[Guest]

Hello everyone,



I'd like to share one problem, to see if this is just my sample, or it is a general issue.



I have a Canon 60D + Tamron 17-50 f/2.8 (the non-stabilised version): when I use contrast detection focus, @50 mm, the focusing is never accurate. It is like the autofocus is in "steps" (or jumps) too large to be really spot-on.

At other focal lengths, or with phase detection, everything is fine.



Anyone else experienced this?



Many thanks,

Davide

[Brightcolours]

[quote name='wizoo' timestamp='1307358872' post='9054']

Hello everyone,



I'd like to share one problem, to see if this is just my sample, or it is a general issue.



I have a Canon 60D + Tamron 17-50 f/2.8 (the non-stabilised version): when I use contrast detection focus, @50 mm, the focusing is never accurate. It is like the autofocus is in "steps" (or jumps) too large to be really spot-on.

At other focal lengths, or with phase detection, everything is fine.



Anyone else experienced this?



Many thanks,

Davide

[/quote]

It is not uncommon for contrast detection to not be able to find focus correctly with certain lenses. The lenses simply do not make small enough steps to be able to "see" when contrast is best, and focus gets "declared" when the subject in fact is still out of focus.

My Sigma 18-50mm f2.8 has similar problems, and trying to focus with contrast detection with a Tokina 12-24mm f is gives ridiculous results (EOS 450D).



So, I guess what you are noticing is "normal", and has to do with the lens' electronics/motor.

[janzu77]

[quote name='wizoo' timestamp='1307358872' post='9054']

Hello everyone,



I'd like to share one problem, to see if this is just my sample, or it is a general issue.



I have a Canon 60D + Tamron 17-50 f/2.8 (the non-stabilised version): when I use contrast detection focus, @50 mm, the focusing is never accurate. It is like the autofocus is in "steps" (or jumps) too large to be really spot-on.

At other focal lengths, or with phase detection, everything is fine.



Anyone else experienced this?



Many thanks,

Davide

[/quote]



I have also the same Tammy and have experienced the same. Phase detect AF is tack sharp, but contrast one seems to misfocus time to time. This same happens occasionally with my other lenses (Canon made) as well, even USM does not necessarily work any better. So I think that it's a feature, not a problem <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='' />

[Guest]

[quote name='janzu77' timestamp='1307450692' post='9063']

I have also the same Tammy and have experienced the same. Phase detect AF is tack sharp, but contrast one seems to misfocus time to time. This same happens occasionally with my other lenses (Canon made) as well, even USM does not necessarily work any better. So I think that it's a feature, not a problem <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='' />

[/quote]



LOOOL janzu, they advertize contrast detection as being potentially more accurate! Luckily we have the 10x magnification to check the focus before the shot...

[janzu77]

[quote name='wizoo' timestamp='1307533661' post='9075']

LOOOL janzu, they advertize contrast detection as being potentially more accurate! Luckily we have the 10x magnification to check the focus before the shot...

[/quote]



Yep, it should be accurate, but I've noticed several times that it isn't always so.... When it works, it's accurate, but for example with EF 100/2.8 USM macro I've noticed several times that the focus is hunting back and forth without finding the correct focus.



I think it's mostly dependent on the scene. If there are clear contrast differences where the focusing is done then it works the best, also it the lighting is not too dark, that helps too.



Liveview & MF is the most efficient way to me if viewfinder cannot be used <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='' />