Construction Common to All 76/Centennial Variations: 
1)  It is back focus only , and has non-tapering bellows, which results in the front standard being approximately the same size as the rear standard.
2)  The platform has a single rack inlet down the middle of the platform for rack and pinion focus.  The edges of the platform have "brass guides", sheet brass installed to project slightly over the edge of the platform.  The rear standard, in turn, has a metal undercarriage with a slot in which the guide moves as the camera is focused.  The guides are a necessary part of a camera having a single, middle rack and pinion; without them, the focus is hopelessly wobbly.  An exception is Variation 1.0, which has a push-pull focus and no brass guides.  Variation 1.0 is thought to represent an early version of The 76 Camera.
3)  The front standard: is a box-jointed square, mounted on a ~1/4 bottom plate, the whole screwed to the front of the main platform; an ~1/4" thick facing holds the rise mechanism and the lens board.  On the bottom of the front standard, there is a quarter-round trim linking the vertical standard to the horizontal platform.  The front standard adjusts up or down, held in place by a male knurled thumbscrew.
4)  The rear standard: is a box-jointed square, which screwed to a frame.  Even though the frame is the same thickness as is the bottom plate of the front standard, the rear box has to be slightly smaller than that of the front standard, since the rear standard frame rides slightly above the platform on its rack and pinion gear system.  A second and separate box-jointed square in the rear standard is hinged on the bottom.  It tilts backwards to provide a single swing for the camera.  The amount of swing is controlled at the top by a thumbscrew and slotted piece of hardware which doubles as a latch for the hinged ground glass frame.
5)  The folding platform or bed is hinged, and made rigid by either a thumbscrew (pre-1886) or a rod and piston device (patented by Mathias Flammang Oct. 20, 1885).
6)  The bellows on early examples are fabric coated with a black rubberized paint, red Russian leather (a later example).
7)  The ground glass frame hinges down, and is latched up using a spring-loaded clip which has the same shape and design for all variations except Variation 1.2, which is uniquely complex.
8)  The lens board consists of a three-piece base on top of which is a shifting three-piece section.  An exception is Variation 3, which has a simple non-shifting lens board.  This camera is thought to be an inexpensive Scovill version of The 76 Camera, and therefore fitted with a less expensive non-shifting lens board.  The camera was normally sold without lens, assuming perhaps that a photographer would want to choose their own type and brand of lens.  Additionally, lenses of view cameras were hardly permanent, and it is common to find a camera with a replacement lens board and/or a different lens, even one made by a competitor.

Variations:

There are five variations , four of which are marked as products of American Optical Co. via a prominent silver-colored label, and one of which appears to be a Scovill version of the American Optical product.  This American Optical vs. Scovill version dichotomy also appears to occur amongst camera variations known as Waterbury Cameras.  See Waterbury Camera Variation 1 for the details as well as links to all the Waterbury variations. 

The 76 Camera Variation 1.0 (Wet Plate Version)

     The 76 Camera Variation 1.0 differs from the archetype Variation 2.0 by possessing the push-pull focus rather than rack and pinion discussed above.  This type is very rare, though, and so is not considered the archetype 76 Camera.  It no doubt is earlier than Variation 2, as it is a wet-plate camera.  The first description of The 76 Camera, in 1876, states that the camera had a fine-focus screw - a piece of hardware that combines one thumbscrew for firmly setting the rear standard at one spot, and another thumbscrew that allows fine-focusing (see American Optical View Camera Boxes No. 1 (view from the right and behind).  Therefore, Variation 1.0 is intermediate to the fine-focus screw 76 Camera and the rack and pinion focus 76 Camera Variation 2.0.  It is no wonder that the engravings don't quite know what type of focus to illustrate: there were three types of focus made very close in time to one other.

     The push-pull focus on this variation is secured by a lever on the back of the rear standard.  When rotated in the clockwise direction until pointed straight back, the rear standard moves freely.  The lever can be used as a handy item to pull on to achieve the desired focus.  When rotated further clockwise, the lever binds tightly to prevent the focus from moving when the plate holder is inserted or removed. 

     It does not appear to have a stamped assembly or serial number.

     The camera is indeed from the 1876-1881 wet plate era, as shown by the last photo above, taken of the surface directly below where the plate holder sits during an exposure.  Black stains, undoubtedly stains from the silver-halide-containing collodion, are visible - just where they commonly are found on cameras in which the wet-plate process was used.  Assuming that the earliest 76 Cameras had fine-focus screws as described, this camera is mostly likely from about 1878-1881.

