Distances

I am a new to this hobby and so this question may sound a bit daft.Is there a way I can calculate how far a subject is away( bird/wildlife )and also what distance would I expect to get an in focus photo at 400mm on a Bigma.Sorry if it is a daft question.

Graham

Most lenses have distances marked on them, so focus on something and read off the distance on the lens.

The second part is called depth of field. At a given distance there will be things in focus in front of and behind where you have focused. A large aperture (small f number) will have very shallow DOF, for example throwing a background out of focus to make it less obtrusive. A small aperture (large F number) will have much more in focus as it will show increased DOF.

Hoping the pedantic amongst us don't want to confuse you, telephoto lenses have shallower DOF than wide angle lenses.

There are DOF tables, but the best way to get an idea is to shoot lots of images at different distances and apertures. then see what the effect is.

Hope that helps for starters!

Thank`s for that John.Am I right in thinking that if I focus on a certain point the subject could become more in focus if I change the f stop (in AV mode obviously).

Graham

In a way, yes, assuming the subject isn't a flat one. If it's flat, then it's all at the same distance so that would be in focus completely at any aperture. If it has depth (more usual) the as you stop down to smaller apertures more of the subject will be sharp.

To add to John's answer, if your focus is slightly off, then stopping down will improve the sharpness, but you must be careful, since when you stop down, the exposure time will increase, maybe to a point where movement blur will show up, defeating the purpose of stopping down.

Thanks again for the great info,I need to get there and take lots of photo`s using various settings and notice the differences.
Thanks once again.