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I am preparing for a photowalk with the purpose of catching earthshine (the part of the moon unlit by the sun but slightly glowing/visible because it catches some sunlight reflected by the earth). I hear the crescent phase gives best chances, and the moon just entered the first quarter. What settings should I use? More general advice will be also appreciated (e.g. when to catch it, how the position of the sun with respect to the moon affects it, and any other experience you guys have with earthshine).

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2 Answers 2

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The best time to shoot Earthshine is when the Moon is practically new, because the illuminated portion of the Moon's arc must be completely and utterly blown out in order to capture detail in the part of the Moon not illuminated by the Sun.

You will need to use a tripod and cable release. Mirror lock up may not be a necessity depending on your shutter speeds. If they are longer than 1-2 seconds mirror vibration won't be enough of an issue to require it. Use the longest focal length lens you have available.

Canon 5D mk II, ISO 400, EF 70-200mm f/2.8 L IS II @ 120mm and f/3.2 exposed for 3.2 seconds. Exposure +.33 in post. The sky was considerably darker than it appears when this exposure was taken. Notice Comet PAN-STARRS about to be lost in the atmospheric haze. Moon and Comet at twilight

The moon five minutes later. Same camera/lens. 5 2/3 stops less exposure: ISO 100, 200mm (heavy crop), f/4 for 1/2 second. Exposure pushed +2 in post. As you can clearly see, you can not get details from both sides of the terminator on the Moon using the same exposure settings. The directly illuminated limb of the Moon is blown, yet the Earthshine illuminated part of the Moon is still fairly dark. I normally shoot the moon at ISO 200, f/5.6, 1/125th second to properly expose the illuminated part. That is six stops darker than this exposure and 11 2/3 stops darker than the first image! I do usually also shoot the Moon when it is higher in the sky which means less of its light is absorbed by the atmosphere. New Moon

Another five minutes. Same camera/lens. ISO 400, 200mm (moderate crop), f/2.8 for 1 second (net exposure increase 4 stops). Exposure -.17 in post. enter image description here

Canon 7D, ISO 1600, EF 70-200mm f/2.8L IS II @ 105mm, f/2.8, 2.5 seconds. Exposure +.17 in post. enter image description here

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I didn't realize the Sun had phases... –  Michael Clark Sep 7 '13 at 22:06
    
<trivia> The reflectance of the earth's illumination (albedo) is roughly 37% and varies due to phase of the year and cloud cover. </trivia> :) –  Stan Sep 8 '13 at 1:39

I have not done this, but you are going to be be shooting across a huge dynamic range. The lit crescent of the moon will essentially be lit as daylight, while the remainder of the moon (and the night sky) will be many stops darker. That said you are trying to capture the much darker portion of the moon, so you will need to increase your exposure to make it visible.

Getting down to the mechanics:

We have a number of competing options, you will want to use a long focal length to show a lot of lunar detail (100+ mm), but the moon is surprisingly fast moving, so you will need to keep your exposure times around or below 250/{effective focal length}.

In practical steps:

  • On a tripod
  • With a cable release
  • With mirror lockup (or live view if you have a camera that gives you mirror lockup for free in live view).
  • Pick your longest lens
  • Set your aperture to one stop down from wide open
  • Set your exposure time to 250/{focal length} if you have a full frame camera, or 156/{focal length} on a APC Canon, or 167/{focal length} on most other crops.
  • Take a look, if it is too dark push up the ISO, too bright (unlikely) use a shorter exposure time. As you get more advanced you may want to take multiple images that are slightly under-exposed and stack them, but given the movement of the moon this will be a lot of work.

You will likely want to cleanup the resulting images by taking a few with a much shorter shutter speed to get a better capture of the crescent and then blend the exposures.

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Shooting at twilight might be a good idea - it tightens the dynamic range considerably. Indeed, Earthshine is often visible even to the naked eye at that time. –  JohannesD Sep 7 '13 at 7:01
    
+1 for noting the relatively high speed of moon and a nice formula how to set exposure time. –  Esa Paulasto Sep 7 '13 at 11:20
    
I am a little confused about calculating exposure time. I have Rebel t3i/600D, and EF 70-300 mm lens. Do I need to divide 167 by 300? –  Lena Borisova Sep 7 '13 at 20:47
    
@LenaBorisova almost (edit fix sorry), with the equipment you describe at your maximum focal length, you would want to limit your exposures to about 1/2 second (157/300 ≈ 0.52 seconds). Your Rebel has APC sized sensor which is a 1.6 crop, rather than the 1.5 crop of Nikon and most other DSLR makers. –  Patrick Hurley Sep 8 '13 at 2:07
    
Exposure times needed to eliminate motion blur is always dependent upon intended display size. A 3-4 pixel blur is very obvious when viewed at 100% magnification, but is not perceptible when, for example, a 20MP image is displayed at 5X7 or even 8X10. See the examples in the other answer. Some of those images were made using shutter speeds twice the limit of your formula. –  Michael Clark Dec 8 '13 at 18:41

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