Question about focus

[Jace]

I realize that this may be addressed in the tutorial section, but may be under something that I'm not familiar with yet. I also know how fast this forum moves and as soon as my question is answered this thread will be buried, lol.



OK, what is the process or technique for this:


You have a person standing in front of a fence, leaning on it that is, and behind them is a forest. How would you have just the person and the fence in focus, making the forest blurred. Same thing for having two people on a lane or in front of a building, and the entire focus on them, the background, even close to them, blurred somewhat.


Again, I know this has probably been answered, I'm just afraid that it deals with aperture or shutter speeds and I wouldn't be able to find it, yet.

Thanks!


Oh, a tack-on question. I only have a PowerShot XS20 IS, though it isn't a DSLR it does have p-m settings. (I know I need a DSLR, but you try telling my wife that when we just bought her a new camera last weekend...)

 

[PJL]

What you're talking about is depth of field, which is determined primarily by aperture, but also by focal length and distance from you to your subject (and from your subject to the background).

Depth of field determines how much of the picture is in focus, so you want a relatively shallow depth of field if you want part of the picture to be in focus, but the rest to be out-of-focus. You'd do this by using a wide aperture (small f/stop number), using the longest focal length you can comfortably use to frame the shot while being relatively close to your subject. Also, the further the background is away from your focal point, the more out-of-focus it will be. Try putting your camera into P or Av mode (if you can) and setting it so that the f-stop is the lowest you can make it. Granted, you're not going to get as good results as if you were using an SLR, but it's a start.

 

[Big Mike]

Every photo has what we call the 'Depth of Field' (DOF). The DOF is the range of distance (from the camera) that will be in focus. Things that are outside the DOF, will be blurry...the further out, the more blurry they will be. What you are looking for is a shallow DOF.

There are 3 main things that control DOF.
The first is the lens aperture. A larger aperture (represented by a lower F number) will give you a more shallow DOF. And opposite to that, a smaller aperture (higher F number) will give you a deeper DOF. So to get what you want, try to use a large aperture (small F number).

The next one is focal length. A longer focal length gives you a shallower DOF, so use a long focal length (more zoom).

The next one is distance to the subject. The closer you are to your subject, the more shallow the DOF will be. So get close to your subject. This will likely have to be a compromise with using a longer focal length, because you may not get the composition you want if you both zoom out and get closer.

So using those tools, you can shorten your DOF. But another point to think about, is how far behind your subject the background is. The further away it is, the further out of the DOF it can be...thus the more blurry it can get. So if you can get your subjects further away from the background, that will allow you to blur the background even more.

Lastly, you are at a bit of a disadvantage with your camera. Like almost all 'point & shoot' digital cameras, yours has a very tiny image sensor. This tiny sensor causes your camera/lens to give you a much deeper DOF than if you had a larger sensor. So when you see all those nice photos with blurry backgrounds, it's very likely that they were taken with SLR type cameras and not digi-cams. But you can still get the effect you want, if you use the techniques mentioned above...but maybe not to the degree that you've seen else where.

 

[PJL]

Mike, you're following me around this morning :hug::

 

[Jace]

Sweet I think I did it! Thanks!

 

[Big Mike]

Mike, you're following me around this morning :hug::

I've noticed that.
I guess that means I can take a break, because you're doing a great job at answering people's questions.

 

[KmH]

Focal point to image sensor distance affects DOF more than a specific lens aperture, but all 4 of the factors that affect DOF have to be considered.

Many dSLR cameras have a DOF preview button, though because the main mirror is only 50% reflective to allow auto focus, the DOF preview provides a pretty dark viewfinder image when used.

Here is a good DOF tutorial: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

 

[PJL]

Mike, you're following me around this morning :hug::

I've noticed that.
I guess that means I can take a break, because you're doing a great job at answering people's questions.

Nah, don't do that. I have to get some work done here eventually