Why? lenses not searching for focus!
p.2 #1Why? lenses not searching for focus!
mogul wrote:
The manual focus ring is your friend. Just give it a whirl to get everything moving.
yes that has been the override that works but ...........
Thanks
Karl
The manual focus ring is your friend. Just give it a whirl to get everything moving.
yes that has been the override that works but ...........Thanks
Karl
May 30, 2026 at 07:00 AM
p.2 #2Why? lenses not searching for focus!
QuietOC wrote:
I've noticed this fairly often with the Sony FE 85mm F1.8.
Phase-detect focusing relies on pattern recognition in the phase domain. I suspect the shape of the out-of-focus point-spread can cause false positives. Somewhat similar to the focusing problems with undercorrected spherical abberation like the Sigma 45mm F2.8--except with those are more not detecting when they should.
Remember Sony mirrorless can only detect contrast horizontally. Point at horizontal high-contrast. Bumping the ISO up to the second gain also seems to help in lower contrast situations.
Now it's making sense. Fault by design
Thanks
Karl
I've noticed this fairly often with the Sony FE 85mm F1.8.
Phase-detect focusing relies on pattern recognition in the phase domain. I suspect the shape of the out-of-focus point-spread can cause false positives. Somewhat similar to the focusing problems with undercorrected spherical abberation like the Sigma 45mm F2.8--except with those are more not detecting when they should.
Remember Sony mirrorless can only detect contrast horizontally. Point at horizontal high-contrast. Bumping the ISO up to the second gain also seems to help in lower contrast situations.
Now it's making sense. Fault by design
Thanks
Karl
May 30, 2026 at 07:02 AM
p.2 #3Why? lenses not searching for focus!
QuietOC wrote:
I've noticed this fairly often with the Sony FE 85mm F1.8.
Phase-detect focusing relies on pattern recognition in the phase domain. I suspect the shape of the out-of-focus point-spread can cause false positives. Somewhat similar to the focusing problems with undercorrected spherical abberation like the Sigma 45mm F2.8--except with those are more not detecting when they should.
Remember Sony mirrorless can only detect contrast horizontally. Point at horizontal high-contrast. Bumping the ISO up to the second gain also seems to help in lower contrast situations.
Yes many a tree trunk has been my friend to regain focus
!
Thanks
Karl
I've noticed this fairly often with the Sony FE 85mm F1.8.
Phase-detect focusing relies on pattern recognition in the phase domain. I suspect the shape of the out-of-focus point-spread can cause false positives. Somewhat similar to the focusing problems with undercorrected spherical abberation like the Sigma 45mm F2.8--except with those are more not detecting when they should.
Remember Sony mirrorless can only detect contrast horizontally. Point at horizontal high-contrast. Bumping the ISO up to the second gain also seems to help in lower contrast situations.
Yes many a tree trunk has been my friend to regain focus
!Thanks
Karl
May 30, 2026 at 07:03 AM
p.2 #4Why? lenses not searching for focus!
EB-1 wrote:
The Canons that have it are the R1 and R3, and that was done by alternating orientation of verticals/horizontals. OM cameras with quad pixels have it. AFAIK Nikon and Sony don't have it.
EBH
Interesting and helpful, thank you!
Karl
The Canons that have it are the R1 and R3, and that was done by alternating orientation of verticals/horizontals. OM cameras with quad pixels have it. AFAIK Nikon and Sony don't have it.
EBH
Interesting and helpful, thank you!
Karl
May 30, 2026 at 07:04 AM
p.2 #5Why? lenses not searching for focus!
snapsy wrote:
@EB-1@ covered the direct technical reason why the on-sensor PDAF pixels can be blind to a severely-OOF subject and not know which way to drive the lens (or by how much). Why many MILCs choose to give up in this scenario and do nothing rather than at least attempt a speculative focus, even if it involves a time-consuming focus rack from infinity <-> MFD or alternatively, a contrast-detect cycle, is what's surprising. This tells me perhaps there are other, more common scenarios that yield the same PDAF pixel blindness, where those time-consuming focus-seeking actions would be more disruptive. For example,...Show more →
Makes sense Adam. Most often it happens when trying to get focus on a very OOF subject. Many missed opportunities on fast moving little birds. Lower light too certainly plays into it (far less contrast)
Thanks good to hear from you
Karl
@EB-1@ covered the direct technical reason why the on-sensor PDAF pixels can be blind to a severely-OOF subject and not know which way to drive the lens (or by how much). Why many MILCs choose to give up in this scenario and do nothing rather than at least attempt a speculative focus, even if it involves a time-consuming focus rack from infinity <-> MFD or alternatively, a contrast-detect cycle, is what's surprising. This tells me perhaps there are other, more common scenarios that yield the same PDAF pixel blindness, where those time-consuming focus-seeking actions would be more disruptive. For example,...Show more →
Makes sense Adam. Most often it happens when trying to get focus on a very OOF subject. Many missed opportunities on fast moving little birds. Lower light too certainly plays into it (far less contrast)
Thanks good to hear from you
Karl
May 30, 2026 at 07:07 AM
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p.2 #6Why? lenses not searching for focus!
Choderboy wrote:
I think many of us knew this going into mirrorless and adapted.
Most just get used to quickly pointing at something (very) roughly at a similar distance and focusing on that so the lens is far more likely to focus on the actual subject.
