Focus Indicator: Wider range with f/4 than with f/3.5

tempelorg · 07-02-2014, 01:35 PM

While analysing focusing issues with my K-5 and K-3, I came across another quite surprising behavior on the K-3:

When in MF (manual focus) mode with a AF lens (in my case: DA 50 f/1.8), the camera confirms focus (using the Focus Indicator, i.e. the green dot in the View Finder, along with the optional beep and red light over the screen) depending on the currently set aperture, as if it tries to tell me if the spot is still in focus based on the effective DOF.

More surprisingly, though, it does not seem to work with MF lenses (I only tried the A 50 f/1.7, though). Depite them both behaving the same: Both measure wide-open and close the aperture blades only during exposure.

Check for yourself:

* Put a lens with a large aperture on your K-3.
* Set the mode dial to Av and dial in the widest possible aperture (e.g. 1.4 or 2.0).
* Set the camera on a tripod so that the focused object remains invariable.
* Focus on something flat, contrast rich and well lit, to make sure that the camera only focuses on a single, constant distance.
* Turn off AF by setting the switch from AF to MF.
* Press the AF or shutter half down to confirm that the camera still sees the object in focus by verifying that the green "Focus Indicator" in the VF lights up.
* Now carefully turn the focus ring so that the targets gets slightly out of focus, just up to the point where the Focus Indicator does not light any more.
* Now change the dial to reduce the aperture. When you get from 3.5 to 4, the focus indicator turns on (at least that's what I found). Going back to 3.5 and it turns off again.

Can you confirm this?

Oddly, it only does this at f/4. I'd tried to put the lens a bit more out of focus again and then dialed the aperture down to 22, but it didn't light up the Indicator again. This shows that it doesn't really take the actual DOF into account, but has just some - odd - fixed switching behavior at f/4.

I also tried this with my K-5 and the same lens, but it didn't show this behavior.

Weird, isn't it?

Giklab · 07-02-2014, 02:25 PM

I'm calling f/2.8 points vs "normal" points. Try this with other AF points (except the centre one and the one above and below that).

07-02-2014, 01:35 PM	#1
tempelorg Senior Member Join Date: Apr 2011 Location: Munich Photos: Gallery Posts: 203	Focus Indicator: Wider range with f/4 than with f/3.5 While analysing focusing issues with my K-5 and K-3, I came across another quite surprising behavior on the K-3: When in MF (manual focus) mode with a AF lens (in my case: DA 50 f/1.8), the camera confirms focus (using the Focus Indicator, i.e. the green dot in the View Finder, along with the optional beep and red light over the screen) depending on the currently set aperture, as if it tries to tell me if the spot is still in focus based on the effective DOF. More surprisingly, though, it does not seem to work with MF lenses (I only tried the A 50 f/1.7, though). Depite them both behaving the same: Both measure wide-open and close the aperture blades only during exposure. Check for yourself: * Put a lens with a large aperture on your K-3. * Set the mode dial to Av and dial in the widest possible aperture (e.g. 1.4 or 2.0). * Set the camera on a tripod so that the focused object remains invariable. * Focus on something flat, contrast rich and well lit, to make sure that the camera only focuses on a single, constant distance. * Turn off AF by setting the switch from AF to MF. * Press the AF or shutter half down to confirm that the camera still sees the object in focus by verifying that the green "Focus Indicator" in the VF lights up. * Now carefully turn the focus ring so that the targets gets slightly out of focus, just up to the point where the Focus Indicator does not light any more. * Now change the dial to reduce the aperture. When you get from 3.5 to 4, the focus indicator turns on (at least that's what I found). Going back to 3.5 and it turns off again. Can you confirm this? Oddly, it only does this at f/4. I'd tried to put the lens a bit more out of focus again and then dialed the aperture down to 22, but it didn't light up the Indicator again. This shows that it doesn't really take the actual DOF into account, but has just some - odd - fixed switching behavior at f/4. I also tried this with my K-5 and the same lens, but it didn't show this behavior. Weird, isn't it?

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07-02-2014, 02:25 PM	#2
Giklab Veteran Member Join Date: Jan 2012 Location: Slovenia Photos: Gallery Posts: 2,182	I'm calling f/2.8 points vs "normal" points. Try this with other AF points (except the centre one and the one above and below that).