The Nikon D300 was tested using a Nikkor 70-300 F4.5-5.6 VR lens and compared to the Pentax K20D using a DA* 50-135 F2.8 lens. Images below show the performance of these cameras on a typical night scene at each ISO sensitivity. These are all 100% crops from maximum quality full-resolution JPEG images taken at night in manual mode with automatic white-balance and set ISO sensitivity.

Night shots are always the most difficult for any digital camera as noise is much more noticeable in dark areas and shadows. Since such scenes consist mostly of dark areas, they represent the worst cases of image noise. Looking at the samples below, we can see that there are several factors at work. As usual, noise starts very low at ISO 100 and increases steadily until ISO 6400. Up to ISO 400, images from both cameras a virtually noise-free. From ISO 800 on, noise levels of the Nikon D300 increase a lot slower than the Pentax. By ISO 3200, the K20D is significantly more noisy than the D300. On the Nikon, only ISO 6400 shows truly excessive noise.

The other important aspect to consider is sharpness and image detail at each ISO. Clearly, from the crops below, the Pentax K20D produced much sharper images with more details at all ISO levels except for 6400. Contrarily to the D300, the K20D softness increases slowly with each ISO stop. Softness changes with the Nikon D300 are more complex. To understand why, we must take note that as sensitivity increases, shutter-speed decreases. This causes the D300 to apply more ISO noise reduction but less long-shutter noise reduction. This causes the ISO 6400 image to look sharper than lower ISOs, albeit with more image noise, since the shutter-speed is 1/8s which probably does not get any long-shutter noise-reduction.

Another factor for the differences in softness at low ISO comes from the lenses used. The Nikkor 70-300 F4.5-5.6 VR is a rather soft lens, particularly compared to the excellent Pentax DA* 50-135 F2.8. Unfortunately, we did not have comparable lenses on hand. Note that a lens at a given focal length and aperture does not change softness with ISO. So any change in detail between ISOs must be caused by internal image processing.