Depth of Field Calculators/Aidsgreenspun.com : LUSENET : Large format photography : One Thread
I am looking for a quick and easy DOF aid or calculator that will only take about 15 seconds to use (once I'm comfortable with it) and will give me a quick approximation of the best f-stop. I've seen the Rodenstock calculator/slide card and found it too complicated to be of any practical use. I do a lot of near/far compositions, tilting to find the best compromise plane of focus. What tool do I use to help me decide the best f stop? Also, when there is more than one plane that I want to keep in focus, how do I decide which is the best plane to focus on or how to compromise between the various planes as well as using an appropriate f-stop? I don't want to carry around a polaroid back -- are any of these calculators/cards really good, light and easy to use? Finally, if I want super sharp prints, up to 20" x 30" and am shooting 6 x 9 format, what is the appropriate circle of confusion? Thanks for your help. Howard.
-- Howard Slavitt (email@example.com), May 10, 1999
Which camera are you using?
-- Ellis Vener (firstname.lastname@example.org), May 11, 1999.
Which camera are you using? In general, from experience I'd have to say that the built in Sinar calculator is the fastest followed closely by the Arca-Swiss Brainbox. Both of these have different DoF scales (based on acceptable circles of confusion for different formats. If you want to be extremely careful then stop down an extra 1/2 stop.
-- Ellis Vener (email@example.com), May 11, 1999.
I am using a Horseman VH, 6 x 9, technical field camera. I am using the following lenses: 58 mm, 75 mm, 135 mm, and 240 mm.
-- Howard Slavitt (firstname.lastname@example.org), May 11, 1999.
"Also, when there is more than one plane that I want to keep in focus, how do I decide which is the best plane to focus on or how to compromise between the various planes as well a using an appropriate f- stop?" This is as much an aesthetic question as it is a technical one. I could say a good rule of thumb is an out of focus background is more acceptable than an out of focus foreground, but I can easily hink of exceptions to that rule. It is also one of the questions that can be answered by carrying around and using a Polaroid back. I find it better to spend a few minutes making and studying a Polaroid before making the real photo than to gnash my teeth and wail after the film has been processed. I find I will discover things (focus placement, spatial relationships, tonal relationships, objects I don't want in the frame, better compositional choices, lighting effects & placement, & other little things like that. In short: I can see how the image works as an image) in a Polaroid that I miss just looking at the ground glass.
-- Ellis Vener (email@example.com), May 11, 1999.
I've been told that the Arca Swiss Brainbox is no longer available (one supplier told me it was a vaporware product - they had in their catalog, but never released it). I've was also told by Arca Swiss (Chicago) that a new version of the product will be available at some point in time (no release date available).
-- Larry Huppert (Larry.Huppert@mail.com), May 13, 1999.
Well let's see exactly how complicated computing DOF is with the Rodenstock Calculator:
Of course every step on the calculator is numbered.
Step 1 is to set the angle the camera is to the scene (inclined or level?)
Step 2 is to set the film size (35mm to 8x10") on the scale.
Step 3 is to set the reproduction ratio (1:1 to infinity)
Step 4 is to measure the difference between the near and the far point you want in focus (the difference in mm on the rail) a mm scale is on the calculator if your camera is not calibrated.
Step 5 is to read the aperture required for that displacement and to set it on the lens.
Step 6 tells you if any additional exposure is necessary and, if so, how much.
Since everything is numbered on the scales this is really quite easy to do.
The other side of the calculator is also numbered and computes the required tilt for any required plane of focus for 4x5 to 8x10 formats.
-- bob salomon (firstname.lastname@example.org), May 13, 1999.
It seems that Rodenstock Calculator that Bob described is quite a useful tool, I was unaware of it being on the market. B&H shows a Linhoff calculator for $500. If you want such a device, I would investigate that one first to see if it meets your needs. From the description Bob gave, it sounds easier than most other methods you may try. However, it may not do all the things you desire. I will try to find some literature on the Rodenstock calc.
For a fast and painless way to make your own calculator, you can look at the front page of this forum, under Bob Wheelers LF calculations. He offers an excellent set of programs that can be down loaded into your PC. From there you load the information from your PC to a programable calculator, I have the TI89 and highly recommend it..$159. With his downloads, you save yourself the trouble of learning and performing a lot of the programing required to enter the equations. I programmed my TI89 with information from various sorces and find it a life saver. The nice thing about it is you do not have enter the same information over and over, it will remember the last focal length entered and use it for all equations you want to use. The other nice thing with the "numeric solver" is... you can enter a formula once then use it with anyone of the variables being an unknown, and it will solve for whatever variable you asked it to solve for. (assuming you filled in the rest of variables) This saves you the trouble of re-entering the formula which would need to be solved for each variable.
As for what c of c to use for 6x9 format. I try to get to .2mm on an 8x10 print which to my knowledge exceeds any papers resolving power today, the best is .3mm, you may want to check that figure with paper manufacturers. This .3mm is also better than any eye can resolve on 8x10 at 15 - 20" viewing distance. After you get to .2 or .3mm on 8x10 then any additional magnifications from there, which reduce the sharpness of focus is equally offset by the greater viewing distances required. Therefore the image will look just as sharp as an 8x10 viewed approx. 15" from the eyes. So to arrive at .2mm on 6x9 format, divide .2 by 3.5 (which is the magnification required to get from 6x9 to 8x10) which equals .057mm for c of c on 6x9. Keep in mind also that all 6x9 formats are not the same dimensions, be sure to check yours and dived by 8x10 converted to cm.
