Beehive Cluster (M44) comparing 1.3 and 1.6 second exposures

After realizing I accidentally photographed the Beehive Cluster earlier this winter, I tried for an honest attempt on February 12, 2013. I tried two different exposure durations to see if I could tell the difference between 1.3 seconds and 1.6 seconds in terms of the length of star trails.

24 subs, f/5.6, 300mm, 1.3 sec each stacked in DSS

According to the 500 rule, I shouldn't be able to see noticeable trails at 500 ÷ 1.6 (Canon image sensor crop factor) ÷ 300 (for 300mm focal length) = 1.042 seconds

According to the 600 rule, this time would be 1.25 seconds

There's a lot more to it than that (and much better resources than mine) to help you figure it out. I'm also limited by a smaller f/5.6 compared to other f/2.8 lenses, so I went with 1.6 vs. 1.3 sec to see if I could even tell the difference.

Turns out you can definitely tell a difference, and looking back I probably should have been around 1 sec rather than 1.3 or 1.6 sec.

I'm glad I at least got to experiment with this photo because for some reason my light .CR2 files wouldn't load into DSS, so I was stuck with my JPG's and couldn't even use my dark or bias frames even though they would load fine. I think it's because I was messing with them in Photoshop before stacking them, and that might have done something to the files - not really sure. I just know that next time it'll be straight from the camera to DSS and no mucking around!