While shooting landscape on a bright, sunny day should I decrease the aperture? - 1

I have a wideangle lens on my Nikon D3100 and I like to take wideangle, high depth of field landscape shots. I've realised that by decreasing the aperture (increasing the f number), we get a high depth of field. But the shutter speed decreases and I don't get sharp photos. If I increase the shutter speed, the photo either turns out darker or it loses depth of field in spite of being quite sharp. Why does it lose depth of field upon increasing shutter speed?

Is there any way out of this? This is quite a big dilemma. And I'm really new into DSLR photography, so far having played with only point and shoots.

On a bright sunny day, the sunny 16 rule would apply, ie shutter speed is 1/ISO at f16.So if you're shooting at ISO 200, then f16 at 1/250 will be the rough guide for your settings.

You don't need to go above f16 (if fact, you shouldn't stop down too much as the image quality will degrade - you get diffusion and chromatic aberrations at v.small apertures) and 1/250 should be ample shutter speed to stop camera shake, especially with a wide angle lens. Strictly speaking though you should be on a tripod - most pro landscape photographers use tripods.
At f16, if you're focused, say 1/3 into the scene (at the hyperfocal distance), then everything from a few feet in front of you to infinity will be in focus.
Depth of field is controlled by 3 factors, aperture being one of them. However camera to subject distance and focal length of the lens are the other two, and wide angle lenses have an intrinsically deeper depth of field than, say, telephoto's. That means you can have a wider aperture on a wide angle lens and still get away with deeper depth of field.

Shutter speed does NOT affect depth of field - I'm assuming you are in an Auto mode like P or S - what's happening is that when you increase the shutter speed, the camera is opening the aperture and THAT'S what reduces your depth of field.

In dimmer conditions you may have to slow down the shutter speed to get enoguh light for the aperture you want (or increase the ISO, at the expense of noise).

Maybe check out this dof calculator;
http://www.dofmaster.com/dofjs.html

There are many correct combinations of shutter speed and aperture for any given light level, if you use a faster shutter speed you need to let in more light for a shorter duration. Larger aperture yields less depth of field. If you choose a small aperture you are letting in less light and need a longer exposure interval (slower shutter speed). As Scotty said, "Ye canna change the laws of Physics!"

You options are to use a tripod or IS (if your lens or body supports it) or choose a higher ISO (depending on the circumstances this may give more noise in your image). Practice also to release your shutter carefully, you may be surprised how long a shutter speed you can handhold once you are aware of the camera shake issue and don't be afraid to borrow support, just leaning against a doorframe or car makes you a sort of soft, organic tripod and will steady your shots a good bit.

A wide angle lens ha more DOF than a longer one. So you can probably just leave it at F8 @ 1/250 if you have the ISO/ASA 400.

With most lenses, the best quality is around F8, midway on the aperture dial. At wide open (F2.8), you get some amount of lens distortion, at fully closed (F16 or more) you get some distortion from the aperture blades. You change aperture as the shooting situation requires. If you're shooting a closeup of a flower, with a mountain in the background, you shoot at F16. If you're shooting a portrait, you open it up to F4.It's not that F8 is your only option, it's just a good starting point.

So, on a sunny day, using F8, you would be set at F8, ISO 200 1/800 of a second.

You lose depth of field as you increase shutter speed, because the camera is adjusting the aperture according to shutter. F2.8 at 1/4000 is same as F11 at 1/250.

Shoot on aperture priority until you get comfortable with it all. Look at the shutter speed, and make sure it's around 1/800 in morning and early evening. At noon, it will be around 1/1000.

Another tip, when you're shooting at dawn or dusk, you need to use exposure compensation. The camera will want to "expose for daylight", so a dimly lit twilight scene will be overexposed, and it will look like a daytime scene. I usually use a -0.7 stop exposure compensation. So you decrease exposure of the scene. This make shutter speed go up a bit, so it extends you shooting time some, i.e. If camera is metering 1/60, F2.8 ISO 200, the -0.7 will make it 1/100, F2.8 ISO 200.