As for deciding which plane of sharp focus to favor, that would be a compostion decision. I reccomend Merklingers book (Focussing the View camera) and his web site that explains some of this in detail. He has tremendous knowledge in this area and has made my life much easier when it comes to placing the plane of sharp focus where I want it. Unfortunatly his ability to communicate this information is fair at best, so you have have to read between the lines.
In addition to my TI89 programable caclculator which I carry, I developed cheat sheets for all my lenses. 90% of my focus applications are covered by my cheat sheets, so I rarely bring my calculator out of the bag. It only is a total of a few sheets that I laminted, I use them on almost every shot, and they are very accurate. I recommend this first, and the calculator second. YOu can do all of your calcs on a PC for your cheat sheets. You can list standard DOF field for all your lenses, near and far, tilt angles for specific (j) distances below the lens, Hyperfocal distances, etc. I also developed a simple scaled sketch system that allows me to nail the plane of sharp focus accurately every time. I know it sounds like a pain in the butt, however, I discovered if I take my time and do the right calcs and sketches, (2 minutes) I get it right the first time and get the shot, while the estimations methos combined with trial and error waste more film and time than thinking it through. Sometimes I can wing it and do well, but most of time I can be decived by the angles and distances at play.
I also agree with Ellis, there is no substitute for a Polaroid back. The main reason for this... what you see in the ground glass is not always what appears on film. If you were to shoot at the same wide open f stop, it should come close, but rarely do any of us every shoot at 6.5 or 9. So therefore, the effects of stopping down are not so easy to anticipate as when no movements are used. If you stop down and try to view the ground glass under the f stop you plan to use, you do not have enough light to see the focus properly to assess your potential for success. This is why a Polaroid can not be replaced. Also, I find the Polaroid helpful for other things such as vignetting from a lens hood or filters that was not visible on the ground glass but quite obvious in the Polaroid.
Best of luck with your venture, you are on the right track.
-- Bill Glickman (Bglick@pclv.com), May 13, 1999.
Actually the Rodenstock calculator is easier and more convenient than the Linhof but we are happy to sell either!
-- Bob Salomon (email@example.com), May 13, 1999.
I don't know if this will help or not but,
Kodak's Professional data guide includes a depth of field calculator for 4 X 5 and 8 X 10 with the more common focal lengths. Some have pointed out that they don't like Kodaks Circle of Confusion formula, I can't recall now, but I think it was something like Format Normal Focal length/1000.
Jim Stone's book has the simplest description of tilt angle and focusing I've seen, but that's my taste, many like Merklinger. Stone's approach is basically focus near, focus far, mark difference, tilt, re-focus near, re-focus far, check the difference. If the difference is less, then you're going in the right direction. Repeat. If the focus spread comes up markedly different from the previous focus spread, like maybe it gets smaller and smaller and then suddenly gets farther, you've gone too far.
Lastly there's an article in Camera & Darkroom a year or two ago that describes the focus spread technique. If you dig around in the older posts on D.O.F. I imagine you'll find it. B&H and maybe Adorama sell a Linhoff focus "calculator" a small square with the focus spread in mm and the appropriate f/stop for each, for each format. There was a copy of this device in Harris' book on Interior Photography. Lemme know and I can photocopy most of the above and mail it to you if you'll send an S.A.S.E.
-- Sean yates (firstname.lastname@example.org), May 13, 1999.
Bill's maths concludes 0.057mm, and I can't argue with it. But I would add a note of caution: it depends what you mean by 'super sharp prints'. I have done experiments, and found that people can easily rank the sharpness in 10x8 prints made from negatives that were slightly out of focus, but stll well within the standard CofC limits. Not with loupes, but looking at 10x8 prints from a distance of a couple of metres.
One conclusion that I have come to is that 'acceptable CofC' depends on the quality of the lens (and other components in the chain). If you have a very good lens (film, etc), you will only tolerate a very small CofC, possibly one-tenth the size of the accepted numbers. With a lower-quality lens etc, you can can accept a relaxed CofC, essentially because the sharpest point on the print isn't really very sharp.
-- Alan Gibson (Alan.Gibson@technologist.com), May 14, 1999.
Larry, Yep, that is a piece of vaporware sitting on my Arca's back rail section. Norman McGrath and maybe Jack Dykinga have Brainboxes as well. I thought the new version of the Arca brainbox had been released already. For what is is forth I am planning on purchasing one of the Rodenstock calculators as well for use with DLC and my V-pan. A cool tool for traveling fools!
-- Ellis Vener (email@example.com), May 14, 1999.
Ellis: I don't doubt you have an Arca-Swiss Brainbox. Maybe you were among the lucky ones. The dealer I spoke with said they had over 50 people wanting them, and Arca-Swiss never delivered on the item. I only report what I was told.
Dealers can't get them (as told to me by Arca-Swiss), and the new version isn't available (as told to me by Arca-Swiss). I hope you are right about the new version being available soon. Sometimes outside sources hear information faster than factory representatives.
-- Larry Huppert (Larry.Huppert@mail.com), May 14, 1999.