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?

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


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.

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

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."

I just tried my D6. The camera focuses quite well at f/16. So your position is all wrong and no links to anywhere won't change the fact.

I used a Nikkor AF 85mm f/1.4D which has an aperture ring. When I set the menu option f6 to Aperture Dial, I can control the aperture manually on the lens. I turn the aperture dial to f/16 and the aperture remains stopped down to f/16 when I do the focusing in Live View.

So the assessment that DSLR cameras cannot focus with small apertures is wrong, They can, if they use CDAF just like the point and shoot cameras.

I think you are right about there not beeing a limit to F-number on CDAF. Maby there is a limit to on sensor PDAF. Still, the slower aperture will make the sensor see only darkness earlier than with a brighter lens.

There not being a limit to CDAF and aperture, does not change the fact that mFT, APSC and FF all seem to max out at around EV-4.

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