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Focusing racks are useful in close-up and macro photography. In these types of
photography, it is common to set a magnification first (by choosing a focusing
distance or reproduction ratio with the lens focusing ring), and subsequently
to focus by moving the camera and lens back and forth as a whole. Small adjustments of the distance
between camera and subject are best performed with a focusing rack.
A focusing rack has a fixed platform with one or more threaded holes for
attachment to a tripod head, and a moving platform with an attachment for the
camera (or lens foot) that slides along a prismatic metal bar or a pair of
parallel metal rods. A rack-and-pinion gear or a screw mechanism allows the camera platform to
move smoothly in small increments. Most bellows possess a comparable mechanism for moving the bellows, lens and camera as a
whole. In some cases, a focusing jack can be
used as an alternative to a focusing rack.
Since macro photography is my main area of photographic work, I expect a
focusing rack to be sturdy, durable and reliable, and have little patience with
equipment that hampers my work, rather than helping it. A focusing rack of high quality must satisfy several requirements:
- It must be rigid, and the platform must not wobble, i.e., there must be
no play between platform and rail(s). This must be true both while moving
the platform and after locking it. In addition, locking the platform should
not cause the composition and field-of-view in the viewfinder to change
noticeably.
- There must be provisions for locking securely the sliding platform in place
by using a minimum of force.
- The platform must carry the weight of the camera and lens without
creeping. A critical test of this characteristic can be carried out by
mounting the focusing rack vertically. With the locking mechanism unlocked,
release the turning knob and check whether the camera platform creeps
downward. If it does, the mechanism is too loose. Some focusing racks have
provisions for adjusting the friction between platform and rail(s). This can
take care of creeping as well as play. Of course, no creep should take place
also when the platform is locked.
- The platform must move smoothly (i.e., without jumping or "sticking").
- The focusing knob must turn without requiring excessive force.
- Travel of the platform must be precise, but still sufficiently fast.
Both focusing racks that move the platform too fast, and those that require
many turns of the focusing knob to move a small distance, are impractical to
use.
- Aluminium-against-aluminium sliding parts simply don't work - this metal
is too soft, and may stick under load even when lubricated.
Aluminium-against-brass is marginally better. Plastic adds wobble, mushy
locking and low durability. The best choice of materials that guarantees
smooth movement, secure locking and durability is lubricated
steel-against-brass or brass-against-brass. Unfortunately, I have yet to see
a photographic focusing rack built with these materials (more on this
below).
Four models in my possession are shown and discussed below.
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Unknown brand and model (above). This is mostly aluminium
alloy and moderately heavy. The prismatic rail runs in a nylon insert of
the platform. The platform has both 1/4 and 3/8 in. sockets. The large
knob turns a metal gear that meshes with a plastic rack at the bottom of
the rail. The small knobs locks the platform. Small screws hold the
nylon insert in place, and can be used to adjust its pressure against
the rail (thus controlling friction). Movement is smooth, but the
plastic rack under the rail is reason to worry about premature wear,
especially if the rack is mounted vertically. Locking still allows creep
under a heavy load.
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Velbon Super Mag Slider (above). This is a current model
made mostly of magnesium
alloy, and therefore very lightweight. It actually consists of two racks
mounted at 90 degrees from each other. The two racks can be separated by
using a supplied hex key. The larger platform can be used by itself as a
conventional focusing rack. The shorter rack could be used in a similar
way, if a few mechanical parts are added. Each platform runs on the rods
on plastic bushings. Instead of a gear, both racks have a third,
threaded metal rod. In the smaller platform, this rod is turned by a
knob. In the larger platform, the threaded rod is fixed, and the knob
turns a threaded nut (via a gear) that revolves around the threaded rod
and moves the platform. There is no need for a locking knob, because
this mechanism does not allow creeping of the platform under load. The
movement of the platform is smooth, but it takes several revolutions of
the knob to advance the platform by a small distance. This can be useful
at high-magnification macrophotography, but is too slow at a 1:1
reproduction ratio or lower. As a whole, there is no wobble or play, but
a slight flexibility of the whole construction that might invite
vibration.
