Knowledge is gold

Started Jul 31, 2012 | Discussions
kitsios_spyros
kitsios_spyros Senior Member • Posts: 2,722
Knowledge is gold
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awaldram
awaldram Forum Pro • Posts: 13,271
Re: Knowledge is gold

Hadn't read Rogers single point AF blog.

pretty much sums up and blows away all the myths we see peddled repeatedly in this forum , good work.

Some extracts of particular note.

The conclusion is pretty obvious: If you want to shoot wide aperture prime lenses and you don’t want to use microfocus adjustment, you just refuse to cope with reality.

Microfocus adjustment pulls good phase-detection AF results up to a par with LiveView, but it doesn’t eliminate the small amount of shot-to-shot variation that phase-detection AF has.

Would be interesting if he extended it to assess LV and PD on moving targets and at what point LV fails.
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Roland Karlsson Forum Pro • Posts: 29,193
Re: Knowledge is gold

Thank you!

Phase detection AF is problematic.

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rogerstpierre Veteran Member • Posts: 4,710
Re: Knowledge is gold

Roland Karlsson wrote:

Thank you!

Phase detection AF is problematic.

That's not what the BLOG says. Phase Detection AF is less consistent, and more likely to require calibration (quite understandably when you know how it works).

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kitsios_spyros
OP kitsios_spyros Senior Member • Posts: 2,722
Re: Knowledge is gold

"Would be interesting if he extended it to assess LV and PD on moving targets and at what point LV fails."

Valid comment and my question τοο when Ι fnished reading these articles. Especially after the great impovement of the AF speed of latest Olympus/Panasonic cameras.

What I really liked in these tests is that the combination of last generation of cameras + last generation of lenses is much improved in the Canon ecosystem. I believe that the rest ought to do the same, if they have not already. And they better publish it accordingly. What I did not like is that one needs to change all ones gear for best results. Upgrading the camera only will not neccessarily mean that the lenses are upgraded too. FW updates maybe?

A dear friend has told me a few times that the PD AF method can not be further improved. It has been a long time around and what to be done is already done. This tests show that mirrorless probably gave a good push to the dSLR manufacturerers to find ways to improve their methods for improving accurnacy and repeatability of their AF methods.

After quite a few months of AF problems due to a combination of
a certainly problematic camera,

another camera without AF-FA abilities that maybe moved its fix/setting over time

a brand new zoom lens with different AF-FA setting for the long vs short end of it's zoom from day 1

2 lenses bought new that started presenting the above problem after a couple of years of usage
several attempts of service
I conclude to the following

  • "If you want to shoot wide aperture prime lenses and you don’t want to use microfocus adjustment, you just refuse to cope with reality. " as the reviewers say

  • There should be a law to ban selling dSLR/dSLT cameras without AF-FA available to the user

  • Camera companies (maybe lens companies too) should offer us a clear and easy method for adjusting the AF-FA. Especially now that (almost) all dSLRs offer cdaf along dpaf in their live liew mode.

Dear Roland, I don't believe that these reports say that "Phase detection AF is problematic." It clearly notes that any camera+lens combination needs calibration or that there is a clear and obvious need that cameras and lenses producers should allow for smaller variations of AF accurancy before releasing a product in the market. I strongly believe in the second sentence. Now the comparison with the CD live view cameras does not allow for further cheating.

Kind REgards,
Spyros

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Roland Karlsson Forum Pro • Posts: 29,193
Re: Knowledge is gold

rogerstpierre wrote:

That's not what the BLOG says. Phase Detection AF is less consistent, and more likely to require calibration (quite understandably when you know how it works).

Thats problematic

You have to understand that to feel comfortable with the problems you might get with phase detection AF. Inconsistencies and calibration is a part of it. If you expect consistency and dont want to calibrate, you might get disappointed.

On the other hand you get speed.

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kitsios_spyros
OP kitsios_spyros Senior Member • Posts: 2,722
Re: Knowledge is gold

Lack of speed can be very problematic too -:)

It is a big deal to me that the need to calibrate is not highlighted by the manufacturers. And the lack of easy-to-get-and-use tools to do so.

Having said that, i'd love my dSLRs to have live view as fast as the latest m4/3 mirrorless have. K-01 would love that too.

Kind Regards,
Spyros

Roland Karlsson wrote:

rogerstpierre wrote:

That's not what the BLOG says. Phase Detection AF is less consistent, and more likely to require calibration (quite understandably when you know how it works).

Thats problematic

You have to understand that to feel comfortable with the problems you might get with phase detection AF. Inconsistencies and calibration is a part of it. If you expect consistency and dont want to calibrate, you might get disappointed.

