7″ X 10″ Graphite Pencil on Strathmore Smooth Bristol Paper.
From photo by Michele Filoscia
Completed September 2011
7″ X 10″ Graphite Pencil on Strathmore Smooth Bristol Paper.
From photo by Michele Filoscia
Completed September 2011
You may recall Intergraph was a CAD company that selling turn-key systems to architects in the 1980’s. I was working for them then. Yesterday a Swedish company named Hexagon bought Intergraph for $2.13 billion. They make surveying equipment and measuring instruments. Although this technology isn’t used much for architecture (yet) it is quite well established in the Global Information Systems (GIS) and Process, Power & Marine (PP&M) areas. Here is a link to a presentation given by the CEO of Hexagon yesterday.
Although he doesn’t talk about architecture, the middle part of his presentation is quite informative as to the current state and projected future of merging scanning technology with CAD.
I also found the current leader in converting 3D scans (point clouds) into AutoCAD. It is a company called Kubit. You may want to check out their web site.
I would be interested in talking to anyone who is currently using scanning technology in conjunction with AutoCAD or Revit to create architectural drawings.
In an effort to find a new job I have created a Career Portfolio blog at http://ronnyhart.wordpress.com/ . If you know of anyone that may be looking for a CAD Consultant or CAD/BIM Manager, please till them about that site.
(Adapted from an original text by Chris Dennehy and published with his permission.)
These thoughts are concerned with the long term archiving of drawings and other documents and are not about the day to day backing up of computer documentation though some bits may be relevant to daily back up. They also raise the specter of unauthorized amendments by other parties.
Documents may be required for a number of reasons, firstly a client might just possibly come back for a second round or secondly, one might be unfortunate enough to have to mount a legal defense, appraising things from the latter viewpoint should take care of the first instance.
In either situation you require drawings and possibly correspondence and relevant product documentation. With the advent of computer technology this is the first time since written records were kept, in whatever form, that we have been unable to see the record with the naked eye, obviously it is therefore necessary to maintain some method of retrieving this information in a form we can read, with the way technology is changing this is very difficult indeed.
It should be noted that insurance companies tend to sue everybody and anybody remotely connected with you and/or the project in question in the hopes of striking the jackpot and getting somebody other than themselves to pay up.
The printed image:
In days of old we ended up with just one negative on tracing paper, suitably scratched out and amended all over with (hopefully) revision notes that actually meant something capable of being correctly interpreted in years to come by somebody unfamiliar with the job.
If we were lucky it was actually on tracing paper and not on one of those modern long life films that discolored and shattered into fragments after a few years.
This single negative presented storage problems, placing them in rolls is/was a sure fire way of making them more or less unprintable after a few years, though some offices still do it. The one thing it did have was clear evidence of amendment which was generally acceptable as normal practice for the time, it was/is possible for experts to say whether the amendment was recent or dated back to the time of origin of the drawing if things become really difficult.
To mount a successful defense to-day, it may be necessary to show the complete history of the job.
The current practice of maintaining a copy on disk of each revised drawing with it’s revision notes as it is issued has a lot going for it as it provides a record in chronological order of each change made. The disk space required is, of course, enormous as it the storage space required for storing the negative if retained. Keeping a copy of revisions as they are made is relatively simple under most Architectural CAD programs.
Changes in printing techniques are now beginning to, or will, cause problems perhaps in the not very distant future. The dyeline technique is now almost gone except for the smaller office which clings onto obsolete machinery. The A0 photocopier machine is costly, has a large footprint and heavy maintenance costs, the quality of its prints is generally disliked and it is gradually being replaced by machines that print directly from the HDD (and which can also scan in drawings but see note below). When it comes to upgrading their plotters, many offices which do not have high printing volumes are now replacing their plotters of various sizes with the newer types which can, in theory at any rate, produce a plot in 45 seconds, and have dispensed altogether with large format printing machines.
The change from pen plotters to ink jets has itself made changes in reproduction techniques, if you take a file designed for pen plotting and now plot it on an ink jet without any amendments the chances are that it will look very different from the original. When plotting with pens, lines were heavier because of problems with the pens themselves and it was also common practice to use a colored ink pen for shaded areas as this printed on the dyeline machine in different weights of gray adding depth to the drawing.
All this means that the chances of reproducing something in a few years time that looks exactly like the paper original the client has tucked away someplace and handed to his lawyer is getting more and more remote; just think how much mileage a good lawyer is going to make out of two documents claimed to be identical but which look different. A simple font change is going to give them a field day.
