28.06.23 - An evening with the new Pentax K-3 Mark III Monochrome at the observatory

In the course of the new introduction of the PENTAX K-3 Mark III Monochrome, its suitability for astrophotography is of particular interest. After all, the noise behaviour of this camera is predestined for photography in which only black and white images are often used.
For a well-founded assessment, the author of many professional articles and Pentax photographer Peter Mein (link) took a closer look at the camera.

We thank him for his blog post

Blog post written by Peter Mein (specialist for astrophotography):

An evening at the observatory – with the new Pentax K-3 Mark III Monochrome

There have been lots of tests and debates on the new Pentax K-3 Mark III Monochrome. But: How good is it for Astro-Photography? Let’s take it to the ultimate test: On the 20-inch telescope of the Dahlewitz Observatory.

The Dahlewitz Observatory

Dahlewitz is a small town just south of Berlin that has a well-equipped observatory: The “Schul- und Volkssternwarte” (Public/ School Observatory) features a modern 20-inch telescope and even a small Planetarium with 25 seats. Lectures and guided tours, open to the public are held every Friday from September to March. Interested visitors are welcome. The program and more information can be found on www.stewada.de.

The CDK20 telescope features a 20-inch primary mirror and has a focal length of 3.5 meters. It’s seated on a German equatorial mount and features a GoTo control.

The 20 inch Reflector Telescope of the Dahlewitz Observatory

Cameras can be connected to the telescope via a 2-inch camera adapter and a “T-Ring” M42 to Pentax-K mount to connect the Pentax K-3 Mark III Monochrome. The telescope is then comparable to a manual camera lens with F7 and 3500mm focal length.

The  Pentax K-3 Mark III Monochrome attached to the telescope

Aiming for Moon and Venus

Photographing the moon

The top subject to picture at this evening was the waxing moon, just 5 days after new moon. Moon photography is a very special discipline of Astro-Photography: Single shots of the moon appear normally “blurry”, even when you focus very accurately and use short exposure times. This is caused by thermal induced movements in the atmosphere, something you can also spot when looking through the telescope at the moon. To get sharp results, you need to combine several pictures. During this so called “stacking” process, commonalities get enhanced and differences get removed. And in the end this will be combined in one single picture. The most efficient method of getting lots of pictures for stacking is to record a video. So I used the most likely hardly ever used feature of the Pentax K-3 Mark III Monochrome: The 4k Video Mode.

Different to the original PENTAX K-3 and the PENTAX K-3 II (both shooting videos only in “Full HD”), the Pentax K-3 Mark III  and Pentax K-3 Mark III Monochrome feature a 4k Video Mode with 8.3 Megapixel. For this, the frame of the sensor is “cropped“, so only the middle 8.MP of the 26MP sensor are used. The picture in Video Mode is slightly “zoomed in” by a factor of 1.6. When you now shoot a Video of 1 minute length, you get 1800 frames, all with 8.3 MP.

Processing and results

With a dedicated software for Astro-Photography, every single frame of the video can be analysed for picture quality. Then the best 5 to 10% of the pictures are stacked, resulting in a high quality, really sharp picture. Here some examples:

Southern lunar hemisphere with craters and mountain ranges

Northern hemisphere with dust planes and canyons. On the left side of the picture the large crater Theophilus.

To complete the project, I combine the pictures to one large panorama (please excuse the small missing corner at the edge). This picture has now a size of 7000*4000 pixels and shows the whole waxing moon in a very high quality with lots of details. This picture could also be used for professional use.

High resolution panorama, as a combination of 6 pictures

Summary

The High Resolution pictures are among the best I ever did in Moon Photography. The new Pentax K-3 Mark III Monochrome delivers also in video mode sharp and high-contrast results. Color noise, as you get on the K-3 Mark III from a certain ISO level onwards, does not exist on the monochrome sensor, also contributing to image quality. After this evening at the Observatory, the conclusion is that the Pentax K-3 Mark III Monochrome has delivered really convincing results in Moon Photography.