Astrophotography Japan / How Critical is 55mm Backfocus? (Episode 44)

In this video I investigated the tolerance of the required 55mm backfocus distance for corrective lenses like a reducer/flattener. I varied the distance of the backfocus to the camera sensor around the optimal focal plane by several millimeters, and took photos with the ASI533MC Pro and ASI678MC cameras. The small sensor cameras mentioned here showed no optical artifacts at 55mm +/- 5mm on the M35 star cluster or the M1 Crab nebula. The video includes discussion about the differences between small sensor and large sensor cameras with regard to backfocus requirements.

00:36. Video Update / Critical Considerations
03:04. Comparison of ASI533MC Pro and ASI678MC cameras (ZWO)
04:21. Arranging proper Backfocus in Optical Tube Assemblies
07:16. Experimental Plan Overview
07:54. Focused Image Circle Considerations
09:19. Part 1 Experimental Design (star cluster)
09:50. Part 1 Details of Imaging Plan
11:00. Star Cluster close-ups of Variable Backfocus Images
12:50. Part 2 Experimental Design (nebula)
15:42. Part 2 Details of Imaging Plan
17:11. Nebula close-ups of Variable Backfocus Images
18:45. Conclusions
21:50. Crab Nebula (best image)
22:15. Final Comments

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