A Small Miracle For True Photogeeks

Nikon has just introduced a new 24 mm PC-E Nikkor f./3.5 ED and rumours are, that we might expect a new PC 45 mm and a new PC 85 mm later this year. If the rumours prove to be right, the new range of PC lenses will open a wide gate of new possibilities for those Nikon professionals and photogeeks, who will go through all kind of trouble to get the ultimate images in outstanding quality.

Converging lines

But what is a PC lens ?

The abbreviation "PC" sounds very computerlike, but that is far from correct. A PC lens is not automatic, it is very much manual.

PC is an abbreviation Nikon uses for the concept of "Perspective Control", ie. the possibility of controlling foreshortening perspective or converging lines in the subject. The abbreviation was introduced by Nikon in the early sixties.

Converging lines are the phenomenon, that vertical lines in the subject, for example a building, has a tendency to taper to a point, if the camera is turned upwards in order to get the whole building into the viewfinder. The effect is most distinctly with wideangle lenses and are well known by all seriously working photographers.

There are three possible solutions:

Cropping during exposure

The first solution is to keep the film-/sensorplane absolute vertical during the exposure and later on crop the lower half of the raw image away while you are keeping the upper half of the image with the the building. The downside is that you loose almost half of the effective picture area and you will have to double the enlargement of the image, which leads to poor quality.

Correction and cropping during copying

The second solution is to correct the converging lines during "copying". It can be done in the oldfashion way in the darkroom by an enlarger or in the "digital darkroom" such as Photoshop or alike applications.

Correction in the darkroom was done by tilting the enlarger - in Photoshop it is done digitally by "Lens Correction" or by the help of the "Skew"-function.

In both cases the price is cropping away precious negative area or valuable digital pixels.

With slightly converging lines the cut-away area is tolerable, but if the lines are tapering to a nearby point, the manipulation and cropping will be unacceptable, if you want a top quality image print.

The PC lens

The third solution is for professional photographers and photogeeks who's goal is ultimate quality regardless of price and efforts. You might still find photographers who gladly continues to use their 4x5 inches bench cameras, because the bench camera gives them total image control, including converging lines. This is possible because back and front of a bench camera can be tilted and shifted in every thinkable way.

But using a bench camera is troublesome especially outside the studio. Therefore Nikon developed the world's first PC lens for the 24x36 mm format. The construction, which was presented in 1961, was a 35 mm f/3.5 lens  (read more here) with the possibility of moving (shifting) the lens in relation to the lens bayonet socket attached to the camera. In this way converging lines can be partly dealt with.

A shift lens cannot overcome the same range of converging lines as a bench camera, but it will suffice some of the way, depending on the focal length.

The PC 85 mm is not first choice in practical architectural photography. Even at full shift the 85 mm's performance of correcting converging lines are limited. But with the new PC 24 mm we will have an all together different situation. We plan a review in some weeks.

Controlling Depth of Field

On the other hand, the PC 85 mm performs very well when it comes to creative controlling of sharpness and unsharpness. The tilt function of the 85 mm PC lens offers the possibility of controlling the Depth of Field (DOF) far beyond the common aperture stop down-method.

What is actually going on is a little complicated to explain. But make the assumption that the camera is always placed in the center of a great "sharpness-ball". Then we can define the DOF as the thickness of the ball's wall. Everything this side of the the wall will be unsharp, the same goes to everything placed on the far side of the wall.

When we increase the focus range by turning the lens' focus adjustment ring, it corresponds to blowing more air inside the sharpness-ball. The wall will move outward. At the same time the wall will be thicker.

When we stop down the aperture ring of the lens it corresponds to making the sharpness-wall thicker without moving it.

When we make the exposure, we will discover (as the smartest might have guessed) that the image will not show the whole ball. We will only get the slice allowed by the lens. The size of the slice is determined by the lens' picture angle. Wide angle lenses offers (surprisingly) a wide picture angle, telelenses a narrow angle.

But none withstanding the lens' picture angle, the picture slice will always be cut at a right angle. This goes for wideangles, normal- and telelenses - with one exception: the PC lens.

Moving Depth of Field

The PC-lens' tilt-function allows us to move the picture slice around along the wall of the sharpness ball ... and now it is getting exciting to be a photographer.

For example, we can move the picture slice towards the bottom of the sharpness ball. Here the wall curves under the camera, making the DOF much broader or deeper.

