speed to accommodate. If you can raise the aperture that would be good. 5.6 or 6 and above. The image would be sharper and the lower the iso the less grain.
NOTE: Also, 1600 to 800 ISO was used on high school Friday night football. Still may be used on that, but stadiums have gotten better lighting and cameras have been getting better with their ISO.
2.) A running bull in that light, you could get closer to it, change your ISO to a bit lower, and pop a flash on it. Maybe even angle the flash a bit up so the light isn't directly hitting the bull, or use a good diffuse filter on the flash. Lower the iso not much lower at all maybe to 1600 or 3200, maybe raise the aperture to 6 or above, raise the shutter to 1/60, or keep it at 1/30, to stop the action some or a flash may stop it a bit for you and it may have some left to right action blur.
Hopefully, you'd get more bulls running through for more chances on that one.
