Moon Shot, take Ⅱ

The quarter moon offers much more contrast than a full moon, and this time I used a telephoto lens: Canon EF-S 55–250mm f/4–5.6 lens on its longest position.  I used the Canon 70D on a tripod, ISO 100, 1/160 at f/5.6 ×3 exposures.

Quarter Moon

It’s difficult to get focused, and about 1/3 of the bursts were out of focus even though I used the touch screen “Live View” to indicate what to focus on.

The lens has optical stabilization, but I suspect it’s turned off automatically if the steadiness of a tripod is detected, as that is a feature listed on some lenses. Unfortunately faster exposure times were subject to blurring anyway. I didn’t bother to use a remote shutter release, but that might help. I don’t know if this is (usual) vibration of the camera lens, or caused by atmospheric turbulence making the image move around. f/5.6 is the fastest aperture at the 250mm end of the zoom, which is also the size where diffraction starts to be noticeable.

Exposure-wise, 1/40 second still (only barely) has no clipping, so would be the optimum for ETTR to capture the most detail and least noise. 1/125 is the good-looking natural exposure, and at 1/640 it shows visible noise.

I improved the contrast by using the “highlight” slider as well as the overall “exposure” slider in Adobe Camera Raw. The difference between the limb and the terminator was still vastly different lighting, and bringing out better the rays of Kepler would darken the terminator and bring the shadow farther in to make more of a crescent than a quarter. So I used “curves”, leaving the darks alone and changing the contrast of the mid-to-bright.

The color is as-shot, with no white balance adjustment or B&W conversions.  The underexposed pictures came out brown, and the bright ones are very neutral.

I merged three exposures as follows:

  • Cancel all adjustments made in Lightroom while evaluating the exposures.  Noise reduction is turned all the way off, but sharpening is left as proper for the basic “developing”.
  • Transfer the burst to Photoshop as layers
  • Double the resolution
  • Auto-align the layers, specifying “reposition only”.  Leaving it on auto can make PS complain that it can’t find anything.
  • Use the stacking mode Median or Mean, whichever works better.  For longer bursts the Median gets rid of outliers, but for low-noise images Mean is more accurate.
  • Rasterize the stack.

The doubling of the resolution allows for alignment to half a pixel in the original images, and combining exposures this way actually increases resolution as well as removes noise.  With non-noisy images, the increase in clarity is due to the “dithering” of different exposures.

After combining the original exposures, then adjust the exposure, apply noise reduction, and so on.  This is easily done using Adobe Camera Raw as a (smart) filter in Photoshop.

Now sharpening is also done in the Adobe Camera Raw filter, at the same time as the other adjustments.  Because the resolution was doubled and the image is not pixel-sharp to begin with, a large radius value is warranted.  I set it to 3, which allows more aggressive processing without introducing fake detail from noise.

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