troubled with focusing

[deepakaa]

Hello

I use D7200 with nikkor 50 mm f1.8 prime lens.

I am facing a lot of challenges photographing running/playing kids...i don't get to keep them in focus and the snaps don't come out sharp enough...

The way i was doing is :

I shot using AF-ON with Back Button keeping AF setting on AF-C d51.
I used centre focus point and focus on the kid then recomposed while keeping the back button pressed and then kept the back button pressed while i kept shooting the kids running around..
Aperture was between f4 to f6 and distance from the subject was far enough to get good dof...
shutter speed was at least 1/250 or more... as i shot some snaps using external flash, was limited to 1/250....but other times used higher speed...

but most of the images turned out soft....

could you pls throw some lights what am i doing wrong or how to focus on such scenario...

Also, when we focus using AF-ON with AF-C d51 then focus and recompose, and keep the back button pressed ...where does camera focus...? does it focus where the focal point is or where the focal point was prior to recompose ?

Getting soft images is to do with the lens ?? is it that 50 mm prime lens is not fast enough to keep running kids constantly in focus ? do i have to use higher quality lens like 70-200 ??

Looking forward to some good help pls.
Thanks in advance.

 

[Peeb]

Shutter speed high enough?

 

[deepakaa]

oh yes, thanks i forgot to mention...shutter speed was at least 1/250 or more... as i shot some snaps using external flash, was limited to 1/250....but other times used higher speed.....
i have updated initial post
looking forward to some insight on the subject...

 

[vintagesnaps]

At least part of it is your aperture is probably too large so the field of view is too shallow. Set for a smaller aperture so the field of view will be larger (more deep) and more area will be in focus.

If you're closer to a subject you could go to a larger aperture for a close up shot. With sports or action you're usually trying to get a number of subjects all in focus.

Maybe try a faster shutter speed, although 1/250 could be fast enough; depends on how fast the subjects are moving. Try various settings and write down what you did so later you can go through your photos and figure out what worked better.

 

[snowbear]

Post an example with the EXIF (shutter speed, ISO, aperture, etc) an someone can probably tell you what's happening.

 

[Overread]

Few thoughts:

1) You say that you focus with the middle AF point and then recompose the scene. If you do this then remember that focusing isn't smart. It's not picking up the subject itself its just detecting a contrast difference at the closest point under the AF sensor whilst the AF sensor is active. If you recompose the plane of focus (think of it like a book parallel to the front of the lens with teh thickness of the book being the depth of field - ergo aperture) then you can move that plane of focus off the subject.

IF the subject is also moving then chances are the subject will move right out of the plane of focus very easily.


I would recommend use whichever AF point feels comfortable for the scene when working with action. Practice and a good camera can let you use other AF points, but sometimes its just a LOT easier to use the middle point and compose a little wide and then crop the result to suit taste - better that than missing shots.

2) 1/250sec is rather slow for action; I would lean closer to 1/500sec as a rough slowest shutter speed; any slower and things start blurring. Using flash is likely not helping; the built in flash is small and will throw a very harsh light; plus if you're at any distance chances are its not giving you a very good light anyway. Better to use a higher ISO and a wider aperture - you should be able to shoot most sports/action with f2.8 or f4 with reasonable success (depending on what you want of course; this is only a "rule of thumb" so by all means vary your apertures to suit your desires and scene

3) A 70-200mm is a go-to lens for many shooting sports. It suits the situation really well especially as you're back from the action. A 50mm is doable but can be a bit of a pain and you might have to crop a fair few shots. Of course a good quality f2.8 (ideal) or f4 (good solid choice; just not as wide a maximum aperture - important if you're ever shooting sports indoors or in the evening/morning/dull days).

 

[dennybeall]

A point or two.... shutter speed if camera is fixed and kids are subject at 1/250 should be good enough But if camera and kids are both moving then need more speed. Try 1/500 and jack up the ISO to handle it with iris at f8 or perhaps f10.
Also - put camera on tripod and shoot a fixed object. See if the photo is as sharp as you want it to be. That way you'll know the lens and camera can take sharp photos and you can start trying other things like speed and DOF.

 

[deepakaa]

Thanks alot for the feedback everyone.

@ Overread :
so, i understand that i should not focus and recompose ....my question now is how does AF-C work ?
lets say i am photographing two kids running around. Both Kids are running from Point A to Point B together and i will take 5 successive/continuous pictures (on single shot mode, not burst mode) between their running from point A to point B.

Now, camera is set on AF-C d51. I am focusing using BBF. I use 50 mm f.18 prime lens on d7200.
Camera setting is f4, s 1/250, iso 800 and i am far enough from the subject to get good DOF.

while taking the 1st picture, i focus on the Kid 1 using lets say focal point A by pressing back button.
Now to take the next pictures i keep the AF-ON button pressed and click successively 4 other pictures (on single shot mode, not burst mode)

So question is how focusing works in such situation. As i am using AF-C d51, will the camera sort of "track" the subject (i.e, the kid 1) and keep it in focus in all 5 pictures even if i keep camera steady while i see kids running from point A to point B in my view finder and also don't move my focal point ?

or, in order to keep my subject (i.e, the kid 1) in focus in each picture i have to move the camera with the subject to keep the focal point A on the subject all the time in all pictures while keeping AF-On button pressed ?

 

[Overread]

or, in order to keep my subject (i.e, the kid 1) in focus in each picture i have to move the camera with the subject to keep the focal point A on the subject all the time in all pictures while keeping AF-On button pressed ?

This is correct, the camera cannot "see" a child. What it looks for is a difference in contrast under the autofocus point and it locks onto that. So you've got to keep pointing at the child in order to keep telling the camera that is what you want in focus; if you keep the camera still and the child moves past the AF point the camera will lock into a new contrast difference.

The AF mode you are using does try to use AF points either side of the active one to help keep the subject in focus; it is trying, but its only helping. You've still got to keep the Af point moving with the subject.



Note that the contrast difference is why when you try pointing the camera at a white wall or a blue sky it can sometimes fail to focus; because the scene has no difference in contrast for the camera to easily lock onto (of course in reality there can be subtle changes that do let it lock on most times).

 

[benhasajeep]

Your camera should have a setting that shows what AF point was used in taking the picture. Turn that on in your settings menu's. It will then show up on the monitor (not in final .jpg) when you review the pictures on camera. Also take the camera out of D51 and go to either Single point (just 1 af sensor) or D9. With D51 you have all 51 of the sensors active. And the camera could actually pick any of them.

No matter if your using back button focus or shutter release focus. AF-C is the mode you would used for kids moving around / playing. But the different AF point selections makes a difference. Single point, D9, D21, and D51. With D51 all the primary AF points are active. With D9 the one you picked and only the 8 around it are active to pick up / track AF.

Depending on how far / close you are to the kids. F/4.0 to f/6.0 might not be enough range of sharp focus. The closer you are the smaller the area of sharp focus is.

And last, the AF system is not fool proof. Especially if you have AF confirmed turned off for shutter release.

And one last tidbit. You should test the lens to see if it's front focusing or back focusing. There are many articles on the internet to test your lenses for this.