January 13th, 2010 by ariana
I have been getting a lot of questions about focus recently, and I think it’s a good topic to discuss because so many of you are new to DSLRs and focus can be a sticky issue at first (and always to some extent!)
Here is a common scenario:
You get a new DSLR and you immediately realize that when you use program mode with your kit lens, the camera wants to use the flash all the time but your pictures look god awful, probably not much better than your point and shoot! So you do some research and maybe come across a post like mine that tells you to NEVER us your pop up flash. Aha!
So you set your DSLR to force the flash off. Now, you are maybe still in program or even AV or TV mode but you notice that your images are always blurry.. so you do some more research and learn that you need to upgrade that crappy kit lens to something like the universal first upgrade lens the 50mm 1.8 (nifty fifty).
Now, you can open up your aperture all the way to 1.8 and let TONS of light in.. yippee!! And at first you are so happy, because you are getting tons of beautiful lens blur (bokeh) and your images are staring to look more artistic. Awesome. But then, as your eye starts to become more trained you notice that your images look “soft” if not downright out of focus compared to the images of photographers you admire.. but you don’t know why.
Sound familiar? Yeah, to me too, because this was ME a year ago!
There are TWO main reasons (Ok actually three in my case, but the last one is more rare) that you might not be nailing focus:
1) Focusing technique
2) Settings (aperture/depth of field and shutterspeed)
3) A problem with the lens itself – again, rare but it happened to me so I want to include it.
Let’s tackle them in order..
Focusing Technique – Yes, there are actually techniques to achieving good focus!
The first focus rule is that you should always (except for certain artistic situations) strive to have the subjects eyes in focus, so you should use the forward eye as your focal point. Ok, that one is easy, but I have to say it because I didn’t realize this when I first started shooting!
Now for the more technique part: There are TWO methods to focusing, one is called “focus recompose” and the other is to toggle the focal points on your DSLR to manually choose the focal point closest to the eye of your subject in the composition in front of you.
There are actually two other types of focusing, one where your camera automatically tries to select one or two focus points FOR you and also AI Servo mode, but I don’t recommend these modes because we are striving to learn and control our focus, not let the camera make it’s own decisions. So for the purpose of this post, lets assume and/or turn our focus mode to use manual focus select. To do this, you need to press the autofocus select button – on canons it’s the button circled on the top right and then use the joystick arrows to move the focus points around on the rebel models:
OR my preferred method which is to use the wheel that is just behind the shutter to toggle:
Ok, so lets put this to practical use..
So assume I want this composition for my image:
Notice his right eye is closest to me and the one that I want to focus on:
So I want to use that focus point that is closest to his front eye by manually toggling my focus points to get to the one closest to where I want to focus which is what I actually did to take this image.
Now, you can imagine the downside to this is that if you want to change your composition around a lot, it can take a bit of time to keep toggling these points. So that’s where the “center recompose” method comes in more handy.
To focus recompose you set the center point as your focus point, then you move the center point to the area you want to focus on, lock focus and then recompose.
So for example to compose this image I would move my camera over Jasper’s face until the center point fell on his forward eye. I would depress the shutter halfway to lock focus and then without lifting my finger I would move the camera back to compose the image the way that I wanted even and only THEN would I press the shutter all the way down to take the picture. For you visual learners, here is a youtube video demonstrating that method.
There is a rather large caveat when using the focus recompose method which is that when you are shooting with a VERY narrow depth of field it can actually cause focus errors because even that little shift to his eye and back will cause your focus to be off. There is an entire web page devoted to “why focus recompose sucks” and it is true in certain situations. Those situations are when you have a really narrow Depth of Field (DOF) caused by your settings and distance to subject (and also your lens’ focal length.)
Narrow DOF is a bit beyond the scope of what I want to discuss today (click here to read about it on wikipedia), but as a general rule the closer you are to your subject and the wider your aperture, the shallower your DOF will be and in THOSE situations, even the slight shift of your camera angle while focus recomposing can actually make the focus fall somewhere other than where you intended.
Furthermore, if your DOF is extremely shallow and your subjects eyes are not squarely facing you on the same plane, it’s likely that even if you do get the front eye in focus, the back eye will not be because it is further back or on a different focal plane. This is why shooting at wide open apertures when subjects are close to you is very tricky for nailing focus, and one of the reasons that people start to notice they have focus issues when upgrading to the nifty fifty..