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Pentax focusing rack (above). This is an old
model, which I have owned for more than 25 years. It is an all-metal
construction and relatively heavy. This is the sturdiest and most rigid
(when locked) of the four models, and the only one of these with metal-against-metal
sliding surfaces. The rods and gear are chrome-plated brass, while the
casing is cast aluminium alloy. There are several provisions for fine adjustments of
the alignment of rods and gear, mostly hidden under threaded metal caps
that cover the adjustment mechanisms. Friction can be somewhat uneven
and sticking may occur under heavy load,
but lubrication with viscous fat and a careful adjustment of the rack
can fix this. The small lever is a locking mechanism, but can be used
also to control friction and eliminate residual play. Among these models, this
and the following are the only ones that could be called a precision mechanism.
It is certainly very durable, and the only one that somewhat approaches
(but does not equal) in performance the focusing mechanisms of
microscopes. In particular, some play when unlocked and a tendency to
stick when used vertically with heavy cameras and lenses detract from
its reliability.
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Olympus OM focusing rack (above). This is
also an old model no longer manufactured, but now and then it appears on
eBay (unfortunately, most times at ludicrous prices). The top
platform was sold separately from a set containing the prismatic rail and bottom platform
(which are the same used in OM bellows). This may
make it difficult to acquire all necessary parts.
This is the heaviest of the focusing racks discussed here and, because
of the double platform, the one that provides the largest range of
movement (262 mm when both gears are used). The prismatic rail and
platforms are built in aluminium alloy, and are quite rigid and heavy.
The platforms slide on the rail on thick nylon inserts. The larger knobs
operate the gears, while the smaller ones lock the platforms by pressing
the nylon inserts (via metal disks) against the rail. Thus, the
platforms can be locked tight without
fear of marring the rail. Each platform has also two small adjustment
screws that can be used to tighten the nylon inserts against the rail.
They are conveniently used to take up any slack, and as a friction
control. The gears and racks are precision-machined in chrome-plated
brass. Like all focusing racks with nylon-against-metal surfaces, the
rail and nylon inserts should not be lubricated. A small amount of fat
can be used on the racks, gears and their shafts.
This otherwise very rigid and precise mechanism has two main weaknesses.
The first is that the racks are not rigidly mounted onto the rail. The rack is mounted onto springs that push
it outwards, and the screws that attach the racks to the rail are
designed to allow a movement of about 1 mm. The central portion of the racks also slightly bulges
outward. This is intentional, and presses the rack against the pinion to
take up any slack. Unfortunately, this construction allows the rack to slide
back and forth and sideways a fraction of a mm, which results in a dead play
of about half a mm when reversing the direction of rotation of the
focusing knob. If you are mechanically inclined, you can add a thin shim
under and along the side of the rack to correct this problem. Changing
the screws that attach the racks to the rail to ones with slightly larger heads also helps.
The second weakness is that the locking knob gradually increases
friction against the rail, but never quite locks the platform in place.
Even when tightened very hard, the platform still can move under a heavy
load. This can cause creep with heavy cameras and lenses mounted
vertically. This problem cannot be eliminated entirely. Without this
problem, this focusing rack would be my clear choice. On the other hand,
this focusing rack displays no tendency to stick, and minimal wobble and
no play of the platforms even when unlocked.
In time, this focusing
rack became my favourite for studio close-up work with a
tripod-mounted camera - until I came across the following one. The
Olympus OM rack is still useful to me when I need a relatively portable
focusing rack.
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| The above Zeiss focusing rack came to me as part of a
second-hand, incomplete Zeiss epi-microscope. I did buy it because I was
looking for a focusing rack for a Zeiss Tessovar,
which it is designed to fit. In time, I also found a table-top focusing stand for the
Tessovar, which is much more useful. Therefore, I resolved to modify an
unused attachment ring for a Zeiss stereo microscope (cutting off most
of the ring) to transform it into a focusing rack usable with camera
equipment. The aluminium platform attached at the top allows mounting a
camera, lens shoe, bellows or quick-release shoe system. This platform
can be released from the rack with the small thumb-screw at the side of
the mount, leaving it free for use with the Tessovar or other Zeiss
equipment. Incidentally, I can mount the top platform of this rack also
on the vertical column of the table-top Zeiss stand, which is useful for photomacrography.
