Best low light FF Canon DSLR

Started 3 months ago | Discussions thread
Dr_Jon Veteran Member • Posts: 6,079
Re: Uni

Mako2011 wrote:

Dr_Jon wrote:

Mako2011 wrote:

As you stated earlier, "while ISO doesn't change the amount of light the sensor collects",... only by changing the shutter speed and/or aperture and or scene luminance is more/less light let in

I'm sorry, you do get there is such as a thing as a correct exposure (I am pretty certain)? .

I was only speaking to the fact that the ISO setting doesn't really change the amount of light the sensor collects. What constitutes "Correct" exposure can be unrelated. As an example.... take the same high DR scene and two photographers. One shooting UNI-WB and the other not. Both exposures will be "correct" but very different actual exposure settings

...or ETTR, but whatever you do if you halve the ISO you'll be able to collect more light (as the usable sensor saturation will increase).

We do seem to have spent a lot of time arguing about something I don't disagree with (quite the opposite) but did not mention as it wasn't relevant to my point:

* How many electrons a sensor collects depends on incoming photons, aperture, shutter speed and some stuff about what the camera loses going from incoming light to electrons (I started to write that bit, but it went on too long).

(That matters more for stuff like ISO invariance, where using a lower ISO enables you access to more highlight data, although you have to post-process the image to see the picture.)

However I wasn't talking about this, but whether a faster lens enables you to collect more light, so have less noise (which the OP wants), which it only does if you can lower the ISO. This is because:

* The camera will be able to use about twice as much light when you halve the ISO.

* If you keep the ISO the same but use a faster aperture you'll have to reduce the light you collect somehow (e.g. faster shutter speed) or you will just lose the highlights as you go past the sensor's maximum saturation.

The reason for this is, which the person seeking less noise probably doesn't care about:

* The amount of the data in the sensor that you can access roughly doubles when you halve ISO, as the ISO amplifier will no longer clip that data.

For example - a 6D at ISO 1600 gives you access to about 5,100 electrons which it will count for you and give you a digital number. If you capture more than that you just get 5,100 returned. If you use a faster aperture you need to reduce the extra light by increasing the shutter speed to stop going over 5100. A 6D at ISO 800 gives you access to about 10,300 electrons, which it will count for you. You can adjust your exposure to capture twice the light of a successful ISO 1600 exposure and it will look similar (but with less noise).

My point remains the one in bold above, as it always was. The OP wanted to use a faster lens to get less noise, they need to understand the two caveats:

(1) You need to be able to live with the lower DoF

(2) You must be able to reduce the ISO to see a noise advantage (if you can't it won't help)

The second assumes you do whatever you did for exposure the same way at the lower ISO (camera automatic, ETTR, etc.)

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