If it is decided to dispose of drawings to reduce storage requirements, I suggest that door schedules and any other documentation relating to fire precautions are retained. In a recent fire in a domestic situation, several people were killed in circumstances where this should not have been the case, investigations showed that the owner/occupiers had replaced fire doors with “nice glazed doors”.
As the legal system seems to be light years behind the computer industry and it’s practices, it will be interesting to see what happens when somebody arrives into court waving a CD and saying its all here judge but we can’t open it.
The problem is further exacerbated by :-
Programs that come with a hardware lock/key/dongle whatever you wish to call it, present particular problems in relation to backwards compatibility and the possibility of having to resurrect long dead drawings, the legal considerations of this does not appear to be fully considered by program vendors.
e-mailing drawings etc.,
E-mailing your drawings/documents to others presents certain problems of authenticity, how do you prove that the drawing you sent was changed by the other party and the defects that arose were due to that change. On the other hand e-mailing drawings to other members of the design team does have certain advantages, generally they either overlay their own information on top of yours (services engineers) or axe out anything not of interest to them (structural engineers), this means that there is at least some semblance of your drawing floating around which can be resurrected if your system fails.
I have no idea how this could be made to work, but to obtain protection from defects caused by unauthorized changes to drawings, some form of data lock is going to have to be found that allows others to add their information to your drawings while at the same time preventing your drawings from being amended. Such a lock would have to extend to the layer structure, layers turned on/off could cause as much trouble as amended drawings. Apart from interchange between offices all using the same CAD system, most drawings are either exchanged using .dwg or .dxf formats. Therefore, such a system would have to extend into these realms. To reduce the risk as much as possible, I suggest that drawings issued electronically should be cut down as much as possible and only incorporate such detail as is required by the recipient.
Is data interference far fetched? I don’t think so. As sure as God made little apples, somebody somewhere is going to find themselves on the wrong end of a defects case and decide that the best way out of it is to alter the other persons drawings and shift the blame.
Drawing issue sheets are all very well but they are unlikely to provide a definitive proof of the issue of drawing. Someplace, sometime, a drawing has got out without one and that’s the one that’s going to be quoted at you.
One reaction is likely to be that only printed copies should be issued, in the electronic age however, this would represent a retrograde step and is unlikely to prove acceptable to the construction and engineering industries.
Can be a help in proving the date of a document, a simple procedure is to enclose documents that might be contentious in a registered letter and mail them to yourself where they are retained in a secure vault (doubtless everybody has one), unopened until you are in court, you are then relying on the post office to maintain their proof of delivery dockets and to prove delivery on a specific date.
It is generally recognized that a magnetic disk has a maximum life of around 5 years but as manufacturers only give around 3 years guarantee with their product then I think it unwise to rely on a drive for more than this period, I suspect that removable drives have a much shorter life span than their guarantee because of the abuse they suffer and are, in my opinion, not really suitable for long term storage.
I don’t think that tape drives can be relied on for much more than short term storage, most manufacturer’s only give a 2 year guarantee on the unit, they also rely on the software operating systems and programs being maintained in use and/or the retention of old machines in working order that can be relied on to operate them.
There is also the problem of wear with drives which deposit data on a tape using helical based technology, the screw can apparently become misaligned over time and trying to open data placed on a tape say a couple of years previously may not be possible.
As tape drives change all the time (continuous improvement is the manufacturer’s term for finding how to take another shortcut and make it cheaper), trying to open an old tape on a new drive could be interesting.
The life of a tape should also be taken with a grain of salt, they might last the number of years specified, but will you still have the operating system and equipment to run them, then of course there’s Murphy’s Law, the break in the tape will contain the data you want.
This looks like the best bet at the moment as every machine has a CD drive but they also rely on the software operating systems and programs being maintained in use to retrieve the data. New types of CD are supposed to arrive next year with greater capacities but I don’t know if you can use them in the same drives or if they can be re-written.
[[[Placing pdf files on CD’s may not be a bad idea. Kodak claims a 200 year shelf life! Acrobat reader could be on every CD to help ensure future readability.]]]
DVD or Blu-ray
I know this has tremendous potential but think I’d wait and see how this one’s going before I plunged.
