Photography Jigs and Notes

A Balanced Tripod Mount

With the rise of digital cameras and their high sensitivity to light (Nikon D3/D700 go to ISO 25,600), monopods and tripods are much less necessary than they used to be. But, tripods are still valuable for precise composition of photos, especially macros, for taking HDR sequences, for photos under starlight, and for remote-triggering. The swing to zoom lenses has made regular working lenses much longer and heavier than was the case with primes. That presents a problem: the center of gravity of a body+zoom-lens is now well in front of the body, so using the body tripod socket leaves the assembly very front heavy and inclined to droop with the slightest softness in body-tripod contact or tripod-ground contact. Long focal length lenses have long come with their own tripod socket to deal with this problem, but working range zooms don't. Canon provides a lens ring for some of their intermediate focal length lenses so they can be balanced, but not for regular to short ones; Nikon doesn't at all. And, some zoom lenses don't have any place where such a ring could be attached. Here's a solution - a fixture that offsets the camera body socket from the tripod socket so the body+lens is balanced on the tripod. It's a simple piece of stiff flat metal, easy to make with only hand tools. The only critical measurement is the length between body tripod socket and the balance point of body+lens - 47 mm for a D700 plus 24-70 mm. All other measurements are simply to match your camera and tripod. The Nikon D700 comes with a soft pad around its tripod socket - not reliable when out of balance. So, three grub screws are used to bypass the pad and connect the fixture firmly to the body, metal-to-metal. Pads on the tripod head are of less concern with this method, since the load is balanced there, but should also be replaced with metal-to-metal contact if really soft. My version uses a quick-release tilt-rotate head. A single control loosens or tightens both ball and rotation, and the ball is large enough to be reliably steady with a load of 2 kg (the weight of Nikon D700 with 24-70 lens). A flat-head 1/4-20 screw attaches the fixture to the tripod quick-release plate, a finger-friendly screw to the camera. I usually don't need a tripod, so elected to keep a screw to attach the fixture to the camera body, rather than using a second quick-release unit which would add yet more weight to the camera. My already-heavy telephotos do have their own quick-release plates pre-attached. It's solid, and makes framing much easier and more stable.

A Travel Tripod

In the field, when long treks preclude carrying a heavy tripod, the adaptor allows a combination of a Rowi travel tripod and a Vivitar rack&pinion to be solid. Whether used as a tripod, screwed to a fence post, clamped to a table top, or used with a macro stand, everything stays in balance.

A Panorama Mount

Stable Long Lens Collars Most long lens collars are too flexible, too sensitive to vibration that blurs images. Bulky and expensive aftermarket collars are provided by several companies such as Manfrotto and RRS, but why not just fix what you've got? Small, light, and practical. Here is a solution. Carve a piece of hardwood to fit firmly into the collar of the lens. The lengthwise grain of the wood runs vertically - it's the grain direction that changes in length the least when moisture varies. A thin teflon sheet between wood and lens provides elasticity that avoids excessive force on the lens and is low friction to allow the collar to be rotated and removed easily.

