Lens for dog agility / action

[neuroanatomist]

There is some additional info here:


http://www.the-digital-picture.com/C.../Aperture.aspx

And even more here:

http://www.the-digital-picture.com/P...Explained.aspx

And here:

http://www.canon.com/camera-museum/tech/report/2011/09/

I was referring to the concept that twice as much light from the larger aperture was being directed towards the AF Sensor, which will increase AF acquisition speed, and why an f/2.8 lens set at 5.6 will focus faster than a f/5.6 lens set at 5.6. Of course this will be accentuated in lower light conditions and/or at faster shutter-speeds in which the aperture will be open for a shorter duration.

I expect we're somehow talking at crossed purposes, here. Fast shutter speeds have nothing to do with AF acquisition speed - phase detect AF is performed with the mirror down and the shutter closed. An an f/2.8 lens set at 5.6 will not necessarily focus faster than an f/5.6 lens set at f/5.6 - depending on the scene, it may actually be slower. If there's extreme defocus, the f/5.6 sensor will be used first, then the f/2.8 sensor - in that case, with an f/5.6 lens the AF would be finished after the f/5.6 step, whereas with an f/2.8 lens (aperture chosen for the shot is irrelevant for AF), the AF system would subsequently refine the focus with the f/2.8 sensor - therefore, the f/5.6 lens would actually focus faster (albeit less accurately).

The bottom line is that true AF speed is a composite of many factors - the specific lens being used (not just the aperture - some f/2.8 lenses focus faster, due to better motors or smaller/lighter focusing elements), the camera (faster Digic means faster calculations, 1-series bodies drive the lens AF motor faster due to the higher voltage), and the scene being focused on (a beat up old 300D with an 18-55mm kit lens will focus faster on a contrasty starburst focus target than 1D IV with 400/2.8 II will focus on an elephant in the fog at twilight).

The next question becomes, if the f/2.8 AF sensor slows down AF, is it actually going to reduce servo performance? The camera will have to work harder to lock onto a bouncing non-constant speed object. Will the increases sensitivity combined with the slower performance mean fewer focus locks, and therefore, fewer shots?

Practically speaking, no. An f/2.8 lens activates both f/5.6 and f/2.8 sensors, and as I stated above, AI Servo actually relies more on the f/5.6 sensors. The 70-200 II is a very fast-focusing lens, at least on my 7D and 5DII.

[Richard Lane]

I expect we're somehow talking at crossed purposes, here. Fast shutter speeds have nothing to do with AF acquisition speed -

Fair enough!

I was trying to infer something else, although poorly, that the latter f/5.6 max aperture lens will focus slower in lower light (due to smaller maximum aperture, less light hitting the sensor) and that this 2-stop loss (4 times less light) as compared to the f/2.8 lens, and that this situation will be worsened when you need faster shutter-speeds, because you are approaching the limits of the lens.

I'm assuming similair lighting conditions and that the user maintains his/her subject on target.

I love your article, by the way!

Rich

[Busted Knuckles]

And even more here:
(a beat up old 300D with an 18-55mm kit lens will focus faster on a contrasty starburst focus target than 1D IV with 400/2.8 II will focus on an elephant in the fog at twilight).

I have no dog in this debate (grin) just thought Neuro's comment was worth a second telling for the humor.

[thekingb]

I'm not a huge cross processing fan, but I really like the second shot of Zuni. Great action shot.

[Richard Lane]

There is some additional info here:

http://www.the-digital-picture.com/C.../Aperture.aspx

[DavidEccleston]

I saw someone's post on indoor agility shooting with a 5DmkIII ( http://www.fredmiranda.com/forum/topic/1103203 ). Shooting @ f/2.8, they required an ISO of 10000 to get 1/640s, which really, is the lower end of acceptable shutter speeds for dogs. Considering these parameters, I don't expect to shoot anything indoors. Having the f/2.8 lens won't make indoor shooting viable.

I'm leaning towards the 70-300L, as from 70-155mm the aperture (thus speed and blur) are the same, or just about the same, as the 70-200 f/4L. On the last 45mm there is a noticeable difference, 2/3 of a stop, but that's offset by the extra 100mm of zoom. We'll have to head out to a store and see how both lenses feel. Perhaps my wife will find them all too heavy, and we'll get the 70-200 f/4L non-IS (for versatility) , or one of the primes (for speed and sharpness) in the end.

Thanks to everyone who contributed, even if I am exactly where I was at the start of the thread.

[HDNitehawk]

Perhaps my wife will find them all too heavy, and we'll get the 70-200 f/4L non-IS (for versatility) , or one of the primes (for speed and sharpness) in the end.

Thanks to everyone who contributed, even if I am exactly where I was at the start of the thread.

My first thought when I read the thread, is that you will end up with the 70-300mm L because of its compact size. I just need to find who is running the pool for which one you buy, so I can get my money in.

[Sheiky]

I personally would vote for the 70-200 F4L IS. I really like mine and have considered the 70-200 f2.8L IS as well before. The f4L IS wide-open is really nice. Like every lens it gets better stopped down, but I don't hesitate to use it wide-open at all. Which I would prefer not to do with the old F2.8 IS lens.
I personally like the weight and the size of the F4L IS over the F2.8 version. It is just really a step bigger.
For most times, like 9/10 times, F4 is plenty and paying double for the new F2.8 lens wasn't worth it to me since I'm just a hobbyist. Since you plan to use the lens for your dogs, you will get plenty chances and I doubt the F2.8 would be really worth paying double.
Especially outdoors F4 will do good enough. F2.8 will do better of course, but for real low-light or indoors you will probably still get your primes.

I have upgraded from the non-IS F4L lens to the F4L IS lens and I really like the added IS on this focal range. It's nice for sports(with IS mode 2), but now you could also use it as a landscape lens/walk-around lens when you would like to stop down to f10 or so or shoot wildlife when it gets darker. That was the main factor to me to upgrade to IS.

Since most of my shots are with the 5D2 or 40D my shots aren't really good examples, because your camera is a lot quicker and I don't have a dog(I shot some motocross, but those guys are just a little bigger and slower) But I can say that I am convinced that the 70-200 F4L IS is quick enough even on my 5D to take photos of dogs running towards me. So I'm pretty sure it can do the same and better on your camera.

As for the 70-300L. I would not like the F5.6 aperture at all. I'd rather give up IS than a full stop of aperture for shooting sports/dogs if that's the main purpose for the lens. Also the F5.6 makes it harder to get a nice amount of blur.

So my vote: 70-200 F4L with or without IS. You can always add an extender if you want to go to 280mm.

Have fun choosing a new lens!

[Andy Stringer]

Joel is right about technique being at least as important as the lens. You will be rewarded for reading about the focus custom functions and spending time practicing.

Does anyone have demanding servo sample images, equivalent to what we might see in agility, that they could share crops from? Something small, fast, moving towards the lens.

Denise has provided some excellent examples with her primes. To show what can be achieved with a variable aperture zoom, here are a couple of shots I took with my 100-400mm. I think you should be able to achieve something similar with a 70-300L since your 7D has a 1.6 crop sensor compared to the 1.3 crop of my 1DIV. These were taken at 400mm, 1/1000s, f/5.6, ISO 400.





For the situation you describe, outdoors, I think the 70-300L would be a great choice.

[DavidEccleston]

Thanks Andy.