common equipment: the enlarger as a macro camera
originally published in Ilford's Photo Educators Magazine 1996
|Michael R. Peres
Chair, Biomedical Photographic Communications
School of Photographic Arts & Sciences
Rochester Institute of Technology
Rochester, New York 14623
Producing effective and interesting photomacrographs does not require elaborate and expensive equipment. In fact, some very common equipment can be utilized to produce high quality results. The enlarger can be a very useful photomacrographic camera, however some different approaches than normally used for printing will be required. Consider for a moment that every time the enlarger is used for printing, the enlarger magnifies a small subject (the negative), projecting it down to a sensitized product. Using that concept as a starting point, it should be easy to transfer darkroom techniques used in traditional enlarging to photomacrography for semi-transparent subjects.
All enlargers will work for this purpose, however some types have advantages. An enlarger that is capable of accepting at least the 4 x 5 format will work best. For subjects smaller than 1 x 1.5 inches, a 35mm format enlarger will work just fine. There are several types of enlargers. Diffusion, cold light, condenser, as well as point light enlargers and each will vary in their contrast potentials. The diffusion enlarger provides the least amount of contrast while the point light source is the contrastiest. A condenser enlarger or point light type will work best for projected light photomacrography.
The enlarger works effectively as a camera for subjects that are transparent or semi-transparent. Subjects that are totally opaque will not allow light to pass through. Consequently, opaque subjects will not be useful for the examination of the structural details. Subjects such as leaves, insect wings, fabric or other subjects with similar characteristics work well using this technique. Prepared microscope slides can also be imaged very successfully using this technique.
Any photographic negative or positive material can be used to produce images using this technique. Some emulsions will work better than others. Typical criteria for a film would be very fine grain, good resolution( 65-75 lines/mm), a panchromatic spectral response, medium to low speed, (ISO 12 -100), and a medium contrast potential that is easily adjustable through alternative processing techniques. An example of this would be Ilford FP-4. Concerns with regard to reciprocity law failure and latitude are typically not warranted for this technique as a result of each image being custom produced.
Two problems specific to the technique need to be discussed here. One concern is inherent to the material's sensitivity(ISO) while the other problem is in the material's spectral response. In comparing photographic papers to photographic films, films typically will exhibit more sensitivity than papers. As a result, methods may be necessary to reduce the brightness of the enlarger if required. Common exposures for film might be found to average between 1 sec and 1/1000 second. These times will be too short for the enlarger to handle. Reducing brightness by closing the aperture is not a viable option for this type of work because of image degradation as a result of diffraction.
The problem lies within the darkroom timer which is not capable of delivering short exposures times such as 1/1000 second. Very short exposures times are not desirable for custom printing and darkroom work. Imagine trying to dodge a 1/500 sec exposure? One common method to reduce exposure is with the use neutral density filters. These filters, often manufactured in increments of .1, .2, .3, 1.0 and so on, can be used alone or together to reduce the enlarger brightness. The filters can be placed in the bellows directly behind the lens. By raising the head, access to the rear of the enlarging lens can be achieved and the filters can be placed there. If neutral density filters are not available, a polarizing filter will function adequately for this purpose. Using two polarizers together, will allow various amounts of brightness to be produced.
In addition to the use of neutral density filters, brightness can also be reduced using a voltage reducer, often referred to as Variac. This apparatus takes the 120 line voltage and reduces it in the same manner as a rheostat or dimmer switch accomplishes the task in household applications. Care must be taken in sequencing the voltage reducer with the enlarger and timer. Many of the new digital timers will be damaged if the input electrical signal is below the recommended threshold. Consequently, the reduction must occur after the timer. Since the lamp will be dimmed using this approach, color temperature of the lamp will not be matched to any color material's response. Color should probably not be tried because of the many challenges.
It should also be mentioned that films, unless otherwise specified, are panchromatic. Consequently, working with safelights such as the Kodak OC or OA, will provide less than satisfactory results due to fogging. Using the enlarger as a macro camera will necessitate working in total darkness .
One last consideration and potential problem using this technique involves tone reproduction. Many photographic materials have been designed to work using an input brightness range of 160:1 or approximately a 7.5 ƒ stop range from shadow to highlight. As result of this design, development strategies are determined accordingly which produce a film response that renders a contrast index (C.I.)of .56 or produces a negative with average contrast. Contrast index is a prediction of a photographic material's contrast potential as influenced by the type of developer, the time in developer, as well as the concentration of developer. One film can thereby deliver many contrasts, (C.I.'s)based on the time, concentration and type of developer used. Development data found in technical literature on product releases can be assumed to be based on average and will produce a C.I. of .56. Any alteration of time , temperature, or concentration will effect the C.I. C.I.'s higher than .56, will deliver more contrast while C.I.'s lower than .56 deliver less contrast. Producing images with the enlarger as the camera will typically include an input(subject brightness) range less than adequate for full tone results. The brightness range often found in this application is typically 8:1 or 16:1 which is only a 3 - 4 stop range. Consequently, most subject photographed using this technique will require extended development times to produce a negative with a C.I. of approximately .8. This can be achieved by adding approximately 25% more development.
High Contrast ORTHO Materials
Sometimes even increasing the C.I. when using a common emulsion will not satisfy the contrast requirements of the subject. A common remedy to this problem is through the use of high contrast materials developed in active tone developers. An example of this would be Ilford's ORTHO emulsion developed in Kodak D-72 or an equivalent paper developer. Images produced this way will exhibit both the contrast and resolution of necessary for subjects photographed in this fashion. One shortcoming of these type of emulsions might be their spectral response. They typically are orthochromatic and will render the red regions of a subject as absolute black void of detail in the print as a consequence of no response in the red spectrum. This deficiency can be easily offset when considering the films can be handled in red safelight.
Easels and film management
When using film below the enlarger, some strategy will need to be developed for holding it secure. Cut film holders work especially well for this purpose, however a jig will need to be devised for registration and focus. A sheet of white paper can be inserted in one side of the holder for focusing and composing while the other side can be loaded with the chosen sensitized product. When using an enlarging easel, a dummy sheet of film will be needed as a focusing aid as with above. More importantly, the surface of easel is often painted yellow or white for ease of composing and focusing. This is great for enlarging papers, but not so good for film. Much better results will be achieved with the use of a piece of exposed and developed paper or film with its black Dmax underneath the film when exposing. This technique will minimize back reflections and back scatter from the easel which will lower contrast. Lower contrast will influence the appearance of sharpness and resolution.
Lens and Aperture
The lens is a very important component. A enlarging lens might have a negative influence on results when used for traditional printing, however when magnifying smaller structural details using this technique, a poor lens' performance will be enhanced. Consequently, a good PLAN(flat field) enlarging lens is ideal. Flat field lenses render edge to edge sharpness with no distortion.
Shorter focal lengths will be better for this type of work, although subject size requirements will ultimately decide the lens requirements. In magnification photography, greater degrees of magnification can be achieved using shorter focal lengths, i.e. 50mm or shorter. Consequently, a 50mm lens will produce greater magnifications with less working distance(distance from the paper to the lens) than a 150mm lens.
Another very important aspect in the lens' operation is the aperture selection. Often apertures are chosen indiscriminately and based only on brightness requirements when enlarging. Small apertures will however also produce diffraction. Diffraction is the bending of light caused by an opaque edge. The result of much diffraction will be a loss of resolution or fine detail. For this reason, the use of the lens' "optimal" aperture becomes paramount for fine detail rendering. Often this aperture is located two stops from the maximum opening. The more open the lens can be operated, typically the higher the detail. Sometimes with thick subjects, such as a leaf, more depth of field(D.O.F) will be required. Consequently for thick subjects, using a more closed aperture has value when producing pictures with larger DOF requirements. In photomacrography, there is a constant balancing of a subject' s DOF requirements as contrasted to the critical detail requirements of the subject.
For this techinque to be optimized, the enlarger must be in total alignment. There are many excellent alignment kits on the market, however if one is not available, a small spirit level from the local hardware store makes an excellent second choice for gauging the orientation of the lens, the negative stage as well as the easel.
Subjects that are semi-transparent are ideal for this technique. The simplest method by far, is to place them in a glass negative carrier. This can be easily accomplished if one is readily available. If a glass carrier is not available, a modified carrier can be created by using thin pieces of glass similar in size to the negative carrier. The subject should be placed in between the pieces of glass and taped firmly closed with photo tape. Care should be taken to keep the glass surfaces as clean as possible. All dirt and extraneous artifacts will require retouching in the negative after development. The subject can then be placed into the enlarger and projected down onto the film.
Another successful approach is through the use of a 35mm glass slide mount and a mounted transparency carrier for the enlarger. As with 4 x 5 glass carriers, the subject can be sandwiched in between the two pieces of the glass in the mount. In this fashion the subject will be presented to the film in its best possible orientation for the maximum DOF.
One last consideration needs to be the amount of brightfield or extraneous background illumination allowed in the system. The smaller the field of background illumination used, the crisper the image. Simply composing tightly by cropping at the easel does little to manage the flare light that is inherent in system using backlighting. Ideally the subject needs to be masked off in the enlarger so that the smallest field necessary to illuminate the subject is transmitted. This can be achieved by using black photo tape, or a piece of film with Dmax as was suggested for the easel. If the photomacrographic image does not adequately cover the film, lithographer's tape or opaque can be applied later after processing to add density to these regions.
Prepared Microscope Slides
When photographing prepared microscope slides or whole mounts, the slide can be inserted into a 35mm negative carrier. Place the microscope slide with its cover glass side down in the carrier. In this fashion, the subject will experience minimal distortion from the glass from the slide.
Even when using contrast producing techniques, there may be a lack of tonal separation. In the event more contrast is needed, various contrast producing filters can be utilized such as Kodak Wratten #25, 47 or 58. These filters can be handled in a similar fashion as the ND or polarizers discussed above. Choice of such a filter should be based on the desired result as well as the subject requirements. Remember like colors will lighten themselves at the print and that all filters will remove light. Exposures using filters will be longer.
When producing pictures this way, the simplest and most effective way to focus is by moving the entire enlarger up and down. First rough focus and size the image using the lens. When the lens to subject distance is changed, the image magnification is also changed. With the rough adjustments completed, critical focusing can be done by raising and lowering the entire enlarger head. Focusing this way adjusts the working distance for that lens keeping the magnification constant.
Negative exposure testing
Once the sample has been prepared for photography, it can be inserted into the enlarger. The image can then be composed and sized using the best method available. The image can be focused using a focusing paper by changing the enlarger's working distance. With the image crisply focused, the system's optimal aperture should be selected and a test for exposure can begun. In a fashion similar to making a test print with different exposure times, a test negative should be produced. If using a cut film holder, the dark slide can be slid across the film and a series of exposures made to the film. The film should be processed for the time determined to deliver the increased contrast requirements for the subject.
With the film exposed and developed, the negative should be critically examined for shadow detail as well as a clear field with adequate density in the clearfield and highlight. This strategy might seem common sense to many, however many subtle differences in shadow detail might not be evidenced without close inspection in this region while balancing the need for adequate density in the clear regions A negative with adequate density in both regions will print nicely on a medium grade paper with a touch of tone in the highlight.
One approach that can aid in the production of better negatives, is through the use of dodging during the exposure. The same approache used when enlarging should be used for dodging when making negatives. Dodging may deliver negatives with a better overall density and contrast range by holding back exposures where necessary. This technique will greatly enhance contrast when dodging the background during exposure.
This procedure will produce photomacrographs of transparent as well as semi transparent subjects. With appropriate sample preparations, very high quality images can be achieved using the enlarger. The choice of the appropriate film and development strategies will be a factor influencing the negative's ultimate contrast. Since an original negative is being generated using this method, critical care must be taken with each step. Small errors here and there will compound themselves and the resultant images could appear "quite" soft. However with care and attention to detail, high quality results are easily obtainable. Glossary of technical terms that might be fun to define
neutral density filter
Some basic understanding of magnification is relevant for those who wish to go further. Magnification is defined as the size of the image divided by the size of the object and is expressed as:
I/O = m
where m = the film magnification. I = the subject size or distance, and O = the object size or distance. Using this one equation, all image magnifications can easily be determined. It must remembered that magnification may go beyond the negative stage, and that magnification continues throughout the entire process up through and including reproduction. Consequently, the final print mag, would be expressed as M.
To use this equation, the subject should be measured. this value should be recorded and then the image should be measured using the same unit(inches for example) as well as the same reference distance. These values are then plugged into the equation which is solved. Once the magnification is determined, measurements can be made from the image for use as appropriate.
For critical work, images of transparent rulers can be made along side the image of the subject. It can produced separately or as a composite with the subject an used as appropriate
Gibson, H.L., Close- Up Photography and Photomacrography, N-16, Eastman Kodak Company, Rochester, NY 1975
Lefkowitz Lester, The Manual of Close-Up Photography, Amphoto Garden City, NY 1979
Stroebel, L, View Camera Technique, Focal Press, Boston, Mass 1986
Stroebel, L. and Zakia, R, Focal Encyclopedia, Focal Press, Boston, Mass 1993
Vetter John P, Biomedical Photography, Focal Press, Boston, Mass 1992