Depth of Field - 4x5greenspun.com : LUSENET : Large format photography : One Thread
I currently own a Canham DLC45 with a Rodenstock 210mm lens. Can anyone give me a quick & simple method for figuring depth of field while in the field without having to resort to a slide-rule, laptop computer, abacus or sextant??
I was taught some quick method many moons ago, but I can't remember it. Please help if you have any suggestions. Thanks!!
-- Scott Mittelsteadt (firstname.lastname@example.org), November 17, 2000
the two quickest and easyiest ways to figure out depth of field are these polaroid, type 55 negs work especially well for these but any polaroid will get you most of the way there. Also if you have a nice heavy darkcloth that you can really wrap yourself up in, simply close down then lens to where you are going to shoot and look. these methods work for me. I don't mean to be flippant but alot of people tend to spend to much time with the math and science of photography rather than the art of it.
-- doug (email@example.com), November 17, 2000.
I respectfully can't agree with Doug regarding Polaroids. You simply can not tell much about what is or is not in focus with them. They are fine for composition and exposure tests, however. There are a million ways to approach depth of field problems and many are discussed in various places on this site. Take the time to check them out. Probably the the easiest way to get going is to print out the table for your focal length from the Schneider website http://www.schneideroptics.com/large/depth/depthof.htm
Good Luck Paul
-- Paul Mongillo (firstname.lastname@example.org), November 17, 2000.
Doug is probably refering to using the negatives from Type 55 polaroid. For over 16 years I have successfully used Polaroid Type 55 negatives to check depth of field in both studio and field work.
Scott, try this method: You have a scale on the DLC rails. Make note of where your near focus point is and then focus to your far focus point and make note of that. Now refocus two thirds of the way back to the near focus point and close down to f/22, or f/32 if the distance between the two points, as measured on the rail, is great. Now do a visual check with the lens stopped down and then shoot a Type 55 Polaroid and inspect the negative. You can clear it with simple water or although this will take more time than using the sodium sulfite clearing bath. Once again I have found using the Type 55 negative to be an extremely accurate method of judging the focus while I am shooting.
-- Ellis Vener (email@example.com), November 17, 2000.
There is no single, universal answer to your questin because what is acceptable depth of field varies depending on enlargement size, viewing distance, personal preferences, and probably other things I'm forgetting. However, if you want something quick and simple, Linhof has a table that works like this. Focus on the near, focus on the far, set the lens midway between the two points. Then measure with a ruler or estimate the difference between the near and far and set the aperture as follows: 1.6 mm difference, F 16, 2.2 mm difference, F 22, 3.2 mm difference, F 32, 4.5 mm difference, F 45, etc. etc. You get the idea. It's easy to remember for obvious reasons. The measurements don't actually have to be down to the tenth of a milimeter, just something close and stop down one more will also work. These numbers assume enlargement of a 4x5 negative to 8x10 or 11x14. Again, they make certain unstated assumptions concerning what is acceptably in focus to most people at some unknown viewing distance but they seem to work pretty well most of the time and the measurement is very easy to do.
I've personally never been able to tell anything about depth of field from using a Polaroid but obviously some people can.
-- Brian Ellis (firstname.lastname@example.org), November 17, 2000.
The easiest and quickest is the Rodenstock Pocket DOF and Scheimpflug circular calculator.
-- Bob Salomon (email@example.com), November 17, 2000.
I have a the Rodenstock calculator that Bob mentioned. If all you are going to use it for is depth of field and not tilt estimates, than just do what Brian suggests. I have my own table taped to the back of mine, because the Rodenstock f stop estimates are not small enough to get the sharpness I want. I don't have it here with me at work, but I think they are pretty close to Brians. Also, I would be carful about setting the focus at the mid point if the far point is at infinity. If thats the case I would set the focus point about 2/3's of the way to infinity (not sure I worded that right).
-- Paul Mongillo (firstname.lastname@example.org), November 17, 2000.
Did you read http://www.cs.berkeley.edu/~qtluong/photography/lf/fstop.html While it sounds complicated at first, the method that is described there is actually the easiest and fastest I have found. That's it relies on sound optics doesn't hurt. If you don't have metric scales on your DLC, Keith Canham will upgrade that for a small fee.
-- Q.-Tuan Luong (email@example.com), November 17, 2000.
1/16" or 2mm = f5.6, 1/8" or 2.8mm = f8, 5/32" or 4mm = f11, 1/4" or 5.6mm = f16, 5/16 or 8mm = f22, 7/16" or 11mm = f32, 5/8" or 16mm = f45, 7/8" or 22mm = f64, 1 1/4" or 32mm = f90, 1 1/2" or 45mm = f128,
Focus on near object, mark rail. Focus on rear object, mark rail. Measure distance of the two marks and refer to chart. This will give you the minimum aperture needed for both objects to be in focus.
-- Allan Fontanilla (firstname.lastname@example.org), November 17, 2000.
reset your focus 1/3 the distance from the front mark.
-- Allan Fontanilla.com (email@example.com), November 17, 2000.
