[snappyhoffy]

I am intrigued... the latest Firmware release (v1.20) suggests that "Improved the individual AF fine-adjustment settings to identify the attachment of the HD PENTAX-DA AF REAR CONVERTER 1.4X AW.".

How do you make those adjustments? Do you have to fit it to every lens you use it with and then make the adjustments for that combination as if it was a separate 'lens'?

I have never considered that this was necessary but now it is mentioned seems obvious.

[UncleVanya]

I am intrigued... the latest Firmware release (v1.20) suggests that "Improved the individual AF fine-adjustment settings to identify the attachment of the HD PENTAX-DA AF REAR CONVERTER 1.4X AW.".

How do you make those adjustments? Do you have to fit it to every lens you use it with and then make the adjustments for that combination as if it was a separate 'lens'?

I have never considered that this was necessary but now it is mentioned seems obvious.

I assume so. Not every lens is going to react the same. Also there’s not much point to using the converter on non-telephoto or macro lenses. I’ve done it, but mostly for just the heck of it. The number of lens combinations where you need this level of adjustment with the converter is bound to be small.

[snappyhoffy]

I assume so. Not every lens is going to react the same. Also there’s not much point to using the converter on non-telephoto or macro lenses. I’ve done it, but mostly for just the heck of it. The number of lens combinations where you need this level of adjustment with the converter is bound to be small.

I only have one prime (DA*300) but have found it useful on my 50-135 as well.

I assume that there is a unique identifier for the combination of lens and TC when combined.

[niels hansen]

The way pdaf works is a mistery for me. If a traditional SLR is well calibrated the microprisme/ splitfield works with any lens, at least in the center where field curvarture has no effect.. Thats not the case with DSLRs. Every lens has its own valule, for me it is the same as if evry lens in SLR should have its own screen. Maybe it is a silly comparison. Can anyone make me wiser
thanks

[UncleVanya]

The way pdaf works is a mistery for me. If a traditional SLR is well calibrated the microprisme/ splitfield works with any lens, at least in the center where field curvarture has no effect.. Thats not the case with DSLRs. Every lens has its own valule, for me it is the same as if evry lens in SLR should have its own screen. Maybe it is a silly comparison. Can anyone make me wiser
thanks

I think a few things are wrong in this comparison:

1) 35mm film cameras output was rarely viewed large and so focus accuracy was rarely challenged on the commonplace 4x6” images.

2) very high resolution sensors and easy pixel peeping has increased the need for extremely precise focusing.

3) fine focus tuning on film cameras required specialized tools that most people did not have access to so few could validate if it was required.

[pschlute]

The way pdaf works is a mistery for me. If a traditional SLR is well calibrated the microprisme/ splitfield works with any lens, at least in the center where field curvarture has no effect.. Thats not the case with DSLRs. Every lens has its own valule, for me it is the same as if evry lens in SLR should have its own screen. Maybe it is a silly comparison. Can anyone make me wiser
thanks

Split-prism focussing aids and autofocus are separate things. It matters not whether your camera is a film SLR or a DSLR, it is entirely possible for the focus screen (split prism) to be misaligned when compared to the AF sensor, which again could be misaligned to the film/sensor.

[mysterick]

PENTAX-DA AF REAR CONVERTER 1.4X AW.".

Could it be that the exif readout showed something like "RC 7.4" and not describing RC 1.4

[niels hansen]

Split-prism focussing aids and autofocus are separate things. It matters not whether your camera is a film SLR or a DSLR, it is entirely possible for the focus screen (split prism) to be misaligned when compared to the AF sensor, which again could be misaligned to the film/sensor.

Thanks, I see that I have made a comparison between manual and auto functions, but I still dont understand why each lens demands its own fine tune value in pdaf
regards

[pschlute]

but I still dont understand why each lens demands its own fine tune value in pdaf

A very interesting question.

PDAF is not 100% accurate. My experience when doing testing for autofocus adjustment is that it is around 80-90 % accurate. By that I mean that an average lens when tested on an unambiguous target will return exactly the same focus position only about 8 or 9 times out of 10. I have also noted that on some lenses a different majority result will be obtained depending on whether the lens is made to focus from a starting point of closest focus distance compared to infinity.

My personal view on why this happens is that different lenses have different designs.... screwdrive versus internal motor... different focus "throws".... different weight and mass of glass to be moved. When the PDAF sensor detects focus and tells the lens to stop focussing it can over-shoot and be fractionally further or closer than the ideal focal plane. Not enough for the PDAF to request a refocus, but enough to be noticeable if one looks at a test chart.

Just my personal view.

[snappyhoffy]

A very interesting question.

