When you need that extra bit of sharpness (most lenses are not sharp fully opened), when you need large depth of field (focus on things in foreground as well as far away, usually comes at F/8+), when there's so much sun that you are getting overexposure even at the lowest iso and high shutter speed, or when you don't want the high shutter speed (want to capture a blurry feeling of motion)....

If you're trying to take sport shots or shoot something that is moving fast then you may need to shoot with a certain speed as the primary concern..

But if speed isn't the issue then it all comes down to what you want from the shot and I think the basic question is do you want the background blurry or not. At least the way I look at it from my beginner point of view..

I've tried to take shots of my dog in the f/2 range and if I focus on the eyes but get her looking straight at me her nose can be out of focus. The result can be funny but it can also ruin the shot. If I take a picture of a few people inside sitting on a couch or standing near each other, I might have to get into the f8 range just to be sure everyone is in focus. If I'm taking a shot on vacation while standing in front of a moment or an interesting object then I definitely need to go into the f8 to f11 range to get everything in focus because I not only want the person in focus but also the background..

Hope that helps. I also hope I didn't make you more confused - I'm still learning too..

Misc equip : Canon 610, Canon 400D, Canon 10D (about to sell), EF 50mm f/1.8 II, EF 85mm f/1.8 USM, EF 24mm f/2.8 (not so sure about)..

" When is it not best to shoot wide open if handheld?".

When light is so bright that will overexpose the image. Outside at bright sunshine for example. If you still want blurred background (portrait, macro) - use CPL filter + ND filter(s) to reduce light that will allow opened diaphragm use..

Wide open should be used for max light when light conditions are dim (indoors, overcast day, late evening, early morning). It created very shallow focus area, background blur), will not work at landscapes when some subjects are close to you, some are very far. Could be used at landscapes when all subjects are far only..

Handheld - camera shakes because of your hands move(natural stuff)..

Wider angle lens used - longer shutter speed could be used with acceptable level of motion blur in photo detail. Longer telephoto - shorter shutter speed..

Rule that I follow when shoting at ISO 100 to get acceptable quality for 5X6 prints:.

20mm lens - 1/20 sec and faster50mm - 1/60sec and faster100mm - 1/125sec and faster300mm - 1/300 sec and faster.

If exposure requires longer shutter speed I use tripod. Honestly, I try to use tripod always when I have chance(time)..

For large prints(high resolution) you should understand that slight motion blur will be unacceptable.

Http://www.stan-pustylnik.smugmug.com..

Depth of field is awful when lenses are wide open (at maximum aperture).

When you are handholding a camera and press the shutter release, the camera locks on the focus point. If your body sways just a bit, and the subject moves just a bit, that locked focus can be very inaccurate when you press the shutter rlease the rest of the way..

Say your are four feet from someone and focused on someone's eyes, and you sway two inches back, and he sways two inches back. and now you are focused on the the end of his cigar. Might be a nice picture, but not what you intended..

Also, what else is in the shot. With some lenses, focusing on the side of a barn will get the entire side of the bard sharp even though the edges of the barn are farther away from the camera than the middle of the barn. Imagine a string tied to the lens. Stretch it straight ahead for, say, fifteen feet. Then holding that same spot, move to the side. Notice how the distance from lens to subject is an arc..

Depending on the lens, you'll get the flat field (most lenses that have one focal length and the word Macro on them) or the arc most other lenses. Wide open, the edges of the picture will be out of focus, depending on the lens used and whether the subject is set up along the arc or not..

Stopping down the lens (reducing the aperture) "pulls" the edges into focus via increased depth of field..

BAK..

Dude, take a look here:http://www.flickr.com/photos/j_wijnands/.

In those 336 pictures only 6 are not handheld..

Reasons not to shoot wide open:.

1. you have too much light to shoot wide open.

2. you want to use your lens at it's best and sharpest (which is for the cheaper lenses definitely NOT wide open)3. You want more DoF so you stop down.4. You're using one of your cameras fully automatic modes.Don't wait for the Nikon D-whatever, have fun now!http://www.flickr.com/photos/j_wijnands/..

BAK wrote:.

Depth of field is awful when lenses are wide open.

??!?!!!????.

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Speechless...

Got it, thanks, some of this I understood, I was just wondering why I was having so much trouble with handheld shots in what appeared good light, to get my shutter speed to acceptable non shake levels, I was having to shoot a lot wider than I had anticipated. I guess I am going to get more use out of the tripod which I brought then I thought... thanks for the excellent rule of thumb on shooting without blur, although for handheld without blur I am trying to work mostly above 1/5oth for now, I will get even quicker speed sfor telephoto (combinging my leanring on the spot, with questions here, with that great book "Understanding Exposure," I think thats the name of it...).

Shooting wide open more, just surprised at hoe much my idea of good light and my cameras idea sometimes differs....

Next questiuon I will pose, and I saw there is already an active thread on it, is shooting RAW vs JPEG.....