Closeups to 100x Camera lenses are made almost entirely with spherical surfaces because non-spherical surfaces are much more expensive to produce. Spherical lenses don't form perfect images: spherical aberration, coma, astigmatism, field curvature and field distortion result. Lens materials bend light differently at different wavelengths, resulting in chromatic aberrations. The larger the aperture of the lens is relative to its focal length, the more severe almost all these aberrations are. Aberrations also differ for different distances between the object photographed and the lens, because the light rays come in at different angles. That has to be taken into account in close-up photography because most lenses are designed to minimize aberrations for objects 10x or more the focal length away from the lens. A lens used outside this range will have larger aberrations than within its design range. Macro lenses are designed for a wide range of object-lens distances, which is done by making them more complex and by using small maximum apertures. High quality close-up photography starts with them. However, most lenses can be used outside their design range if the aperture is reduced enough. (Note that some aberrations, field distortion and lateral chromatic aberration in particular, are not reduced by stopping down.) However, light consists of waves, and waves head off in all directions when they come close to an edge. The smaller the aperture, the greater diffraction is. Ultimately, close-up images are a balance between small aperture (large diffraction) and large aperture (small depth of focus). Peter Forsell has an excellent page on how to calculate the magnification available with these techniques. All macro photography benefits from the use of a slide stage that moves the camera plus lens to focus, as shown. There are a number of ways to balance all these factors to obtain fine closeup photographs. Here are the ones I've found to be the best. Macro Lens: Quality closeup photography begins with a lens designed for the job, a macro lens. Most modern ones focus from infinity (0x) to 1:1 (1x). Since all lens info is sent to the camera, you can determine the exact size of everything in the photo. Just take a series of photos of a ruler to enable you to convert the distance recorded in the EXIF to magnification for each closeup lens you use. Reversed Lens: Lenses have to have an aperture ring to be used reversed. The best results are obtained when the lens is designed to work at close-to-equal object and image distances. In short, a macro lens works best this way. And, there's a trick that lets one operate at its full potential: put the object at the same distance as the camera film plane would be and move the body away with bellows or extension rings so it's where the object would be. Here's how to do it. Make a jig using a rear lens cap and a piece of plastic tube so that a focus pattern is held at the correct distance from the flange of the lens, 46.5 mm for Nikon F-mount (others here). Mine is shown at right. Set the lens at the magnification desired using the built in scale. It's still accurate, it's just reversed too. Next focus on the image using the bellows. Finally, remove the jig and move the assembly as a whole until your subject is in focus in the viewfinder or live-view. Your macro lens is just as well corrected this way as when operating normally. Another option is to use filter spacer rings as at right, each marked with the magnification to set on the lens. Most fixed focal length lenses produce acceptable results at small apertures when reversed. Small wide-angle lenses generally work best. A good approximation to the real f# of a reversed lens is the indicated f# multiplied by (1+M/p) where M is the magnification and p is the pupil magnification. p is close to 1 for prime lenses in the 50-100 mm range, greater than 1 for reversed tele lenses, less than 1 for reversed wide angle lenses. The pupil magnification can be estimated by looking into the front and rear of the lens and measuring the diameters of the apparent apertures. p equals the entrance pupil diameter divided by the exit pupil diameter. Coupled Lenses: When one lens is reversed in front of another with both focussed at infinity (afocal coupling) the magnification is the ratio of the two focal lengths. The rear long focal length lens should be wide open to avoid vignetting and the aperture controlled with the front short focus one. The real f# is the indicated f# multiplied by (1+M/p) as above. You'll find vignetting prevents you using many lens combinations, but the ones that don't vignette will work well; both lenses are operating as designed so are fully corrected. Microscope: A camera can be mounted on a microscope. The highest quality is obtained with an adapter that includes a flat field projection eyepiece designed for photography. However, it's much less expensive and more flexible to use standard interchangeable eyepieces and a camera lens. The last photo shows a 60 mm lens focussed at infinity coupled to a microscope with a simple coupler - the conical lens surround sits on the eyepiece and is kept aligned by a filter ring adaptor turned on an electric drill with a file; it slides on the microscope column. With 10x eyepiece and 5x objective, I get 11x on the camera sensor; up to 100x is practical. Microscope objectives are rated in numerical aperture (NA); the indicated f# for use in the formula above is close to 1/(2*NA). Poorer Methods: Extension rings, that go between lens and camera, work acceptably with most fixed focal length lenses when small apertures are used, but produce unusably poor results with most zoom lenses as the resulting field curvature is not reduced by stopping down. Simple closeup lenses, even achromats, give much poorer quality than a true macro lens. Multi-element close-up systems such as those produced by Raynor are better, but still not as good as a quality reversed macro. If the strength of a lens is given as, say, 10x, this refers to the minimum focussing distance of the human eye, 25 cm; divide by 4 to get the strength in diopters.

60 mm macro lens at 1x focussing jig for reversed lens reversed macro lens at 1.6x reversed macro lens at 6x microscope adaptor microscope 11-100x

Notes on Focussing

Depth of field tables and hyperfocal distance are based on a fallacy, that human eyes work the same way as a mathematical equation based on circle of confusion. They don't! Some things are much more important to our eyes than others.

Here are the guidelines I use to focus.

When as many things in the image as possible are to appear sharp in the image, set aperture at the diffraction limit for the camera: f/11 for my primary camera, a Nikon D700. Then, if one object is critical to the bite of the image, usually the item with the finest detail, focus on it. Otherwise, focus on the farthest object that is wanted in focus - that's where the lack of detail usually shows first. If this procedure doesn't show everything important to the image in sharp focus, recompose the image. Stopping down further than the diffraction limit kills bite.

A different way of looking at focussing is based on the recognizability of objects. Look in the front of your lens and close down the diaphragm until it appears to be the size of the smallest objects you want to be recognizable in the image. Not sharp with bite, but recognizable for what they are to our eyes. Focus on the farthest such object. Then, all objects of the iris size or larger that are closer to the camera will be recognizable no matter what distance they are from the camera. For people's faces, the iris size should be a maximum of 5 mm, no matter what the lens focal length.

When something is to be thrown sufficiently out of focus that its detail is not recognizable, a physically large aperture is needed. That's easiest to get with a lens of long focal length, so begin by choosing the longest focal length that will include all of the objects wanted in the image. Focus on the wanted object, then use the formula
S/I=d/D, where
S is the size of the largest detail on the unwanted object that will make it recognizable,
I is the iris size,
d is the distance between the object that is wanted and the one that isn't, and
D is the distance to the object that is wanted.

d and D must be in the same units, S and I in the same units, but S and I don't have to be the same units as d and D. Use percentages: if d is 50% of D, then S must be 50% of I. The iris diameter in this case must be double the size of the largest detail of the unwanted object. Today it's usually easier to use Photoshop's soften function on the desired areas than to do it all with the lens.

