Help with AF mode and metering

[Michele]

I saw there was another thread with indoor basketball question, but I didn't want to hijack that thread. So here are a couple questions I have. I have my AF point set on center, and the camera set on AI Servo. I am getting lots of blurry pictures that I think shouldn't be. Look at these 2. I focused the center point right on #45, but why is one shot coming out blurry?

And then with the metering, I have it set on evaluative. I am snapping these shots on continuous mode, so they are just seconds apart. But look at the strange coloring, half the picture dark in the first one and the middle of the picture dark in the second one.

Are the AF focus point and metering mode my problems?

More details: I am using the Canon 40D, 50mm 1.8 lens for the speed, f/1.8, ISO 1250, Shutter-various, mostly 1/250


Thanks for any input.

 

[jann1033]

i don't have my glasses on( disclaimor) but it looks to me like you are missing your intended target.. the guy behind the kids in the jacket looks sharper to me..at 1.8 you have such a shallow dof it's hard to get a right on focus. for kids in the row, do you have a dof selection( the last one on the dial on my rebel xt) ? it's for a line of something so they are all in focus.
can you up your f stop some? at 1/250 neither of those examples are really moving fast( and 250 isn't rally fast enough to stop action anyway) and it would help enlarge the area in focus. you could go to 70 ish shutter with your lens( or whatever 50x1.6= )
noise levels look good though for 1250

 

[MICKEY88]

if the first 2 are posted in order they were taken it's possible that first is blurred due to camera movement, since the 2nd was fired in succession the camera movement will have already occured, so it would be sharper..

with the cheerleader pics, although they are similar, the one shows more of the center ceiling light , that's enough to change your metering,

if the light is fairly consistent from one spot in the gym to the next, try setting your shutter speed as well, that way your pics will be more consistant, if you shoot raw it will be really easy to make minor exposure corrections..

 

[GrillMouster]

It looks like focus was on the background in the first shot, then it was on the foreground kids in the second shot. It's easy for this to happen , especially when the background and the foreground are so close to each other around the AF point. Also, the camera could have just been hunting for focus. Sometimes in our haste we release the shutter fully before the AF has a chance to reach focus. Often AF is just too slow, particularly in low light. In these situations you may want to consider manual focus. Additionally, notice that in the second photo, the boy in the center is in relatively sharp focus, but the boys at camera right are not as sharp. This is due to the shallow depth of field. Sometimes DOF can be so shallow that even the focus + recompose technique with the center AF point can be problematic.

The differences between the two shots of the cheerleaders aren't hugely dramatic, but what Mickey88 is true. Even slight changes in the scene can afffect metering. A tiny bit more of the ceiling lights are in the frame in one image than the other. It may have been just enough to cause the meter to select a different shutter speed, since you're using evaluative metering (which takes the entire frame into consideration). The difference in ambient light exposure (notice the yellow flag on the wall) suggest this is the case. Center-weighted metering or spot metering might not have done this, but I am NOT suggesting that you should have used either of those metering modes in this situation. Evaluative/Matrix/whateveryourcameracallsit is pretty darn good in most situations. It might be helpful to know the exact EXIF data for each of these images.

I don't think there's any defect with the camera or the AF/metering settings you're using. They're probably working exactly as designed. With practice you'll learn the nuances of your camera and know when it's appropriate to compensate.

 

[caniswolfie]

I think I can answer the focus issue. Since you had the camera in the AI Servo mode of focus, the camera is constantly trying to capture focus. AI Servo mode is usually used with subjects that are in constant motion and need focus to track the target. Sometimes if the subjects are not moving, the camera gets confused and hunts focus. You might have caught the camera adjusting focus during the continuous shots.

I have also heard that the lights in Gyms are typically very hard to work with. Things like the lights tend to warm up and cool down causing weird color casts and light issues. It's possible some of the lights were in the middle of a color/luminance shift and that the metering was confused.

 

[handicap18]

What are you using for the auto focus? Is the camera selecting the subject or are you using one of the focus points?

In the first 2, the background is clearly in focus and the kids in the line up are out of focus in the first and it is opposite in the 2nd. This is a focus point thing? I would make sure your using one of the options where YOU choose which focus point is going to be used for focusing, not the camera.

When using a very wide aperture, your best bet is probably to use One Shot AF and Spot Metering. (doing a quick internet search, there seem to be a lot of Canon users who agree that One Shot Focus is more precise in low light situations) I would use the center point as the focus point, then hold the focus and recompose the shot if needed. If there was more movement, then AI Servo AF would be better. From what I understand of Canon's AF, AI Focus will make the camera choose what focus points to use and what will be in focus.

 

[Groucho]

Another possibility is that the camera doesn't even think it's focused when you take the shots... I'm not sure how yours works, but on mine, when in continuous AF mode, it will allow you to take a shot "right now" even if it hasn't grabbed focus. If you want to guarantee focus, you wait for the focus confirmation light/beep. This threw me the first few times when I was using that mode in challenging light - in PotC, I think. I hadn't used that most often on my previous DSLRs since it took a visit to the menus on those rather than an external switch.

