CLOSE-UP
There are two methods used to obtain close-up pictures. One is the optical approach which is used by supplementary filters and some close-up zoom lenses. This method uses optics to magnify the image, similar to magnifying glasses. The advantages of this approach lies in the ease with which close-up pictures can be taken and, especially, because no compensation for exposure change is needed. The disadvantages are that the degree of magnification is limited to a maximum of about life-size (1X) reproduction, and that the image quality is less than optimum because these optics not only magnify the image but also magnify the curvature of field and any aberrations of the prime lens. These show up as fuzzy edges or poor definition in the pictures.
The other approach to obtaining close-up pictures is the mechanical method. In this method, the lens is physically moved away from the film and the magnification is increased. There are a variety of ways to create extension between the lens and the film, for example, bellows, extension tubes and reversing rings, but they all basically work the same way. The advantages to this approach are that the range of magnifications that can be achieved are enormous and special flat-field lenses can be used which are designed for high magnification ratios and virtually eliminate problems associated with curvature of field and other aberrations. The disadvantage is that exposure compensation is needed. As the lens is moved away from the film, the light passing through the lens is dispersed over a wider area and less of the light illuminates the film. In order to compensate for this light loss, the aperture must be opened, the shutter speed slowed down, the intensity of the light increased, or a faster film selected.
A TTL metering system simplifies this exposure compensation tremendously as the meter responds to any light loss due to the extension and recommends a compensated exposure. To obtain optimum results it is essential to meter off of a grey card, coffee cup or other suitable object when using a TTL meter, as with any other area of photography.
Unfortunately, this metering method is often of limited use in close-up photography, however. Under bright conditions and with a limited amount of extension the TTL meter will operate correctly, but photographers frequently find themselves in less than bright conditions, and the meter may not indicate the correct amount of compensation. Under low- light conditions, such as a cloudy day, or a stopped-down lens, or a dark forest floor, or with a large amount of extension, or dense filtration, the lower sensitivity limit of the meter may be approached and the meter may become sluggish, inaccurate or inoperative. Therefore, manual compensation for the extension is often necessary. It also is a good way to check to see if the meter is operating correctly under close-up conditions.
There are a variety of formulas that can be used to determine how much to compensate for the light loss, and which formulas are chosen depends on personal preference, the equipment being used, and how the compensation is to be made. The approach used here is not only straightforward, but very accurate as well. All the formulas used here are designed to compute an exposure factor (EF) for the amount of extension which is then used to change the shutter speed, aperture, film speed or incident light intensity.
EXERCISE 29-1 COMPENSATION FOR AVAIABLE LIGHT CLOSE-UP EXPOSURE
1.Determine the correct exposure for the scene in the normal way using a grey card, incident meter or other method. If using a TTL camera meter take the exposure reading without the close-up equipment attached; a normal lens is fine for this.
2.Attach the close-up gear and compose the shot.
3.Determine the magnification using the formula:
M = EX/OFL
where
With view camera equipment this is determined by measuring the distance from the film plane to the lens board and then subtracting from this distance the flange focal length of the lens being used. The flange focal length of the lens is the amount of extension the lens needs to focus on infinity. This can be quite different from the optical focal length of the lens. For example, a 600mm telephoto may have a flange focal length of 375mm. This length can be obtained from the manufacturer or it can be measured in millimeters from the film plane to the lens board when the lens is focused on infinity.
With SLR equipment the amount of close- up extension can usually be determined with a scale engraved on the side of the equipment. If it is not listed it can be measured from the rear mount of the lens to the front mount of the camera, in millimeters.
Many macro lenses prefer not to list the amount of extension on the side of the lens but, rather, list the magnification directly, such as 1:2.
This nomenclature does not refer to 2X (twice lifesize) but rather to 1/2X or a magnification of .5 (half- lifesize). These fractions etched on the side of the macro lens can be used directly as the magnification if they are first converted into decimals.
