Moon camera comparison: DSLR & planetary cameras

This is my first attempt at a comparison between a DSLR sensor and planetary camera image, under the same conditions and processing. Both sensors are considered at the top of their class. I expect to repeat this experiment when I'm more familiar with the planetary camera. I believe that these results give a good representation of comparable images from each type of camera.

The DSLR APS-C size sensor is in a Sony a6300 mirrorless camera. The a6300 has an all electronic rolling shutter mode very similar to the electronic shutter in the planetary camera. It is able to image the entire lunar disk in one shot with 24 mega pixels of 4 microns in size at up to 3 frames per second.

The planetary video camera in the comparison is the well regarded ZWO ASI120 MC. A color video camera with a rolling shutter it captures 1.2 mega pixel images of 3.75 microns in size. The smaller chip is only able to capture a small part of the moon in a single shot. Because of the lesser amount of data in each image capture rates can be up to 35 fps.

More data over a smaller part of the Moon from the video camera

If your target of interest is small and fits in the field of view of the planetary camera, it can capture more images in a given time allowing more and higher quality lucky images to be found for stacking. If you want to image a larger area (e.g., the full lunar disk), multiple overlapping images are needed to create a larger mosaic image. This can negate any advantage for the small field of view camera. The comparison image was kept small to fit on the page at full resolution and to maximize the advantages of the small FOV planetary camera. The data sets used in this comparison reflect this; with 100 images captured by the Sony mirrorless camera and 500 by the ZWO video camera. Of these the 9 best images were stacked from the Sony and 18 were stacked from the ZWO.

Telescope

A Questar 89mm telescope was used with both cameras at prime focus. The Questar has a nominal focal length of 1350 mm at the axial port for the cameras and is well suited to viewing the moon. Different adapters and camera flange to sensor distances result in a slight difference in focal length between cameras. Diffraction limited performance on the Questar corresponds to a sensor sample pitch of 4.25 microns. The 4 and 3.75 micron sized pixels of these sensors are well matched to this telescope.

Processing

Images were graded, selected, stacked, sharpened and normalized as follows:

  • The best images were stacked with the 8 parameter affine parameter alignment in Nebulosity. Because the Sony images were full disk images of the moon, I expect that the final stacked images for it are less optimized, in the final image area, for seeing variations than the small field of view ZWO images.
  • The stacked images were sharpened with nearly identical LR deconvolution and wavelet sharpening operations in Lynkeos.
  • The images from the two cameras were aligned and 1:1 cropped to show the same region of the moon at 640 by 480 pixels.
  • The images were then converted to monochrome and intensity and gamma normalized.

You can see a full disk lunar image made from the Sony data. The final cropped image from the Sony a6300 APS-C sensor camera is shown below:

The final cropped image from the ZWO AS120 MC 1/3" planetary video camera:

The benefits of more data and the small FOV stacking optimization are visible in reduced noise and more detail in the planetary camera image.

Content created: 2017-03-31

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