Manufacturer’s change their specifications from time to time. A 20 year old brochure showed that a defendant had met the manufacturer’s specifications at the time, thus relieving him of responsibility for the fault which developed. The standards were well below those currently in operation. The opposing lawyers were rather disappointed.
A person was doing house inspections for a lending company. A fault developed and a house purchaser sued. The company by whom he was retained stepped back and he was not in a good position. Fortunately for him, he unearthed an old written company instruction sheet listing what was to be inspected. He had followed the instructions to the letter and was saved, so keep the client’s brief.
One further point, occasionally everybody has to report on the condition of a building. If you notice something that needs to be repaired or replaced, it is not enough to say so. You must also say when it is to be repaired/replaced. When inspecting a pumping station a consultant recommended that a pipe carrying chlorine be replaced. The client noted the report but took no action. The pipe failed and a workman received serious injuries. The judge ruled that the consultant was 80% responsible because he had not stated when it should be replaced. To be on the safe side, include a carefully worded definition of all the times you give such as “immediately means – on receipt of this document”. Bear in mind however that the period given to repair/replace an item should allow, where necessary, for its manufacture and/or delivery, therefore include a note to that effect in your report when calculating the time for an action to be taken, otherwise you could be faulted for being unreasonable. Send the report as fast as you can by registered/recorded delivery or some other approved method where a record of delivery is obtained and can be verified, maybe years later. Very careful thought has to be given to the method of delivery, it has to be verifiable, somebody is going to have to sign for it, at the same time it has to be as fast as possible so you can’t be faulted for delay and the opportunity for somebody to refuse a report and leave you unable to deliver it has to be removed.
There are a lot more whereas’s, heretofore’s and whatsoever’s than mentioned above that should be included in a report and the definitions of times and method’s of delivery of a report, particularly one that could be contentious, is a lot more complex than indicated in the foregoing paragraph which barely indicates the tip of the iceberg – take care and keep several copies.
If the maintenance of an archive that is fully up to date is essential then:
Keep a record of the dates on which operating systems were introduced and upgraded.
Do the same for all changes in software programs and hardware reproduction and storage systems.
Keep a hard paper copy of every document relating to a project in a place that is safe from water, fire, vandalism, general decay and any other risk you can think of.
Upgrade every computer generated document each time you change operating systems and programs on to the most robust storage medium available at the time.
Keep duplicate copies of everything in separate locations and I don’t mean each side of the desk.
Change your hard drives on a regular basis.
Review your long term storage media and retrieval systems on a regular basis and update when necessary.
Maintain an insurance policy that covers electronic data loss. This should also include a lump sum payment for somebody to redraw lost drawings. Remember the computer industry says that a firm experiencing data loss has a good chance of going out of business within 6 months.
It is perfectly obvious that most of this is not going to happen unless you want to give up architecture and become an archivist, so whatever you do, it is going to be important to show that you have taken all reasonable precautions. Make sure your definition of reasonable prevails.
For those of you who haven’t tried it, scanning hand drawn drawings into CAD systems may not be as attractive as it first sounds unless they are to be stored and printed without amendment. Hand drawing is not accurate in computer terms and although lines on the drawing may look vertical/horizontal to our eyes they are probably wavy to the computer, by the time you have everything straightened out, including hand drawn text, removed coffee stains and the like, it may well be quicker and easier to redraw it directly into the program.
Now the traditional disclaimer:
Anyone who relies on the above personal opinions/thoughts and bases their approach to document archiving/storage and general and data security on them without doing their own research, taking appropriate technical and legal advice and checking things out for themselves is a raving lunatic.
Any in-house CAD training program that you implement should be designed to take your company’s employees that have a requirement to operate your CAD program as a function of their job through 5 levels of abilities. These levels are relevant to whichever CAD/BIM program your company uses.
1. Computer Literacy
This is the ability to:
A. Access programs and data
B. Find data fast
C. Store data securely
D. Make and retrieve backups
E. Perform security procedures (virus checks, etc.)
2. Basic CAD Skills
This is the ability to:
A. Access CADC databases and drawings
B. Define the capabilities of your CAD program
C. Control the CAD system
D. Create work
E. Save work
F. Be self supporting (know how to get help)
3. Complete CAD Skills
This is the ability to:
A. Use the CAD program’s features needed to do their job
B. Be organized and effective
C. Use any customized features
D. Create complete output (draw, display, dimension, plot)
4. Advanced CAD Skills
This is the ability to:
A. Enhance production
B. Utilize short cuts and techniques
C. Use advanced features and processes
D. Optimize the creation of data for maximum utilization of the CAD program’s capabilities
5. Optimization Skills
This is the ability to:
A. Customize the operating environment
B. Customize the CAD program’s
– Custom programs
You must also establish a set of office standards and procedures.
