Pentax 645Z Review

Daytime High-ISO

It is somewhat of a challenge to illustrate high ISO performance since post processing for noise reduction is a compromise between reducing noise and preserving detail. One can't get both. We will therefore present our test images in a couple of different ways and also make 100% crops as well as RAW originals available for download so that you can do your own noise reduction and analysis.

First up is a run through the ISO range 100 to 204,800 with noise reduction applied to the images to our liking in Adobe Camera Raw and no subsequent sharpening.

We'd like to add that the 645Z's huge ISO range is class-leading among medium format DSLRs.

The test scene:

This image was shot at ISO 102400. The quality is impressive. Unless one pixel peeps or blows up the image to or near 100% the image is perfectly usable.

We used the smc Pentax-DA 645 55mm F2.8 lens at F16 for this test.

The images were developed using Adobe Camera Raw (ACR) and luminance noise was reduced in ACR. Below we've cropped the images to 25% of the original size area wise and scaled them to fit your screen. Click on a thumbnail to enlarge and browse (warning - even cropped these images are about 4MB in size). Follow the links below the images to download the cropped images without any scaling applied ("100% crops"). You can also download the DNG files; note that these have our adjustments applied.

ISO 100 | 100% cropped JPG from RAW | DNG with adjustments

ISO 200 | 100% cropped JPG from RAW | DNG with adjustments

ISO 400 | 100% cropped JPG from RAW | DNG with adjustments

ISO 800 | 100% cropped JPG from RAW | DNG with adjustments

ISO 1600 | 100% cropped JPG from RAW | DNG with adjustments

ISO 3200 | 100% cropped JPG from RAW | DNG with adjustments

ISO 6400 |  100% cropped JPG from RAW | DNG with adjustments

ISO 12800 |  100% cropped JPG from RAW | DNG with adjustments

ISO 25600 |  100% cropped JPG from RAW | DNG with adjustments

ISO 51200 | 100% cropped JPG from RAW | DNG with adjustments

ISO 102400 | 100% cropped JPG from RAW | DNG with adjustments

ISO 204800 | 100% cropped JPG from RAW | DNG with adjustments

As the ISO increases, contrast and resolution decrease and noise is introduced. The images from the 645Z, though, are usable at a higher ISO than we have seen with other cameras. How high you can go depends on the use and magnification intended for the final image. ISO 204800 gets quite muddy and is for emergencies only, but in some cases ISO 102400 may be acceptable despite the loss of dynamic range and detail. 

Compared to the Pentax K-3

Next we will compare the 645Z to the K-3 to determine how much of a benefit the much larger sensor in the 645Z turns out to be.

For the 645Z we use the same test images as shown above, but reduced in size to match the size of the images form the K-3. We used an smc Pentax-DA 31mm F1.8 Limited on the K-3. 31mm on the APS-C corresponds roughly to 55mm on the 645Z so we get the same perspective and magnification in the two sets of images. The 31mm was shot at F13. The K-3 originally overexposed the test scene so we had to use an EV correction of -1 EV.

Click any thumbnail to enlarge and browse. The K-3 images represent 100% crops when enlarged, whereas the 645Z images were down-sampled to match in magnification.  

ISO	Pentax 645Z	Pentax K-3
100
200
400
800
1600
3200
6400
12800
25600
51200
102400
204800

From the above we can infer that the 645Z has about a 2.5 stop advantage over the K-3 at higher ISOs. Up to ISO 1600 the K-3 can keep noise down close to the level of the 645Z at the expense of a loss of resolution.

Verdict

The Pentax 645Z controls noise very well, and even ISO 102400 is usable for smaller sized images.  ISO 204800 is mostly for bragging rights, as you can see, and it might as well have been left out (the same goes for ISO 51200 in the K-3). The 645Z has about a 2.5 stop advantage over the Pentax K-3 with its 24MP APS-C sensor. That there is a difference is no surprise since the area of the 645Z sensor is larger and the pixel density lower, but we had not expected this much difference.