4.Determine the exposure factor by using the formula:
2 EF = (M + 1)
where
5.Once the exposure factor is determined, using whichever method is appropriate, it is used in a formula to compensate for the light loss by adjusting the shutter speed, the aperture, or the film depending on the situation and the personal preference of the photographer. The formula varies slightly according to which exposure variable is to be changed.
a.To compensate for the light loss by a change in the shutter speed use this formula:
Adjusted Metered speed = speed * EF
Multiply the metered shutter speed by the exposure factor. To do this, it is necessary to convert the fractional shutter speed into a decimal number. An example will simplify this process for non-mathematicians.
Imagine a situation that calls for a shutter speed of 1/60 and an exposure factor of 4. Follow the following steps:
1.Convert the shutter speed to a decimal. 1/60 = .0167
2.Multiply by the exposure factor. .0167 * 4 = .0667
3.Reconvert to a fractional shutter speed. 1/.0667 = 15
4.Use 1/15 of a second instead of 1/60.
This process can often result in odd shutter speeds, such as 1/23, which cannot be dialed into most cameras. As a result shutter speed changes are only useful for larger or full- stop compensations. The table in Appendix E is helpful in converting exposure factors into shutter speed changes.
b.Especially for small changes, it is usually easier to compensate for the light loss due to the extension by making changes in the aperture using this formula: Adjusted f-stop = Metered f-stop/@EF Divide the metered f-stop by the square root of the exposure factor, and the result is the correct f-stop. Dial the corrected f-stop into the lens without changing the shutter speed and expose the film. While this is usually easier than attempting shutter speed changes, unfamiliar f-numbers often result, such as f-3.2. Once again Appendix E will be useful in dealing with hard to place numbers.
c.A third alternative way to compensate for the light loss due to the extension is to change the film; replace the original film with a higher ISO film speed, one needing less light.
The formula is as follows: Adjusted ISO = Original ISO * EF Multiply the ISO of the original film by the exposure factor to obtain the ISO for a correct exposure at the metered shutter speed and f-stop. It is important to note that the ISO's mentioned here refer to your personal ISO's and not the ISO that is printed on the film box.
Occasionally, especially with large compensations, a photographer may opt to compensate for the light loss by adjusting more that one exposure variable.
This can be accomplished by using the information in Appendix C.
These formulas will produce excellent exposures with symmetrical lenses, but if asymmetrical lenses are used, such as true telephoto or retrofocus wideangle lenses, the formula for the exposure factor will be inaccurate. These lenses, for practical reasons, are designed to have flange focal lengths that are physically shorter or longer, respectively, than their actual optical focal lengths. One consequence of this design is that the diameter of the aperture as seen from the front of the lens can be different from the diameter as seen from the rear of the lens. This "pupillary effect" changes the exposure factor and will result in over- or under-exposed pictures if an additional compensation is not made when engaged in close-up photography. Under some circumstances, a TTL camera meter will automatically compensate for the light change caused by the pupillary effect, but when manual compensation for the light loss is being made, telephoto lenses will require additional compensation while retrofocus lenses will require less compensation than called for by the standard formula.
To determine the pupillary effect in each of your lenses proceed as follows:
EXERCISE 29-2 Determination of Pupillary Effect
When using lenses reversed on a single lens reflex camera, it may be very difficult to determine the exact amount of extension. The extension scale frequently found of the side of the close-up gear is useless because it doesn't include the extension created by the front of the lens when it is reversed. Measuring the extension by hand is also difficult because the extension can no longer be measured from the front mount of the camera to the rear mount of the lens, as the entire length of the lens would end up being included as extension. Exact methods of measurement vary with the optical system of the lens so its best to avoid reversing the lens, not only to avoid exposure problems but to ensure optimum results. Use a lens designed to be attached in the normal position at the desired magnification. Some manufacturers supply exposure information for reversed lenses and this makes calculations feasible with these optics.
Another problem lens when used with a single lens reflex camera is the bellows lens. Designed to be used on a bellows, they are sometimes referred to as "short mount" lenses because they lack the normal barrel of an SLR lens.