Macro Photography

First, if a fine corner-to-corner matte screen exists for your camera, get it and use it. Unfortunately, since the rise of autofocus, such screens are only available from third-parties such as KatzEye. The only alternative to breaking your warranty is to get a camera with what Nikon calls LiveView, to preview images on the rear screen at the lens opening to be used for the image. It's a poor alternative though, because stabilizing the camera against your face is one of the best there is for anything that moves too fast for tripod setup. And, don't forget to close the eyepiece shutter if you are relying on autoexposure.

Second, move the camera to focus, not the focussing ring. Set the focus ring to choose object size, and leave it alone after that. Moving the camera gives consistent results with any lens. The magnification and f/# stay the same and the focus plane moves with the camera in precise step with it. (further details)

With a tripod, get a macro focussing stage such as that shown above. Hand held, brace a part of your body on a solid object and pivot about it. For example, lean one shoulder firmly against a tree, and rotate about that shoulder while rotating your head to keep the camera aimed at the object. Close to the ground, put elbows on the ground, then pivoting can be nearly perfect, sufficiently under control for 3x magnification. At higher magnifications than that, a solid tripod with macro stage is pretty well essential.

As with normal photography, avoid stopping down below the diffraction limit. But, the effective f/# now depends on magnification. It gets small, quickly. As with normal photography, if depth of field is inadequate for an image, try to recompose. However, with a macro stage, there is another option, focus stacking software like CZM. It's techie stuff, but it works.

John Sankey

Notes

These are the internet firms I've dealt with for photography stuff that I've found trustworthy for Canadians:
Vistek
MostlyDigital
CameraFilters (USA)
Canadian Telescopes
Breguet Camera (Hong Kong)

1. The effect of changing focus with the focus ring depends greatly on the lens. A simple lens focusses closer by moving the lens away from the sensor and towards the object at the same time, so magnification increases and effective f/# decreases. At close range (twice the lens focal length or closer), focussing is strongly non-linear (actually hyperbolic). The Nikon 55mm macro I have works this way. Many new IF macro lenses change the focal length of the lens to focus, keeping a more constant distance between lens and subject than is possible with a simple lens. This is done to compensate for non-linear focus-movement effects so autofocus can work. Some lenses are part way between, such as the current Nikon 105mm macro. And some do more complicated things still, such as the Nikon 70-180 macro I have that is designed to keep constant effective aperture with focussing. With cheap macro lenses, the field curvature changes with focus ring movement as well. So, unless autofocus is the only option to keep up with a scurrying bug, move the camera not the focussing ring with macro photography.

D700 Active-D and Shutter Timing
Active-D for the D700 has two parts. First, it changes the shape of the overall gamma curve to lower contrast as shown at right (measured at ISO 200, picture control neutral). Second, it scans the image for detail in shadows and increases their local contrast in a manner similar to HDR programs. Such a process, a generalised sharpening, increases the visibility of noise in the image so is best used at low to moderate ISO. From the effect on buffer memory, it seems that it stores the sensor RAW in buffer, transforms it into another RAW, and only then converts the second RAW into TIFF/JPEG for transfer to the flash card. The process takes close to a second per image, so must be turned off when taking rapid sequences (CH mode).

The shutter times for the Nikon D3/700 are chosen to be in a precise ratio of 1/3 stop to each other, with the exception of the longest, 30", which should be 32.9 s but is in fact only 32.0 s. They are not based on 1 s, but are 3% longer to minimise the differences from the power line frequencies of 50 and 60 Hz. The actual times must be used when taking multiple exposures e.g. the interval timer must be set to 33 s for taking star and other light trails when the shutter is set to 30". Measurements made by Marianne Oelund.

marked	actual	marked	actual
30"	32.0s	1.3	1/1.224
25"	26.1	1.6	1/1.542
20"	20.8	2	1/1.94
15"	16.5	2.5	1/2.45
13"	13.1	3	1/3.08
10"	10.4	4	1/3.88
8"	8.24	5	1/4.89
6"	6.54	6	1/6.17
5"	5.19	8	1/7.76
4"	4.12	10	1/9.78
3"	3.27	13	1/12.32
2.5"	2.59	15	1/15.5
2"	2.06	20	1/19.6
1.6"	1.63	25	1/24.6
1.3"	1.29	30	1/31.17
1"	1.030	40	1/39.1
		50	1/49.3
		60	1/62.0
		80	1/78.0
		100	1/98
		125	1/124
		160	1/156
		200	1/196
		250	1/247
		320	1/310
		400	1/392
		500	1/490