The enlarging lens is a critical part of any enlarging system. A modestly priced enlarger equipped with a good lens can produce excellent prints, but an expensive enlarger equipped with a poor lens will never produce great results. This guide is provided to assist you in selecting the lenses that are most appropriate for your needs and budget.
Enlarging lenses are supplied in different focal lengths to match the requirements of different size negatives. The rule of thumb is that the focal length required for a particular negative format will be the same as the diagonal of the negative. Hence a 35mm negative requires a 50mm enlarging lens, a 6x4.5cm or 6x6cm negative requires a 75mm or 80mm lens, and so forth. A lens longer than normal focal length can be used, for example a 75mm lens can be used to enlarge a 35mm negative, but the degree of magnification will be reduced. A lens that is too short for the negative will cause noticeable vignetting in the corners of the print. The following table can be used as a general guide for the focal length required for common negative formats:
Lenses differ in their specifications. For example, all 80mm enlarging lenses will cover 6x6cm negatives, but some will cover up to 6x7cm. Be sure to check the specifications of a lens to ensure that it will cover the negative size you intend to use it with.
Ideally you want to purchase the best lens you can afford. The general rule of thumb is that you want the enlarging lens to be of equal quality to the camera lens that created the negative. But how does one evaluate the quality of different lenses? One way is to examine the differences in construction and specifications. In general, enlarging lenses can be categorized in four distinct groups - 3-element lenses, 4-element lenses, 6-element lenses, and specialty lenses.
3-element Lenses - These are the low priced lenses, sometimes referred to as "starter" or "economy" lenses, that are most frequently included as part of basic enlarger packages. While many people dismiss them as poor quality, that's not altogether true. Even prestige lens makers such as Rodenstock and Schneider have made 3-element lenses. They are quite capable of delivering quality results if used within their limitations. As a general rule, the shorter focal lengths can provide excellent results in print sizes up to 5"x7", and the longer focal lengths up to 8"x10".
Brand names you will frequently see are "EL-Omegar" (from Omega), "Beslar" (from Beseler), "Rogonar" (from Rodenstock), and "Componar" (from Schneider).
4-element Lenses - The additional lens element in 4-element lenses provides an extended range of magnification before quality begins to decline. In general, the shorter focal lengths will provide excellent results up to 8"x10" and the longer focal lengths up to 11"x14". 4-element lenses are less common than either 3-element or 6-element lenses, as the majority of buyers opt for either the least expensive or the best quality lens, but 4-element lenses can be an excellent choice if you intend to make prints within the indicated magnification range.
The EL-Nikkor 50mm f4 and 75mm f4 are examples of 4-element lenses, as are the series of Omegaron lenses from Omega, the Rogonar-S series from Rodenstock, and the Comparon series from Schneider.
6-element Lenses - These lenses are considered the top-of-the-line, and provide the greatest usable magnification range - up to 16"x20" for the shorter focal lengths, and 20"x24" for the longer focal lengths. In addition, their more complex optical design allows greater correction of chromatic (colour) aberrations, and 6-element lenses are therefore the best choice for colour printing.
With the exception of the two 4-element lenses mentioned above, the EL-Nikkor enlarging lenses are 6-element, as are the Rodenstock Rodagon series, and the Schneider Componon and Componon-S series.
Specialty Lenses - This category includes a number of different types and the lenses vary in the number of lens elements.
Lenses with an "APO" (apochromatic) designation are highly corrected for chromatic aberrations and are therefore especially suited for critical colour printing.
Wide Angle (WA) lenses have a greater circle of coverage compared to "normal" lenses of the same focal length. For example, a 40mm WA lens is able to cover a 35mm format negative. Wide angle enlarging lenses therefore have the effect of providing greater magnification compared to the "normal" focal length at the same elevation. This can be useful when ceiling height restricts how far the enlarger carriage can be raised, or when the length of the enlarger column does not provide the desired degree of magnification. Note, however, that in most cases wide angle lenses are not recommended for use with condenser enlargers.
There are also special series of lenses designed for high magnification mural size enlargements (Rodagon-G), and lenses optimized for very small or 1:1 reproductions (Rodagon-D).
One thing that you must consider is what will be required to mount the lens on your enlarger. Over the years the industry has more or less standardized on the 39mm "Leica" mounting thread for enlarging lenses, and the majority of enlarging lenses for small and medium format will be offered in this mount. However, some older, and some short focal length lenses may have a smaller mounting thread, 25mm or 32.5mm for example. Many longer focal length lenses will have a larger mounting diameter.
Some enlargers have the lens stage pre-threaded to accept only lenses with 39mm "Leica" threads. Enlargers that use interchangeable lensboards may have 39mm threaded boards available, while in other cases the lensboards will have only a hole of the specified diameter and will require a retaining ring (sometimes called a "jam nut" or "lock ring") to attach the lens to the lensboard. Many lenses with 39mm thread are not supplied with a retaining ring, but if required, 39mm rings can be purchased separately for a nominal price. Lenses with mounting diameters smaller and larger than 39mm will most often require a retaining ring or lens flange. If mounting the lens on your enlarger will require a lock ring or flange, check to see if it is supplied with the lens, as replacement retaining rings or flanges for lenses other than 39mm can be relatively pricey.
Some of the more recent lenses have added convenience features that may make them more desirable in certain conditions.
Illuminated Aperture Scale - An illuminated aperture scale can make the lens easier to set to the desired aperture in safelight conditions or in total darkness. Note that the scale on these lenses is only illuminated when the enlarger lamp is on.
Disengageable Click Stops - Virtually all enlarging lenses will have click stops to ensure a high degree of repeatability of exposures. However, when working with an enlarging meter or colour analyzer, there can be situations when the meter requires a setting just on the edge of a click stop, and the aperture mechanism will tend to click into the adjacent stop. Some lenses therefore have a feature allowing you to disengage the click stops to allow very precise setting with a meter.
Preset Aperture - It is customary to open the lens fully for composing the image and focusing. The lens must then be stopped down to the working aperture for the exposure of the print, either by counting click stops or visually observing the aperture scale. Some lenses have a feature that allows you to set a stop point at the working aperture. The lens can then be adjusted from fully open to the working aperture by simply turning the aperture ring as far as it will go.
Used enlarging lenses are subject to a number of defects which can affect performance. Lenses should be carefully examined for these defects.
Aperture Mechanism - The aperture ring and aperture blades should move smoothly and easily. Click stop mechanisms are subject to wear, so check that click stops are positive. The appearance of oil on the aperture blades may not immediately affect the operation of the lens, but it is an indication that the lens requires service.
Lens Blemishes - Examine the front and rear lens elements for scratches and pitting in the glass. Examine the coating for "cleaning marks" which are very slight scratches in the coating, not serious enough to have affected the glass. Cleaning scratches may not affect the lens performance to a great degree, but are undesirable nonetheless, and reduce the value of the lens.
Fungus - The adhesive used to cement lens elements together is organic in nature. Unfortunately this means that it can become a medium for the growth of fungi. Look for odd "spidery" patches within the inner elements of the lens. Fungus is difficult if not impossible to remove. In severe cases the fungus may actually etch the glass. Any lens in which fungus is present should be rejected.
Lens Separation - In some instances, the lens elements that have been cemented together will begin to separate. This has the effect of increasing flare and reducing contrast to a varying extent. Look for patches of discoloration in the inner elements that may resemble "oil on water". Lenses with this problem can still be used, but will not have optimum performance so are best avoided.
Dust - It is expected that dust may be found on the external surfaces of a lens, and this can be removed with normal lens cleaning methods. But you may also find dust between the inner elements. This is most often seen in inexpensive lenses which are generally not well sealed against dust penetration. A few small spots of dust will usually not have a significant effect on lens performance. With better lenses, the lens can be disassembled and cleaned, but the service should be performed by a qualified technician, and this will be an additional expense.
In use you will want to avoid using the lens either wide open or at the smallest apeture. To appreciate why you must first understand that lens performance at any aperture is something of a compromise of several factors. Virtually all lenses provide highest resolution at the widest aperture. However, more than offsetting this is the fact that lens aberrations (optical defects such as coma, astigmatism, distortion, flare, etc.) are also at their maximum with the lens wide open.
As you stop the lens down, the effects of diffraction (at the edges of the aperture blades) cause a gradual reduction in resolution, but at the same time the lens aberrations are minimized more quickly. By stopping the lens down by about 2 stops, you reach a point where the aberrations are well controlled but resolution is still high. As you continue to stop the lens down further, resolution is further reduced, but there is little further improvement in aberrations. Better lenses may provide 2 or 3 stops that would be considered optimum for printing, while lesser lenses may have only one optimum f-stop. We recommend making a series of test prints with a test negative to determine at which settings each lens provides the best results.
It is also important to note that poor prints are not always the fault of the enlarging lens. For example, film flatness and enlarger alignment are two common factors which also affect overall print quality.
No lens will provide optimum results if it is not focused accurately. The use of a focusing aid is highly recommended!
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