yeah, that makes sense. Thanks for all of the comments.
I've been keeping the full table which shows the minimum and max focussing distances and the hyperfocal distance at the different focal lengths but I suppose what all I really need to know is the hyperfocal distance which is just one value per f/number so it would be easy enough to make up a table.
I think that the most useful single number you need to know is not the hyperfocal distance, but the near point in the hyperfocal range. That's what you need to know when selecting the appropriate f/number, then just double that distance and that's your hyperfocal focusing distance to set. As further described on the thread I linked to above.
The thing is I want to take landscape shots with my wide angles lens (for the full scene) and a telephoto lens to zoom in from a distance and frame a composition within the landscape.
What I'm finding is that my zoom lens has a focal distance reading from 2.2m to 50m and that the hyperfocal distance is greater than 50m (according to DOF master) at f/22 at around 150mm. So this is presumably the maximum focal length I can use if I want to get sufficient front to back sharpness.
I dont think this is a problem because when I am trying to do a longer focal length I'm generally on higher gound focussing into the distance so I dont need forground sharpness. If I look at the tables for f16 and 450mm it says If I focus at 50m then the DOF ranges from near/46m to far/54m. So this clearly isn't going to be sufficient for a landscape shot. To get to the hyperfocal distance I'd need to focus at 633m which is way off the scale (but I dont need the foreground sharpness anyway).
As you have found out, hyperfocal distance settings don't really work with longer lenses. Infinity is just too far away to stretch the near distance focus close enough at sensible f/numbers. The upside is that it usually doesn't matter, you just don't need that kind of sharpness range with the kind of detail landscapes you tend shoot with long lenses. I'd be surprised if it troubled you often in practise, if at all.
So what I'm trying to work out is if I just focus on the infinity sign on the lens is this going to be the maximum dof I can get for distance shots??? And is this sufficient or is my lens just not really suitable for this kind of work?? I know telephoto lenses are more usualy used for wildlife but I've seen books with good shots like this with lenses at 500mm. Maybe they are professional and v expensive lenses??
Professional/expensive lenses have identical depth of field charateristics to any other lens of the same focal length and f/number. It's physics at work, not expensive glass.
With distant subjects, rule of thumb is if you focus very roughly one third into the zone that you want sharp you will maximise depth of field. You then use the highest f/number you dare to ensure maximum sharpness. 'One third in' is only a rough guide but it works pretty well at distance, eg you have stuff you want sharp ranging from 100m to 400m away, if you focus on 200m you will maximise the depth of field either side of that point.
That might sounds a bit rough and ready, but given the large number of variables and assumptions that go into DoF calculation, a few meters here and there isn't going to make much odds.
