hyperfocal distancegreenspun.com : LUSENET : Large format photography : One Thread
I struggle to obtain foregound sharpness in my shots...am I just asking for too much depth of field for the lens I use (150mm)? Would I be better buying a WA 90mm..or would I just have the same problems...I try not to stop down further than f32 to avoid diffraction problems?
I use a Wista 45DX field camera (with 150mm Nikon), I am a total beginner to LF and would like some help on obtaining maximum depth of field. I take landscapes, therefore need everything sharp from as close to the camera as possible to infinity !
Am I correct in assuming that the hyperfocal distance is the exact point at which you must focus in order to obtain maximum depth of field for a given aperture ? If so, how do you know exactly what the distance is that you are focused on using LF lenses (as there is no indication on the lens barrel as in 35mm) ? Can I rely on the lens manufacturers calculations relating to hyperfocal distance, or are these inadequate ?
-- Mark J A Iveson (M.JA.IVESON@TALK21.COM), April 08, 2001
Probably the hardest thing for me to get used to was a lack of a depth of field scale. Coming from a 6X7 that had a excelent system it was difficult, but once you figure out the process it becomes almost second nature.
First the hyper focal rule of thumb (remember this is a broad generalization and depends on how your image is set up) is to focus on a point one half of the distance between the hyperfocal point and the furthest point in the scene. If you have the chart for the lens it will say that at (this is an example these figures are not correct) f22 when the camera is focused at infinity the hyperfocal distance is 100 feet. You would then focus half way between 80 feet and infinity. It takes some practice determining where these spots are at on a view camera and in the scene. This is also a complicated process, but kknowing how it works gives you a base to work from. Even if you are not at the half way pooint the next tip I give you will help compensate for teh error.
The most useful tool is back tilt. When using back tilt, focus on the far (the bottom of the ground glass) and tilt the back until the near (the top of the ground glass) comes into focus. You will have to refocus on the far and re tilt and re focus on the near until "everything" comes in to clear focus. You may find that the very center stays a bit out of focus. It takes a little fussing until you get used to it. Now stop down and watch as the center comes in to focus. I think you will find that with a 150mm, f22 to f32 should give you good depth of field.
Lastly, don't be afraid to use f45 or f64 if you have them. Getting everything in focus is better than worrying about a diffraction problem that may only be noticable at a room sized print. You are starting out and I would suggest that using every available aid be it tilt, fstop, etc. would be the best approach. If after you have polished your technique you find diffraction is a problem then work to eliminate it.
-- Marv (firstname.lastname@example.org), April 08, 2001.
There are a number of specific sources for information on focusing, DOF, and hyperfocal distance, including Harold Merklinger's book. You should also check out the article index at ViewCamera.com and the threads listed under "technique" in this forum.
Independent of the focusing question, you may want to try a wide angle lens like the 90mm, especially if your previous work in 35mm or MF relied on the use of wide angle lenses. Many landscape photographers use this lens and it seems to be a standard in most suggested lens kits.
Finally, I would rethink the statement that everything needs to be sharp in a landscape photograph. This may be appropriate if your goal is to produce an Ansel Adams type photograph. There are, however, many approaches to landscape photography in which the degree of DOF and the use of sharp focus vary considerably. I would learn to control focus and DOF using aperture, camera movements, etc. but I would not be bound by some "iron law of landscape
-- Dave Willison (email@example.com), April 08, 2001.
Care must be taken with WA lenses too. The curvature of the field of focus will fool you if you don't look all the way to the corners. I have seen so many wonderful shots where they are tack sharp until you get to the corners and then the focus falls off considerably. Learn to use the tilt and swing functions of your camera and you will be able to get all the depth of field you want within reason. If anything has to be out of focus let it be the background. And diffraction isn't the big bugaboo it's made out to be. Look at the tech notes of some of the better landscape photographers around like John Sexton. He uses f64 quite often and his images are tack sharp all the way through. james
-- james (James_mickelson@hotmail.com), April 08, 2001.
Just a few additional pointers. Remember that when you tilt the camera back, you also distort the image. If you don't care to distort the image, then tilt the lens to control depth of field. Remember that in optics, infinity is finite. There is a particular finite point for a lens of a given focal length beyond which increases in lens to subject distance will require no further adjustments in focus. That finite point is photographic infinity. The point you focus on should not be halfway to the horizon, but rather much closer than that. Remember that when you work with wide angle lenses, you usually move in much closer to the foreground area of your subject. In the end, doing this can put you back into the same boat of having depth of field problems. You might still have to stop way down to get adequate depth of field. This kind of thing has an awful lot to do with your own photographic style.
-- Ken Burns (firstname.lastname@example.org), April 08, 2001.
If you go to Scheinder Optics web site they have depth of field tables for common focal lengths including hyperfocal distances. This will help with some of your questions. As for the desire to have everything in focus I agree with the previous posts that say depth of field is a conscious artistic choice and should be thought of along with everything else.
