Hyperfocal distance in LF, i.e. for 90mm SA XL at f/22greenspun.com : LUSENET : Large format photography : One Thread
I am usually focus using hyperfocal distance in 35mm with my Nikkor 28PC lens with DOF to spare at f/16-f/22. Of course, in 35 mm, the procedure is simple: I just stop-down and look at the scale on the lens barrel, turn the focus ring until "infinity" is within the DOF range for that f-stop and shoot! My question #1-- how is this done in LF? (Givens: 90mm SA XL, 4X5 format, and a DOF table from Schneider web site found with the help of this group TNX). BTW, I noticed that at the bottom of the Scheider 90 mm DOF table, one row is labeled "[hyperfocal Distance] [NEAR(ft)]" and gives distances for each f-stop column. Hence, question #2: what are these distances?: a) the focus point which will give DOF from an even nearer point to infinity, b) the near "cut-off" point of the maximum DOF? or C) other: _______________. My reasoning leads to: (a) by intuitively looking at the table. Pardon any misuse of terms, this is all new to me! (My Horseman LE from Badger is being shipped as we speak). Question #3: how do I focus the camera to the hyperfocal distance once I know it? (via GG image w/magnifier while I get a tree to "stand-in" at the required distance?:)? via some alchemic LF formulae that would give me lensboard to film distance in cm.?) I do appreciate to helpful denizens who inhabit this remarkable LF group! Best, Paul Chaplo
-- Paul Chaplo (firstname.lastname@example.org), April 30, 2001
Hi folks, I cannot answer this question directly, but I have an interactive Hyperfocal Table program on MS Excel if anyone wants one. You enter the crucial data - circle of confusion, apertures, focal length and camera to subject distances and it shows a table of depth of field and the hyperfocal distance.
Drop me a line if you want one.
-- Clive Kenyon (email@example.com), May 01, 2001.
I'm not sure if you are aware of front lens tilt or not. That should take care of your focus issue.
-- Dave Anton (firstname.lastname@example.org), May 01, 2001.
Paul: Set up your Horseman on a tripod or other support and focus the lens at about 12 feet with the 90mm. Mark this distance on the focusing track. You can use pencil marks or tape and mark the tape. As long as the lens returns to the same place every time, the focus will remain true. It takes longer to write about it than to do it.
-- Doug Paramore (email@example.com), May 01, 2001.
Paul - I too am a newcomer to LF, and await my recently shipped camera, and had the very same question as you do. There is a book named "View Camera Technique" by Leslie Strobel which is well worth the price of admission. He deals at length with this issue, and once you read and understand the material, you will know the principle behind hyperfocal distance, and instead of just dialing it in as you had on your smaller format camera, you will need to estimate the distance ratio between near and far objects requiring sharp focus, and then focus at a fraction into the scene depending on that near/far distance. He also mentions a "Quick Focus" gauge which can be used, and other add-on gizmos to acheive maximum DOF.
-- Mike Mahoney (firstname.lastname@example.org), May 01, 2001.
Paul: There are two books available by Harold M. Merklinger that will tell you everything you will ever need or want to know about focussing the view camera. The books are "Focusing the View Camera" and "The Ins and Outs of Focus". Merklinger has a very interesting web site at http://fox.nstn.ca/~hmmerk/.
-- Ken Burns (email@example.com), May 01, 2001.
If the camera is focussed at the hyperfocal distance, the range of acceptable sharpness in subject distance (the depth of field) extends from one-half the hyperfocal distance to infinity. The "near" distance given in your tables is probably the nearest distance of acceptable sharpness and should be one-half the hyperfocal distance.
I harp on this "acceptable sharpness" thing because is it rather subjective. Only an object at the distance focussed on will be in perfect focus - objects farther from this point will be increasingly fuzzy. A cut-off point of acceptable fuzziness is chosen to define the depth-of-field, hyperfocal distance, etc.
The amount of fuzziness is characterized by the diameter of the "circle of confusion." This CoC is the circle on the film plane due to a point source of light in the subject. A point at the focussed-on distance will be rendered on the film (ideally) as a point. As either the subject, or film-lens, distance is changed, the point will appear as a circle.
The diameter of the circle is a somewhat subjective thing, but most people use about 0.1mm for 4x5 (and 0.025mm in 35mm). If you don't like this, you can recalculate hyperfocal distances youself.
The formula is easy:
H = f*f/(c*N)
where H is the hyperfocal distance, f is the focal length of the lens, c is the circle of confusion diameter, and N is the f-number. Remember to use all the same units (millimeters, for example).
The suggestion to mark your camera for hyperfocal distances is a good one.
-- John H. Henderson (firstname.lastname@example.org), May 01, 2001.
go to: http://www.schneideroptics.com/large/depth/depthof.htm this liste contains all schneider lf-optics by, montespluga
-- montespluga (email@example.com), May 01, 2001.
H is over rated in its LF usefulness. It may work to focus on H with a 28mm lens (with its inherent DOF) and will possible work for you with a 90mm lens on 4x5 with its limited enlargement (i.e., bigger neg). But with large prints and any longer lenses, you will be disappointd in the results. After all with the focus-on-H method, you're placing two very important points of most images---the very foreground and the horizon---on the ragged edge of being out of focus.
Another point, the commonly used CofC allows for too much confusion. Fudge that down if you expect to enlarge more than three times.
Last, think tilts, tilts, tilts if the nearest object in a scene is close at all. Then you don't need so much DOF. But a little often goes a long way. Usually I am in the range of 1 to 5 degrees of front tilt. I second the motion on Merklinger's site and books but don't be put off by the density of his approach to the subject and ignore his method of computing H.
So far as I know, the main books on this subject are not covered too well in the texts like Simmons, etc. It has been many years since I looked at them I admit. Someone should take Merklinger's depth and detailed grasp of the subject and fold it into the more general-purpose and easier-to-read lf books.
-- John Hennessy (firstname.lastname@example.org), May 01, 2001.