Can someone please explain--preferably not using the confusing language of many books--exactly what the definition of hyperfocal distance is?

For every aperture with a given lens, there is a hyperfocal distance. This is defined as the closest distance you can focus on, and still have the background (infinity) reasonably sharp. Many photographers don't agree with the standards for "reasonable", and use different distances.

I'm nit-picking (occupational hazard!) but I think it's "for every aperture for a given focal length and film format..." The hyperfocal distance for an aperture with a zoom lens will change as you alter the focal length. Also a 50mm at f2.8 will have a different hyperfocal distance in 35mm format than with 6x4.5, 6x6, etc. Forgive me for stating what may have been the "bleedin' obvious"! Regards, Frank ...A child's middle name is so he can tell when he's REALLY in trouble.

Yes, hyperfocal distance is a characteristic of lens focal length and aperture. Typically hyperfocal distance manifests itself in the manner that at the point of true focus one third of the hyperfocal distance is in front of the point of true focus and 2/3 of the distance is to the rear of the point of true focus.

"When a lens is focused at infinity, the closest distance that is still in focus for any given f/stop is called the "hyperfocal distance". The practical value of this measurement lies in the fact that if the lens is focused on the hyperfocal distance, everything from *half* that distance to infinity will be in focus. When used as a focusing point, the hyperfocal distance provides the greatest possible depth of field that can be obtained with a given lens at a specific aperture." - The Enctclopedia of Photography - Vol 10. p. 1793 Some lenses, I'm looking at a Hasselbald Sonnar 150 mm right now, have a scale on either side of the focusing index marked with f/stops to indicate the limits of "acceptabe focus" when focused at any given distance. As an example, with this lens, at f/22 and a primary focus of 25 meters, everything between 13 meters and infinity will be "acceptably in focus"; at f22 and a primary focus of 5 meters, everything from 3.8 meters to 8 meters will be "acceptably in focus". There are mathematical formulas to figure this out -- but I'm trying to keep it simple.

I just remembered, if you happen to have a palmtop that runs Palm OS, there's a handy little shareware program called fcalc that will tell you the hyperfocal distance for a given film size, focal length and aperture. It also does upteen other things like depth of field calculations and angle of view. It should be available somewhere on www.tangentsoft.net

Andrew, since you're in the 35mm forum, I'm supposing you might actually be planning to use the depth of field scales on your lens to determine hyperfocal settings at a given aperture. Be aware that the lens DOF engravings are very optimistic, i.e., assume a small final print. to make a satisfactory 6x9 inch print from 35mm you should be shooting 2 stops smaller then the DOF scales indicate. For example if you shoot at f8 set your hyperfocal distance using the f4 mark on the lens to obtain a reasonably sharp print. take care, Tom

The calculation of a "hyperfocal distance" is a theoretical one ... and one of the most important factors in its calcualtion is called the "circle of confusion". The "resolution" of any optical sytem is a measurement of the smallest distance separating two points - where the points remain recognizable as two points, and do not blur into one. It is properly given as an angle: the resolution of a telescope is usually given as 1/4 second or something like that. To simplify (? - debateable) things, we generally speak of camera lens resolution in terms of "lines per millimeter" - and this brings back memeories of the "Air Force Resolution Target" of 1951 (not certain of the year) and hours of peering through a microscope at aerial images on an optical bench. The "circle of confusion" was simply the "resolution at the film plane" given as the diameter of a circle - and most lens manufacturers have accepted an arbitray value based the Zeiss formula of [ Diagonal of Format / 1760 ] (am I remembering correctly?). Remember - that is a theoretical value, and the actual resolution is not considered. It may be that a lens that cannot resolve a whole lot of "lines per millimeter" will not be "accepatbly sharp" to the ( *subjective* ) eyes of individual photographer, therefore he may chose to use a smaller aperture to try to obtain a greater depth of field than that indcated by the "hyperfocal scale" on the lens. Theory is good - but it is never an adequate substitute for experience.

I don't know the exact address, but google search "shuttercity". They have an automated depth of field calculator that gives depth of field and hyperfocal distance for any lens length at every Fstop on any format up to 11x14 I think. It also allows you to enter in focus distances and then will list every Fstop with its depth of field for every format. Of course every lens mfg will probably vary slightly but it will get you into the ball park. It provides a table that when printed provides an easy reference for the field.

something else to remember is that about a third of the area within the hyperfocal distance is in front of perfect focus and about two thirds are behind it (excepting focus at infinity).

Andrew, If you were confused before, I think we both are now! Whooee, I love photo making stuff! Charlie................................

Just focus your cameras and use your DOF preview you lazy bums! Just kidding of course!!! By the way, the 1/3 in front, 2/3 in the back will become very apparent very quickly, and is a very, very useful phenomenon to learn about and take into account. The first time you try to shoot three people in a row, lined up at a 45 deg angle to your plane of focus, you will really appreciate it! Peter.

An after thought, is any one else confused when attempting to apply the 1/3, 2/3 rule with some soft focus lenses? If you are unsure of what I am talking about, ask Jim Galli. Charlie.............................

Hi Folks. I didn't notice anyone referring to dofmaster.com. There one will find a very instructional software package that is Windows friendly, and which has tunable parameters for focal lengths, formats, circles of confusion, etc. The program puts a DOF calculator on the screen, sort of a circular slide rule. It can be changed, operated, and even printed out to make a field serviceable DOF calculator. This may be of interest to people who have cameras without DOF indications, or to students who want to understand DOF better. There is also a Palm Pilot variant on the same website. It is all available via FREE downloads.

I made a set of discs for my LF lenses a couple of years ago using this software but forgot where I go it from - thanks for reminding me! Works very well. Cheers, Bob.

In landscape photography, hyperfocal distance can be effectively doubled using a simple trick... If you require everything in focus from infinity to as close as possible, set the aperture as small as possible (f16 for expample). Rotate the focus so that the infinity mark is opposite the f16 hyperfocal distance mark on the lens (if you've got these markings on the lens). 'In theory' the hyperfocal distance will then be from the one f16 hyperfocal distance mark to the other one. The image may look blurred in the viewfinder. You can double check whether the setting will work if you've got a depth of field preview button on the camera. As others have already said, the hyperfocal markings on the lens are a bit optamistic, so allow a bit of a 'fudge factor' if you intend to blow the image up to any reasonable size. The lens manufacturers definition of 'acceptable focus' is similar to the legal term 'reasonable length of time'. My Voigtlander 25mm lens has click stops on the focussing ring. If I click the lens to the 3m setting and shut the lens down to f11, there's virtually no need to focus the lens as everything will be in focus from infinity to about 2m. This 'trick' is often employed in point & shoot and single use cameras. The lens is permanently focussed at a distance less than infinity and a small aperture is used to get as much into focus as possible.