The barrel of the lens is created by the bellows and allows more flexibility than when using regular lenses on a bellows.
For example, a 100mm bellows lens can focus on infinity when on a bellows while a regular-mount 100mm lens can't focus on infinity when attached to a bellows. This makes extension measurement with bellows lenses difficult, for the bellows scale is designed for non-bellows lenses. When a normal 100mm lens is attached to a bellows with 100mm of extension, the magnification is 1; when a 100mm bellows lens is attached to the same 100mm of extension the magnification is about .6. Normally it is easier to check the manual of the bellows lens for the amount of compensation at a given bellows extension than to try to calculate it all by hand, especially if the bellows lens is asymmetrical or reversed.
If a filter is being used in addition to the close-up equipment, multiply the exposure factor of the close-up extension by the exposure factor for the filter (do not add them together) and then proceed to compensate by changing the aperture, the shutter speed or the film. If compensation for the extension is made by adjusting the shutter speed, make sure to compensate for reciprocity rule failure, if needed, after the shutter speed is adjusted for the light loss due to the filters and the extension.
In summary, when using close-up equipment determine the exposure compensation in one of the following ways:
Close-up photographers quickly discover that they frequently need to use electronic flash. Available light is rarely sufficient because as the image is magnified so is any blur the normal shutter speeds can cause. Faster shutter speeds are needed to prevent this blurring, precisely when slower speeds are often used to compensate for the light loss due to the extension. Compensation by opening-up the lens is problematic because as magnification increases, the depth-of- field decreases. Faster films can be used to compensate for the light loss but this produces an increase in grain at a time when fine detail is the goal. Electronic flash eliminates these and other problems, such as low light levels, by greatly increasing the available light. It's so fast that is freezes any motion in the camera or subject; In fact, close-up pictures can even be taken without a tripod. The light is so bright that depth-of-field can be increased to the maximum and the finest grain films can be used, preserving the fine details of the subject.
To avoid making calculations in close-up photography when using electronic flash, many photographers use automatic exposure features; although appealing, these automatic features are not without severe limitations. First, the TTL meter in most cameras is useless because it can't read electronic flash light.
The automatic mode of the electronic flash is similarly useless because it has no way of knowing if or how much extension is being used. A few cameras employ an automatic TTL flash feature that can be used under these conditions but it too has severe limitations.
TTL flash, just like other exposure systems assumes that the subject reflects 18% of the incident light, which is often not the case in close-up photography. In addition, the TTL flash reads the light after it is reflected off of the film during the exposure and if the film is lighter or darker that 18% reflectance, which is usually the case, the exposure will be off. Another problem with using automatic flash exposures in close-up photography is that it is often difficult to point the flash and the sensor at the subject; Some companies have developed systems to overcome this problem but the sensor may not be reading the scene in the same way as the lens.
Consequently when using electronic flash in close-up photography, exposure is more accurate by using a combination of manual flash calculations and manual close-up calculations. It is somewhat more time-consuming, but the results are worth it; proceed as follows when using a single flash:
EXERCISE 29-3 Close-up Compensation with a Single Flash
Fill-in flash is frequently used in close-up photography in order to eliminate the harsh shadows created by the main flash. When using a fill-in flash, proceed as follows, after performing the first nine steps listed above for a single flash:
EXERCISE 29-4 Close-up Compensation with Fill-in Flash
A.Select a lighting ratio to your liking.
B.If compensation for the extension (and filters) was originally made by adjusting the f-stop or changing the film, compute the flash-to-subject distance for the fill-in flash(es) with the normal fill-in flash formula: D = (GN * @R)/f-stop where D = fill-in flash-to-subject distance.
GN = guide number for the fill-in flash at the original, unadjusted, personal ISO.
R = selected lighting ratio.
f-stop = original, unadjusted f-stop.
C.If compensation for the extension (and the filters) was made by adjusting the main flash-to-subject distance, compute the flash-to-subject distance for the fill-in flash(es) using the amended formula: D = (GN * @R)/(f-stop * @EF) where EF = exposure factor for the extension (and filters).
