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DSLR Pentax K-3 Mark III in practice: camera for astrophotography

After a long wait, the Pentax K-3 Mark III is finally on the market. The centerpiece is a new 26-megapixel sensor with a light sensitivity of ISO 100 to ISO 1,600,000. At least on the data sheet, it clearly surpasses the predecessors K-3 (from 2013) and K-3 Mark II (from 2015), because the older models “only” work with a 24-megapixel sensor and cover an ISO range of 100 to 51,200. But what does the user get from the increase in light output? And has the camera’s noise behavior improved so that you can really use the new Mark III with significantly higher ISO values? I tested this in comparison to the previous model and using astrophotography as an example.

This discipline is particularly suitable for this, because here so-called “light frames” (individual images of an astro motif) are collected over hours and then combined into a total image using “stacking” and “stretching”. And yes, the technology is now so advanced that most astro amateurs can now easily produce images that would have required a medium-sized observatory 30 years ago. Unfortunately, when processing the images, it usually turns out that, depending on the camera, there is a certain ISO limit for the light frames, which when exceeded, the results inevitably “rustle away”. Personally, I only take photos in the “Deep Sky” area with a maximum of ISO 1600 (Pentax K-3 Mark II) or ISO 800 (with my astromodified Pentax K-3).

You have a similar limitation when you connect the camera to a telescope, record videos of the moon and then “stack” them. The older K3 models only record moving images with a resolution of 1920 x 1080 pixels (Full HD). The longest possible shutter speed is then 1 / 30th of a second (at 30 frames per second). To make matters worse, lenses (such as a Barlow lens) used for enlargement (for example, for close-ups) noticeably swallow light. Since you don’t want to increase the ISO number arbitrarily for high-quality recordings, it limits the maximum possible magnification. Anyone who has ever looked at the moon through a telescope has also noticed the “flickering” of the image due to the unrest in the air, which is why the following applies here: the shorter the shutter speed, the better.

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