40D AF Limitation

[mantarey]

I posted this reply in another thread in response to JP's comment on "incoming" BIF shots. I thought of posting it here, hoping to get your thoughts about this. Thanks a lot for your indulgence.

Quote:

For incoming birds, I noticed that the 40D's AF capability is not that good. I found a spot where a lot of the birds were flying towards me and have taken at least 10 to 15 shots of that nature. The 40D was able to lock focus maybe twice, the rest were OOF. Going sideways or away from me, the AF is great but for incoming birds it performed very poorly. I don't know if it's a lack of technique on my part but I've also read about that problem somewhere. By the way my cam settings were the one's always used by the master himself.

Maybe the Mastah Birdman can shed some light.

[Ding Carpio]

Hmmm. Were you on one-shot focus or servo?

[Neon Rosell II]

May 2, 2008 13:02:26 GMT @mantarey said:

I posted this reply in another thread in response to JP's comment on "incoming" BIF shots. I thought of posting it here, hoping to get your thoughts about this. Thanks a lot for your indulgence.

Quote:

For incoming birds, I noticed that the 40D's AF capability is not that good. I found a spot where a lot of the birds were flying towards me and have taken at least 10 to 15 shots of that nature. The 40D was able to lock focus maybe twice, the rest were OOF. Going sideways or away from me, the AF is great but for incoming birds it performed very poorly. I don't know if it's a lack of technique on my part but I've also read about that problem somewhere. By the way my cam settings were the one's always used by the master himself.

Maybe the Mastah Birdman can shed some light.

I think the problem is acquiring the target, if the camera focuses already it tend to stay focused but sometimes get off when you let the target off centered, and you know getting the target centered all the time is a feat in itself.

What I do is half pressing the shutter again when it loses focus so that it will acquire the target once more and pressing the shutter when the focus is spot on, doing this several times in one go. This is done in AI servo mode. It needs some patience and practice. ;D

Also a bare lens without TC would greatly help, the lens will focus a lot faster. My two centavos.

[mantarey]

Thanks a lot Neon and Ding for the replies. I think the standard settings are pretty much covered, like I said it's the same as Ka Romy's (i.e. f7.1,1/1600 on good light, ISO 320-400, AI Servo) and I don't use TC's. Please allow me to elaborate further.

Acquiring the target is actually easier when the bird is coming towards you becuase it's in a straight line without the sideways movement that requires good panning skills. It's also a lot easier to keep the target in center focus becuase the movement "seems slower" and that's what puzzles me more as the results are not as good when the birds are going sideways.

I would normally lock on the bird as it approaches and would also continually bump the shutter if it loses AF while waiting for the bird to come at an acceptable distance and starts firing away (even have time for that). Almost always I can see that the camera has AF lock while I'm pressing the shutter but it seems the AF can't compute very well if the target is coming towards me. So what else should I consider guys?

[Romy Ocon]

The features and capabilities of Canon DSLRs are usually documented in what they call "White Papers", which are normally better written and more readable than the manual that comes with the camera. If you haven't read the 40D's "White Paper" yet, here's a link.

www.usa.canon.com/uploadedimages/FCK/Image/2007/White%20Paper/40D/EOS_40D_WhitePaper_070817.pdf



From the said 40D white paper:

"Predictive AF can track a subject approaching at 50 kph/31 mph up to about 26.2 ft./8m away with an EF 300mm f/2.8L IS USM lens."

This means that if you're using an f/5.6 lens, the AF is much slower because light hitting your 40D's AF sensor is only 25% (2 stops of light) of that of a 40D + 300 2.8L IS. Also, if the bird is coming towards you at more than 50 kph, it's virtually impossible to track even with an ideal 40D + 300 2.8 + perfect panning.

Moving objects with a rapidly changing distance from the camera are tough AF jobs even for 1Dxx bodies and using excellent panning techniques. (Hehe... some people even misfocus with a stationary subject! ;D)


As Neon said, you have to keep the bead on the subject perfectly to feed reliable info to the 40D's AF computer. The camera uses predictive AI servo to foretell where the subject is in future frames based on previous frames.

Hence, the first couple of shots in an AI servo burst are sometimes imperfectly focused, but the succeeding ones are better focused because the AF processor already has more data points on which it can base its next AF step. This assumes of course that your panning/tracking is flawless, the bird is not flying towards you faster than 50 kph and it's always at least 8 m away.


With the 1DMxx, life is much simpler when using AI servo, as the camera has a second CPU dedicated exclusively to AF duties, unlike the single-CPU xxxD bodies. That said, it's still not impossible to grab the birds from the air using the 40D/30/20D bodies.... one just have to pan more accurately and expect more wastage.


40D + 100-400 L IS, 1/1250s f/5.6 at 400.0mm iso400, hand held




40D + 100-400 L IS, 1/1600s f/5.6 at 400.0mm iso320, hand held




40D + 500 f4 L IS, 1/1250s f/5.6 at 500.0mm iso400, 475B/3421 support





40D + 500 f4 L IS, 1/1250s f/5.0 at 500.0mm iso400, 475B/3421 support





Romy

[mantarey]

Thanks a lot Master Romy, as I have thought you knew the aswer. Great BIF samples by the way.

Apparently I'm working outside the parameters where the 40D's AF capability on approaching target can work accurately. I'm at f5.6 and surely the Night Herons which are fish hunters can fly a lot faster that 50 kms per hour (did a quick research).

Upgrade to a 1D? I like the idea but it's too expensive for me at this time. Anyway, I'll just be content catching them the easier way.

But then again, approaching BIF images looks really great. Oh well....

[Neon Rosell II]

May 3, 2008 1:00:48 GMT @mantarey said:

Thanks a lot Master Romy, as I have thought you knew the aswer. Great BIF samples by the way.

Apparently I'm working outside the parameters where the 40D's AF capability on approaching target can work accurately. I'm at f5.6 and surely the Night Herons which are fish hunters can fly a lot faster that 50 kms per hour (did a quick research).

Upgrade to a 1D? I like the idea but it's too expensive for me at this time. Anyway, I'll just be content catching them the easier way.

But then again, approaching BIF images looks really great. Oh well....

He he he, Rey if you switch to a 300 mm f4 on a 40D body you'll be able to get this jet fast birds while it is approaching head on at 200+ km/hr . As what Master Romy said you just aim and center the bird and wait for the AF AI servo to focus and press until the buffer is full ;D surely you'll get 1 out of the 9 frames that is good enough.

Purple Needletail (Hirundapus celebensis)
40D + 300mm L f4 IS, f4, 1/800 sec, ISO 400, Manual Exposure, Hand held, RAW capture, jumping up and down and shaking with excitement!! ;D

[mantarey]

Getting 1 out of 9 frames that is "good enough" may not be good enough, but if the 1 that is good is this good:



and this good,



then I may think of changing lens hahaha. But so far I think the EF400 is still a great BIF lens.

[Neon Rosell II]

May 3, 2008 10:25:07 GMT @mantarey said:

Getting 1 out of 9 frames that is "good enough" may not be good enough, but if the 1 that is good is this good:

then I may think of changing lens hahaha. But so far I think the EF400 is still a great BIF lens.

He he he, you are right the 400 is the best BIF lens, I'm just depressed that I don't have one and languishing in jail while you guys have all the fun!! ;D

[mantarey]

May 3, 2008 15:11:24 GMT Neon Rosell II said:

May 3, 2008 10:25:07 GMT @mantarey said:

Getting 1 out of 9 frames that is "good enough" may not be good enough, but if the 1 that is good is this good:

then I may think of changing lens hahaha. But so far I think the EF400 is still a great BIF lens.

He he he, you are right the 400 is the best BIF lens, I'm just depressed that I don't have one and languishing in jail while you guys have all the fun!! ;D

DOn't worry Neon, just a few more weeks, I'm sure you can still find some more nuggets in your HD goldmine.

[Ralf Nabong]

@romy - "With the 1DMxx, life is much simpler when using AI servo, as the camera has a second CPU dedicated exclusively to AF duties, unlike the single-CPU xxxD bodies. "

Rey - 1D,1D,1D,1D,1D