AutoFocus - controlling factor
Discussion
I attempted to shoot my nephew at his TaeKwon Do competition in, what turned out to be, a dimly lit sports hall.
I didn't take my flashgun as I thought they wouldn't be allowed. So all I had was my 350D and Canon 28-135 IS. Despite shooting at max speeds of 1/40th at F3.5 and F5.6 I managed to get some good shots in (with blurred arms/legs due to movement). However, my question is this:
Is it the body or the lens that controls autofocus?
On some of my shots, despite the red dot focus indicator (whatever it's called) being slap bang in the middle of my nephews chest, the object in sharp focus is 2, maybe 3, feet behind him so he is slightly blurred. What gives, please? I have no idea why this happens. I wondered if the lens needs looking at, or the body, or ME
Thanks,
Scott
BTW - ImStab was ON - I need it
I didn't take my flashgun as I thought they wouldn't be allowed. So all I had was my 350D and Canon 28-135 IS. Despite shooting at max speeds of 1/40th at F3.5 and F5.6 I managed to get some good shots in (with blurred arms/legs due to movement). However, my question is this:
Is it the body or the lens that controls autofocus?
On some of my shots, despite the red dot focus indicator (whatever it's called) being slap bang in the middle of my nephews chest, the object in sharp focus is 2, maybe 3, feet behind him so he is slightly blurred. What gives, please? I have no idea why this happens. I wondered if the lens needs looking at, or the body, or ME
Thanks,
Scott
BTW - ImStab was ON - I need it
Sounds like plain old fashioned lack of light.
1/40th of a second is pretty slow (I use 1/60th to pan with slow moving cars, and it creates plenty of background motion blur), so anything that is moving will blur using that kind of shutter speed.
Increasing your ISO setting (maybe to 800) would probably allow you to use faster shutter speeds and freeze the action better. The images may be grainy, but that would be better than having them blurry
1/40th of a second is pretty slow (I use 1/60th to pan with slow moving cars, and it creates plenty of background motion blur), so anything that is moving will blur using that kind of shutter speed.
Increasing your ISO setting (maybe to 800) would probably allow you to use faster shutter speeds and freeze the action better. The images may be grainy, but that would be better than having them blurry
In answer... Both.
The Lens has the AF motors. The body has the AF sensors.
The sensors detect areas of contrast and use the motors to adjust untill theres as much of a split in contrast as possible.
But the sensors are working with the lens and how much light it lets in, AF works at wide open so an F2.8 lens will let in 4 * as much light for the AF subsystem than one at f5.6.
Anothe thing is the 350d is relativly poor in low light - its AF subsystem is rather poor & basic compared to the 20d+ and the modern versions. It doesnt have a cross point , it also doesnt have extra accuracy for faster lenses either. If there was one substantial area (after fa fuill frame sensor) I'd want updated would be the AF system on my 350d.
The Lens has the AF motors. The body has the AF sensors.
The sensors detect areas of contrast and use the motors to adjust untill theres as much of a split in contrast as possible.
But the sensors are working with the lens and how much light it lets in, AF works at wide open so an F2.8 lens will let in 4 * as much light for the AF subsystem than one at f5.6.
Anothe thing is the 350d is relativly poor in low light - its AF subsystem is rather poor & basic compared to the 20d+ and the modern versions. It doesnt have a cross point , it also doesnt have extra accuracy for faster lenses either. If there was one substantial area (after fa fuill frame sensor) I'd want updated would be the AF system on my 350d.
I'm guessing being a cheap canon it's got no AF illuminator either? Never understood that from canon. It's possible that faced with a complex scene, with front to back depth and it couldn't decide the best subject point so went hyperfocal - and focused 1/3rd of the way between the closest and furthest points identified. This would have been ideal at smaller apertures, not so good wide open...
In short try the following in the future:
- Faster lens (forget IS if need be), it will focus better and enable shorter shutter speeds over a similarly priced IS stuff (see all my previous rants about consumer IS lenses!)
- Try a monopod in lieu of IS. I find I get 3 stops with my Nikon VR lens, 2 stops with a monopod and 4 stops VR + monopod. If one isn't allowed, try the piece of string/washer monopod as mentioned here!
- Up the iso if needed, but don't forget to put it back afterwards! If you really have to shoot RAW and underexpose by a stop, then "push process" in photoshop (ie brighten), but this will push the noise through the roof.
- Position yourself so that movement across the frame is minimised if possible.
- Shoot more frames - if you hit one frame in three, take three times as many frames!
- Manually focus! It sounds obvious, but I'm finding myself switching to MF far more often as things go on.
Right, I'm off now before I get any more Rockwell.
In short try the following in the future:
- Faster lens (forget IS if need be), it will focus better and enable shorter shutter speeds over a similarly priced IS stuff (see all my previous rants about consumer IS lenses!)
- Try a monopod in lieu of IS. I find I get 3 stops with my Nikon VR lens, 2 stops with a monopod and 4 stops VR + monopod. If one isn't allowed, try the piece of string/washer monopod as mentioned here!
- Up the iso if needed, but don't forget to put it back afterwards! If you really have to shoot RAW and underexpose by a stop, then "push process" in photoshop (ie brighten), but this will push the noise through the roof.
- Position yourself so that movement across the frame is minimised if possible.
- Shoot more frames - if you hit one frame in three, take three times as many frames!
- Manually focus! It sounds obvious, but I'm finding myself switching to MF far more often as things go on.
Right, I'm off now before I get any more Rockwell.
Thank you for all your input. It helps me to understand what is happening and that it might (small might ) not all be down to me. I also have an idea on how to resolve it in the future. Great stuff.
Due to the poor light and slow shutter speeds I knew anything other than static shots would be a problem. I had no intention of trying any kind of panning shots as I knew they would be complete garbage (plus I haven't been panning for long) so these were static person shots, just with the arms and legs in motion, taken at intervals through their pattern/sparing. Majority of the shots were taken using standard focus option but I did try some on servo mode, just incase any forward movement did occur.
For this kind of event, and for portraiture, I was thinking of getting the Canon prime 50mm F1.4. I've read so many good things about it, I can't believe it's less than 70 squid!!
Thanks again for the good, concise information, advice, and for slamming my choice of camera
Cheers,
Scott
) not all be down to me. I also have an idea on how to resolve it in the future. Great stuff.Due to the poor light and slow shutter speeds I knew anything other than static shots would be a problem. I had no intention of trying any kind of panning shots as I knew they would be complete garbage (plus I haven't been panning for long) so these were static person shots, just with the arms and legs in motion, taken at intervals through their pattern/sparing. Majority of the shots were taken using standard focus option but I did try some on servo mode, just incase any forward movement did occur.
For this kind of event, and for portraiture, I was thinking of getting the Canon prime 50mm F1.4. I've read so many good things about it, I can't believe it's less than 70 squid!!
Thanks again for the good, concise information, advice, and for slamming my choice of camera
Cheers,
Scott
kybo said:
I was thinking of getting the Canon prime 50mm F1.4. I've read so many good things about it, I can't believe it's less than 70 squid!!
It's not, the f/1.8 version is that price, 1.4 is about £240 iirc. I'd have thought you'd need a bit more length than 50mm tbh, but then you have got the cropped sensor so maybe it's not such an issue, it's quite wide on my 5D if you want to fill the frame with a person you've got to get pretty close to them.
My mistake.Gassing Station | Photography & Video | Top of Page | What's New | My Stuff