1Dx focus problems in continuous shooting situations

[lv2rescue]

If I shoot a subject at max frame rate on a supertelelphoto the subject goes from being tack sharp to well out of focus in AI servo by the end of the series. Shouldn't it stay locked on? Thanks in advance for any feedback.

 

[bdunbar79]

Try using back-button AF and keep it depressed while you fire the shot with the other finger on the shutter button. If it's not moving super-erratically, try Case 1 as well and see what happens.

 

[Viggo]

It depends on about 100 different things. The more info you have, the easier it is to give tips on how to tweak the AF and how to make the most out of the situation.

You can not expect to have a 100% hit with extreme shallow dof in poor light at mfd for example.

 

[bdunbar79]

Agree. It's even hard to get a 100% hit rate using say a 400mm lens wide open at f/2.8 during the day. It takes a lot of patience, experimenting, and practice.

 

[Deleted member 91053]

I use case 5 on my 1DX with back button focus. So long as I keep the focus point on the target (that's the hard bit!) then it just focuses. Obviously nothing is 100% but on medium to large birds I expect virtually all frames to be sharp, with some sharper than others. On predictable targets I expect effectively all to be in focus though I did loose 2 out of 2800+ shots at a rallycross race a month or two ago.
Please note I am only referring to the shots where I had the activated AF points on the subject - the 1DX is good but thought controlled AF is not yet in the menu ;D

P.S. I forgot to mention that my 1Dx is set to 10fps - don't know if this would make a difference?

 

[nvsravank]

if you are using the full speed on 1dx i am told that the mirror doesnt come down and so it is not focussing again but depending on the first calculation to move focus for the next shots if in AI Servo mode and so the keepers come down.

Note in this case the different modes of AI servo all work the same as it is not taking any additional reading between shots to figure out how to compensate for movement.

also if you are on long lenses at max aperture the DOF is razor thin and that might cause focus shift to be noticeably bad much faster.

 

[lv2rescue]

Thanks everyone! I will try the back button AF idea. The DOF was definitely tight on an 800 mm at close range, but even though the subject didn't move significantly, you can see frame by frame as it gets further and further out of focus. I thought if the subject didn't move it would stay locked on just by pushing down on the shutter in AI servo. Thanks again!

 

[RunAndGun]

At MAX frame rate(12-14 fps) the camera locks the mirror up and does not track focus. At 800mm WAO(wide @$$ open), your depth of field is very shallow. Someone could basically standstill and just rock forward or backwards and go in and out of focus. Shooting interviews on my C300 at MUCH shorter focal lengths(85mm or 135mm), even stopped down a little, I can still have subjects in and out with minimal movement.

 

[Viggo]

At MAX frame rate(12-14 fps) the camera locks the mirror up and does not track focus. At 800mm WAO(wide @$$ open), your depth of field is very shallow. Someone could basically standstill and just rock forward or backwards and go in and out of focus. Shooting interviews on my C300 at MUCH shorter focal lengths(85mm or 135mm), even stopped down a little, I can still have subjects in and out with minimal movement.

Not 12-14, it's ONLY at 14 fps the mirror locks up.

 

[digital paradise]

Thanks everyone! I will try the back button AF idea. The DOF was definitely tight on an 800 mm at close range, but even though the subject didn't move significantly, you can see frame by frame as it gets further and further out of focus. I thought if the subject didn't move it would stay locked on just by pushing down on the shutter in AI servo. Thanks again!

I could never get used to the BBF and shot with shutter button for years but was used to keeping the shutter ½ pressed between and during bursts. I have recently warmed up to the BBF.

 

[Deleted member 91053]

Thanks everyone! I will try the back button AF idea. The DOF was definitely tight on an 800 mm at close range, but even though the subject didn't move significantly, you can see frame by frame as it gets further and further out of focus. I thought if the subject didn't move it would stay locked on just by pushing down on the shutter in AI servo. Thanks again!

Which 800mm lens are you using? I use the Canon 800 F5.6 L IS and expect a VERY high keeper rate if I do my part! I often use my 800 at close to MFD (sometimes closer with extension tubes) and normally go for F11 to get some depth of field.
Another thing I have found is that my keeper rate is significantly higher with the IS turned off - even more so with moving subjects.