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Re: [OM] I blew my moon shot

Subject: Re: [OM] I blew my moon shot
From: Moose <olymoose@xxxxxxxxx>
Date: Thu, 24 Mar 2011 16:28:54 -0700
On 3/24/2011 2:11 PM, Chuck Norcutt wrote:
> Why does pressing the highlight button work for the moon?  I'd expect it
> to work for the bride's dress but the moon has a much lower albedo than
> that.

You still want it to be the brightest thing in the image, but, as Ken points 
out, short of clipping. It's all relative, 
both bride's dress and moon should be in a specific place in the histogram. If 
there is nothing but the moon in the 
frame, it fine to put it in the middle. But in a shot with other things, it 
should be near the top.

> On 3/24/2011 11:13 AM, Ken Norton wrote:
>> For digital photography, getting a proper exposure of the moon is really
>> dirt easy:
>>
>> ...
>> With film photography, it is highly recommended to spot meter the moon
>> itself. Adjust exposure so it is about two stops above middle exposure. Or
>> with the OM-3 or OM-4 series cameras press the highlight button. Doesn't get
>> any easier than that!

That will only work with at least a 500 mm lens and the moon carefully centered 
in the frame. The OM spot metering is 
supposed to be 2% of full frame, which is roughly what the center spot on a 
1-4n screen measures to be. A bit of math 
shows that the 0.5 deg. subtended by the moon is 2% of the 24x36mm frame at 500 
mm.

Using anything short of 500 mm or missing the spot slightly would include some 
almost black, the meter will average it 
into its reading and overexpose the moon. And remember, the actual spot reading 
involves a drop mirror below the main 
one, so it may not be exactly where the circle is.

If using other cameras with spot metering, you should check the specs. The 5D, 
for example, says its spot is 3.5%, and 
there's no nice circle in the center of the screen. So even 1000 mm might give 
an error. As you say, chimping the 
histogram can save it.

Loony Moosey
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