So, what exactly does shooting at f/2 bring you?

Started 3 months ago | Discussions thread
OM-G New Member • Posts: 6
Re: So, what exactly does shooting at f/2 bring you?

Mark Ransom wrote:

OM-G wrote:

bobn2 wrote:

OM-G wrote:

Low F-number is always good for AF.

There is no automatic advantage to low light AF for larger sensor.
AF has more to do with light intensity per area, and in that regard F2=F2.

I don't think you're right, for any kind of AF. Please explain why you believe this to be the case.

Example: A 1/2.3" sensor will focus fine at F5.6, but you will have to look hard to find a FF camera that will focus past F8, and then just in the centre. The equivalent aperture on FF to the mentioned F5.6 is F32. You wont find any camera that will focus at F32. On a 0.5x medium format the equivalent aperture would be F64 and the sensor would be totally in the dark.

A 1/2.3" sensor will use CDAF, not PDAF. The two focus systems work completely differently, and you can't draw conclusions about one by looking at the other.

But I can, as none will focus at F32, thats my point. Btw, the A7S II I mentioned is only CDAF

https://www.sony.com/electronics/interchangeable-lens-cameras/ilce-7sm2/specifications

A mFT camera with a F2 lens will have around a 2 stop advantage in low light AF compared to an equivalent FF F4 lens.

Example:

Focus sensitivity for the Sony A7S II is EV-4 (ISO 100 equivalent with F2.0 lens)
Focus sensitivity for the Olympus EM1 III is EV-4.5 (ISO 100 equivalent with F2.0 lens)

You can't tell much from claimed figures. It's marketing spin.

Where do you get this from? Sony has a EV-3 for metering on the mentioned camera in the specs, and EV-3 AF for the A7RIV. Do you not think they measure this? Why not put EV-6 on all cameras if its just marketing spin? You usually have to dig in to specs to find these numbers.

Naturally they'll justify those figures with actual measurements, but marketing will tell them the targets they want to hit and the measurement engineers will pull every trick they can to make those numbers. I think "spin" would be an accurate description of the process.

What is this based on? Where can I find info on this?

Same thing applies to exposure metering.

I don't believe that is the case, either. please explain your reasoning.

Se above, or Sony specs.

The point is that you cant just take a FF system with a 2-stop slower lens and think its equivalent in focus and metering. An eqivalent FF lens in this regard would have to be F2 and way bigger.

Since you're just presenting you're beliefs as fact, there's not much I can do except say 'I think you're wrong'. If you provided some theory, reasoning and evidence to back up your statement, perhaps we could discuss it.

I think if you see the specs and compare over more than two stops (mFT/FF), you might see that light intensity plays an important part, nom the size of the sensor.

Here is an old blogpost from lensrentals

https://www.lensrentals.com/blog/2010/07/how-autofocus-often-works/

Look at the part on aperture on phase detection sensors

"Effect of Lens Aperture

No matter what the sensor type, however, it will usually be more accurate with a wider aperture lens."

Yes, absolutely critical for PDAF. Not so much for CDAF.

As the light dims on those CDAF pixels, they lose the ability to see contrast, everything is dark in dim light. Light hitting a FF sensor will be 1/4 the intensity compared to an equivalent mFT setup.

mFT, APSC and FF all seem to max out at obout EV-4, as F4 =F4 when it comes to light intensity. Thats  not an opinion.

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