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January 2014

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Here's the moon, a waxing gibbous from Saturday night; read on for details.

From Nature

My gear: Sony A700, Minolta 500mm f/8 Reflex (a fixed aperture catadioptric lens), tripod.

I found getting good shots more difficult than I had expected. I'm relatively new to photography and while I understand the basics, trying to shoot the moon pretty much causes all those automatic bells and whistles on your camera to become useless.

For starters, the metering system isn't very useful; if you leave it on matrix or center weighted with a lens of this length, it's going to blow out highlights badly due to all the black in the frame. Spot metering is closer to right, but it's still sketchy. The best technique I found so far is going full on manual exposure.

I found that the best results were with shutter speeds in the 1/125 range at ISO 200 (at least, this was the best when the moon was about halfway between the horizon and directly above - it should put off more light the higher it is in the sky). Incidentally, this isn't far off from the "sunny 16" rule, which makes perfect sense when you think about it; the moon is not a source of light in and of itself, rather it's reflected sunlight, so it's logical to use the calculation based on a sunny day. Sunny 16 underexposes by about 2-3 stops in my tests, due to the impact of atmosphere.

Now 1/125 second is going to be difficult to handhold with a 500mm lens. When hand holding, you need the ISO jacked up to around 1600 or better to get shutter speeds high. I try to avoid going that high if I can, so I used a tripod and longer exposure.

Automatic white balance is equally sketchy. It actually did OK sometimes, but it was hit or miss. You either need to set the WB manually, or just plan on fixing it in post processing (I chose the latter).

Now, depending on how accurate your exposure is, you have some work to do in software. The JPEG engine on my A700 did a really poor job with contrast, so I used RAW. I use ufraw and the GIMP; at 1/125 second all I really needed to do was bring up the black point to enhance contrast on the moon's surface. If you underexpose (as I did in this sample) you have to bring the white point down as well.

I had to use the GIMP and ufraw for this since Picasa's contrast adjustments were inadequate. "Auto contrast" is a disaster, but worse is that Picasa "guesses" some initial EV values when using RAW, and those guesses were already clipping highlights. It's not even possible to bring these back down to proper levels within Picasa!

I also applied some unsharp mask (.4 as the value) in the GIMP. I think I'm hitting the limitations of the lens in terms of resolving power, and it just can't fill the A700's entire 12MP sensor. This is another good reason to try and avoid high ISO, as USM will sharpen noise if it exists.

So anyway... that's shooting the moon! It's not hard when you know how to do it, but it took me a bit of time to learn.

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