D.Expose the film.
Electronic flash can be used as a fill for sunlight in close-up work just as it is used in regular photographic work. The above steps must be modified in the following ways:
EXERCISE 29-5 Existing Light Fill-in Flash in Close-up
If a flash unit is to be used as the main light source and the sun is to be used as the fill-in light, the procedure changes somewhat:
EXERCISE 29-6 Existing Light as Fill-in in Close-up
1.Focus on the subject with the close-up gear attached.
2.Set the flash on manual; the sunlight can shut it off prematurely if it is set in the automatic mode.
3.Meter the sunlight normally.
4.Choose the desired depth-of-field(f-stop).
5.Determine the correct shutter speed for the f-stop selected earlier, making sure it falls at or below the synch speed for focal plane shutters.
6.Determine the magnification using the magnification formula.
7.Determine the exposure factor for the extension by using the appropriate exposure factor formula or the lens owner's manual.
8.If filters are being used multiply the exposure factor for the filters by the exposure factor for the extension.
9.Compensate for the light loss due to the extension (and filters) by changing the f-stop, shutter speed or ISO as shown earlier. Compensation cannot be made by adjusting the flash-to-subject distance.
11.If compensation for the extension was made by adjusting the f-stop or the ISO compute the flash- to-subject distance for the main flash by using the normal formula: D = GN/f-stop where f-stop = original, unadjusted f-stop.
GN = Guide Number for the original, unadjusted, personal ISO.
12.If compensation for the extension was made by adjusting the shutter speed compute the flash-to- subject distance for the main flash by using the amended formula: D = GN/(f-stop * @EF)
13.Choose the preferred light ratio and underexpose the existing light in one of two ways:
1.Compensate for the desired light ratio by increasing the shutter speed using the formula: Adjusted speed = original speed/ratio
2.Compensate for the desired light ratio by decreasing the flash-to-subject distance using the formula: Adjusted Original distance = distance / (f-stop)* @R It's easy to see that when using flash for close-up pictures, especially with lower powered units or where greater depth-of-field is sought or when slow speed film is used, that the flash can end up very close to the subject.
The advantages to this is that the flashes can be very easily manipulated. The disadvantage is the possibility of incorrect exposure.
At very close distances, the flash-to-subject distance must be more precise than when it is placed further away.
For example, when a flash is 6 feet away from the subject a change of three inches will change the exposure by 1/8 of an f-stop, but at 6 inches from the subject the same repositioning will cause a two f-stop exposure inaccuracy.
Needless to say, measure carefully. Also, at distances closer that one foot it is necessary to use decimals in the formulas; for example,if you want the flash placed at 6 inches, use .5 in the formula (1/2 of a foot) not 6. Likewise, when the formula returns a decimal as an answer, for example, .25, it is necessary to convert this to inches by multiplying it by 12; .25 * 12 = 3 inches.
Another problem when using an electronic flash at very close range is the inverse square law failure. At very close range, whether or not close-up gear is being used, most electronic flashes no longer operate in accordance with the inverse square law. Due to the severe angle at which the flash is generally held at this distance, compensation must be made to avoid underexposure. Table 29-1 shows how to compensate.
TABLE 29-1 Close-up Flash Compensation Guide Flash-to-Subject Amount to Distance Compensate 12" + 1/2 f-stop 6" + 2/3 f-stop 3" + 1 1/2 f-stop 1.5" + 2 f-stop A special area of close-up work is slide copying. This allows the photographer to make copies of slides and also allows for more creative work such as cropping, color correction and manipulation, slide-to-negative duplication, negative-to-slide duplication, contrast change, grain intensification, over- and under-exposure compensation, multiple exposures, texture addition, and other special effects, such as filtration. In fact, the list of possible manipulations and corrections seems endless.
