Knowledge is gold

Started Jul 31, 2012 | Discussions
kitsios_spyros
OP kitsios_spyros Senior Member • Posts: 2,722
Re: Knowledge is gold

I've spend innumerable hours of reading how to recognize and fix the problem, what can affect it, test AF-FA methods etc but missed the technical part of what causes it. Bummer...
I've just found this great article
http://www.lensrentals.com/blog/2010/07/how-autofocus-often-works

which pretty much explains what happens. The comments below the article are very usefull too. If you can share any other link that would be much appreciated.

Two questions though. What happens with a lens that has intense focus shift on stopping down. If there is an algorythm working to offset the error when choosing an aperture before focusing, why does this algorythm not work when we change the apperture after the af lock. If the lens/camera knows that the actual focus distance will change with the particular lens after apperture has been changed of a already prefocused frame, why doesn't it automatically compensate for the actual focus distance at the time of the exposure? Or is it not a algorythm correction?

Second question. How does the occlusion work when a wider than max possible aperture of a camera's AF system is used (f1.2 for our cameras, right)?

Kind Regards,
Spyros

awaldram wrote:

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

I refer to the title of the thread. More knowledge, more gold, just got (g)older again..

SRT201, I am sorry the title did not please you. But that's how I felt after reading those lensrentals articles. Which, BTW, give us hope that the manufacterers are actually trying to improve on the disadvantages of the -quite capable- PDAF system.

Kind Regards,
Spyros

 kitsios_spyros's gear list:kitsios_spyros's gear list
Pentax K-01 Pentax K-5 II Samsung NX300 Pentax K-3 Pentax KP +13 more
Keyboard shortcuts:
FForum MMy threads