     The sizes of Variation 1.0, Variation 1.2, Variation 1.5 and Variation 3.0 are large - significantly larger than the size of Variation 2.0 (see Variation 3.0 for discussion of size).

The 76 Camera Variation 1.2

     The 76 Camera Variation 1.2 was only found after the identification and naming of the 76 Camera Variation 1.0 and the 76 Variation 1.5.  It turns out that it has one characteristic of Variation 1.0 and one characteristic of Variation 1.5 - therefore, it has been desitnated as Variation 1.2.  The feature exactly like that in Variation 1.0 is that they both have a rounded yet flattened wood molding at the bottom of the front standard, whereas all other variations of the 76 Camera have a molding that is exactly quarter-round.  The feature like that in Variation 1.5 is that they both have (as do all 76 Camera variations except Variation 1.0) rack and pinion focus rather than push pull.  Unklike the other variations having rack and pinion focus, the focus knob of Variation 1.2 has a plain surface; the focus knobs of the other rack and pinion 76 Cameras have a stepped embellishment. 

     It has a stamped assembly or serial number "6" on the upper rear surface of the platform, and on the upper rear standard under the ground glass frame.

    The example camera has a replacement lens board; it original probably would have been a shifting-type, as advertised for the the 76 Camera. 

The 76 Camera Variation 1.5 (Early Plate Holder Clip Version)

     The 76 Camera Variation 1.5 appears to be identical to the 76 Camera Variation 1.0 as far as type of wood, grain and finish and hardware design and finish, except for 1) the substitution of a quarter-round molding for the rounded yet flattened type, and 2) a unique clip and catch that together hold the plate holder to the top of the rear standard.  Fortunately, the camera example has with it a matching plate holder, so the design can be fully appreciated.  The bottom of the plate holder has two holes that fit over corresponding wooden pegs at the bottom of the rear standard, as do many other cameras of the era, but the clip (and associated catch) at the top of the rear standard is unique.  Other variations of the 76 Camera (as well as many other models and variations of Scovill and American Optical cameras have a simple spring-loaded, horizontally-acting clip that engages a simple round head screw shaft on the upper edge of the plate holder (also the lower edge, since the plate holders are double-sided).  However, the 76 Camera Variation 1.5 has a more complex arrangement for the upper clip and catch.  The clip is spring-loaded, but is vertically acting, slipping into a small incised hold and engaging a shaped brass catch that is imbedded in the hole.  The same arrangement must be made on both sides of each plate holder.  It is a very elegant solution to keeping ground glass up and installing the plate holder, but no doubt much more expensive to produce than the later catch and wood screw arrangement.  But even the Variation 1.0 and Variation 1.2, thought to be earlier examples, have the simpler wood screw catch.  It is unknown why this camera has the fancy clip, and good luck finding another plate holder.

The 76 Camera Variation 2.0

The 76 Camera Variation 2.0 is the archetype 76 Camera, in that it most 76 Cameras extant seem to be this variation, and that this variation matches the engravings and descriptions in catalogs most closely.  But this is advertising in the 19th century, and engravings often don't match the actual camera model in detail.

     Considering this, if the written description of a model differs from an engraving of the model, the written description should be considered to be the more accurate.  Given this, the written description of The 76 Camera has the following:  mahogany, polished finish, folding bellows and body, single swing, hinged bed, and brass guides.  The engravings show a shifting lens board - something worth mentioning in the written description, one would think. The engravings also show a push-pull focus  The presence or absence of rack and pinion focus is not in the written description, although one engraving (from the viewpoint of the back right side) suggests a rack and pinion in that it shows a large thumbscrew that corresponds to the thumbscrew for rack and pinion focus on the example cameras.  However, the same engraving clearly illustrates a push-pull focus.  This discrepancy was never corrected, despite appearing in advertising for almost two decades.

     The actual camera differs from the engravings only on the above last point of type of focus,  The vast majority of example 76 Cameras observed so far are rack and pinion focus (push-pull versions must be very rare, as they are so far unique examples having no peers.  Given that the brass guides are required for a single track rack and pinion to function adequately (and expensive enough to not appear on any but the most expensive field cameras), and the lack of American Optical manufactured examples, I am of the opinion that rack and pinion focus is part of The 76 Camera archetype.  The focus is secured by a thumbscrew that is underneath the large thumbscrew, and is only visible on the photo taken of the 5x8" example from the right side.  The 4x5 example has no such thumbscrew, and has to rely on the resistance of moving the rack and pinion to not change focus while inserting or removing the plate holder, a system which probably did not function well.

