PDA

View Full Version : F stop struggles?



tnelson42345
09-29-2008, 12:53 PM
I want to work on blurring out the background and foreground of my pictures. I have played with the fstop feature but I haven't had a lot of luck. To blur out the background would I use a smaller fstop number or larger and I assume the other would be the opposite?

What else do I need to watch for or focus on? It could be a camera limitation I suppose but I have accidently done this a few times. I have a Canon S5. Thank you for any advice!

JLV
09-29-2008, 04:16 PM
Focus on your subject. Use a large lens opening such as F2.8. The lens on many none SLR digital cameras have a larger depth field, that may be why you are having troubles.

Rhys
09-29-2008, 04:49 PM
Ah... Depth of Field depends upon several variables...

Sensor/film size
Lens length
Distance from sensor/film to subject
F-Stop.

Generally it is more difficult to achieve shallow depth of field with smaller sensors. There is a formula used to calculate DOF but quite honestly I'm not all that fond of maths and I don't think most people are either.

Thus...
greater distance = more depth
smaller aperture = more depth
shorter lens = more depth
smaller film/sensor = more depth.

Look here: http://www.dofmaster.com/dofjs.html

JLV
09-30-2008, 04:53 AM
I meant to add extend your zoom to the greatest telephoto length that is practical.

Razr
10-23-2008, 01:39 PM
I want to work on blurring out the background and foreground of my pictures. I have played with the fstop feature but I haven't had a lot of luck. To blur out the background would I use a smaller fstop number or larger and I assume the other would be the opposite?

What else do I need to watch for or focus on? It could be a camera limitation I suppose but I have accidently done this a few times. I have a Canon S5. Thank you for any advice!

Read up on "hyperfocusing" and "hypefocal distance".

You generally neeed fast lenses (at least f/2.8 if a zoom), to sucessfully do what you want.

Tricks:
shoot in AV mode with the widest aperture available to you on your fastest lens.

1. make sure your subject is close to you.
2. make sure your background is clear of clutter and objects like trees, fences and vertical/horizontal lines:
the clearer your background, the more "blur"
3. dark backgrounds help
4. focal lengths of about 140mm+ also help
5. all of the above

Using the proper techniques (1-4) works nearly 100% of the time

zmikers
10-23-2008, 04:19 PM
^^^^^Yup.....What they said^^^^^:

There is one more factor that I haven't seen mentioned yet though. Move the subject further away from the background. So.....

1. Widest aperture possible (small F number).
2. Longest focal length possible.
3. Camera the closest distance to the subject as possible.
4. Subject furthest away from the background as possible.

Using these 4 steps, you should get some sine bokeh (blurred background)

Wesan
10-25-2008, 11:43 AM
tnelson42345 asked how to blur both the background and foreground. So I'd like to add, that by blurring the background using the above tips, the foreground will also be blurred. Larger aperture (smaller number) blurs both the background and foreground. That is, the depth of field becomes smaller. :)

zmikers
10-25-2008, 03:46 PM
tnelson42345 asked how to blur both the background and foreground. So I'd like to add, that by blurring the background using the above tips, the foreground will also be blurred. Larger aperture (smaller number) blurs both the background and foreground. That is, the depth of field becomes smaller. :)

Good point;)

tnelson42345
10-28-2008, 09:01 AM
I went on vacation this weekend and actually figured it out! Well let me say that I succesfully did this. :) Zooming in helped!

jedinite
10-28-2008, 12:27 PM
I went on vacation this weekend and actually figured it out! Well let me say that I succesfully did this. :) Zooming in helped!

Good stuff. It's very difficult to do on non-SLR cameras but it can be done, you just have to find the sweet spot for your camera.

I was listening to TWiP (http://www.twipphoto.com) the other day and here's a very good tip for DoF and Aperture. Though a very wide aperture helps in creating bokeh, it can also cause too small a depth of field. For instance, if you take a picture of someone that is facing you and you have a really wide aperture (2.8 or less) you run the risk of getting one part of their face in focus, say the nose for example, and the rest of their face is very soft (slightly out of focus). This is because you've narrowed your DoF too much. You can still get bokeh (blurry foreground/background effect) by having a slightly tigher aperture, depending on your focal length. I've seen really good brokeh on images with apertures openings between f/4 to f/6, but it all depends on your focusing distance and the lens you are using.

And a final note, a really, really small aperture wouldn't necessarily give you a really deep depth of field. On the extreme ends of aperture, really wide open (f/2.8 and below)or really tight (f/22 and above) will often cause images that get too soft.

A good analogy is to think of getting a good shot like shooting a golf ball. The larger you make your aperture the smaller the hole you are making for the ball you are trying to get in the hole. So a large aperture may give you a golf ball sized hole to aim for, where as a slightly smaller aperture will give you a basketball sized hole to get your ball into, and a very small aperture as a water hazard to get your ball into. You can think of the hole as your focused area, and everything outside of that being slightly out of focused to blurry. It's not a perfect analogy but it will help you in getting the right balance of bokeh and sharpness on the subject.