Focusing Issues and Question

crowl31 · Jun 20, 2008

My brother had a baby yesterday and I was taking some pictures with my Canon 50mm 1.8. The pictures came out great but I ran into a issue.

When two people are together I tend to get one face in focus but the other will be soft or almost blurry like the background.

What can I do to get more focus in the picture?

dEARlEADER · Jun 20, 2008

this is because of shallow depth of field...

you would have to use a smaller aperture (try f7 for example)

depending on lighting... you may have to introduce flash... or longer exposure time on a tripod....

Big Mike · Jun 20, 2008

The problem is that you DOF (depth of field) is too shallow.

DOF is controlled by a few things. The main factor is the aperture that the lens is set to. The larger the aperture (lower F number), the more shallow the DOF will be. So with a lens like that, you might be shooting at F1.8, which is very large, which gives you a shallow DOF. That can be great when you only have one subject and you want the background to be out of focus...but when you have more subjects, you might need to 'stop down' the aperture to increase the DOF.

The focal length, the distance to the subject and the size of the film/sensor will also affect the DOF but aperture is the primary means by which we control it.

Try setting an aperture of F2.8 or F4, that will give you more DOF but it will also mean a slower shutter speed compared to what you get at F1.8...so you have to be careful that you don't go to slow with the shutter, to avoid blur. If you need to, you can increase the ISO to raise the shutter speed.

ANDS! · Jun 20, 2008

If you are keeping the thing in def ault 1.8 - youre not going to get all of their faces in focus. 3.5 and up should be fine depending on your artistic tastes and how tight they are in to each other.

Also, does your camera have a DOF preview?

crowl31 · Jun 20, 2008

I tried to go down F stops but then I ran into the issues with blurry pics because my hand wasn't steady.

If I shot a faster ISO would that help increase the speed and less time of my hand having to be still?

Big Mike · Jun 20, 2008

If I shot a faster ISO would that help increase the speed and less time of my hand having to be still?

Yes.

The exposure is the result of three things. The aperture of the lens, the shutter speed and the sensitivity of the medium (ISO). So if the light stays the same, when you change one setting you (or the camera, depending on the mode) compensates by changing one of the other settings.

So if you were shooting at F2.0, 1/250 at ISO 100. You could stop down the lens two full stops (in Av mode) to F4. That would change the shutter speed to 1/60, which should still be enough to get a reasonably sharp shot. But you could then adjust the ISO from 100 to 400 (two stops) and that would bring the shutter speed back up to 1/250.

The trade off is that higher ISO levels will give you more digital noise...but noise is better than blur so don't be afraid to turn it up.

The rule of thumb for hand holding and blur...is that you want a shutter speed that is the same number or higher than the focal length of the lens. So for a 50mm lens, you will want to keep the shutter speed at 1/60 or above. Faster is better.

crowl31 · Jun 20, 2008

Just for my own sanity, 1/250 is faster then 1/60 right?

So by going to F4 ISO of 400 I will be able to get more focus in the shot and a faster shutter speed?

Big Mike · Jun 20, 2008

Just for my own sanity, 1/250 is faster then 1/60 right?

Yes...they are fractions of a second...so the bigger the denominator, the smaller the actual value (less time = faster).

So by going to F4 ISO of 400 I will be able to get more focus in the shot and a faster shutter speed?

If you started at F2.0, and ISO 100...then you could keep the same shutter speed by going to F4 and ISO 400.

If you needed more DOF, you could stop down the lens two more stops, to F8. Then shutter speed would drop to 1/60 but that might be OK. You could also bump up the ISO to 800 or 1600 but noise will start to be an issue.

It's all a matter of give and take.

I suggest keeping the camera in Av mode, then you select the aperture that you want, that will give you the DOF that you need. The camera will give you the shutter speed...and if you notice that the shutter speed is too slow, then you can turn up the ISO.

Of course, maybe you don't want to turn up the ISO as high as 1600...so then you may need to compromise the DOF that you wanted. Maybe you could move your subjects so that they are the same distance away from the camera, then they would both be in focus, even with a shallow DOF.