Thats my story and I'm sticking to it.
-- Kevin Kemner (KKemner@tatesnyderkimsey.com), April 08, 2001.
The best way to assure you have proper focus is to use a good loupe and darkcloth. The groundglass never lies. You can see whether you are in focus or not. I concur with using the front movements for focus control if perspective is important to the image. Do you have base tilt or axis tilt? And remember that the farthest objects can be slightly out of focus and not be of great visual concern but foreground objects are like a big spot light that says look at me. So if you must choose choose a sharp foreground. And above all, practice those movements so they become instinctive. james
-- james (James_mickelson@hotmail.com), April 08, 2001.
Sometimes this is a bit of a shock, but those tables for hyperfocal distance and DOF are very optimistic. The formula for computing hyperfocal distance is:
Hyperfocal Distance = focal length squared divided by (f/stop times circle of confusion). Or H = (F*F)/(f*C)
Thus, two of the factors are quite specific while C of C is purely subjective. C of C is, simply put, "how much fuzzines can you tolerate?" The tables assume you can either tolerate a lot or that you do not intend to enlarge very much. To be specific, Schneider's and everyones tables assume C to be 0.1mm in a 4x5 neg. That just isn't good enough for many people.
Do read Merklinger's LF focusing book but be prepared becuase it is very murky. And he has a truely bizarre way to compute C. He says C is a fraction (1/1500 I think) of focal length. Ignore that. What is quite clear on the other hand is his PDF file on his website with animations showing how the plane of sharp focus moves. That alone will make you a believer in front tilts and back focus even if you don't mind your landscape's trees leaning over (which is what you'll get with back tilts.)
The main thing to internalize is the real shape of sharp focus space with tilts and that instead of trying to reconcile scene near vs. scene far (as with a rigid camera) you are trying to reconcile near top vs. far bottom.
You may also wish to try the Rodenstock tilt and DOF calculator (about $25 from B&H) but it too uses 0.1mm as C in its DOF calcuations.
-- John Hennessy (email@example.com), April 09, 2001.
The hyperfocal distance is the focused distance that gives you maximum depth of field for a given aperture from infinty. If you don't need the extreme far distance in focus, then you can get a better compromise on foreground focus.
With LF, the tilts and swings are a better way to control the plane of sharp focus than purely using the lens apeture. In fact, camera movements are the main reason to use LF.
BTW, f/64 will give you a perfectly sharp 16 x 12 print from 5x4, no problem.
-- Pete Andrews (firstname.lastname@example.org), April 09, 2001.
Yeah....what the other John H. says. Hyperfocal distance is easy to calculate. If you don't like the commonly used 0.1mm for 4x5, calculate your own table.
It bothered me when first trying LF to find that the CoC was allowed to get bigger with the format. You'd be told to use 0.025mm for 35mm, but 0.1mm for 4x5 because it is (about) 4 times (linearly) larger, so it only has to be enlarged 1/4 as much. Which raises the question in my mind of, "So why bother with LF if you're going to allow the sharpness to degrade?" Still does bother me some. So you can use 0.025mm of 35mm and get the sharpness of 35mm on the film but with more film. But note that for equivalent angle of view, the focal length for 4x5 is 4 times (about) that of 35mm, and focal length squared is in the hyperfocal distance equation.
Note that when focussed at the hyperfocal distance, acceptable sharpness (defined by your choice of CoC) is from half the hyperfocal distance to infinity.
For subjects that do not extend to infinity, you will often hear it quoted to focus 1/3 of the way from the nearest object to the farthest object that you want in focus. This is only a rule of thumb and is not very accurate.
Counterexample: You are focussed at your hyperfocal distance and for your situation, it is 16 feet. So near focus is 8 feet (half of hyperfocal) and far focus is infinity. (16-8)/Infinity = 0. You're focussed 0% into the depth of field. OK. So that's the extreme example, but how far into the scene you focus depends upon the distance of the objects and is rarely 1/3.
What is correct is that you want the lens to film plane distance to be one-half of the span between when you're focussed on the near object and when you're focussed on the far object. I.e., focus on the near object and note the position of the front standard (if you're focussing by moving the front standard). Focus on the far object and note the position of the standard. Now adjuest focus so that the standard position is half-way between the two noted positions.
-- John H. Henderson (email@example.com), April 09, 2001.
Pick up a copy of the Kodak Professional Data Guide, you can order it from Silver Pixel Press or a local camera shop. It is a compact (camera bag size) encyclopedia of information. Admittedly, all of the film info is Kodak related but, it contains much that can be interpolated. It also contains a nifty dof calculator that I think is worth the price of admission by itself. It's a circular slide rule calculator that is a snap to use and, for us mathmaetically challenged, seems to be accurate.
-- Joseph A. Dickerson (firstname.lastname@example.org), April 09, 2001.