A standard is something you do, a procedure is how you do things.
Use of layers per drawing type
Naming of drawings, repeated items, etc.
Furniture numbering system
What drawing sheets are required on a project (by project type)
Naming of text files and reports
Documentation of sigmacs and menus that you create or customize
System clean-up (keeping trash off the network)
Creating plans, elevations, etc.
Filling out Architectural schedules
Maintaining a system log of problems
Example in-house training Schedule
Schedule one class each month. Start over again next year, new people and refresher class for the infrequent users. If you have the luxury of a dedicated training room where each student can have his own workstation (or a maximum of 2 students per station) you can cut these training times by about 25%. If you have to use a single station for teaching I recommend 50% lecture / demonstration and 50% hands-on. Typically alternation between 1 hr. in the training room and 1 hr with each person at his or her own workstation for hands-on practice. All aspects of the topic should be covered with special emphasis on those procedures which the employee is most likely to need in the performance of his regular duties at your office.
You may be wandering why I am including this guide to (film) photography in a blog about CAD software. To master 3D computer rendering, a firm foundation in photography can be an asset. Whether you are taking digital photographs of the site to use as a background for your computer model, or setting up the rendering options in your rendering software, an understanding of film photography will provide a strong background for correctly configuring all of the different options you may have available. Or you may just want to dig out that old 35MM camera.
The following is from an old text file (1989) that I have on my computer. I am not the original author. I am posting it here for general information only. I have lost track of where it came from. If anyone can identify the author of this, or if you are the author, please let me know so I can give you credit. If the author objects to my posting this, I will gladly remove it.
HOW LIGHT AFFECTS FILM
With print film you create a negative which is projected in an enlarger to create the print, which is actually a “positive.” As you expose the film to light in the camera a chemical reaction causes the film to become darker. The darkest areas in the subject come out as the lightest areas in the negative because that part of the negative is receiving less light. The brightest or lightest areas in the subject come out as the darkest areas in the negative because that part of the film is receiving more light during exposure. With slide film, also called “reversal film,” you do not make a negative; you make the positive slide directly; the slide film in the camera is developed and mounted for projection. A slide is actually a “film positive,” also called a “transparency.”
THE MECHANICAL SEQUENCE FOR 35MM SLR CAMERAS
When you press the shutter-release button:
THE F-STOP AND SHUTTER SPEED RELATIONSHIP
The f-stop is the number representing the setting of the aperture of the lens. You adjust the aperture to control the amount of light passing through the lens. The f-stop settings are marked on the lens and clicks may be felt when stopping-up (opening) or stopping-down (closing) the aperture. F-stops are inscribed as such on most lenses: 1.2, 1.4, 1.8, 2.8, 4, 5.6, 8, 11, 16, 22, 32. When you open up the lens aperture one stop, you let in twice as much l ight for exposure, as long as the shutter speed is not changed.
When you close down the lens, each stop you reduce the amount of light by 1/2 — as long as the shutter speed is not changed. Note: the smaller the f-stop number is, the more light will come through the lens. The shutter speed is the setting of what length of time the light passing through the lens will be allowed to expose the film. It is set by a rotating dial on the top of your camera with click stops.
Special Shutter speed settings:
B – The shutter stays open as long as the button remains depressed.
T – The shutter is locked open after the button is depressed, until you move the shutter speed dial.
A – Automatic.
Shutter speeds are expressed as and are fractions of a second.
1 = 1 second, 2 = 1/2 second, 4 = 1/4 second, and so on…
Similar to f-stops, each change of exposure either doubles the speed of the exposure or cuts it in half. F-stops deal with the amount of light coming through the lens, while shutter speed deals with the length of time the film is exposed to that light.