Imagine, that you want a picture of your mobile phone. Put it on a table and place the tripod-mounted camera behind and above the table. But regardless how much you stop down the aperture, you will only get two rows of keys sufficiently sharp.

Put instead the PC lens on the camera and tilt the lens front downwards. Adjust angle and distance, until the phone once again fills the viewfinder area. Now the effect is clearly visible: you have curved the DOF along the length of the mobile phone and the phone appears sharp from top to bottom. Make your exposure and enjoy - the sharpness does also show in the image.

But the real magic emerges when you discover that the PC lens not only offers you the means to control the sharpness. It will also let you control the areas of blur. If you want to, you can increase sharpness in areas of importance - and put the background and unimportant areas into a nice blur or "bokeh" - which seems to be the term today.

Of cause there are limits, but the possibilities of the PC 85 mm's tilt-function are truly astonishing, especially if you are used to "stiff" lenses only.

Optical quality

There is another valuable side-effect, working with a carefully crafted PC lens. Because of the shift and tilt functions, the lens must have a noticeably larger "picture-circle" than a comparable non-PC lens. The lens must also be extreme sharp and well corrected to produce high-quality images, when tilt and shift are used to their full extend. Therefore the optical engineers have spared no efforts and thats why the price of the lens must be high. 

But with a bit of luck, the result is an outstanding optical construction. The Nikon 85 mm PC is such a chunk of gold. It does effortslessly place itself at line with the worlds best renowned lenses. When I'm working with my 85 mm PC, I have the same comforting feeling of mecanical and optical quality as I sense, when I handle my old favorite Tessar (a relatively simply constructed Zeiss classic from 1902 which delivers first rate sharpness and contrast, but has shortcomeings in other fields). 

If you want to take a closer look at some 85 mm PC- images, you are welcome to visit my website www.subview.dk . The images in the serie "Craft & Spirit" are all done by the 85 mm PC.

Working with the PC lens

Because of mechanical limitations it is very hard to make PC lenses compatible with camera functions like autofocus, program automation and so on. The shift- and tilt-functions does not allow mechanical coupling and the optical charateristics vary depending on the usage of tilt and shift.

Therefore PC lenses are basically manual. Furthermore the camera must be mounted on a sturdy tripod if you want to make close-up images with precise control of DOF. The adjustments must be done and kept with utmost accuracy.

The lens has no automatic stop-down aperture function. You must adjust focus and tilt/shift at full aperture and then stop down to the predestined aperture by depressing a button.

Partly depending on the camera the automatic light measurement does not work either. You will typically work in M (manual) mode, but the lens will still be coupled to the light meter and the result are pretty correct, if you keep tilt and shift in neutral. Are you doing out-of-the-studio photographing, then the camera's histogram-function will prove invalueable. This way you will be able to judge the exposures precisely and make adjustments if necessary.

The lens' focus mechanism is coupled to the camera's focus sensor, but not to the focus motor. The focusing is done manually by turning the lens' focus ring, and the camera's sensor will oversee your actions and reward you with a "go for it"-signal at the bottom of the viewfinder, when your focusing is ok. This feature does not work however, when the lens is shifted or tilted.

Working with the PC lens is clearly more troublesome than operating an up-to-date automatic lens. But with a little practice you will do fine - and the results will be more than worth your efforts.

In most cases I work with the camera directly coupled to the computer, using Nikon's Camera Control. I make the exposures directly from the computer and in a few seconds the image pops up in the monitor. This way it is easy to make all necessary corrections until I am rewarded with a satisfying image.

Conclusion

The Nikon 85 mm PC is a specialized lens, no doubt. In most situations it is not useable with a handheld camera, the camera's automatic functions are at best supportive and in the beginning you will make a lot of overexposed images, because you "just" forgot to depress the aperture stop-down button.

But the 85 mm PC does also offer great advantages. Primarely the outstanding optical quality and the shift/tilt functions. Furthermore the lens allows aperture stops down to f:/45 and macro down to an image ratio of 1:2 at 15.4 inches.

This makes the 85mm PC extremely well suited to close-ups of relatively stationary subjects.

The optical quality also calls for use in the field of insect photograpy. There is only one "minor" problem: when you are finished adjusting the DOF, stopping down the aperture and making a few exposure test shots, the beetle or the caterpillar has wandered anywhere else long ago.

