In general, Pentax's medium format lenses are much larger than their 35mm (full-frame) counterparts; if you mount a telephoto lens on the 645D, such as this FA 400mm F5.6, things start getting out of proportion:
The lenses we used for this review are much more comparable, however. Let's take a look at their relative sizes:
The Nikon 50mm lens is the smallest of the three, while the Nikon zoom is the longest (though it has a smaller diameter than the Pentax). The Pentax lens is the widest overall, but is still quite small compared to the size of the 645D body.
Here's a quick look at the specifications of each lens. While it's not available in a bundle with the 645D, the 55mm is meant to be its "kit lens", as it was released alongside it back in 2010.
Nikon 50mm F1.4
Pentax 55mm F2.8
Nikon 24-70mm F2.8
|Optics||8 elements, 7 groups||9 elements, 7 groups||15 elements, 11 groups|
|Aperture Blades||9, rounded||9, rounded||9, rounded|
|Dimensions||73.7 x 53.3mm||81.3mm x 68.2mm||83.8 x 132.1 mm|
|Field of View |
|46 degrees (full-frame)||53 degrees||84 - 34 degrees (full-frame)|
|Aperture Range||F1.4 - F16||F2.8 - F22||F2.8 - F22|
|Lens Coating||Super Integrated Coating||Aero Bright Coating*||Nano Crystal Coating*|
*These are the respective manufacturers' premium coatings
Below are side-by-side photos of the lenses mounted on our cameras.
The 50mm really makes the D800E quite compact and easy to hold, while the 24-70mm gets it to closely resemble the 645D setup in terms of size and weight.
First of all, it's worth mentioning that due to the 645D's larger sensor size, you have to shoot about half a stop slower than on full-frame in order to get the same depth of field. This also means that smaller apertures can be used with the 645D before diffraction sets in.
With that said, 645D lenses are generally slower than Nikon lenses, and no Pentax 645 lens is faster than F2.8 or slower than F5.6. 645D lenses are also very expensive, with the 25mm F4 wide-angle and 90mm F2.8 macro lenses both priced at $4995. These and the 55mm pictured above are the only lenses available new in the US; older FA and A series lenses, listed here, must be imported from Japan or acquired second-hand.
Overall, Nikon gives you a much wider and more affordable lens selection, full of many different zooms and primes. However, compared to the Pentax K mount, the Nikon F mount doesn't support nearly as many old/legacy lenses (i.e. M42 screwmount lenses).