Focus Question

[Bo4key]

I was at the zoo a couple weeks ago and kept missing my focus point. It was very frustrating. I would select my focus, press the shutter half way, and recompose the image and release the shutter fully.

What am I doing wrong?

I've read through the manual a couple times and have done a few Google searches and am still confused. I though pressing the shutter half way would lock the focus so I could recompose my image and shot.

I'm using a Rebel T2i, and a Canon 55-250 IS lens, and have my focus set to AI-Focus. All shots we in manual mode with AF turned on on the lens and IS.

 

[Robin Usagani]

Set the focus to One shot. You cant focus and recompose with AI-Focus unless you change your focus button setup (back button focus).

 

[Big Mike]

Yes, to do it that way, you have to be using One Shot AF mode.

 

[OrionsByte]

Were you shooting through bars and cages? The best thing to do in that situation is use manual focus, because auto will focus on the bars or cage 95% of the time.

EDIT: Just saw the other replies, so, yeah nevermind.

 

[Robin Usagani]

Not if you use 1 point focus.

Were you shooting through bars and cages? The best thing to do in that situation is use manual focus, because auto will focus on the bars or cage 95% of the time.

EDIT: Just saw the other replies, so, yeah nevermind.

 

[Overread]

My advice is a few stages:

1) Use AI-servo not AI Focus for AF. In general AI Focus attempts to work out if you want one shot or AI-servo for your focusing, and sadly a lot of the time it can get it wrong; its a mode very few indeed use on their cameras.

2) When using AI-servo if you want to focus and recompose or work in tricky areas like zoos or reed beds by the water then the bet thing to do is use "Backbutton AF" control. This is where you * button starts and stops AF activation and the shutter button has no effect at all. This means you can start and stop AF with the * button only, allowing you to focus - release the * button - recompose and then press the shutter button (because the shutter is no longer engaging AF).
This essentially lets you live in AIservo mode without having to shift to one-shot AF mode.

3) Single Af point selection is best for zoos and action photography in general - however remember even with a single point your camera can still catch foreground elements (like the bars) - esp in cases like big cats which often have two barriers so you can't get right up close to the main bars.

4) Focus and recompose has to be used carefully because when you change your composition the plane of focus (like a paper sheet parallel to the front of the lens) will shift, and if it shifts too far with a wide aperture then chances are the point you focused on might well slip out of focus unless you manually adjust the focus.


Note focus and recompose as well as backbutton af works best with lenses that have all time manual focusing (eg USM lenses) allowing you to adjust the focus manually on the lens without having to change the AF/MF switch (great with backbutton because - again - you just don't press the * button)

 

[halestorm]

I would use this problem as inspiration to explore the world of manual focus!

 

[eUgalde13]

After reading this thread I decided to see how the * button works and it doesn't seem to work :/ . I followed you and the manual directions and it's just not doing anything. Press the shutter half way and let it focus the objective, press the * button for up to 4 sec but nothing. It works with the FE (flash exposure) tho. . Any idea on what I'm doing wrong? I already tried on each AF mode. Thanks.

 

[Overread]

Double check the manual instructions and make sure that the backbutton AF control is setup correctly as there are a few options and you might have selected the wrong one by accident. Activating the back button AF should disable the * buttons regular flash exposure mode (a downside on the lower end cameras, the middle and upper ranges have a dedicated AF backbutton as well as the *)

 

[Bo4key]

Thanks for the tips!

 

[christian.rudman]

Depending on the camera as well, I continually find myself accidentally switching it over from single af to continuous, so that would be my first guess. The wide angle point by Overread is another. Also, with my Nikon I have found that there are some issues now with AF-Fine tuning and not having the camera properly set up for the lens I am using (Focal points change ever so slightly with each different lens length...). Best thing to do however is figure it out yourself and find a way to combat it! Good luck with your hunt.

And halestorm is totally on to something about the manual focus exploration

 

[Neiby]

I had a similar problem last weekend trying to shoot a parade. By default, my 60D would AF on objects closer than my desired subject. I switched to a single, center AF point in One Shot focus mode. Problem solved.

 

[Bo4key]

I had a similar problem last weekend trying to shoot a parade. By default, my 60D would AF on objects closer than my desired subject. I switched to a single, center AF point in One Shot focus mode. Problem solved.

I think this is what was happening. I was using a single focus point but not One Shot mode. Hopefully this solves my problem.

Thanks everyone!