This rack has a
collar for adjusting tension (not visible in the above picture), and is
extremely rigid and precise. The large, gray-painted support to which
the nickel-plated brass prismatic slide and geared rack are attached is
a 251 mm long solid aluminium bar. The black platform at the bottom is a
large Manfrotto quick-release plate (dwarfed by the rack). This rack has
a movement range of 172 mm.
There is simply no way to compare this focusing rack with those
designed as photographic accessories that I have seen in my entire
career. The Zeiss rack is extremely solid, extremely smooth, extremely
precise and extremely versatile. It can easily hold any of the lenses I
own, including a 300 mm f/2.8 (I don't really have a practical reason
for doing so, but this rack can take it and more). With reasonable care,
this type of focusing rack will last much longer than I do.
There is only one problem with this rack. It is extremely heavy, and
putting it in my camera bag for using it in the field would effectively
double the total weight of the macro equipment. It would also force me
to carry along my heaviest tripod and head. In the studio, where weight
is not a problem (and actually dampens any vibration), I am forced to
use it atop my heaviest three-axes head and a heavy tripod. I would not
risk using it on a ballhead, because its weight would force me to strain
myself all the time to avoid the head and camera equipment from tipping
in all directions whenever the head lock is released (and no ballhead
would be able to carry this suddenly unbalanced load when unlocked).
With a three-axes head, I only have to worry about one direction at a
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Several other models of photographic focusing racks are available.
- The Novoflex, Kirk and Really Right Stuff models seem to be solid, precision-built and smooth-moving.
They are also quite expensive. I
cannot endorse them because I only looked at them, and never tried them in practice.
- The Manfrotto 454 (= Bogen 3419) uses a micrometer screw instead of a gear, and
metal-against-metal slides (actually, painted aluminium against painted
aluminium). The
construction is relatively rough and quite some play exists between rail and platform
when not locked. The shape and placement of the controls are also questionable.
The screw, locking knob and internal parts are made of non-plated brass, and
likely will oxidize and corrode. All in all, this rack looks more like something out of a Soviet-era factory than
a piece of precision photo gear.
- The Velbon Macro Slider is earlier than the Super MagSlider (but still
available) and made mostly of aluminium alloy. It has a worrying amount of play, and a tendency to stick.
- A few cheap models made in China are either too imprecise or too mushy to be useful,
except for occasional, non-demanding use.
In conclusion, the quality of focusing racks sold as photography accessories is very variable,
but never excellent (at least among the models I tried). There are flimsy ones that
obviously are unsuitable for any serious use, and relatively good ones that are very
expensive. The only focusing racks that I regard as
excellent are the ones I salvaged from microscopes and
optical equipment. If you have access to a metal workshop, you can transform one
of these into a marvellous focusing rack. I have done this a few times, and
often this does not require power tools, other than a bench drill.
This is a small collection of salvaged focusing racks, which I recovered from
containers of discarded equipment at university institutions. Most are from
microscopes, while the oversized one at the bottom comes from a large-format camera.
Transforming any of these into a useful tool requires only the addition of an
attachment for a tripod, and one for a camera. All these racks are made to hold
heavy equipment in a vertical position, and therefore do not creep under load.
They are also very rigid. Typically, they are made of brass and steel, and
therefore very durable. In fact, all-metal microscope focusing mechanisms built
in the mid-20th century are far superior to later ones, which often employ
plastic inserts and even plastic gears.
Because of their weight, focusing racks built with salvaged equipment are
most suitable for studio work. Most would be far too heavy to justify
carrying in the field. Because of their extremely narrow mechanical tolerances,
they are unbeatable for precision work, and will last literally a lifetime or
longer. A general drawback of these racks is that typically they allow a range
of movement limited to about 30-50 mm.
A microscope stage can also be very useful in high-magnification
macrophotography in the studio. Oversized stages designed to hold large
microscope slides, like the one at the top left above, are especially useful. You can insert
a glass, metal or plastic plate onto the stage to hold the specimens to
photograph, and use the micrometer controls to move it in two dimensions. The
cost of new equipment of this type is prohibitive, but second-hand microscopes
and microscope parts are common on eBay and other auction sites, and prices may
be reasonable.
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