f2.8 EIGHT TIMES MORE LIGHT THAN f8
f4 FOUR TIMES MORE LIGHT THAN f8
f5.6 TWICE AS MUCH LIGHT AS f8
–> f8 Starting Aperture Setting <–
f11 1/2 THE LIGHT OF f8
f16 1/4 THE LIGHT OF f8
f22 1/8 THE LIGHT OF f8
1/15 EIGHT TIMES MORE TIME THAN 125 ( + 3 stops )
1/30 FOUR TIMES MORE TIME THAN 125 ( + 2 stops )
1/60 TWICE THE TIME OF 125 ( + 1 f-stop )
–> 1/125 Starting Shutter Speed Setting <–
1/250 1/2 THE TIME OF 125 ( – 1 f-stop )
1/500 1/4 THE TIME OF 125 ( – 2 stops )
1/1000 1/8 THE TIME OF 125 ( – 3 stops )
Remember that a change in shutter speed is also a change in the absolute amount of light.
or, expressed as a ratio — F-STOP : SHUTTER-SPEED
Only the combination (or ratio) of f-stop and shutter speed adjusts or determines the amount of light to be exposed to the film.
CHOOSING A SHUTTER SPEED
All of the following exposures allow the film to be exposed to the exact same amount of light:
1/15 @ f22
1/30 @ f16
1/60 @ f11
1/125 @ f8
1/250 @ f5.6
1/500 @ f4
1/1000 @ f2.8
If you increase exposure time (shutter-speed) and at the same time decrease the lens opening, you do not change the total amount of light reaching the film — the f-stop/shutter speed ratio. So, you can choose whatever combination you want without altering the lightness or darkness of the print, negative or slide.
1. To avoid blurry pictures when hand-holding the camera, never use a shutter speed longer than the focal length of the lens. For example: with a 50mm lens do not use a shutter speed of 1/15. A shutter speed of 1/60, however, would be sufficient.
2. 1/125 of a second is generally the slowest speed that will freeze motion.
3. If you want to use a particular f-stop setting then you can only use one shutter speed setting, unless you go to a different ISO (speed) film.
EXPLANATION OF ISO — FILM SPEED
(ALSO REFERRED TO AS “ASA”)
The higher the ISO number, the more sensitive the film is to light. Double the ISO, double the sensitivity; half the ISO, half the sensitivity. Each doubling or 1/2 reduction of the ISO represents a difference of one f-stop, or, a change of one shutter speed. ISO 400 film is four times faster than ISO 100 film, a difference of two f-stops. ISO 200 film is half as fast as ISO 400 film, a difference of one f-stop. Use ISO to help you decide which film is right for the type of pictures you are taking and your lighting conditions, and to serve as a setting for your light meter.
Five things to consider when choosing ISO:
Notes on Color Films: Most color films are “balanced” for exposure under daylight (outdoor) conditions. Some color films are designed for different types of light:
Tungsten Film — for use indoors under warm light bulbs.
Daylight film can be used under warm indoor room light by using a blue filter over the lens. Using Tungsten film indoors with a flash, or in daylight will produce an orange cast in the picture. Using daylight film with warm light bulbs will produce an orange cast. To use daylight film with fluorescent lighting, use a magenta filter, usually marked “FL.”
TYPES OF CAMERA’S AND FILM FORMATS
I. Small Format: 35mm camera’s. The normal lens is 50mm.
A. SLR – Single Lens Reflex. You view and meter through the lens by way of a mirror/viewfinder system. The shutter is in the camera body.
B. Rangefinder 35mm Camera. You do not look through the lens at all, but through a hole in the camera (placed on the upper left or middle) which is aligned with the lens. There is no mirror. The shutter is in the lens. An internal rotating prism mechanism which superimposes two images together in a square box in the viewfinder is the focusing method. As you turn the focusing ring on the lens, the two images in the box align when the picture is focused to maximum sharpness.
II. Medium Format: Negative sizes 6×4.5cm, 6x6cm, 6x7cm
A. 6×4.5 cm — SLR’s only. Examples are Mamiya 645, Pentax 645. The normal lens is 80mm.
B. 6×6 cm — SLR’s: Hasselblad, Rollei SL series, Bronica 6×6 TLR’s: Mamiya C330 and C220, Yashica A TLR (Twin Lens Reflex) has two lenses aligned together. Viewing and composing is done though top lens but the picture is taken by the bottom lens where the shutter is. The mirror does not move up and down. The normal lens is 80mm. The Mamiya C330 is the only TLR with interchangeable lenses, viewfinders and focusing screens.
Note: There are only two types of shutters, focal-plane and leaf shutter. A focal plane shutter is inside the camera body. It moves vertically or horizontally, depending on the camera. A leaf shutter is always in the lens and opens and closes just like the aperture in a human eye. Leaf Shutters are always mechanical.