     The wood appears to be naturally dark, Cuban mahogany, of a rather plain, straight grain figure.  The hardware has the draw-file finish, and screw heads are aligned, as can be seen from the eight screws in the Flammang patented rod and piston device on the 4x5 example above, in which five are aligned and the other three probably have been unscrewed at some point and put back in mixed up order.  In summary, the camera is just what is to be expected of an American Optical manufactured product; the corroborating label and stamping are merely icing on the identification cake.

     Variation 2.0 has a stamped assembly number on the rear of the platform.

     Variation 2.0 is physically significantly smaller than Variation 1.0, Variation 1.2, Variation 1.5 or Variation 3.0. 

The 76 Camera Variation 3.0 (Scovill Version)

     A third variation exists that shows almost all of the characteristics common to 76 Cameras, yet is distinct from the other variations.

     This variation matches Variation 2.0 in that:  its construction is the same, its wood is French polished, its hardware is draw-filed, the screws on the front (the only place where two or more are next to one another) are aligned, it has a single track in the middle of the platform for rack and pinion focus, it has a small thumbscrew under the large focusing thumbscrew whose purpose is to clamp the large thumbscrew (and thus the focus) securely in place.

     It differs from Variation 2.0 in three ways:

1)  Its wood is a light-colored mahogany, that is very unlike the dark, Cuban mahogany that normally is found in American Optical products.  It is more like the wood found in Scovill products, such as the Waterbury View Camera Variation 1.  It probably is Honduras mahogany, a type of wood still available today from tree farms.

2)  The lens board is a simple three-piece type that does not shift, rather than the shifting lens board found on Variation 2.0.

3)  It has a ground-glass frame (and thus bellows and both standards) that is considerably larger than that of either Variation 1.0 or Variation 2.0.  Hence the entire camera is also considerably larger.  A comparison of the sizes is shown below.  This discrepancy in size between those cameras thought to have been made in the American Optical factory and those cameras thought to have been made in the Scovill New Haven factory is similar to the discrepancy found for the variations of the Waterbury View (see Waterbury View Variation 1 for comparison photos).  The difference in construction may be due to Scovill not precisely duplicating the tools and jigs used to make the camera in one factory vs. the other.  The company may have merely left the details of construction to the tool- or camera-makers from each location.  It is not that Scovill cameras are always larger than American Optical cameras; in the Waterbury example just mentioned, the American Optical Waterbury Variation 1 is larger than all the Scovill Variations.

4)  It has no American Optical label or stampings.  Instead, it has a stamp on the lens board and a stamp in the rear of the platform that read: "Scovill Mfg. Co., N.Y."

     Variation 3 has a stamped assembly number on the lens board, front standard, front of platform, and also at the rear of the platform.

     Because of its wood and Scovill stampings, The 76 Camera Variation 3.0 is thought to have been made by Scovill, most likely in its New Haven factory.  This is despite the American Optical quality wood and hardware finish.  If so, the workers at the New Haven factory knew how to finish a camera in high style when they wanted to.

     Above are examples of a 4x5" example and a 5x8" example.  Note the slight variation in hardware to raise or lower the lens board.  The 5x8" example was probably made prior to 1886, since it lacks the patented rod and piston device to make the platform rigid.  The 4x5 example was made in 1886 or later.  It has the patented rod and piston device; it also has red leather bellows, and a slightly different piece of hardware to raise or lower the lens board.

     The 76 Camera Variation 3.0 fits a very large American Optical plate holder size (see Accessories-c.1885 plate holders in case).  Its back is the exact same size as The 76 Camera Variation 1 (Wet-Plate Version) , the earliest variation of The 76 Camera, and the American Optical Waterbury-Type Variation 1, a rare Waterbury-Type camera that is larger than its more common Waterbury brethren.  Despite the fact that the size of the holders is exactly the same as the camera backs of these two cameras, neither of these cameras has its holder peg locations exactly the same as the holders just mentioned, demonstrating that, in this era, not all the parts on these cameras are not interchangeable.  It would take Henry Ford to pioneer that concept.

Comparison of the size of The 76 Camera Variation 2.0 to The 76 Camera Variation 3.0 (Scovill Version)

References: