Switching to Nikon

[Haydn1971]

Bikersbeard was suggesting the 7D was worse than the 5D...   The AF on the 7D is more up to date, my question really was is that due to the lower light collecting ability of the lesser lens used on the 7D

[Mt Spokane Photography]

Bikersbeard was suggesting the 7D was worse than the 5D...   The AF on the 7D is more up to date, my question really was is that due to the lower light collecting ability of the lesser lens used on the 7D

The 7D AF is very good.  It is designed to allow tracking and keeping focus for fast moving subjects, certainly much better than my 5D MK II. 

However, in low light, a FF camera with its larger AF sensor and larger main sensor gathers more light and will function at a lower light level.  Its the same for other FF camera bodies.

This is assuming that we are comparing the cameras with the same lens under the same situation.  Using a f.1,4 lens on a 7D versus a f/5.6 on a 5D MK II might give opposite results.

Remember, we are talkiing about photography where it is almost totally dark.   The kind of low light where a 7D would not get a good image even if it did autofocus.  Night clubs, Theatre, very dark.

From my testing, the 7D can focus quite well in low light up to the point where the sensor only produces very noisy images that you would not like anyway, so I'm not knockiing it, it is well balanced.  But, when my 7D quits for lack of light, my 5D MK II is still going strong.

[Haydn1971]

I was having just this problem tonight in very low light, about an hour after sunset, trying to focus my 15-85mm at 85mm (f5.6) on my 450D with some fill flash, ended up pulling the 50mm f1.4 out, which worked much better, even though it wasn't as tight as I was wanting.

Good job I wasn't having the same trouble with the BBQ though ! Yum !

[UncleFester]

I was having just this problem tonight in very low light, about an hour after sunset, trying to focus my 15-85mm at 85mm (f5.6) on my 450D with some fill flash, ended up pulling the 50mm f1.4 out, which worked much better, even though it wasn't as tight as I was wanting.

Good job I wasn't having the same trouble with the BBQ though ! Yum !

Were you using AI focus with flash?

[AdamJ]

AI Servo AF is the one area that disappoints me about my 5DII. I don't expect 1DIV performance from it but I think I'm within my rights to expect it to do a better job of tracking my nine-year-old daughter in a sports day race.

I'm probably a typical 5DII user - an amateur enthusiast with only one camera body who can't afford either a second body or a 1D/s. Given these constraints, I don't want my camera to be a landscape / portrait camera, as the 5DII is now widely viewed. I want my one and only body to be a good all-rounder. And it would be, if only the AF were more sophisticated.

I've never tried a 7D but on paper, it's AF looks a lot better. I hope the 5DIII gets that system.

Anyway, in summary I do understand the OP's frustration but I agree with the comments of others who say the grass is always greener. What you might gain in some aspects by switching to Nikon, you lose in others.

[motorhead]

Once I had learnt the vital lesson that I had to keep the AF point nailed on the target at all times with no drifting off, I have been very happy with the AI Servo AF on my 30D. I'm surprised to hear that the 5D11 is not as good.

Why should that be? I don't understand how full frame or crop can make any difference to the mechanics of the operation. 

[Mt Spokane Photography]

Once I had learnt the vital lesson that I had to keep the AF point nailed on the target at all times with no drifting off, I have been very happy with the AI Servo AF on my 30D. I'm surprised to hear that the 5D11 is not as good.

Why should that be? I don't understand how full frame or crop can make any difference to the mechanics of the operation.

Most actual owners say its fine, and, yes i own one.  However, it is not and was not intended to be a sports camera, and the really fast moving sports will be a challange.  The image I posted above was one of a series of images taken as the runners neared the hurdles, and all were in reasonably sharp focus, so the 5d was tracking fast moving runners coming at me just fine.  If I'd been really close, it probably would have been tougher, since there would be less depth of field to coverup and slight misfocus.

Rent one and try it, it is a super popular camera in its range for a reason.

[neuroanatomist]

If I'd been really close, it probably would have been tougher, since there would be less depth of field to coverup and slight misfocus.

Or, if you'd been using a lens faster than f/4.  I've taken bursts of a toddler running toward me with the 85L at f/1.2 on my 7D, and had ~80% of the shots focused on the eyes as I intended.  With the 5DII i nthe same situation, I'd be lucky if even one of the shots was in focus.

[Mt Spokane Photography]

If I'd been really close, it probably would have been tougher, since there would be less depth of field to coverup and slight misfocus.

Or, if you'd been using a lens faster than f/4.  I've taken bursts of a toddler running toward me with the 85L at f/1.2 on my 7D, and had ~80% of the shots focused on the eyes as I intended.  With the 5DII i nthe same situation, I'd be lucky if even one of the shots was in focus.

In the case of the 85L, fast AF might be more lens limited than camera limited.  You are more expert on the 85l, what do you think?

The 70-200mm f/4 IS has quite fast AF.  Since the photo was captured at ISO 100 f/8 and 1/320 sec on a very bright day, a f/2.8 or a f/1.2 lens would not have changed much, I'd still have kept to f/8, since I did not want shallow depth of field, but to get all the runners in focus.  I could have easily increased ISO to 200 or 400 and used a faster shutter speed, and I'd probably do that in the future.

[neuroanatomist]

In the case of the 85L, fast AF might be more lens limited than camera limited.  You are more expert on the 85l, what do you think?

The 70-200mm f/4 IS has quite fast AF.  Since the photo was captured at ISO 100 f/8 and 1/320 sec on a very bright day, a f/2.8 or a f/1.2 lens would not have changed much, I'd still have kept to f/8, since I did not want shallow depth of field, but to get all the runners in focus.  I could have easily increased ISO to 200 or 400 and used a faster shutter speed, and I'd probably do that in the future.

Yes, the 85L has slow AF (despite a USM motor, it's a lot of glass to move and an old USM design).  But in this case, it's still camera-limited.  The issue isn't really AF speed as much as AI Servo AF accuracy.  Shooting at a narrower aperture (whether by necessity due to a slow lens, or by choice as in your case) means the deeper DoF will mask any errors in focus accuracy.  I have the same issue with my 70-200mm f/2.8L IS II and 135mm f/2L, which from a lens perspective both have blazingly fast AF - in AI Servo, the AF on the 5DII cannot keep up with a subject running toward or away from the camera with a wide aperture, whereas the 7D can do so much more effectively.  Yes, I could stop down for more DoF to compensate, but when I'm shooting just one subject, I usually want the separation from background that comes from the wide aperture.

[UncleFester]

It's the action running out of the dof faster than the camera can keep up.