Bruce M. Loc: Longueuil, Quebec, CANADA

I have a Nikon Bellows and would like to know if using a Flat Field lens as opposed to a 35 - 70 mm Micro lens (Nikon designation) on it will show a marked difference.

bsprague Loc: Lacey, WA, USA

Back when I had those for a Nikon film camera I remember that the only really useful thing for a flat field lens was taking pictures of flat things like stamps or paintings.

RWR Loc: La Mesa, CA

A flat-field (macro or enlarging) lens will produce better edge definition, and better overall definition at higher magnifications.

Apaflo Loc: Anchorage, Alaska

Depends on what you photograph!

Taking pictures of 3D objects with a Flat Field lens may or may not be ideal. But when shooting things that are 2D, like documents, stamps, coins and so on, the Flat Field lens is a real benefit.

Note that almost all lens designs today are what is technically called a "flat field design". Which means flatter than a simple lens, and isn't very significant to this discussion. A "Flat Field Lens", however is not flat either... it's just a lot flatter than a regular lens, which will have a shorter focus distance at the edges of an image than at the center.

The trick with any lens is to use enough depth of field (or use focus stacking) to get all important parts into sharp enough focus. The limit for that is when diffusion becomes too great as the lens is stopped down. A more curved field means needing to stop down farther, and thus getting more diffusion, to keep everything within the limited Depth of Field.

Apaflo Loc: Anchorage, Alaska

Not necessarily in either case.

amfoto1 Loc: San Jose, Calif. USA

Any Micro Nikkor you might choose is probably a flat field lens anyway. Most macro lenses are.

A flat field lens is designed to render edge-to-edge sharpness and brightness - minimize optical vignetting - at close focusing distances.

Most non-macro lenses are optimized for focus around 6 or 8 feet and beyond. They are not flat field designs. If you put extension tubes on them and make them focus really close you will see softness and vignetting in the corners of the images, particularly at larger aperture.

This isn't necessarily a bad thing. It can be used to good effect. For the following image I deliberately used a standard (non-macro) 50mm lens with extension tubes and a large aperture, so that these effects would occur.



However, most of the time people want edge-to-edge sharpeness and even illumination.... so most macro lenses are flat field designs that are optimized to produce these at very close focus distances. This included older ones, even when used with extension tubes. The below image was shot with a vintage, manual focus Tamron 90mm macro lens that's only able to do 1:2 magnification on it's own. A 20mm extension tube was added to it, to increase magnification:

Bruce M. Loc: Longueuil, Quebec, CANADA

Thank You all. This makes my decision a lot simpler.

shagbat Loc: London

True, it is it's main purpose. Any decent, enlarger lens will work, but will need a 39mm adaptor. It may be easier to scan.
My opinions only, but I used this setup with Russian bellows and a Nikkor 5o f3.5 (enlarger) lens.
Have a play with it, will only cost you pennies.

Apaflo Loc: Anchorage, Alaska

Another consideration, that will probably be more important than flat field, will be how optimized a lens is for close focus distances.

Today most lenses use an "internal focus" design. The lens stays at a fixed distance from the sensor, and focus is accomplished by moving internal elements in relation to each other. The front element might not move at all. The lens is optimized for sharpness at that sensor to lens distance, and putting it on a bellows to focus closer by moving the lens away from the camera will increase a number of aberrations. The effect will vary with different lenses, but won't be good.

Older macro lenses, enlarging lenses, and microscope objectives have a different specific characteristic. But first consider how they differ from a general purpose lens.

Before internal focus design was used commonly, the problem was correcting for astigmatism or a wide focus range. Regular lenses were optimized to allow sharp focus at infinity which meant that close focus suffered more astigmatism. The focusing helical was designed to limit how close was accepted. If such a lens is used on a bellows it is not sharp.

Macro lenses were instead optimized at close focus ranges, and were not particularly sharp at infinity. Or even a moderate distances, which made them sort of good to also use as a "soft focus" portrait lens! The main thing was that when used on a bellows with added extension they did not suffer more astigmatism. Microscope objective lenses are similar, and in fact not using enough extension is more likely to cause unsharp results than extra extension. Enlarging lenses usually work best if reversed, to put the smaller object to be photographed at the back of the lens, and otherwise they are well optimized for macro focusing distances (they do suffer from flare).

To summarize what it means about selecting a lens for use on a bellows... the results with Internal Focus lens will not be optimal, but the variations are unpredictable too. Older macro lenses that do not have internal focus designs will work very well. Reversed enlarging lenses are also really great for magnification up to maybe 5x. For magnification above that a microscope objective lens is the best choice.

Note that virtually any non internal focus macro lens will do well on a bellows. Enlarging lenses require doing at least a little research decide on which one for a given situation. Microscope objectives require a lot of research!

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Bruce, all lenses have a curved field of view - but many are corrected enough to appear flat field - which becomes a non-issue when you stop the lens down.

For macro, a true macro lens is corrected to have a pretty flat field at close distances. The other approach is to use a reversing ring, and mount the lens backwards - the flat field that would normally project the image onto the sensor is used to capture the image. It does work very well, and the ring is usually less than $20.

RWR Loc: La Mesa, CA

True, reversing the zoom lens could be an equalizer.