Depth of Field question

[karma88]

Hello,

This is my first time posting! I'm having trouble getting this depth of field thing. I've got a Powershot A620 and I know that in order to blur the background the aperture needs to be set low but how fast do I set my shutter speed and how far away should the background be in order to get the blur effect I'm after?

Thanks!

[ajaynejr]

You should take some practice shots.

Set a fairly large aperture. Focus on the subject. If the background is still not defocused enough,enlarge the aperture. Alsotry setting the camera focus to be closer than the subject itselfreally isand see if the subject is still acceptably focused.

Depth of field refers to a range of distances, the extremes of which are subjective. In your case you want your subject to be within that range (acceptably focused)and the background to be outside that range (noticeably out of focus).

For stationary subjects shutter speed does not matter except to go with the aperture and make the correct exposure.

[Caboose]

This is the area most p&s cameras suffer. That f2.8 aperture on your A620 is the equivalent of f/11 on a 35mm camera. So you end up with a very large depth of field. Make sure you have a lot of distance between you subject and the background. For portraits I'm not sure focusing in front of your subject is going to get the sharpness you would want in the eyes, but it might, you will just have to try it and see.

[karma88]

Thanks. I'll try all of your suggestions. I knew I should have gone with the Rebel!!!

[AlfaBeta]

Hi,

I am interested in your discussion as Irecently bought the Canon A520 Powershot.

I would like to know if it is possible to make the background in focus, while the subject is blurred?

I am familiar with the Portrait setting on the dial which will do the opposite.

I am also familiar with the AV setting which gives you a bit more control over the f stops.

(It seems the more you zoom in, the higher the Fstops will start from…can someone explain this phenomena??)

I will probably experiment later today, but thought I might try to get some tips.

Thanks heaps…
Regards

Alf….

[AlfaBeta]

I also would like to take close ups ofsubject with blurred back ground in the distance.

and also use the Macro setting for real close subjects etc.

Caboose, when you say: "This is the area most p&s cameras suffer. That f2.8 aperture on your A620 is the equivalent of f/11 on a 35mm camera. So you end up with a very large depth of field. Make sure you have a lot of distance between you subject and the background."

Can you explain your last sentence a little more?

Thanks

ALf

[Tom LaPrise]

I'll take a stab at that last sentence.

Basically, you want the subject to be fairly close to the camera and the background to be fairly far away. That way, when you focus on the subject, the background will be as blurry as it can be considering how little control you have over the lens' depth of focus.

If you set a 50mm lens on a 35mm camera to f/2.8, the aperture iris will make a pretty large opening (giving the lens an effective diameter of close to 18 millimeters). Since your digital camera has a sensor that's much smaller than a 35mm film frame, the focal length setting on your camera to give roughly the same field of view or apparent magnification as the 35mm camera's lens would be around 11mm; with your aperture set to f/2.8 at 11mm focal length, the iris will give your lens an effective diameter of 3.7mm. That diameter, with the 50mm lens on the 35mm camera, would be an aperture setting of f/13 or so. So even with your aperture "wide open," you'll get the same depth of focus as a 50mm lens at f/13 on a film SLR--pretty deep.

If you focus on the subject and the background isn't REALLY far away, the background is probably going to be in reasonable focus too. All you can do is get pretty close to the subject and make sure the background is as far away as you can have it.

[Caboose]

AlfaBeta wrote:

Caboose, when you say: "This is the area most p&s cameras suffer. That f2.8 aperture on your A620 is the equivalent of f/11 on a 35mm camera. So you end up with a very large depth of field. Make sure you have a lot of distance between you subject and the background."

Can you explain your last sentence a little more?

Thanks

ALf

Tom hit the nail on the head with his reply. On the other hand the point and shoot cameras have a huge advantage when it comes to wanting everything to bein focus, because your aperture at the other end is probably close to f64, which us DSLR user can't come close too.

[saturndude]

I'm new here, and wondering about this too.

I've seen some digicam tutorials. The focal length numbers printed on the lens are different because of the smaller CCD sensor. (Why do they say 1/2.5"? Wouldn't "0.4 inch" be proper for grammar?)

But I haven't seen any tutorials that explain any differences in the aperture numbers.

I've taken several hundred photos between 1990 and 1997, with a 35mm manual-focus "rangefinder" (fixed 50mm lens). So I have some experience with photography (until the soldering on the selenium solar-cell lightmeter failed and I couldn't fix it). Now that I've ordered a digital camera, the "cost of failure" (film developing) is essentially zero, and I couldn't be happier!

I am used to everything being in perfect focus, perhaps this is from watching too much American television. Choosing a shorter depth of field (say, 100cm instead of 100km) has some interesting artistic possibilities!

What is the "true" aperture on my 2.7(W) to 3.5(T) Canon S3? Where can I find some good tutorials? Thanks in advance!

[AlfaBeta]

Hi Guys,

THanks for the well presented explanation...

a few questions...

Tom said:

"If you set a 50mm lens on a 35mm camera to f/2.8, the aperture iris will make a pretty large opening (giving the lens an effective diameter of close to 18 millimeters)"...

..."with your aperture set to f/2.8 at 11mm focal length, the iris will give your lens an effective diameter of 3.7mm."

• phew...18mm > 3.7mm is a large drop!!!

"So even with your aperture "wide open," you'll get the same depth of focus as a 50mm lens at f/13 on a film SLR--pretty deep."
[/*]

• Does pretty deep meanlarge depth of field? [/*]
• Does this mean that I can't focus on images in the background and make the foreground blurry?[/*]

At the same time, I also purchased the larger Canon "S2 IS" with the 12x zoom, thinking I would get greater depth of field control...(didn't do my research that well...) (The a420 was bought later, as the S2 IS was too large...) Would the aperture rules on this camera be the same as the A420??

Again thanks for the tips,

Have a great weekend....

Alf...