Mirrorless focus systems in low light

[Erty]

I use a DSLR to take pictures of fast moving people in the dark (typically ISO 8000+, F/2.2, 1/200s). I've a question about mirrorless focus systems. The focus system on my DSLR doesn't care what aperture, ISO or shutter speed I use, it focuses with the aperture wide open and the shutter speed and ISO make no difference. My understanding of mirrorless is that the camera views things as the picture would be taken, so at the least the aperture is going to be stopped down a bit. The higher shutter speed might also apply to the focus sensor so reduce the light getting to that. The focus sensors in mirrorless are also smaller as they have to be no larger than a single pixel.

Can mirrorless cameras be set up to view the scene at a lower shutter speed or wider aperture than the camera will actually take the picture and then compensate for the extra light in the electronic viewfinder by lowering the brightness? This would let the focus system get more light onto the focus pixels. I'm very much of the opinion that silicon is silicon and the camera needs to get enough light onto the focus sensors to work properly.

 

[Phil V]

My understanding of mirrorless is that the camera views things as the picture would be taken, so at the least the aperture is going to be stopped down a bit. The higher shutter speed might also apply to the focus sensor so reduce the light getting to that.

Your understanding is 50% correct.
Whilst most people use their mirrorless viewfinder in ‘exposure simulation’ mode most of the time, it’s simple to switch it to just view the scene exactly as you’d expect with your DSLR. It ‘should’ happen automatically when you pop on your flashgun I believe.

However, I always set C1 for flash, which turns off ‘exp sim’ and gives me a fixed ISO, with a starter SS and aperture in M mode so that I’m in control of the ambient/ flash mix.

I’ll be doing this at a presentation evening tomorrow night, where I’ll start with my normal setup of auto iso, Ap priority, min 1/250 SS, for candids, then switch to C1 for presentations, then maybe some slow SS shots on the dance floor.

 

[Phil V]

I’ve said it before and I’ll say it again; the R6 makes my photography easier than any camera I’ve ever owned, with a little effort to set up I can do most things with 1 or 2 settings changes.

 

[woof woof]

Can mirrorless cameras be set up to view the scene at a lower shutter speed or wider aperture than the camera will actually take the picture and then compensate for the extra light in the electronic viewfinder by lowering the brightness? This would let the focus system get more light onto the focus pixels. I'm very much of the opinion that silicon is silicon and the camera needs to get enough light onto the focus sensors to work properly.

As Phil say above... But I just thought I'd add something.

I can't actually remember the last time I used the wide open mode (whatever it's called,) I just use my mirrorless cameras in exposure simulation mode as most of the time in low light I'm using wider apertures anyway. If using something like f8+ in very low light / night time you'll maybe begin to see some stuttering of movement in the VF which will get worse as you stop down but shooting at around and after sunset and even into darkness using a tripod and f4-5.6 or so I don't remember any ill effects in the VF which were bad enough to register with me and make me change modes and this is with my old first generation Sony A7. Newer cameras may cope better.

I suppose the best way to see if you'll need to change modes or not would be to try a mirrorless camera. The experience even in exposure sim mode might not be bad enough to get you to bother swapping modes.

Good luck if you go this way.

 

[Nostromo]

Your understanding is 50% correct.
Whilst most people use their mirrorless viewfinder in ‘exposure simulation’ mode most of the time, it’s simple to switch it to just view the scene exactly as you’d expect with your DSLR. It ‘should’ happen automatically when you pop on your flashgun I believe.

However, I always set C1 for flash, which turns off ‘exp sim’ and gives me a fixed ISO, with a starter SS and aperture in M mode so that I’m in control of the ambient/ flash mix.

I’ll be doing this at a presentation evening tomorrow night, where I’ll start with my normal setup of auto iso, Ap priority, min 1/250 SS, for candids, then switch to C1 for presentations, then maybe some slow SS shots on the dance floor.

I've just set my camera up for flash and assigned it to C2. The amount of times I'd forget to put the ISO back to base or have to go into the menu to turn off expo simulation, turn off electronic shutter.
It's so much easier now.

 

[Erty]

Thanks for the replies. It is really interesting on how they work. Slow for me is 1/125s but half the dancers are motion blur at that speed. No flash as it annoys the dancers.

 

[Phil V]

Thanks for the replies. It is really interesting on how they work. Slow for me is 1/125s but half the dancers are motion blur at that speed. No flash as it annoys the dancers.

If you’re using only ambient light, the exposure simulation shouldn’t be a problem for you, on the basis it is showing you what your image will look like.

No problem if you’d rather turn it off for a slightly brighter view, but it shouldn’t be dramatic

 

[snerkler]

One thing I’ve found is that in AF-S it focuses wide open then stops down to take the shot, however in AF-C it’s wide open briefly to get acquisition and then stops down whilst continuing to try and get focus which, if stopped down enough, can cause it to struggle and hunt if you’re in a dark environment like a studio.

I would imagine f2.2 would be no problem but at, for example, f11 it would likely struggle.