The future

The 85 mm PC is constructed of six individual elements, arranged in five groups, while the new 24 mm PC is a rather more complicated affair with 13 elements in 10 groups, ED-glass, aspeherical lenses and nanocoating. I look forward to see if the 24 mm will match the old 85 mm's optical quality. In lens constructions "complicated" is not always "beautiful".

From my point of view the 24 mm is primarily aimed at architectural photographing. In this field the shift-function's ability to correct converging lines will be valuable, while the lens' tilt-function will be of lesser importance, according to the wideangles greater native DOF.

If the rumours about a new 45 mm PC proves to be true, this lens will be a very interesting choice for close-ups in the picture ratio range of 1:5 and above. In this range the focal length of the 85 mm is often inconventionally long, especially when used with the smaller sensor of the D2X or the D300.

The 85 mm PC is sovereign when it comes to picture ratios from 1:2 to 1:5. The working distance is comfortable, it is easy to put up lights and the picture angle is so narrow, that is is piece of cake to keep the subject in front of an useable background.

I doubt that a new 85 mm PC will offer conclusive improvements except for nanocoating and the gold print on the lens casing. It is hard to believe that Nikon or anyone else will be able to conjure remarkable improvements up, considered the outstanding quality of the present version.

From the seventies and up to now, even Nikon addicts must admit that Canon has been in the leading position of the PC-lenses segment. But if Nikon is introducing three new PC lenses this year and the mechanical and optical quality matches the performance of the present 85 mm PC, then Canon will get a lot very serious competition.

Test images

Comparaison

I consider the 85 mm PC one of the very best pieces of glass, I ever worked with. Therefore I have compared it with a "stiff" lens, namely the Nikon 85 mm f:/1.8D. This lens construction is also some years old, but is is still considered among some of the best Nikon lenses.

Resolution

To compare two lenses relatively sharpness scientifically, you need an optical test bench. Currently I cannot find any in my cellar, so I am reduced to more simple methods.

One of the most popular is to use test boards with a large number of fine lines spreading out from a single point. When you enlarge such test images, you will be able to compare the lenses by looking at their ability to separate the lines.

I am printing my own testsheets with an Epson Stylus Pro 3800 in app. 2.800 x 1.400 ppi. The resolution limits of the printer make the lines float together in a four-clover-like structure from the centre and app. one inch outwards. Furthermore there is some "exiting" moire structures at the horizontal plane app. 3 inches from the centre. 

Nikon 85 mm f:/1.8 D is a classic portrait lens, probably optimized to an image ratio of 1:15, while the 85 mm PC is a macro, optimized to an image ratio of 1:5, I guess. This difference ought to be taken into consideration when the test images are compared.

The differences in image ratio also reflects in the different "closest possible" focus range. The Nikon 85 mm f:/1.8D will focus down to 33,5 inches while the 85 mm PC has its focus limit at 15.4 inches.

To avoid putting the 85 mm PC at a disadvantage from the very beginning, I chose to make the test images at a distance of 100 centimetres or app. 39 inches. But as soon as I started analysing the test images, I found that the resolution limits was the limits of the test board itself. This was both encouraging and depressing at the same time. Encouraging because of the proof of the lenses optical performances, depressing because I had to alter my test setup.

Next I chose a focusing distance of 200 centimetres (79 inches). This would give the 85 mm f:/1.8D a slight advantage, but I had to live with that.

These test images proved to be more useful. This time it was not the testsheet resolution, which made up the limits, but the correlation between the lens definitions and the D2X's sensor. The test images showed a great deal of moire because of interference between the testsheet's fine lines and the chip's individual pixel size sensors.

The conclusion must be that both the Nikon 85 mm f:/1.8D and the 85 mm PC are able to suffice approximately as far as the camera allows. When this is the case, we cannot demand much more.

Contrast

Nonwithstanding there is an explicit difference between the two lenses. The 85 mm f:/1.8 D showed a noticeable colder reproduction of the subject - or in other words, the lens produce images with a bluish tint. To check this effect I made a few control exposures with a 70 - 200 mm zoom, only to find these images neutral just like the 85 mm PC images.

Furthermore a closer inspection of the test images of the 85 mm PC showed slightly better resolution than those of the 85 mm f:/1.8 D. But what is equal important, the 85 mm PC shows distinctly better contrast than the 85 mm f:/1.8 D.

At this point a little basisic knowledge migt be in place. The resolution is the lens' ability to separate points or lines from one another. Contrast is the lens' ability to reproduce the transition between different tone values.