Slide copiers come in a variety of forms to fit in with any current close-up equipment you may have, and they are relatively inexpensive. If you own a bellows, the manufacturer may offer a slide copier which attaches to the end of the bellows and allows the use of a variety of lenses and magnifications. If you don't own a bellows, special copying units can be purchased which attach to the front of the camera; these units replace the standard lens and come with special close-up optics built-in.
A variety of light sources can be used with a slide copier. Sunlight is the most obvious source; while it is cheap it is not always available when you need it. Another inexpensive light source is a slide projector which you may already own. If you have access to a color enlarger with a diffusion head you have an excellent light source for slide duping. Another popular alternative is to use an electronic flash as the light source.
Whichever light source you choose it will probably require filtration to precisely match the color balance of the film. Fortunately, slide duplicating films can be purchased which are balanced for either daylight or tungsten illumination. In addition, using a colorhead from an enlarger greatly simplifies this process due to its built-in filters.
Finally, as will be seen shortly, the light source can effect how compensation is made for the light loss due to the close- up extension(and filters).
When copying slides several factors can cause light loss for which compensation is needed.
A.Bellows extension -- this is compensated for just as it is with any close-up exposure.
B.Filters -- any filters that are used for color balance cut out light and must be compensated for in the normal way.
C.Diffuser -- copiers incorporate a diffuser between the slide and the light source to give soft, even illumination over the slide. These normally cut out one f-stop of light and require compensation.
D.Distance -- The distance between the diffuser and the artificial light source, whether projector, flash or colorhead requires compensation similar to the inverse square law.
A TTL camera meter will compensate for light loss due to any of these factors, but the reading it gives may not be accurate for several reasons. First, as with any close-up work, the lower sensitivity range of the meter may be reached. For example, a 50mm bellows lens with 150mm of extension requires four f-stops of compensation due to the extension. The diffuser requires one more f-stop of compensation, and filters can require one or two f-stops more. If slide duplicating film is used with an ISO of 8 on a sunny day at f-16 the calculated shutter speed will be 15 seconds with heavy filtration.
Once reciprocity is accounted for, the actual shutter speed needed will be 80 seconds.
Most TTL camera meters will not be able to provide a reading at the setting. First, most ISO knobs cannot be set for speeds as low as ISO 8. In addition, many camera exposure meter scales only readout down to 1/2 second. Even opening the bellows lens to the maximum aperture setting -- about f- 4.0 --to get a reading requires a shutter speed of one second, below the capability of many meters.
Even if the TTL camera meter gives a reading it may be inaccurate as is often the case in low light situations. In addition, as with any scene, the meter assumes that it is pointed at an 18% reflectance subject, and a light or dark slide will bias the results. Filtration can worsen problems with inaccuracy. For best results, when using a TTL meter use as bright a light source as possible. Next, if the ISO knob cannot be set at the ISO setting for the duplicating film, for example, ISO 8, set it at four times the ISO -- in this case ISO 32 -- and after getting the meter reading remember to open-up an additional 2 f-stops or shutter speeds in order to compensate for the change in the ISO. Thirdly, instead of metering the slide you wish to duplicate, meter an 18% grey subject. Take a shot of a grey card using slide film and use this as a metering substitute for the slide to be copied.
Temporarily substitute the 18% grey slide and obtain a reading before reinserting the slide to be duped. In addition, if any filters are to be used add them to the lens when metering the 18% grey slide.
If you doubt the accuracy of your TTL meter or if you prefer to use electronic flash as a light source, manual compensation for the light loss can be made. The procedure varies slightly depending on the light source.
EXERCISE 29-7 Manual Slide Copying Compensation
1.Determine the light intensity at the slide duplicator diffuser. If using filter on or in the light source, make sure they are not in place.
2.The exposure factor for the diffuser is 2 (1 f-stop), although this may vary slightly from brand-to- brand.
3.Determine the exposure factor for any filtration by checking the owner's manualof the filter or colorhead. Appendix E may be of some help here.
4.Determine the exposure factor for the extension and the lens by using the lens owner's manual or the appropriate formula.
