How important is autofocus when you are just shooting landscapes and macro?

I will be buying my first DSLR camera soon. I was pondering over whether to get a cheap, entry level camera and a good lens or a good, full frame camera and a fairly cheap lens. I have opted for a good lens with a cheap camera. I favour nikon and will go for the Nikon D3100 but it has no built in autofocus motor and this is a problem with the lens i wanna buy which is the Sigma 28mm f1.8 Aspherical Macro EX lens. This lens also doesn't have a built in motor so i will have to use manual focus. Will this make life difficult for me when i'm shooting macro and landscape? Also, any recommendations will be appreciated.

If your vision is decent you shouldn't have a problem. Shooting landscapes you will probably be using smaller apertures giving you more DOF. Focusing manually will be a little more forgiving. Flip the switch on the body to Manual Focus and go to work.

I regularly use my collection of classic prime lenses for landscape and close up work. I prefer manual focus for this type of work where I want to decide the exact point of sharpest focus to maximise depth of field.

http://aviewfinderdarkly.com.au/2007/09/12/how-to-use-old-lenses-on-a-digital-slr/

For reportage and sports lenses with their own fast focus motors are preferable to those that rely on the in camera motor.

When you are shooting landscapes or macro, you typically have the time to be paitent and do things properly.

Landscape and macro are relatively slow disciplines, compared to other styles. Take advantage of it. Get it done right and learn to do it without relyong on a fleet of computers. That is why i enjoy shooting landscapes.

Te 28mm might not be a well suited lens for macro though. 100mm micro lens will be better suited.

When I first began photographing I would only use auto focus because it was easier and I didn't have to do much, but now that I've become more experienced I lean more toward the manual focus. Manual focus, in my opinion, give you much more freedom because you're choosing what the camera focuses on, rather than having the camera do your thinking. Auto focus is helpful when you need to grab a quick shot, like action, but for landscapes and macro shots manual focus will work quite lovely.

That lens will be horrible for macro. For landscape it should be OK. Then again, landscapes are shot stopped down. I'd be really surprised if the sigma outperforms the nikon 18-55 VR at 28mm.

So… I wouldn't. I'd start with the 18-55 and start saving for a proper macro lens.

Honestly you do not need AF for landsape or macro.AF usually focuses on what it thinks is right, however often what the camera thinks is totally wrong.

For landscapes you'll want a lens with a distance scale and some hyperfocal charts. You need a wide (and the 28mm isn't really wide enough) and a telephoto lens, one is for big scenes, and the other is for picking out an interesting things at a distance. The 18-55mm lens that is normally kitted with a D3100 does the job well, except in lacking a distance scale, if you can afford it the 18-105mm is the better lens for this.

For macro, you want a lens that can focus to 1:1 really, and I'm afraid you will need a proper macro lens. Sigma's 105mm is a very good macro lens.