A lens might be able to define fine details and at the same time letting the edges merge together.

The web-published test images does not show this effect clearly, because the contrast is accenturated to make them viewable at the relatively low resolution possible with web-based media. In this case one must examine the original test images.

Out of regard for Lars Troels, who is kindly hosting this review at his website, I also made some of the brick shots Lars Troels usually do, when he is making his reviews. In the brick test shots I find the same subtle differences in definition, more significant differences in contrast and the same bluish tint in the 85 mm f:/1.8 D images as in the testsheet images.

Sharpness

test 01:         85 mm PC F:/2.8 D - testsheet / resolution and contrast.

test 02:         85 mm f:/1.8 D - testsheet / resolution and contrast.

test 03:         85 mm PC F:/2.8 D - brick wall / resolution and contrast.

test 04:         85 mm f:/1.8 D - brick wall / resolution and contrast.

The effect of the shift-function regarding tapering:

test 05: 85 mm PC F:/2.8 D: The lens' tilt- og shift function in neutral. Vertical lines are not parallel but taper towards a single point. 

test 06:         85 mm PC F:/2.8 D: The lens is shiftet upwards. The tapering are reduced.

test 07:         85 mm PC F:/2.8 D: The lens is shiftet downwards. The tapering are increased.

The effect of the tilt-function regarding depth of field:

test 08:         85 mm f:/1.8 D: Sharpness appears as a horisontal band across the center of the image.

test 09: 85 mm PC F:/2.8 D: The lens' tilt- and shift function in neutral. Sharpness appears as a horisontal band across the center of the image.

test 10: 85 mm PC F:/2.8 D: The lens is tilted upwards. The area of sharpness is noticeable narrower.

test 11:         85 mm PC F:/2.8 D: The lens is tilted downwards. The area of sharpness is covering almost the whole testsheet.

test 12:         85 mm PC F:/2.8 D: The lens is tilted to the right. The band of sharpness is diagonal across the testsheet.

Test conditions:

All test images are done with a Nikon D2X camera mounted upon a sturdy Gitzo tripod with a total weigth of 20 pounds. 

All test images are exposed at ISO 100 and f:/8 - or so close as the PC-lens permits. Variations up to 1/3 of an aperture stop are caused by the use of tilt, shift and focus extension. 

The test images no. 01-02 (resolution and contrast) are exposed outdoor in shady daylight at a focusing range of 79 inches (200 cm.)

The test images no. 03-04 (brick: resolution and contrast) are exposed outdoor in shady daylight at a focusing range of 39 inches (100 cm.)

The test images no. 05-07 (shift-effect) are exposed with double studio flashs at 1/250 at a focusing range of 39 inches (100 cm.)

The test images no. 08-12 (tilt-effect) are exposed with double studio flashs at 1/250 at a focusing range of 39 inches (100 cm.)

The test images no. 05-12 are exposed with the D2X coupled to the computer and adjustments and shooting managed through Nikon Capture Pro.

Variables

Focus adjusted manually in advance of every single exposure.

The camera's position is adjusted vertically and horizontally during the test sheet exposures to keep the centre of the testsheet in the viewfinder's central focus point. 

Lens adjustments

Shift:

The test board in vertical position, the exposures made from below in an angle of app. 30 degrees.

test05.jpg:                          Lens in 0 degrees tilt, 0 mm shift, rotation 0 degrees.

test06.jpg:                          Lens in 0 degrees tilt, 12,4 mm shift upwards, rotation 0 degrees

test07.jpg:                          Lens in 0 degrees tilt, 12,4 mm shift downwards, rotation 0 degrees.

Tilt:

The test board in horizontal position, exposures made from above in an angel of  app. 30 degrees.

test09.jpg:                          Lens in 0 degrees tilt, 0 mm shift, rotation 0 degrees

test10.jpg:                          Lens in 8,3 degrees tilt upwards, 0 mm shift, rotation 90 degrees

test11.jpg:                          Lens in 8,3 degrees tilt downwards, 0 mm shift, rotation 90 degrees

test12.jpg:                          Lens in 8,3 degrees tilt to the right, 0 mm shift, rotation 0 degrees

Postprocessing

On account of the restricted resolution offered by the web media, the contrast in the test sheet images are increased in Photoshop.

No artificial sharpness added, neither in the camera or during the postprocessing.