5.Multiply all the exposure factors together.
6.Compensate for the light loss in any of the following ways.
7.Expose the film.
Copying slides also allows the photographer to correct for slightly over- or under-exposed slides. If a slide if over-exposed -- too light --, underexpose it when duplicated. If a slide is under-exposed -- too dark -- over-expose it when it is duplicated. The amount of over- or under-exposure compensation that is required depended on how bad the original exposure was. Grossly inadequate exposures are beyond recuperation; minor errors require small adjustments. There is no perfect way to determine the amount of compensation that is needed in the duplicating process, but a general rule of thumb is to examine the offending slide or your records of the exposure and calculate, in f-stops, how far off the original exposure was. Take half of this figure and compensate in the opposite direction when duplicating the slide. It's always good practice when duplicating an incorrectly exposed slide to bracket the duplicating exposures.
Copying slides is often used as a method for reducing the contrast in a scene through a process called pre-exposure or fogging. A weak pre-exposure of the entire piece of film will hypersensitize the light sensitive crystals in the film so that the shadow areas will respond more completely to the scene exposure and display more detail. This process can be used with any type of photography although it is more commonly used in the darkroom than in the field. To fog film, proceed as follows:
Exercise 29-8 Pre-exposure Exposure Determination
Another area of close-up photography which requires special exposure consideration is the microscope. Most camera manufacturers produce microscope adapters which allow shots to be taken with most types of microscopes. Exposure through a microscope has its difficulties, however. First, are the standard problems associated with any type of close- up photography -- light loss due to extension, pupillary effect, TTL meter sensitivity range limits, reciprocity rule failure, etc. -- but there are additional problems. In microscopic work the subject can be opaque or translucent. With an opaque subject, the exposure is determined by measuring the incident or reflected light as with any close- up photography. With translucent subjects, the exposure can be determined in two ways because the subject can be lit in two different ways. If the subject is lit by reflected light, the standard close-up exposure methods apply, but if the subject is lit by transmitted light, as with a stained- glass window, the exposure determination method is different. Translucent subjects, especially in a microscope, are very likely to vary from the 18% standard that the TTL meter relies on. The subject itself is typically very light and transmits a large quantity of the background which can be very light (bright field) , a mid tone, or very dark (dark- field). The TTL meter can easily be fooled by these light or dark backgrounds. Consequently, it is necessary to meter off an 18 % object when using a TTL meter with a microscope.
If the subject is illuminated by reflected light a mini-18% grey card will work fine when placed at the specimen stage. When the object is illuminated with transmitted light an 18% transmission object must be metered. A slide of a grey card will work fine when temporarily used to replace the specimen. This will work equally as well with bright field and dark field illumination.
In some instances with a microscope, the TTL meter may still give an inaccurate reading when using an 18% object.
There are two common reasons for this. First, the lower sensitivity range of the meter may be approached; solve this problem by increasing the intensity of the light. Another possible problem is the coverage of the microscope eyepiece, If the eyepiece creates a circle in the viewfinder of the camera, the TTL meter may read the dark edges of the scene and recommend an inappropriate exposure. If this happens, switch to a camera with a center or spot metering system or use a wide-field eyepiece on the microscope for more coverage.
Some hand-held meters offer microscope attachments which have the advantage of extra sensitivity. The use of these meters is subject to the same limitations as the TTL meter.
It is difficult to use standard hand-held meters to meter at the specimen stage because there is little room between the specimen and the lens.
If an electronic flash is used, it is best to use a flash meter with a microscope attachment. Any manual exposure determination is difficult for several reasons.
First, although distance is the only exposure factor which can be readily changed, except for ISO, it is difficult to measure the film-to-lens distance exactly. Second, most microscope lenses do not incorporate apertures and are not rated in f-stops. Third, pupillary effect is difficult to measure in lenses of this size. Fourth, as mentioned, measuring the light at the specimen stage is very difficult.
If manual exposures must be attempted it is best to make tests with instant print film and/or to bracket the exposures.
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