C. 6×7 cm — SLR: Pentax 6×7, Mamiya RB67, Mamiya RZ67 RANGEFINDER: Rapid Omega Series, Linhof, Makina. The normal lens is 105mm.
III. Large Format: 4×5, 5×7, 8×10 inch negatives. Calumet, Sinar, Linhof, Cambo, and many more. The camera must always be mounted on a tripod. Ordinarily, one sheet of film at a time is used, but roll film adapters are available. The shutter is in the lens. Darkness is needed to compose and focus, usually provided by a dark cloth over the photographer’s head and the camera back. The image is upside-down and inverted. Focusing is accomplished by adjusting the actual distance between the lens and the film. The principle advantage is that the angle and height of the lens and film in relation to each other may be adjusted to make optical corrections, often mandatory for professional architectural photography or special effects. The large sheet of film provides maximum detail.
Definition of a properly exposed negative, print, or slide: a negative, print, or slide which has been exposed to the MINIMUM amount of light to achieve MAXIMUM DETAIL in the full range of tones, from the darkest shadows to the brightest highlights. Too much or too little light results in a loss of detail.
Distinction between slide film and print film: with print film your first objective is to achieve a properly exposed NEGATIVE; with slide film your “only” objective is to achieve a properly exposed film POSITIVE. Slides are the actual film that passes through the camera — developed, cut and mounted to be projected. Remember that with negative/print film when you open up the lens, or decrease the shutter speed or both at once, you make the NEGATIVE denser. If you close down the lens, or increase shutter speed or both at once — the negative will be thinner.
Conversely, with slide film you are making a film positive. Exposing slide film, when you close down the lens, or make the shutter speed shorter or both at once, you make the slide denser. The LESS light you give a slide the darker it will be; the more light you give a slide film the lighter it will be. Print film is the opposite. Remember that a slide film is not a negative! A negative film is blank until light is exposed to it but a slide film starts out black and becomes lighter as more light is exposed to it. This is why slide film is called “reversal film.”
With negative films, the print can only be as good as the negative. With slide film you think about the positive on film. Slides are the same as prints in that if you decrease exposure “the picture” will be darker; with negatives if you decrease exposure THE RESULTING PRINT will be darker. The opposite is also true if you increase exposure; slides will be lighter, with prints the resultig print will be lighter.
DRAWBACKS OF AUTOMATIC LIGHT METERS AND CAMERAS
An automatic in-camera light meter, no matter how well programmed cannot think for itself and make intelligent decisions. The amount of knowledge required to produce satisfactory exposures using an automatic exposure meter approaches the knowledge needed when not using one at all. Automatic meters are poor judges of exposure on backlit subjects. The meter will expose for the sky, leaving the face black. On partially cloudy days they get very perplexed. Only on a consistently overcast day or photographing a low contrast subject are they partially reliable. Automatic meters look for the “average” exposure, disregarding the main subject matter. APERTURE PRIORITY meters adjust the shutter speed in response to the preset lens aperture. SHUTTER PRIORITY meters adjust the lens aperture for the shutter speed you have pre-selected. PROGRAMMABLE METERS are in theory supposed to produce adequate exposures using a combination of aperture and shutter priority.
MANUAL EXPOSURE SYSTEMS
35mm camera’s are not being manufactured these days without some form of automatic metering. If you disable the automatic feature you have a manual metering system; you get a light reading and the aperture and shutter speed settings are up to you. An option is to purchase a hand-held meter. These are the most accurate, and the most expensive. SPOT METERS usually measure only one degree of light reaching the subject, thus, from approximately twenty feet away from a person’s face one may accurately measure the difference in reflected light from the darkest to the lightest areas.
DEPTH OF FIELD
Depth of field (DOF) is the area between the nearest and the farthest points from the camera that are acceptably sharp. The more that is in focus, the more DOF you have. Depth of field is one of your most important creative controls. By manipulating DOF you have the ability to adjust what portions of the picture are in focus and what are not. Three things affect your DOF, and may be adjusted to give different results:
DOF AND APERTURE SETTING
Adjusting your aperture setting is the only way to change the DOF without changing the composition of the picture. The wider open the lens is (the smaller the number), the less DOF you will have; the smaller the opening (the larger the number) the more DOF you will have. For example: If you want a person’s face to be sharp but the trash cans twenty feet behind him to be blurred out – focus on his face and set an f-stop of, generally, f4 or f5.6. If you want the trash cans sharp too, use an f-stop of f16 or f22.