To be honest, in my case, barely an adaption. I used the same technique with DSLR but it was more of a speed issue.
The DSLR would usually force lens to move to extent of focus range and back trying to achieve focus.
For Canon, there was even a menu setting Lens drive when AF impossible. Using the point...Show more →
If you complain too much the MILS "Mafia" will just try to drown you out about how great MILS are, not remembering what we lost.
EBH
That was the setting I was referring to on Canon! Thanks for input and comments
Karl
I think many of us knew this going into mirrorless and adapted.
Most just get used to quickly pointing at something (very) roughly at a similar distance and focusing on that so the lens is far more likely to focus on the actual subject.
To be honest, in my case, barely an adaption. I used the same technique with DSLR but it was more of a speed issue.
The DSLR would usually force lens to move to extent of focus range and back trying to achieve focus.
For Canon, there was even a menu setting Lens drive when AF impossible. Using the point...Show more →
EB-1 wrote
Canon and Nikon also have the issue. It's a critical limitation of the MILS, supposedly due to the small effective baselength and inability to detect degree and direction of defocus as well as the optical PD in the base of the SLR mirror box. Most sensors only see one direction rather than croos point. I keep the left hand ready to give the lens a turn with the big teles like Nikon and Canon 500/4 or 600/4 if it stalls. With zooms you can you can zoom wider to pick up AF again.If you complain too much the MILS "Mafia" will just try to drown you out about how great MILS are, not remembering what we lost.
EBH
That was the setting I was referring to on Canon! Thanks for input and comments
Karl
May 30, 2026 at 07:09 AM
p.2 #7Why? lenses not searching for focus!
EB-1 wrote:
KarlIt's a critical limitation of the MILS, supposedly due to the small effective baselength and inability to detect degree and direction of defocus
EBH
Can you (or anyone else) explain a bit more about what you are referring to regarding the "small effective baselength" and how that causes "inability to detect degree and direction of defocus"?
Karl Witt wrote
Am I totally missing something that I don't have set correctly or is this a shared experience with others? Curious on whether Nikon of Canon has the same issue as well?Karl
EBH
Can you (or anyone else) explain a bit more about what you are referring to regarding the "small effective baselength" and how that causes "inability to detect degree and direction of defocus"?
May 30, 2026 at 07:56 AM
p.2 #8Why? lenses not searching for focus!
chiron wrote:
KarlIt's a critical limitation of the MILS, supposedly due to the small effective baselength and inability to detect degree and direction of defocus
EBHCan you (or anyone else) explain a bit more about what you are referring to regarding the "small effective baselength" and how that causes "inability to detect degree and direction of defocus"?
PD systems work by splitting incoming light at opposite paths and measuring their phase differential when both are combined on a set of detection sensors. For DSLR PDAF the angle/width of this split is large because the two opposing sensors are physically wide apart, allowing for a wide range of phase differentials to be measured. For MILC on-sensor PDAF, the two opposing sensors (ie, PDAF pixels on the sensor) are very close, limiting the range of phase differentials they can measure.
The baseline width is a measure of the distance between the split light paths.
EB-1 wrote
Karl Witt wrote
Am I totally missing something that I don't have set correctly or is this a shared experience with others? Curious on whether Nikon of Canon has the same issue as well?Karl
EBH
PD systems work by splitting incoming light at opposite paths and measuring their phase differential when both are combined on a set of detection sensors. For DSLR PDAF the angle/width of this split is large because the two opposing sensors are physically wide apart, allowing for a wide range of phase differentials to be measured. For MILC on-sensor PDAF, the two opposing sensors (ie, PDAF pixels on the sensor) are very close, limiting the range of phase differentials they can measure.
The baseline width is a measure of the distance between the split light paths.
May 30, 2026 at 08:12 AM
p.2 #9Why? lenses not searching for focus!
snapsy wrote:
KarlIt's a critical limitation of the MILS, supposedly due to the small effective baselength and inability to detect degree and direction of defocus
EBHCan you (or anyone else) explain a bit more about what you are referring to regarding the "small effective baselength" and how that causes "inability to detect degree and direction of defocus"?PD systems work by splitting incoming light at opposite paths and measuring their phase differential when both are combined on a set of detection sensors. For DSLR PDAF the angle/width of this split is large because the two opposing sensors are physically wide apart, allowing for a wide range of phase differentials to be measured. For MILC on-sensor PDAF, the two opposing sensors (ie, PDAF pixels on the sensor) are very close, limiting the range of phase differentials they can measure.
The baseline width is a measure of the distance between the split light paths.
Thank you for the clear explanation--makes perfect sense.
But, why don't they move the sensors farther apart on the MILC systems? Is the AF implication not enough of a problem or is there an advantage in the MILC configuration for having the sensors close together?
chiron wrote
EB-1 wrote
Karl Witt wrote
Am I totally missing something that I don't have set correctly or is this a shared experience with others? Curious on whether Nikon of Canon has the same issue as well?Karl
EBH
The baseline width is a measure of the distance between the split light paths.
Thank you for the clear explanation--makes perfect sense.
But, why don't they move the sensors farther apart on the MILC systems? Is the AF implication not enough of a problem or is there an advantage in the MILC configuration for having the sensors close together?
May 30, 2026 at 01:07 PM