i have a very dumb question about fixed lenses

[jann1033]

my first fixed was the 50 mm 1.8 and i always seem to have a problem with it focusing where i don't think it is going to ie behind the subject...but i never have a similar problem with my 100mm ...any ideas why? i figured i must not be focusing on the right thing with the 50 but wouldn't it seem i'd have the same problem with the 100 if that were the case? it doesn't seem to matter how far away i am, it( the 50) just never is focused where i intended it to. so am i missing a trick to focusing it or what. that is basically why i only use that lens as a last resort. i used it at a wedding i attended and not one photo was in focus where i wanted the focus ( ie it would focus on the couple behind who i thought i focused on)

 

[MarkBarbieri]

I would perform some tests on something like a ruler where you can see if it is consistently focusing a little behind an object or whether it is just off in random ways.

You may find that it works well in controlled tests. In that case, it may be that your technique needs work and that shooting at f/1.8 makes the errors more obvious.

More likely, you'll find that it mis-focuses in controlled tests. If it does it consistenly, it needs to be adjusted by Canon. If it is random (some good focuses, some a little behind, some way behind), it's probably a bad lens and there isn't much you can do about it.

If you don't want to hassle with sending it in to Canon to fix focus accuracy issues, you might also consider buying a 1DM3. It allows the user to make lens by lens adjustments for consistent focus errors. Some people might think that spending thousands of dollars to solve a problem with a $70 lens is crazy, but I think it's a great justification for buying new, unnecessary gear.

 

[Gdad]

I have the Nikon version and shooting wide open at f1.8 can be difficult. I personally have much better results stopping it down to f2 or f2.8.

 

[boBQuincy]

>i have a very dumb question about fixed lenses

I used to think "there are no dumb questions" but my coworkers proved otherwise! Yours is not dumb, trust me, those guys are pros.

It sounds like your 50 is off. Try what Mark suggested and see how it goes. I know you are no fan of Canon's service (me either), I wonder if anyone else can adjust lenses?

The 1DMk3 can adjust for lenses? That's my camera!!! Now I have to spend months plotting how to convince DW that I need it...

 

[jann1033]

thanks... I'll try the ruler first, then buy the camera to prove my results are accurate

 

[Groucho]

Of course, the larger the aperture, the most important precise focus is... try shooting at F8 or higher and see if the problems go away. Also try switching to spot focus and see if that makes a difference.

 

[gruZ]

Jann,

Use this link, and download the focus test. It's a PDF file, and gives step by step instructions on how to do the test. While the author is a Nikon user and speaks to Nikon focusing, the test works well for all AF cameras. I used it to test a newly purchased lens (which I then had to send back to Sigma for calibration).

Thanks,

Scott

 

[jann1033]

thanks!

 

[tigger795]

How about manually focusing the camera? I find that sometimes, especially when shooting wide open in low light when the camera may tend to hunt for focus, it is just easier to do it myself. Even more especially in a shallow DOF situation. I know it takes a little longer but at least I know I have control over the errors I make.

Kindest regards,

 

[jann1033]

it doesn't really hunt for focus, it appears to be focused but isn't on what i want focused. i'll try the tests when i get around to it...i would just like to use the lens more if it's something i can correct and if something is messed up with it would rather give canon a chance to mess it up more while it's under warranty