Scot, you sure picked a hot topic! Some very good input by the above posters. Just a bit of compilation here.... there is 2 practical ways to get proper DOF after knowing your near point and far point.
The first method will bypass using the desired cc desired on film....as Ellis and others point out, use the camera as a focussing guide, this technique is reasonably sound. The benefit of this system is you do not need to know the distance to your near and far point, you just need to be able to foucs on them and set then set the standard accordingly - and then the f stop. The drawback is, this does not take into consideration the potential enlargement capability of the exposed film. If your enlargement factors are small, (less than say 3x) this method is very fast and sufficeint.
To be more exact, you will need to figure the cc desired on film to accomodate your potential enlargement size. A good goal is .3mm to print, so if you want a 10x enlargement, then use a .03 mm cc in your DOF formula as found on many of the links offered above. With this, you can either make your own DOF focus chart on a piece of paper and carry it in the field or do the math in the field...or of course carry a DOF adj. guide...the chart is the most practical. The benefit of this approach is the exactness of accomplishing your desired enlargement. The drawback is, you need some way to find distances in the field. For example if your chart says focus at 200 ft., you need some way to determine how far away is 200 ft so you can pick an object and focus on it. A little pocket golf rangefinder works fine up to 2000 ft.
So there is many ways to skin a cat when it comes to this, you can choose what works best for you... Polaroids are great if you only want a 4x5 size print, it's a great cross check. But you can not tell from a positive polaroid how much enlargement potential it offers. As mentioned by a few posters above, polaroids with a negative will offer the benefit of knowing enlargement potential if you have a loupe with you... Best of luck!
-- Bill Glickman (firstname.lastname@example.org), November 17, 2000.
Scott.. previous posts span the full range of circle of confusion COC tolerance... Brian's suggestion is about 10x the focus range, i.e. a focus range of 3mm gives about f/32. This assumes a very small COC. Alan's post suggests about 3x the focus range, i.e. a focus range of 2.8mm gives f/8. That will produce a pretty large COC. I have a chart, I think came from Linhof, that suggests a factor of about 5x for 4x5, and 8x for roll film sizes... so, I have been using a factor of 6x with good results.
Thus, for a 2.5mm focus range, I use f/16, for a 5mm focus range I use f/32... etc. I agree that a slight bias toward the front will assure a sharp infinity which seems important in subjective impressions of the image sharpness.
-- Glenn Kroeger (email@example.com), November 18, 2000.
The differences in rail extentions and corresponding f/stops suggested by Glenn Kroeger and Brian Ellis are very useful and realistic for decently sharp prints with any degree of enlargement. Brian Ellis's note says his numbers come from the Linhof chart and Bob Soloman offers the Rodenstock calculator. Actually Ellis's numbers have been (and should have been) sharpened somewhat over the Linhof chart and if you use the Rodenstock gadget, set the format to 6x9 when using 4x5. And Allan Fontanilla's suggestions will produce a circle of confusion the size of bagel.
You need to balance all this effort to get the right f/stop against the problem of defraction. If you're not satisfied until you get down to f/45 or f/64 then your image will be blurry due to difraction anyway. So back off and decide of tilts and/or swings will solve the focus problem with a smaller more reasonable f/stop. That's why we use view camera after all. If that doesn't work, back up and/or use a shorter lens and plan on enlarging more. If that doesn't work, plan on contact printing or think of the image as the one that got away!
-- John Hennessy (firstname.lastname@example.org), November 18, 2000.
If you want to understand some of the number which have been thrown in this thread, I insist that you read the article I mentioned previously. I spent a fair amount of time to make sure to get things right there.
Brian's method uses a CoC of 0.05mm. This will ensure a sharp 11x14 at minimum viewing distance. Allan's method uses a CoC of .17mm. This is appropriate only for a contact print. Glenn's method uses a CoC of .078, which is more in line with what I personally recommend. While those linear approaches are useful for determining whether a certain focus spread is acceptable, their drawback is that they doesn't take into account diffraction.
-- Q.-Tuan Luong (email@example.com), November 18, 2000.
John is correct - the numbers I gave are stopped down one stop from the numbers on the Linhof chart, in part because it's so easy to remember them that way (1.6 mm difference = F 16, 2.2 mm difference = F 22, etc.) but more importantly because Linhof's numbers assume an enlargement to 8x10, whereas I often enlarge to 11x14.
-- Brian Ellis (firstname.lastname@example.org), November 19, 2000.
Does using a 5x7 camera affect the depth of field calculator? Truley a beginner, so forgive me if this is obvious to everyone but me? Thanks.
-- Julie Hancock (email@example.com), November 24, 2000.
Hey!! I just wanted to thank of all you who took the time to respond to my question. I got a lot of great advice, and I hope spend quite a bit of time seeing which methods work best for me. Its great to have this forum....and I can't tell you how much this novice appreciates having the wealth of information that you all provide...at my Internet fingertips.
-- Scott Mittelsteadt (firstname.lastname@example.org), December 01, 2000.