Most of us have heard of the Sunny 16 rule by where the rule of thumb for “proper” exposure on a sunny day would be setting your aperture to f/16 and your shutter speed to 1 / x, where X = your ISO setting. Basically, at f/16 and shooting at ISO 100, we would set our shutter speed to 1/100 and you’d be set (1/200 at ISO 200, etc). Of course there are other variables to take into consideration depending on your desired outcome or subject, but it gets you close enough. Well, after some trial and error (emphasis on the latter) I came to realize that when shooting the moon, I was having a very hard time properly exposing it. Wanting to eliminate as much noise as possible, I was shooting at lower ISOs and after some more trial I found that I was coming in at about f/5.6- f/8 when spot metering and compensating for the extra brightness (I figured I should account for about 2 full stops over midtone) with the same one over rule as the Sunny 16… This got me wondering if there was in fact a night shooters rule of thumb, and there in fact is…
After a bit of google’n, I couldn’t find a name for the commonly referenced guideline, so I just call it the Moony 8 which basically states that at f/8, use the same 1/ISO setting to gain proper exposure for the moon.
Sunny 16 rule: f/16, 1/100, ISO-100 (or 1/200 @ ISO-200, etc)
Moony 8 rule: f/8, 1/100, ISO-100 (or 1/200 @ ISO-200, etc)
Now there is one HUGE difference when exposing your scene using either one of these “rules.” While the Sunny 16 rule will get your scene more or less properly exposed, the Moony 8 is geared to expose for the moon, not really anything else. Because the moon is so bright by comparison to anything it’s illuminating, everything else will go black minus a few bright stars or passing planes potentially, etc. If you want to expose for any nighttime scene, it would probably be best to either exclude the moon itself (lest you want a blown out white splotch in your scene), or blend multiple exposures.
Now, getting close enough to the moon to get any really good detail or texture can be difficult. Assuming we want the moon’s detail to be our subject, I’d say start with the longest focal length you have at your disposal. A higher resolution sensor can also help here as cropping into the image will essentially equal a longer focal length, or using the same long lens on a smaller sensor as our perspective will not change (unless you’re somehow able to hitch a ride on a shuttle). Basically speaking, the moon, shot from the same location, will have the same exact perspective regardless of camera or lens used. We really only retain a higher native resolution if using longer focal lengths (ie: making the moon occupy more pixels in our exposure)*. This may be a great project for your super zoom compact camera seeing that you’ll be shooting at a low ISO so noise shouldn’t be a huge issue :) Keep in mind that you may need to adjust your aperture setting if there is any haze/clouds, or the moon is low on the horizon as this “rule” is based on the moon at full, unobstructed brightness.
*as a side experiment, use two different focal lengths, or lenses from the same location on the same camera and crop into the image taken by the shorter focal length to replicate the same framing, same thing, just lower resolution! Assuming of course optical distortion isn’t a factor, and focus is properly achieved in both shots…
Nothing groundbreaking by any stretch, but this can be handy when trying to capture our orbital tagalong. Share your moony shots in our flickr group HERE.