How will i know where is the Hyper-Focal Distance in my scene?
By using the calculator, you will know how much of the scene will be in focus.
I read in some places that you will have to do an estimation and just go with it. i'm not very good with estimating distances so is there any other way to do it?
There are laser range finders that you can use to get distances if you can't estimate. Generally though, you just need to know a closer distance than the closest thing you want in focus. So, if that's a tree on the other side of a field you're looking at, and you don't know how far away that is, it doesn't much matter, if you know it's more than a few feet away and there's nothing between a few feet away and the tree that you want to be out of focus. You can make the measurement to a few feet away and use that to get the tree and everything behind it in focus.
and if i look at Buckster's photo, there are only three landmarks - flower, tree and clouds. if non of those are in my Hyper-Focal Distance so how do i know where to focus? i'm guessing i'll have to focus first while looking at ground level (or something like this) and then recompose. am i right with my guess?
I don't remember what lens and body I was using, it was a while ago, but let's just say it was a Canon 20D with my 10-22mm lens on it @ 10mm. (that's probably correct)
For that body and that lens at 10mm, wanting everything from a foot in front of me to infinity, all I had to do after consulting a hyperfocal calculator was set my aperture to f/9, then I used a tape measure to set up my tripod two feet from the flower, auto-focused on the flower, switched from AF to manual once I'd achieved focus, and shot. With those settings, everything from about a foot away to infinity was in focus.
and one last Question i'm thinking about right now, if there is no obvious landmark at my Hyper-Focal Distance for my cam to auto-focus on i should be using my Manual Focus? or i should be always using my manual focus when i'm aiming for the Hyper-Focal Distance?
You can use auto-focus to get it dialed in, but you have to know how far away the thing is that you're auto-focused on. It can be very close, and estimated or measured with a tape measure, or it can be further away and measured with a laser rangefinder, but you need to know what the distance is. After you've got the focus, turn AF off and recompose (if necessary) in manual.
Use this link to get your calculations and more information:
Online Depth of Field Calculator