DOF AND CHOICE OF LENS
Choice of lens affects DOF. The longer the focal length of the lens, the less DOF that lens will produce at any given f-stop, relative to a shorter lens.
FOCAL LENGTH OF LENSES (35mm camera’s)
|Less than 35-50mm||Wide angle lens|
|Less than 35mm||Very wide angle|
|Greater than 70mm||Telephoto|
A so-called “normal” lens approaches the way the human eye see’s a subject in terms of perspective. A 200mm telephoto lens set at f11 will not produce as much DOF as a 50mm lens set at f11. If you want to use a smaller lens opening and want to reduce your DOF, use a longer lens. If you want to use a larger lens opening, f4 or f 5.6, and want to increase your DOF (have more in focus), use a wider-angle lens (a shorter focal length). Example: You have ISO 125 film in the camera, a 50mm normal lens, it is getting dark, and you do not have a tripod. You want to photograph a tree 25 feet away and you determine exposure to be 1/60 @ f2.8. The problem is that you want more DOF, more in sharp focus throughout the picture between the foreground and the background. By simply putting a wider angle 35mm or 28mm lens on the camera, the DOF will be considerably increased.
TWO WAYS OF JUDGING YOUR DOF VISUALLY
1. Depress the depth of field preview button or lever on the camera body or lens, if your system has this feature. This will close down the lens aperture. If you turn the aperture ring with the DOF preview button depressed you will see your DOF increase — more of the picture from foreground to background will become sharper. A problem with this method is that at f11 the image in the viewfinder may be so dark as to be difficult to see. When you release the DOF preview button or lever the aperture will open fully again. With the lens wide open at f1.8, if you focus on a person five feet away, the background twenty feet away will be out of focus, even with a wide angle lens. If he were standing against a wall the aperture setting would be irrelevant. The point is that one may judge DOF visually through the viewfinder for creative purposes.
2. There are usually color codings on your lens, vertical lines that line up with the distance scale on you focusing ring to determine DOF. These tell you what your DOF or “field of focus” is. Refer to your owner’s manual for more specific information regarding your particular camera.
Example: I am taking a picture of a person focused 10 feet away with a 50mm lens. Exposure is 1/125 @ f8. On the Nikon lens, the color of the f8 markings are red. The red line on the barrel of the lens to the right of center lines up with the 8 foot mark on the focusing ring. The red line to the left of center lines up with 15 foot mark. This tells me that at f8 with this lens, focused at ten feet, everything between 8- 15 feet from the camera will be in sharp focus.
In sports photography, it is often difficult to follow the action and keep the subject in focus. Instead, focus on point of the track or playing field and choose an aperture that will give you a deep field of sharp focus (f11-f22). Any time the action is in that sharp DOF zone, focusing is unnecessary. Simply release the shutter without worrying.
Suppose you are taking electronic flash pictures in a very dark room. Your exposure is 1/60 @ f8 with a 50mm lens. It is too dark to focus precisely but you know that your subject is about 12 feet away. You can see by your DOF indicating lines on the lens that if you focus the lens at 10 feet, everything from 8-15 feet will be sharp at the f8 setting you are using.
LENSES AND PERSPECTIVE
Perspective is the apparent size and placement of objects in relation to each other within an image. Perspective changes (varies) depending on the focal length of the lens and the distance from the subject. With a “normal” lens (50mm on a 35mm camera) the perspective is the same as the way the human eye would view a scene. The angle of view is about 50 degrees. With a telephoto lens (75mm or longer on a 35mm camera), the longer the lens, the more space is “compressed.” This is called a flattening effect. Distant objects appear to be closer to each other when compared to a normal lens; objects appear closer together than reality. Using a wide angle lens (focal lengths of 35mm or shorter on a 35mm camera) objects close to the lens appear distorted or enlarged. A 50mm lens has no magnification, thus it is 1X (one power). A 25mm lens is .5X, half the magnification of the human eye. A 100 mm lens is 2X. A 1000mm lens is 20X.
CONTRAST AND LIGHT
Contrast is the difference in brightness between light and dark areas within the negative, print, or slide. Contrast refers to the brightness of the picture overall and the number of middle tones or “middle values” in the negative, print, or slide. Middle values are the areas of the picture in the middle of the spectrum of light between maximum black or the very darkest tones/colors and maximum white or the very lightest tones/colors.
