Pentax 645D Review vs. Nikon D3x

Image Quality

We will now take a look at various image quality parameters, as well as a look at how much (or little) depth of field you get with a medium format camera.

Image Noise Comparison

For this test we used the smc Pentax-FA 645 45mm F2.8 lens on the Pentax and the Nikon AF-S NIKKOR 35mm F1.4G lens on the Nikon to yield roughly the same field of view. Both lenses were at F6.3 and as we varied the ISO setting we used Av auto exposure with no exposure correction dialed in. The images have not been sharpened. The Nikon images are a 501 x 501 pixels crop (so-called "100% crops"), whereas the Pentax images were first cropped then reduced to 501 x 501 pixels so as to achieve the same image size in inches/centimeters. One can debate how to compare images from cameras with different resolution; we believe a comparison should be based on the same physical size of the images.

The normal ISO range for the Pentax is 200 - 1000, the extended range is 100 - 1600. The Nikon specifications are 100 - 1600 for the normal range, with the extended range being 50 - 6400.

Comparing ISO performance (same physical image size)

Click on an image to enlarge to 100%

Noise is a non-issue with both cameras up to ISO 1000. At ISO 1600 noise is still well controlled but starts becoming visible. There is no obvious benefit of using ISO 100 over 200 on the Pentax as regards noise suppression.

These test images shows an interesting characteristic. Even though the Pentax images were reduced in resolution to match the physical size of the Nikon images, the rendering of detail appears slightly better in the Pentax images.

Resolution

As a medium-format camera, the 645D boasts a sensor resolution higher than that of current smaller format DSLRs.  Below we examine the effects of such a high resolution.

Comparing the Pentax 645D and Nikon D3x

The scene shown below was shot with both cameras on a tripod and again using the smc Pentax-FA 645 45mm F2.8 and the Nikon AF-S NIKKOR 35mm F1.4G lenses. The Pentax was set to F11 and the Nikon to F8 to achieve (roughly) the same depth of field, and ISO was set to 100. The cameras metered the scene identically at 1/125 F11 and 1/250 F8, respectively - both cameras were tripod mounted.

The Scene
The Scene

Comparing Resolution

Click on an image to enlarge to 100%

Large Resolution Example Pentax 645D

The example below was shot using the smc Pentax-A 645 55mm F2.8 lens at F11. The camera was on a tripod. We only show a small crop from the scene in order to keep the file size down:

The Scene

Large resolution sample
Click the image to show a 100% crop (5MB file)

Rendering of Detail K-7 (APS-C), D3x (24x36) and 645D (33x44)

We have made 100% crops available of some of the General Motors/NOHAB MY locomotive images. The mages were shot in RAW (using a tripod) and postprocessed similarly. The lenses used selected so as to provide roughly the same field of view: 24mm, 35mm, and 45mm respectively. The difference in ability to render detail is easily observed in particular in the grille on the side of the engine.

Pentax K-7Nikon D3xPentax 645D
ISO 200 MY K-7 ISO 200 MY D3x ISO 200 MY 645D ISO 200
ISO 800 MY K-7 ISO 800 MY D3x ISO 800 MY 645D ISO 800
Click on a thumbnail to download the 100% crop (2 to 5 MB files).

Depth of Field

You get less depth of field the larger the sensor for a given desired physical size of the final image. For example, the following will produce roughly the same depth of field:

  1. a 24mm lens set at F5.6 on an APS-C camera
  2. a 35mm lens set at F8 on a 24 x 36mm camera
  3. a 45mm lens set at F11 on the 645D camera

For the DoF illustration below we used the smc Pentax-A 645 55mm F2.8 lens and ISO was set to 100. We focused on the cactus in the center of the frame as shown below. We only used a part of the image in the drop down as illustrated and these crops were also reduced in resolution to reduce the file size.

The Scene
The Scene

Illustrating Depth Of Field

Click on an image to enlarge

Overall Image Quality Comparison

Automatic white balance on both cameras were spot on and we never had to resort to manually adjust the white balance. The sample photos below show the almost identical images produced by the two cameras with respect to color, contrast and dynamic range. but with an edge to the Pentax in resolution due to the larger sensor. We also find a clarity in 645D images, not just in our test images but also in many of the images posted by users on PentaxForums. Perhaps this is due to the absence of an anti-alias filter in front of the sensor on the 645D or perhaps it is just caused by the higher resolution, we cannot say.

The images were captured in RAW and converted in Adobe Camera Raw using the Auto adjustment. Smart sharpening at 110% and a radius of 0.7 was applied in Photoshop CS5 and the images were saved as JPEG files with quality level 11. The full size JPEG files (16 MB and 11 MB respectively) are available by clicking on the images below.

The cameras were on tripod, we used auto focus, ISO 100, f/8 and f/6.3 respectively with these lenses: smc Pentax-FA 645 45mm F2.8 and Nikon AF-S NIKKOR 35mm F1.4G.

Sample photo 645Sample Photo D3x

Pentax 645D                                                            Nikon D3x

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