The Darkroom

© 1999, Darryl C. Nicholas, All Rights Reserved

Enlarger lenses are generally grouped into three price categories: hobby (inexpensive), regular "professional" (moderately priced), and Apochromatic (APO) professional (very expensive). APO lenses are designed mostly for use in precise color separation work, where all three primary colors must be focused at precisely the same plane simultaneously. They are also used for printing large magnification images where there is a need to work the lens at wider open apertures. Non-APO lenses tend to produce a slight scattering of light at the edges of the image when their aperture is wide open, requiring that they be stopped down by at least one f/stop to produce acceptable images. While APO lenses also scatter the light at the edges of the image when wide open, the effect is usually mild enough to allow for the production of acceptable prints.

There are three companies currently making most of the enlarger lenses being sold in America: Rodenstock, Schneider, and Nikon. All three make several different price ranges of lenses. Beseler sells a family of lenses that are made for them--and to their specifications--by Rodenstock.

Both Rodenstock and Schneider make "APO" enlarger lenses. EL Nikkor does not offer an APO enlarger lens.

A 4x5 negative will require a lens of at least 135mm focal length. If you are going to be using a medium format camera and shooting 6x7cm format, you will need an enlarger lens of 90mm (or longer) to print those images. Negatives of 6x6cm or 6x4.5cm require a lens that is at least 75mm long. If you are going to use a 35mm camera, you'll need an enlarger lens of 50mm (or longer) to print that format.

Yes, you can use a 90mm enlarger lens to print 35mm negatives but, because of its longer focal length, you will have to have the head of the enlarger raised much higher in order to make the same size print that a 50mm enlarger lens would make with the head much lower. When you use a very long lens it is possible that you might not be able to raise the enlarger head high enough to make the size of print that you might want to make. Thus, most folks use the shortest lens that will work with a given negative format, allowing them to make the largest possible print with their particular enlarger.

If you only have a 90mm enlarger lens, it is possible that you might not be able to make wallet-size prints from your 6x7cm negatives because the head of the enlarger might not be able to be moved low enough to accommodate the 90mm lens. You might need a 135mm lens in order to make wallet-size prints from 6x7cm negatives. It all depends on your specific enlarger and how low toward the easel you can move the negative plane.

A 90mm lens would commonly be used to make wallet-size prints from 35mm negatives for the same reasons. Most enlargers will not allow the head to be lowered enough for a 50mm lens to produce wallet-size images from 35mm negatives.

If you think that you might want to blowup a small portion of a negative, you might want a very short focal length lens--like a 25mm. But, remember, such a short lens can only be used on a very small portion of a negative. It cannot "see" an area much larger than the size of a disc negative (smaller than a 110 negative). Such a short lens will usually require a "recessed" lensboard.

You might want to use an "extended" lensboard with your longer focal length lenses like the 90mm or the 135mm. An extended lensboard (while not absolutely necessary for routine work) can be helpful when you are trying to make small prints or prints that are actually smaller than the negative (less than 1:1). Use a regular, flat lensboard with a 50mm lens.

Beseler offers a line of "professional" lenses that are made for them by Rodenstock in Germany. They are called "Beseler HD lenses." They are comparable in quality to Rodenstock's Rogonar-S brand. They are available from most photographic dealers, and are perfectly great lenses.

Making Small Images. All lenses are capable of focusing at a magnification factor of 1.0, provided that the enlarger is capable of moving the negative plane low enough, and providing that the bellows is capable of extending the lens far enough from the negative. For a magnification factor of 1.0 to be reached, the negative plane must be exactly "four times the focal length of the lens" above the easel surface.

Most enlargers will only allow the negative plane to be lowered to about 12-14" above the easel surface. This is not quite close enough for short lenses, like 50mm, to produce 1.0 magnification factors.

Remember, a lens cannot be focused if the negative plane is any closer to the easel than four times the focal length of the lens. For example, a 90mm lens will not focus if the negative plane is any closer than 14.04" from the easel surface. A 135mm lens will not focus if the negative plane is any closer than 21.04" from the easel.

Making Prints Smaller Than The Negative. When making prints that are smaller than the original negative, the negative plane is actually further from the easel than the magical distance of "four times the focal length of the lens," but the lens is closer to the easel than it would be at the 1.0 magnification point. At no time--regardless of the size of the print being produced--can the negative plane of the enlarger ever be closer to the easel than four times the focal length of the lens being used. See the accompanying sketches for a fuller understanding of this.

To make a print that is smaller than the negative, first be sure that you have selected a lens with a focal length that equals or exceeds the diagonal measurement of the negative.

Next, be sure that your enlarger is capable of focusing the lens to a 1:1 magnification. That is, be sure the enlarger head can be lowered far enough down toward the easel so that the distance from the negative plane to the easel is equal to or less than four times the focal length of the lens.

Next, even though the negative plane of the enlarger can be lowered far enough, be sure that the lens bellows will extend far enough to allow the lens to be focused. For a lens to focus for a 1:1 magnification, the lens must move away from the negative a distance equal to two times the focal length of the lens. If you intend to go on and make a print that is smaller than 1:1, the lens will have to move even further from the negative plane. Many enlarger bellows are not long enough to accommodate the longer focal length lenses, thus, longer focal length lenses are frequently mounted on extended lensboards to help the bellows extension by providing a couple of extra inches of distance. See the accompanying sketches for the required bellows-extension dimensions (in inches) for typical enlarger lenses.

Finally, move the negative plane to the point where the lens produces a 1:1 size image on the easel, and focus the image. Be sure that you are really at the 1:1 position and not slightly larger (or slightly smaller). A lens cannot be focused if the negative plane is below the point where a 1:1 image is created. However, if the lens has been stopped down a little, it will appear to be focusing. So, be sure that you are doing this with the lens wide open.

Then, raise the negative plane slightly--maybe a 1/4". And refocus the lens by moving the lens further toward the easel and away from the negative. It will focus. Do not refocus by moving the lens back toward the negative. That will only produce a larger image, not a smaller image.

Continue to raise the negative plane in tiny increments (maybe 1/4"), and continue to refocus the lens by continuing to lower the lens toward the easel. The projected image will get smaller and smaller. But, you must move in tiny increments or you will easily overshoot the limits of the lens, and reach a point where the lens can no longer be focused because the image has become "0" in size. As you continue to make the image smaller and smaller you will probably reach a point where the bellows isn't long enough to allow you to continue to refocus the image. At that point you might want to use an extended lensboard in order to gain an extra few inches of distance, and get a slightly smaller image.

Using these techniques it is possible to make some very tiny images. These are the techniques that are used for making photographic images that can later be put in tiny lockets, pendants, and bracelets that men and women sometimes wear.

As the image gets smaller and smaller the depth of focus for a given lens and f/stop gets greater and greater, making it a little difficult to know where the exact focusing point really is. Almost everything will appear to be in focus. Do the focusing with the lens wide open. It will be a lot easier to know exactly where the focusing point really is. Then, stop the lens back down to make the print.

I usually focus the enlarger by holding a strong magnifying glass down close to the projected image. You'll have to get down and hold your eye very close to the magnifying glass, but then you can focus the enlarger fairly accurately.

There is no easy way to mathematically calculate the correct exposure level for images that are smaller than 1:1. I just do a series of bracketed density tests.

If you'd like more help with selecting the best lens for your enlarger or how to use it, you can contact me at: editorial@shutterbug.net.