AF to -6ev, but what about with an F4 lens Canon?

Stuart

Hi there, welcome from an ePhotozine fan. 6D
Jul 22, 2010
254
27
London & Woking
www.ephotozine.com
I love the spec of Canon's new EOS-R focusing down to -6ev when using their new RF 50mm f1.2 lens.

BUT i can't find any information on what it can achieve using a more normal F4 lens - such as the 'kit' 24-105 F4 it might be supplied with?
Is it actually better than my rated -3ev EOS 6D camera with an f4 lens?

I've had a search and can't yet find anything on this, so does anyone know how well AF will work with a more typical lens attached? And perhaps with non center spot focusing all well?
I'm also interested in how does the focusing work differently to achieve this?

The spec says with all its disclaimers - "During still photo shooting, f/1.2, Center AF point, One-Shot AF, at 23°C/73°F, ISO100"
 

YuengLinger

EOR R
Dec 20, 2012
2,232
252
Southeastern USA
I love the spec of Canon's new EOS-R focusing down to -6ev when using their new RF 50mm f1.2 lens.

BUT i can't find any information on what it can achieve using a more normal F4 lens - such as the 'kit' 24-105 F4 it might be supplied with?
Is it actually better than my rated -3ev EOS 6D camera with an f4 lens?

I've had a search and can't yet find anything on this, so does anyone know how well AF will work with a more typical lens attached? And perhaps with non center spot focusing all well?
I'm also interested in how does the focusing work differently to achieve this?

The spec says with all its disclaimers - "During still photo shooting, f/1.2, Center AF point, One-Shot AF, at 23°C/73°F, ISO100"
Have you found accurate specs for competitors?
 

Stuart

Hi there, welcome from an ePhotozine fan. 6D
Jul 22, 2010
254
27
London & Woking
www.ephotozine.com
Nope, nothing from competitors. But i'm interested how the EOS will perform with a more affordable lens; I shoot low light events and hate focus hunt at critical times.
So with he 24-105, perhaps zoomed into a shot, how much better will it really be than my 6D with a current 24-105 f4? Lets say ISO 800 too.
Of is it only any good with the 50mm f1.2 ?
 

YuengLinger

EOR R
Dec 20, 2012
2,232
252
Southeastern USA
A good question. I just take it to mean that, potentially, it works better in low light than other Canon bodies. But that is a kind of vague way to swallow the fuzzy marketing claims.

Searching the user manual doesn't reveal any specific numbers. I wonder how far ahead of the final release of a body these manuals are prepared.

Just like the claim of "8 fps" in single-shot mode, how to unpack? I don't believe a human can manually push the shutter button more than two or three times in a second.

In the link below, you might say Canon's marketing department has gone to new depths to hype their product!

https://www.canon-europe.com/pro/stories/eos-r-daniel-etter/
 
Reactions: Stuart

Kit Lens Jockey

EOS 7D MK II
Nov 12, 2016
441
140
I thought I heard when the EOS R first came out that the standard when rating autofocus is usually with an f2 lens. So if the EOS R was rated like most cameras, it would be rated to -4.5 EV. Is that right?

Either way, the thing pretty much focuses in the dark with an f1.2 lens. It's pretty incredible.
 
Reactions: Stuart

AlanF

5DSR
Aug 16, 2012
4,668
1,173
I thought I heard when the EOS R first came out that the standard when rating autofocus is usually with an f2 lens. So if the EOS R was rated like most cameras, it would be rated to -4.5 EV. Is that right?

Either way, the thing pretty much focuses in the dark with an f1.2 lens. It's pretty incredible.
That is right.
 
Reactions: Stuart

Photorex

EOS RP
Nov 19, 2016
218
22
I love the spec of Canon's new EOS-R focusing down to -6ev when using their new RF 50mm f1.2 lens.

BUT i can't find any information on what it can achieve using a more normal F4 lens - such as the 'kit' 24-105 F4 it might be supplied with?
Is it actually better than my rated -3ev EOS 6D camera with an f4 lens?