After all, with the kit lens you can’t go wider than say 4.0, which means that your DOF is narrow enough that you won’t have these issues! (You may have OTHER issues, but that’s a whole other matter :)
Here’s an example:
Looks ok small, but when you look at it larger, you can see that his back (left) eye is softer focus than the right eye. This is because I was really close to my subject and I was shooting at 2.8. To get both of his eyes in focus I would need to have either backed up, closed up my aperture a bit or positioned him so that his eyes were both the same distance/angle from my camera lens (yea right!).
So don’t be like me when I first got it and dial your nifty fifty all the way open to 1.8 JUST BECAUSE YOU CAN when 3.2 or even 3.5 will still give you enough light and lovely bokeh and a lot more wiggle room in regards to focus.
Which brings me to Part II: Settings!
Settings are extremely important as you can tell from the above few paragraphs, and often the aperture is too wide open, but even MORE likely is that your shutter speed is not fast enough. Well, I shouldn’t say that it’s more likely, what you really need to do is examine your images and see if the entire image is soft or if there is an area in focus but just not the area you WANT to be in focus! If the area in focus is not the one that you intended, chances are you are dealing with too shallow DOF or a focus technique issue. If your entire image is out of focus (OOF) or soft then most likely you are not using a high enough shutterspeed to freeze the action of your quick moving toddler!
The general rule is to double your focal length with shutterspeed.. so if I am using a 50mm lens, I need AT LEAST a shutterspeed over 1/100, but for babies you really need much more than that because I think that rule was written with cooperative adults in mind!
If you had all the light in the world (or are using a speedlite), you would be able to keep your shutterspeed always up over 1/200th or so. But we all know that doesn’t always happen, so what are your options? You can sacrifice either your aperture opening wider OR crank up your ISO to let in the extra light to be able to keep your shutterspeed high. Now before reading this longwinded neverending post, you MIGHT (like I used to) always choose to open your aperture all the way to 1.8, but now you know that you will have a hell of a time getting perfect focus at 1.8, so you might want to compromise and go a little less wide on the aperture and compensate with raising your ISO. Yes, high ISO produces noise on entry level DSLRs (this is one of the main reasons I upgraded to the mark II) but you can run your images through free community versions of noise reduction software like noiseware and neatimage.
I used to always err on the side of lowering my shutterspeed because I HATED the noise I got on my rebel at 400 ISO or above, but then I realized that motion blur was ruining my images a lot more consistently then too much noise – there is no software that can take your OOF image and make it in focus!
All of what I just said in the previous few paragraphs assumes that you are shooting in manual mode. Why? Because if you are shooting in P, AV or TV modes you will not have the kind of control you need to MAKE the correct trade offs and decisions about where you have room to let more light in, SS, aperture or ISO. Ask me how I know this is not the right thing to do…
Ok, I’ll show you!
Here is an image I shot of baby Jasper:
Totally OOF. And now that I look at the settings in Flickr it’s very obvious why! I was shooting in AV (aperture priority) mode with my aperture at 2.8 – ok, fine, but the necessary shutterspeed that the camera gave me for the amount of light I had in the room was 1/15th!!! I should have shot in manual mode, opened my ap up a little bit more AND either raised my ISO even higher or better yet, found more light so I could just raise the shutterspeed with out having to up the ISO higher than 800.
And now the last possible (rare, but not as rare as it should be) reason you are not nailing focus well..
A defective lens
After months of not getting my focus correct, I noticed that almost ALL of my images were not focusing where I wanted them to, even when I DID toggle the focus points and use a wide enough aperture and fast enough shutterspeed. These images look something like this one:
A blurry subject which is where I wanted my focus to fall, but an IN focus area (notice that the zebra stripes in the left foreground are perfectly sharp). Now, this can happen in some images, but this was happening in ALL of my images, even when I did use a narrower aperture or a high shutterspeed. At this point, I started to suspect that there might be something wrong with my lens.
To make a long story short, I STILL wasn’t entirely sure that it wasn’t my fault even after I sent it in to Canon to be serviced, so felt very vindicated when the lens returned from Canon and they confirmed that it did indeed need to be adjusted.
Like I said, this sort of thing is rare for a new lens, so is definitely not the first thing you should suspect if you have focusing issues, but if you really focus on technique and settings and still see no improvement after giving yourself ample time to master these skills, you might start investigating this option.
Ok, now – any questions?? ;)
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