Autofocus problems, help please

wheresdavid

I have a few (several) photos where i was sure i had seleceted the autofocus spot selected on the eye but when i look at my photos the camera focused on the nose? i dont let the camera choose the autofocus point, i choose it and then center it on the eye but the nose is sharp and the eye is soft.

dave

rebel xti, canon 50mm f1.8

wxwax

Do you have an example, with EXIF?

What's your autofocus mode?

Even though you're selecting your autofocus point, are you doing any focus/recomposing?

Scott_Quier

wxwax wrote:

Even though you're selecting your autofocus point, are you doing any focus/recomposing?

And, if so, from how far away are you shooting? The closer you are to your subject, the greater the impact of any errors introduced by the focus and recompose technique.

dogwood

Scott_Quier wrote:

And, if so, from how far away are you shooting? The closer you are to your subject, the greater the impact of any errors introduced by the focus and recompose technique.

That... and on Canon's anyway, Canon advises you to select the focus point based on your composition. They warn there can be back focusing problems if you focus and recompose.

Also, just a personal preference, but I like to change my focus button to something other than the shutter button. That way I don't have to deal with the sensitivity of the shutter as the focus too (sometimes you can focus properly, recompose in say Al Servo mode, and the camera will focus on the nose instead of the eye since that's where you recomposed).

Your best bet is to try some trials at home moving the focus point and trying to focus and recompose. See if there's a difference and you should also be able to narrow down what's going wrong.

If all else fails, there's always manual focus!

wheresdavid

Sorry i havent been able to upload any examples yet. I notice the problem on a "bunch" of photos i took of a woman up close (maybe 3-4 feet away with my canon 50mm 1.8 lens). I dont focus and recompose, i selected the autofocus point on her eye and then took the photo. When i opened the photos in "whatever" software they had at the internet place in cusco, peru i notice that a lot of the photos that i took were focused on her nose and not on her eye.

When i get to a plce where i can upload some examples i will. how do i include the EXIF data?

D

dogwood wrote:

That... and on Canon's anyway, Canon advises you to select the focus point based on your composition. They warn there can be back focusing problems if you focus and recompose.

Also, just a personal preference, but I like to change my focus button to something other than the shutter button. That way I don't have to deal with the sensitivity of the shutter as the focus too (sometimes you can focus properly, recompose in say Al Servo mode, and the camera will focus on the nose instead of the eye since that's where you recomposed).

Your best bet is to try some trials at home moving the focus point and trying to focus and recompose. See if there's a difference and you should also be able to narrow down what's going wrong.

If all else fails, there's always manual focus!

photogmomma

When I had my 1.8, I learned NOT to use it at f/1.8. I usually used it at 2.4 and got MUCH better results. Sometimes it just didn't focus right and now that I have the 1.4, I realize it was the lens and not me.

I think a small part of the problem is that you have such a shallow DOF at 1.8 that even the smallest of movements by you or the subject can throw the focus way off - and you don't even realize it. But I also found that the focus wasn't quite as accurate.

If/when you get the $$ to upgrade to the 1.4, I think you'll find that you get a LOT more photos in focus than you did with your 1.8. I have to tell you, though, that my 1.8 was my favorite lens for a LOOONG time. Now it's my 1.4 - which I miss because I had to send it back for repair. (Speaking of not focusing - i wouldn't even focus manually! They fixed it under warranty even though it was 45 days overdue. Yay!)

HTH!

Long and short - use a smaller aperature (2.0/2.4/2.8) and I think you'll get much better results.