I've had a search and can't yet find anything on this, so does anyone know how well AF will work with a more typical lens attached? And perhaps with non center spot focusing all well?
I'm also interested in how does the focusing work differently to achieve this?

The spec says with all its disclaimers - "During still photo shooting, f/1.2, Center AF point, One-Shot AF, at 23°C/73°F, ISO100"
If you want to know the EValue at f/4 you only need to count the stops from f/1.2 to f/4 than you'll get your answer.
from f/1.2 to f/4 you have 10/third stops (3.3 stops). -6EV + 3.3 stops = -2.7EV

By the way:
The 5DMIV is rated at -4EV in liveview mode with an f/2.8 lens, which means that the 5DMIV would have a focus sensitivity of -6.3EV with an f/1.2 lens.
So the -6 EV of the EOS R is all about marketing as it is not better than a 5DMIV if you compare the EV values with refernc to the same f-stop.
 

Photorex

EOS RP
Nov 19, 2016
218
22
Hello Kit Lens Jockey,

good question. I can't recall it. Maybe I derived it from the fact that the 5DIV is rated in mirror mode at f2.8 (due to the fact that the AF sensor geometry doesn't "allow" a lower rating because even with a faster lens there wouldn't be more light on the AF sensors). So in liveview mode the rating could be better rated in deed as the sensor will receive the same amount of light as the sensor in the EOS R (no mirrors and lightray splitting in the way)
 

AlanF

5DSR
Aug 16, 2012
4,668
1,173
If you want to know the EValue at f/4 you only need to count the stops from f/1.2 to f/4 than you'll get your answer.
from f/1.2 to f/4 you have 10/third stops (3.3 stops). -6EV + 3.3 stops = -2.7EV
I did this calculation correctly a few posts before yours.
If its done solely by light intensity, then f/4 is 3.5 stops higher than f/1.2. Accordingly, that would imply closing down to f/4 would give AF down to -2.5 ev.
The number of stops is given by 2*log(base2)(4/1.2) = 3.5 stops. I don't know why this simple algebraically correct formula (no. of stops difference between f1 and smaller f2 = 2*log(base2)(f1/f2) )is not used in many articles or I think wikipedia but they list just tables of 1/3rd stops etc.
 
Reactions: Stuart

Kit Lens Jockey

EOS 7D MK II
Nov 12, 2016
441
140
Hello Kit Lens Jockey,

good question. I can't recall it. Maybe I derived it from the fact that the 5DIV is rated in mirror mode at f2.8 (due to the fact that the AF sensor geometry doesn't "allow" a lower rating because even with a faster lens there wouldn't be more light on the AF sensors). So in liveview mode the rating could be better rated in deed as the sensor will receive the same amount of light as the sensor in the EOS R (no mirrors and lightray splitting in the way)
This is incorrect. I think you're confusing the fastest lens that the focusing screen allows you to view through the viewfinder with what the AF sensor is seeing.

On the 5D4, you will not see any difference in brightness or DOF mounting any lens faster than about f2.8, due to the way the focusing screen affects the light.

The AF sensor is not affected by this. It sees the light coming through the primary mirror, bouncing off the secondary mirror, and hitting it down in the bottom of the mirror box. The traditional AF sensor in the 5D4 (and also live view) does benefit by putting as fast of a lens as you can on it. It is not limited the same way the view through the viewfinder is.
 

Photorex

EOS RP
Nov 19, 2016
218
22
This is incorrect. I think you're confusing the fastest lens that the focusing screen allows you to view through the viewfinder with what the AF sensor is seeing.

On the 5D4, you will not see any difference in brightness or DOF mounting any lens faster than about f2.8, due to the way the focusing screen affects the light.

The AF sensor is not affected by this. It sees the light coming through the primary mirror, bouncing off the secondary mirror, and hitting it down in the bottom of the mirror box. The traditional AF sensor in the 5D4 (and also live view) does benefit by putting as fast of a lens as you can on it. It is not limited the same way the view through the viewfinder is.
Thank you for correcting my wrong writing. In deed I was confusing the focusing screen and the AF sensors.
 
Reactions: Kit Lens Jockey