PDAF is not 100% accurate. My experience when doing testing for autofocus adjustment is that it is around 80-90 % accurate. By that I mean that an average lens when tested on an unambiguous target will return exactly the same focus position only about 8 or 9 times out of 10. I have also noted that on some lenses a different majority result will be obtained depending on whether the lens is made to focus from a starting point of closest focus distance compared to infinity.

My personal view on why this happens is that different lenses have different designs.... screwdrive versus internal motor... different focus "throws".... different weight and mass of glass to be moved. When the PDAF sensor detects focus and tells the lens to stop focussing it can over-shoot and be fractionally further or closer than the ideal focal plane. Not enough for the PDAF to request a refocus, but enough to be noticeable if one looks at a test chart.

Just my personal view.

That makes a lot of sense so the calibration is adjusting the 'lag' in the focus system rather than the physical elements of the lens (obvious really!)

[pschlute]

That makes a lot of sense so the calibration is adjusting the 'lag' in the focus system rather than the physical elements of the lens (obvious really!)

This also begs the question "why do we not see this in Live View focussing" ?

Again just my personal view, but I think it is this :

PDAF is old technology. When cameras were competing with each other in the late 1980's and 1990's one of the manufacturers goals was to produce faster and faster AF. The faster a lens has it's internals moved the more difficult it is to get them to stop in the right place. With LV CDAF the focussing is a much slower affair and an inherently more accurate design. Thus individual lenses characteristics do not cause the same problems.

[niels hansen]

This also begs the question "why do we not see this in Live View focussing" ?

Again just my personal view, but I think it is this :

PDAF is old technology. When cameras were competing with each other in the late 1980's and 1990's one of the manufacturers goals was to produce faster and faster AF. The faster a lens has it's internals moved the more difficult it is to get them to stop in the right place. With LV CDAF the focussing is a much slower affair and an inherently more accurate design. Thus individual lenses characteristics do not cause the same problems.

An old mans memory is not always reliable, but as far as I remember the pdaf on the K30 gave me no concern , whereas the pdaf on the KP often is a pain.. Is it possible that the algoritms are different, have other PF members the same experience, or is the problem placed behind my KP????????

[UncleVanya]

An old mans memory is not always reliable, but as far as I remember the pdaf on the K30 gave me no concern , whereas the pdaf on the KP often is a pain.. Is it possible that the algoritms are different, have other PF members the same experience, or is the problem placed behind my KP????????

16 vs 24 megapixels is 50% more detail. Easier to see the missed focus in that case. Higher resolution and higher resolution screens to view pixels on also increases the ability to see focusing errors that might have been undetected with lower resolution.

[pschlute]

but as far as I remember the pdaf on the K30 gave me no concern , whereas the pdaf on the KP often is a pain

As UncleVanya points out it is far easier to detect missed focus on a higher MP camera. But it is also possible that the PDAF autofocus sensor is further out of alignment on your KP than your K30.

Autofocus adjustments only became available in camera's menus as the MP count rose. Like other manufacturers, Pentax realised that the tolerance between the two distances (Lens-to-AF sensor versus Lens-to-recording sensor) was becoming more noticeable and that giving the user the option to adjust this themselves was a good thing.

[UncleVanya]

This also begs the question "why do we not see this in Live View focussing" ?

Again just my personal view, but I think it is this :

PDAF is old technology. When cameras were competing with each other in the late 1980's and 1990's one of the manufacturers goals was to produce faster and faster AF. The faster a lens has it's internals moved the more difficult it is to get them to stop in the right place. With LV CDAF the focussing is a much slower affair and an inherently more accurate design. Thus individual lenses characteristics do not cause the same problems.

PDAF in “most” DSLRs is only available outside the sensor. The sensors are calibrated to “match” the optical length of the lens to the sensor - but as resolution has increased the tolerance for any deviation from “perfect” has dropped. Mirrorless cameras started with only CDAF and at that time were much slower to focus than DSLRs. Over time PDAF receptors were added to sensors and fast accurate focusing came to modern mirrorless cameras. Some of these also developed banding due to the placement of these on sensor and the effect it has on interpolating the sensor data. It also isn’t true that mirrorless doesn’t have a need for fine focus adjustment - it’s just less of an issue - so there is some variation outside of simply optical distance from the PDAF detectors not matching the optical distance to the sensor when these are embedded in the sensor. NOTE: At least one Pentax has on chip PDAF - the K70. On this camera in video mode the sensor provides PDAF to aid focusing during “filming“ of videos. As far as I know no one has ever tested to see if PDAF fine focus values impact video focusing on the camera or only are applied to viewfinder focused results of still photos.

Finally, while we tend to think of CDAF as perfect but slow, it isn’t always the case. CDAF can miss focus. And Panasonic added, “Depth from Defocus” (DFD) to the cameras to drastically improve CDAF focusing speed. DFD only works on Panasonic lenses and relies on very specific knowledge about specific lens model behavior that must be baked into the camera firmware.