AI Servo and young children.

toadstool · 31 Dec 2012

Hi! I've photographed my 1 year old niece and my 5 year old nephew quite a bit but they're local and used to my camera. Plus, the 1 year old is a really quiet, content little thing who tends to stay in one place for ages haha. Next week, I'm visiting my sister in Northern Ireland. Her little boy is 15 months old and FULL to bursting with energy! He's not used to anything more than a quickly snapped phone or P&S camera and her house isn't very well lit. I mainly shoot with primes and, due to baggage space, can only take my camera (Canon 500D), 50mm 1.8 and lightscoop.

I've just been reading more about AI servo but can't quite get my head around how to use it. I just practiced on my kittens and despite focusing on a spot, when they moved that was it... not a single shot in focus. My shutter speed was 1/250. I'm also using back button focus (and keeping my finger pressed down to focus the entire time).

So does anyone have any hints/tips/tricks/advice/help/ANYTHING!? And a little (okay, a lot) more help with AI Servo if that's the one I should be using? I don't get out there regularly (I was last able to photograph him when he was 6 months old!) so really want to make the most of this opportunity. :bonk:

carolthomasburns · 31 Dec 2012

Glad you brought this subject up Toni as I can never quite work out AI servo either - My daughters B/F is a camera buff and he did try to explain but it wasnt in laymans terms and went through my head quicker than the wind

Will subscribe so if anyone gives you any advice I can grab it as well if you dont mind

k4stn · 31 Dec 2012

I use Al servo when hand holding at wide open as the DOF is small or when shooting sport, if you or subject move a little you will miss the focus Al servo will keep adjusting the focus as you move.
The better the light the better Al servo works and I may be wrong but I have it in my head that the centre focus point work best on canons

carolthomasburns · 31 Dec 2012

Thanks for that Shane - explains it a lot better .... will remember that little titbit for when i'm trying to catch dancers

john_e · 31 Dec 2012

On the 500D only the centre focus point is cross type so that's the one to use. Back button focus and keeping it held down whilst tracking the subject is the way to go so no worries there. Remember though that the 50 1.8 isn't the fastest focussing lens out there (I'm being generous) so it may well hunt for a bit when it loses focus.

Wozzaaah · 31 Dec 2012

I use AI Servo a lot as I quite often do the photography at our local Parkrun and it works well but it's not without it's problems.
I often track a runner covering maybe 100m or so and have found it's far better to release the BBF and press it again to reacquire focus just before taking the next shot rather than try and track the runner for the entire distance.

Are you sure they're actually OOF rather than it just being motion blur?
Tbh, 1/250 isn't really that fast for a moving subject and as you know the nifty has no IS.

k4stn · 1 Jan 2013

That's what i had in my head (centre focus point is cross type) thank for that John.
I get what you are saying Wozzaaah about 1/250 not been fast may be 1/200 with a flash would be better. For running I would be panning the shot

Wozzaaah · 1 Jan 2013

1/250 sounds fast but on a non IS lens indoors I reckon it's asking quite a lot.
A lot of the shots I take are on a narrow path with runners coming towards me so the AI Servo has to work harder than it would if the runners were passing me.
I tend to shoot at a minimum of 1/640 with a 70/200 f2.8 in good light.

Dazb75 · 3 Jan 2013

I wouldn't use the 50mm f1.8 on ai servo. It doesn't focus quick enough. You need a lens with USM.

martsharm · 14 Feb 2013

Wozzaaah said:
1/250 sounds fast but on a non IS lens indoors I reckon it's asking quite a lot.
A lot of the shots I take are on a narrow path with runners coming towards me so the AI Servo has to work harder than it would if the runners were passing me.
I tend to shoot at a minimum of 1/640 with a 70/200 f2.8 in good light.

Unless you've got the shakes bad, 1/250 is enough to prevent camera shake on a 75mm-equiv so IS makes no difference either way. Since you're using flash (I assume due to the lightscoop) then you'll be limited to something like 1/250 anyway. So shutter speed isn't an issue.

Try and keep the aperture around f/4 so you've got a decent bit of depth of field to minimise any focus errors. The 75mm-equiv focal length is a bit limiting, no? And will reduce depth of field. I'd take something wider or a zoom. A wider angle will make less demands on the AF system accuracy and give increased depth of field for the same aperture. Also easier to keep your desired framing with a zoom. 15-month-olds have a magnetic attraction to cameras in my experience so you're better off starting across the room at full zoom, and pulling back as the charging toddler approaches!

The idea of AF-S is simply that it will continually readjust focus if the subject-camera distance changes, so your idea of keeping the back button pressed is essentially the correct one. There's no magic to it, nothing else you can do. Of course using a cross sensor will help, but that's it. Maybe give the sensor a bit of contrast to work with, plain unpatterned surfaces don't give enough contrast. Keep the sensor over a bit of contrast (maybe a skin/clothes interface).

And it may simply be that the camera/lens combo isn't fast enough for a little bundle of energy. I find a D700 / 24-70 AF-S sometimes isn't fast enough!