Hyperfocal Distance and DOF some expert advice needed

[Daniel Browning]

the ft/m marks (I did properly line the F stop) did not really match up with what the real focus point would be.

How did you measure the distance? If you measured it from the end of the lens, that may be the cause. The actual distance is from the "witness mark", which is the little circle with a line through it on the camera body that indicates where the sensor is. Another factor to consider is that temperature can change the focus distance (which is one reason why they allow the lenses to focus past infinity).


That said, I wouldn't be surprised if the focus distance marks were inaccurate; I doubt that very many people use them.

Also at the hyperfocal length given with the above chart (for instance at F8 for the 35mm is 16.9') much of the background landscape would be out of focus.

That's because the above web site assumes an 8x10 print size. If you blow the image up larger than that (such as by looking at 100% crops), the DOF will be thinner than what the web site says. If you print smaller (say, wallet size), the DOF will be deeper than it says.

So myquestion would be, are the charicteristics of these L lens such that the DOF charts and hyperfocal lengths do not apply or have to be adjusted?

Although individual lenses can have different DOF characteristics (e.g. overcorrected spherical aberration gives more rear DOF), I think what's going on in this case is that you are assuming a different reproduction magnification than the DOF calculator.

2, The DOF chart gives near limit and far limit. Is the actual shape of the DOF of field more of a biconvex shape rather than a flat shape from one side of the frame to the other?

It can be -- if the lens has an aberration called curvature of field. In Canon lenses that tends to be pretty minor, though.



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If it is this shape is there any way to determine how thin it would be on the side of a ff camera compared to the center?

I don't think the thinness really changes, just the part of the scene in object spaces that it covers.