On the other hand you get speed.

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Roland Karlsson Forum Pro • Posts: 29,193
Re: Knowledge is gold

Just as a side info.

Phase detect AF and large apertures is even more problematic.

My K-5 cant really do AF with my FA 50/1.4.

I would be very pleased if Pentax could add the possibility to focus at F2.0 or even F2.8 for such lenses. Then I could use AF more consistently for that lens.

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awaldram
awaldram Forum Pro • Posts: 13,271
Re: Knowledge is gold

Roland Karlsson wrote:

Just as a side info.

Phase detect AF and large apertures is even more problematic.

My K-5 cant really do AF with my FA 50/1.4.

I would be very pleased if Pentax could add the possibility to focus at F2.0 or even F2.8 for such lenses. Then I could use AF more consistently for that lens.

I find PD is incredibly more accurate than LV under low light.

F1.4 focusing for any pentax I've owned is a breeze if calibrated .

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Walt_A Senior Member • Posts: 2,122
couldn't you have come up with a better thread title?

I had read the first article and was waiting for the 2nd one, all very interesting if you own a canon 5dII or 5DIII. I don't think we can extrapolate anything to our lowly pentax pdaf but still a good read, plus I enjoy his writing style and should really bookmark his blog....
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Roland Karlsson Forum Pro • Posts: 29,193
Re: Knowledge is gold

awaldram wrote:

I find PD is incredibly more accurate than LV under low light.

You can always find a situation that supports your point

F1.4 focusing for any pentax I've owned is a breeze if calibrated .

The old FA 50/1.4 is VERY soft at max aperture. It also has a huge focus shift.

Focussing would be way more reliable if it did focus at F2.0.

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awaldram
awaldram Forum Pro • Posts: 13,271
Re: Knowledge is gold

Roland Karlsson wrote:

awaldram wrote:

I find PD is incredibly more accurate than LV under low light.

You can always find a situation that supports your point

Obviously or I wouldn't have a different view

F1.4 focusing for any pentax I've owned is a breeze if calibrated .

The old FA 50/1.4 is VERY soft at max aperture. It also has a huge focus shift.

I wonder if it an issue of the lens rather than the bodies.

If the lens has an astigmatism then the camera would not be able to focus it at wide apertures

Focussing would be way more reliable if it did focus at F2.0.

Not sure what you saying here , AFAIN current Safox systems are capable of focusing down to f1.2 before occlusion sets in.

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Roland Karlsson Forum Pro • Posts: 29,193
Re: Knowledge is gold

awaldram wrote:

Not sure what you saying here , AFAIN current Safox systems are capable of focusing down to f1.2 before occlusion sets in.

What I say here is that a lens with focus shift shall not use the outer part of the lens to focus. At least not if it is used stopped down.

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SRT201
SRT201 Senior Member • Posts: 2,589
Re: couldn't you have come up with a better thread title?

Agreed... I would never have found it if awaldram hadn't pointed it out.

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RStyga
RStyga Regular Member • Posts: 298
Re: Knowledge is gold

PDAF might be phased out sooner rather than later as CDAF and lens technology meet towards more efficient and reliable results.

awaldram
awaldram Forum Pro • Posts: 13,271
Re: Knowledge is gold

RStyga wrote:

PDAF might be phased out sooner rather than later as CDAF and lens technology meet towards more efficient and reliable results.

I think more likley CDaf will vanish as a pro level technology as PDaf gets implented on the sensor ala the Nikon 1

You can't get round the fact Contrast gives no indication of direction of focus and is poor under low light.

Therfore Phase detect will always be faster and if implented on senor will require no calibration.

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kitsios_spyros
OP kitsios_spyros Senior Member • Posts: 2,722
Re: Knowledge is gold

So awaldram, is this the source of the problem, the need for calibration? That the imaging sensor and and the AF sensor are not the same?
I am getting golder these days...

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Russ Houston
Russ Houston Veteran Member • Posts: 6,377
tagged

for future reading.
thanks for the post
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miles green
miles green Veteran Member • Posts: 7,657
Tagged as well!

Very interesting reading!
Why is it i want a 1DX even more now!?
Time to go play the lottery!

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awaldram
awaldram Forum Pro • Posts: 13,271
Re: Knowledge is gold

kitsios_spyros wrote:

So awaldram, is this the source of the problem, the need for calibration? That the imaging sensor and and the AF sensor are not the same?

Yes its the sole source of pd AF inaccuracy.

there will still be a need for AF adjust to cater for Lens errors but then something that isn't picked up on the internet this is also required for CD af but suspect because you only have one source of error can be automated so is transparent to the user.

I am getting golder these days...

Sorry I don't understand

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