A NORMAL CONTRAST photograph has a wide range of tones or values: Low values — the darkest areas…blacks, dark shades or shadows. Middle values — the intermediate areas/tones. High values — Bright areas or tones nearing and including the white end of the spectrum. Highlights. Bright-light colors.
A LOW CONTRAST photograph has no real pure whites or light-bright colors or tones. An extremely low contrast photograph is referred to as “flat.” It has no sparkle. As you decrease the amount of light reaching the film, the result is a lower contrast photograph. It may be judged “underexposed.” The negative will be thinner; the print or slide will be consequently darker. Low contrast lighting is sometimes called “diffuse light.” This refers to generally overcast cloudy days with little or no distinct shadows, no bright sky, and will produce a photograph of less contrast.
A HIGH CONTRAST photograph has little in the middle values, just very dark and very light areas. If there are no middle tones the photograph may be viewed as too having too much contrast. As you increase the exposure, the amount of light to hit the film, the result is a higher contrast photograph. It may be considered “overexposed.” The negative will be thicker (denser) resulting in a lighter print. The same is true for slides. High contrast lighting is the effect of bright sunshine with distinct shadows, or, for example, a snowy scene with very dark buildings. If there are many distinct shadows on a portrait subject’s face because he is standing in open sunlight, the contrast is high.
Making a proper exposure involves controlling contrast. Any change in the shutter speed/f-stop ratio changes the contrast. Contrast is a subjective matter, open to personal interpretation. Just because a photograph is extremely high or extremely low contrast is not a sole determinant of whether or not the photograph is properly exposed.
In implementing the theory above, whether using a hand-held meter or an in-camera meter, the practice is the same. In order to determine exposure manually for a properly exposed negative or transparency it is essential to know how to perform the following
HOW TO CENTER THE METER
Centering the meter is different procedurally with different cameras. With a “needle” type meter you set the aperture/shutter speed so that the needle is in the center. Refer to your camera and owner’s manual. Whenever the meter is centered, the photographer is placing the value of the subject as a MIDDLE GREY, whether in B&W or color. If you point the meter at a black horse, center the meter and take the picture, you will have placed the black horse at middle grey, so the horse should come out grey instead of black in the print. The same holds true for a white horse. The white horse will also come out grey instead of white. This demonstrates the need for plus or minus adjustment (correction) after centering.
POINTING THE METER
1. If you can, isolate the main subject in the viewfinder. In the case of a portrait this is mandatory. Move right up to the person’s face, take a reading centering the meter, then make any correction.
2. Photographing a contrasty subject, take a centered reading of the brightest area in the frame, then the darkest. An exposure alf-way between the two readings is a good starting point. This is called the “averaging technique.”
3. Exposing for the shadows (with B&W film) will produce a negative of sufficient density to make a good print. Point the camera at some shady area, with no bright area in the viewfinder. Center the meter, raise the camera, compose and shoot. It is imperative to pre-visualize the final photograph before exposure. Always expose for the main subject and let the other values fall where they may.
4. Take your reflected light reading from a grey card of 18% standard reflectance. This will always give you an average reading. These cards are available at any photo shop.
Center the meter and take a picture. Then increase exposure in 1/2 or 1 stop increments for 2-3 stops in each direction from center. This uses a lot of film but assures that you will have plenty to choose from, and with a contrasty subject such as a sunset, you will get the balance between the sky and the shadows that you desire.
PLUS OR MINUS CORRECTION
Even when shooting color, this author pre-visualizes in B&W. If the main subject looks like it will reproduce as middle grey no correction is necessary. If you have centered on a person’s face lit by bright sunlight — open up one stop so that the face will be exposed for one stop lighter than middle grey.
|-3||slightly lighter. No detail.|
|-2||Lowest shadows with detail.|
|-1||Slightly darker than middle grey. Dark skin.|
|— 0 —||MIDDLE GREY (CENTER) Skin on overcast day.|
|+1||Highlights of skin on a sunny day|
|+2||Highlights. Dark Blue sky.|
|+3||Almost white. Hazy white sky.|
Photographing is a combination of knowing where to point the meter and correcting the centered setting if necessary to place the subject in its proper value for the attainment of a maximally exposed negative or transparency. This takes practice. The benefit is creative control not possible with automatic systems that place everything automatically” at middle grey.
END NOTE: The discussion on exposure determination is by no means comprehensive. Advanced exposure determination techniques such as THE ZONE SYSTEM have not been addressed.