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All blog post images copyright by Edwardson Tan unless otherwise noted

Monday, October 22, 2012

Half a Luna

Another relatively clear night. Did a whole series of shots from f/5.6 to f/16 (but for some damn reason failed to shoot one at f/8! Maybe, juuuust maybe, it was because I started shooting at f/9 and only after finishing the f/16 shot did I work back to f/5.6). Was in manual mode (of course) with ISO fixed at 100 for all shots. Autofocused in Live View using Live Mode at x10 magnified view. I had (ever since I got the camera) back button focus setting #1 (AE Lock / AF) enabled, so after pressing and holding the star (*) button and after the camera had locked focus, pressing the shutter button wouldn't change the focus. I did focus again several times whenever I switched to the various aperture settings adjusted the tripod head to re-aim the camera to center the ever-drifting subject. To my mind such movements could potentially jar the focus mechanisms.

Mirror lock-up was enabled, but since I was using Live View that was unnecessary. Self-timer was set to 10-second mode to allow any shake to die down after I press the shutter button. At 300mm the image would wobble with the slightest vibration so it was imperative that camera shake was down to the absolute minimum possible. Fortunately there was hardly a breeze. And I had positioned the camera beside a wall to shield it from both light spill from the street lamps and buildings as well as from any possible gust.

To get the exposure right, I relied on the Live View real-time histogram. I dialed the shutter speed until the highlights bumped up against the right of the histo without going over. But in post I discovered every single frame was overexposed by half a stop! Lesson learned. Need to keep in mind that Canon's histo isn't that reliable for mega high contrast astrophotos and so must compensate by dialing the shutter speed down by 0.33 to 0.66EV. Another revelation: Performing pixel peeping at 100% crop, anything below f/8 has horrible, grotesque, will-scare-the-shit-out-of-your-momma chromatic aberration that's difficult to remove even with Canon's lens correction profile. Besides, anything below f/8 is less sharp. So to hell with those aperture settings. For images with lots of detail at least--like the moon.

Canon T3i, 1/15", f/9, ISO 100, EF 75-300mm III @300mm

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