 

[jann1033]

while all these are good suggestions i am betting on the lens, mainly cause i never use that lens at f1.8 because it is a bear to focus . i have some shots that look just like these first 2,taken indoors, outdoors,any light, the only common denominator being the lens at 1.8 you probably have plenty of room to up the f stop since you have a fairly fast shutter speed if most are at 250. for a shot like this that is basically stationary anyway, try it at f4 or even 8 if you can keep the shutter speed up high enough for the lens length
i don't think it's anything wrong with the camera( although i have used the servo with moving objects since that is what it's intended for, i haven't had a problem with it for the occasional still objects. from what i understand it is supposed to lock focus on that object but i can see it could be a problem occasionally) although i do use the center focus point only and center metering since they work better imo. ( mine doesn't have spot)

 

[Michele]

can you up your f stop some? at 1/250 neither of those examples are really moving fast( and 250 isn't rally fast enough to stop action anyway) and it would help enlarge the area in focus. you could go to 70 ish shutter with your lens( or whatever 50x1.6= )

Yes, I should maybe try upping the f stop.

if the first 2 are posted in order they were taken it's possible that first is blurred due to camera movement, since the 2nd was fired in succession the camera movement will have already occured, so it would be sharper..

with the cheerleader pics, although they are similar, the one shows more of the center ceiling light , that's enough to change your metering,

if the light is fairly consistent from one spot in the gym to the next, try setting your shutter speed as well, that way your pics will be more consistant, if you shoot raw it will be really easy to make minor exposure corrections..

Camera movement would seem the most likely culprit, I made extra sure that I had the AF point right on #45, and yes they were fired in succesion so that would make the 2nd one clear. Wait, then again the background people wouldn't be in focus if camera movement was the problem.

With the evaluative metering taking in all the area around the cheerleaders and the lights possibly making that big a difference, do you think partial metering would be a better choice? It would be not as narrowed down as spot but perhaps taking in a bit less of the extreme outer areas.

What are you using for the auto focus? Is the camera selecting the subject or are you using one of the focus points?

In the first 2, the background is clearly in focus and the kids in the line up are out of focus in the first and it is opposite in the 2nd. This is a focus point thing? I would make sure your using one of the options where YOU choose which focus point is going to be used for focusing, not the camera.

When using a very wide aperture, your best bet is probably to use One Shot AF and Spot Metering. (doing a quick internet search, there seem to be a lot of Canon users who agree that One Shot Focus is more precise in low light situations) I would use the center point as the focus point, then hold the focus and recompose the shot if needed. If there was more movement, then AI Servo AF would be better. From what I understand of Canon's AF, AI Focus will make the camera choose what focus points to use and what will be in focus.

I was using the center AF point, that's why I couldn't understand how the 1st one wasn't in focus, I made sure that center point was on #45. I think I should have switched to One Shot AF for these halftime shots. These kids were shifting around on their feet and maybe AI Servo was searching for a focus. But I was taking pictures of the game as well and thought AI Servo would be best for all that movement. When set on AI Servo, you don't get that beep letting you know focus has been locked.

I'll just have to get better at switching all these settings back and forth between the game and the other more stationary action.

 

[jann1033]

sometimes i wonder if just depressing the shutter is enough to move the focus , in number one( again glassless and to lazy to go down stairs to put them one ) the focus looks like it was on the area behind the boy with number 45, that railing appears fairly sharp there as does "Bulldogs"..i've come to the conclusion with that lens i probably really need to use a tripod/remote/timer( not always possible) if i really need to use f1.8, but then really don't need to use f1.8 in many situations if i am using a tripod. one of those catch 22 deals...don't know if i have a heavy shutter finger or what but i was so irritated with that lens i took it out and shot with it all day to see what was going on, with mine it's good at f4-8 or so, even f2+is ok usually but really hard, bordering on impossible, to get the right focus on f1.8. could be my copy I guess but it's one reason i never use that lens. it's sharp if i can catch the focus but for really low light, not all that useful for me..

 

[Michele]

Well, I took the same camera and lens to a game again last night. I tried some of the things we talked about here. I got a much better set of pictures. They were all taken in the same gym.

Just noticed I didn't even post any action shots from Tuesday night. I can't believe the lighting difference in these two pics with exactly the same settings and taken just seconds apart.
These first 2 from the first game, Tuesday night.
f1.8 1/400 ISO 1250 Evaluative metering

f 1.8 1/400 ISO 1250 Evaluative metering

Last night I switched to a higher f stop, partial metering and a bit lower on the ISO and shutter speed. ETA: Also changed to One Shot AF mode instead of AI Servo and chose all AF points instead of center. I got MUCH better results.

f 3.2 1/125 ISO 1000 Partial metering

f 2.8 1/125 ISO 1000 Partial metering

Thanks for all the help! It paid off.

 

[Groucho]

It looks to me like the big difference between the first two is the white balance... I think it's a more yellow white balance which gives the photo a slightly darker look.

The exposure does look a little different, too, though... perhaps from the strobing effect of the lights they're using?

 

[GrillMouster]

I think you're right, Groucho. The exposure on the first two looks pretty much the same, but the color is different; one is warmer. Where you using auto white balance, Michele?

Another thing...I don't know what kind of lighting they're using at the gym, but fluorescent lights can fluctuate in brightness & color. Sometimes you'll notice this happening, but sometimes it's faster than we perceive, but the camera can catch it.

 

[Michele]

It looks to me like the big difference between the first two is the white balance... I think it's a more yellow white balance which gives the photo a slightly darker look.

The exposure does look a little different, too, though... perhaps from the strobing effect of the lights they're using?

Funny, that's one thing I didn't change, I took them on AWB both times. I wondered if the metering mode made the difference. They were taken in the same gym so I expect their lighting would have been the same.

ETA: GrillMouster- I'm not sure what kind of lights they have, but maybe they were flourescent.