Low light focus - what does EV translate to?

[petergabriel]

The x-t1 was updated with firmware 4.0, so it was able to focus in 0.5 EV bettered from 2.5 EV.

 

I own the x100t with its 0.5 EV capability, and its low light focus capability is not exactly impressive.

 

The xpro2 is born with the ability to focus in -3.0 EV, which by comparison sounds amazing, but what does the EV spec actually translate to in real life?

[umad?]

it means, that the X-Pro2 (like most other modern cameras) is able to focus, where 99.9% of buyers won't use it. Near complete darkness. 

EV0 is defined as LV0 at ISO100.

and LV0 is 1 second exposure with an f/1.0 lens. 

 

So EV0 (rounded from 0.5 in the X100T) means you can shot with f/2.0, 4 second exposure and ISO200. Not really real world scenario I guess

 

 

To give you an better example.

Let's say you get a good exposed images with the X100T with the following values: f/2.0, 1/15s (guess, your handholding is very stable ) and ISO6400. The camera focuses. The LV of the subject is somewhere around 1EV. 

 

Now you head somewhere it's 3LV darker: you either have to increase the shutter speed (guess a tripod is needed for 1/2s) or increase the ISO. Both cases, the camera won't focus anymore.

 

The X-Pro2 on the other hand will focus. Staying at f/2.0 and 1/15s you could just increase the ISO to 51200. 

But there is another advantage. Mount an f/1.4 lens and you can either go to 1/30s or decrease the ISO. (f/1.4, 1/15s ISO 25600)

 

 

But then again: f/1.4, 1/15s and ISO25600 isn't an every day scenario

Edited April 9, 2016 by umad?

[petergabriel]

Rather technical explanation, but I get most of it. All I know is that 0.5 EV is not enough as the x100t starts hunting when its not very dark.

[umad?]

Of course it's an technical explanation because we are talking about a technical feature.

 

 

Hunting of AF has many reasons, only one is, that the working area of the pdaf has been exceeded and contrast detection is being used.

 

Mostly it's easy: we only have line (and no cross) pdaf pixels in the camera. And those work best with vertical lines.

If you have not much detail (few lines) and low contrast in general, the camera will hunt to achieve focus. 

[petergabriel]

The hunting starts during dusk, no matter if its contrast AF or PDAF, so if xpro2 improves upon that it would be great. I just didn't know what the EV numbers translated to in real life scenarios.

Edited April 9, 2016 by petergabriel

[milandro]

EV is Exposure value

 

if you want the complicate version 

 

 

where

• N is the relative aperture (f-number)
• t is the exposure time (“shutter speed”) in seconds

 

 

 

 

 

^.......or read the wikipedia page which will give you all of the above + the layman explanation

 

https://en.wikipedia.org/wiki/Exposure_value