A Mystery to me, can you explain it?

I took the 7D mounted with my 500mm F4L out today. This is the first day I had a chance at checking the AF Microadjustment at Plus 1. I didn't find a lot of wildlife to shoot today, so in the mid afternoon I decided to do a few test shorts. I had the set up mounted off camera, with a wimberly bracket that attaches to the plate. I attached the 580EX II by cord, HOWEVER the flash I had turned off. It was not turned on in these pictures. Thus the mystery?


The first picture, is the mystery. It was a blue bird sunny day with the sun directly overhead. Each of these two pictures were taken seconds apart. The two posts are less than four feet apart from each other and fairly close to me (but far enough they were past the minimum focal distance, Adobe Bridge says 5.9 meters for the one with black bokeh and 6.1 for the one with brown) with the sun slightly to my back and left. The one that has the black background, the post was slightly closer:





[View:http://community.the-digital-picture...neric/utility/http://farm6.static.flickr.com/5048/...a2dea7e8a9.jpg]





The Data from this one: F4.0 1/1600 ISO200 Data shows Flash OFF, Metering Mode Evaluative, WB Auto





Now the second:


[View:http://community.the-digital-picture...neric/utility/http://farm6.static.flickr.com/5286/...cfbff67ba2.jpg]





Now other than being shot 20 seconds apart, and a slight file size difference the data is identical.


So the mystery I am trying to figure out, how in the world did I get the background to go black in broad day light without a flash. I would have understood this had it been a bad exposure, but the post shows up.

Weird! The EXIF shows that the exposure settings were the same for both shots... [:S] I'm confuzd!

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Originally Posted by HDNitehawk

...how in the world did I get the background to go black...

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Maybe it's because the background was black compared to the other post.

I notice you were in manual exposure mode, hence the identical settings. It looks like you were photographing the shady side of the first post, so using the same settings caused it to be under-exposed. It needed one extra stop to make the two posts appear similarly exposed, but the background would still have been muchh darker than the second post.

No Mystery. You are shooting two different objects with different backgrounds and background lighting, as well as using Evaluative Metering.


The camera is evaluating the light intensity at multiple points throughout the whole scene to determine what it thinks the proper exposure should be..


Have you tried this same experiment with other metering modes.

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Originally Posted by tkerr

The camera is evaluating the light intensity at multiple points throughout the whole scene to determine what it thinks the proper exposure should be..

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Since he's using manual shooting mode (M-mode). The metering mode doesn't do anything other than telling you that you over- or underexpose in your screen, right? It does't change anything to the exposure, the exposure is a set value for both shots. If it was an auto- or semi-auto shootingmode, the metering mode would be of relevance. At least this is how I understand it.


I don't really understand what was going on here. Since the shots were only 20 sec apart, even shooting from the shadowside shouldn't be making such a difference I think? Perhaps the sun was blocked by a cloud or something during the darker shot? Add a different shooting angle and it might solve the mystery? I cannot think of something else...

I was in manual mode. If I had it set in AV and the metering mode had detected it and adjusted the shutter speed. In manual mode the camera would have shown me that I needed to adjust it, and I failed to so it is possible something changed and I did not catch it.


The two fence posts are side by side, at an old gate on my place. They are the two end posts and are just a few feet apart. I didn

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Originally Posted by HDNitehawk

My thought now is it was some kind of glitch in the camera

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That makes the most sense to me, I think. My first though was along tkerr's lines, but as I noticed it was M mode with the same exposure settings, evaluative metering was irrelevant.

Quote:

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Originally Posted by HDNitehawk

I was in manual mode. If I had it set in AV and the metering mode had detected it and adjusted the shutter speed. In manual mode the camera would have shown me that I needed to adjust it, and I failed to so it is possible something changed and I did not catch it.

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Yeah, it's only relevant if you did change the shutter speed.

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Originally Posted by HDNitehawk

The two fence posts are side by side, at an old gate on my place. They are the two end posts and are just a few feet apart. I didn't move from my spot when I took the picture. It is probable that there is an evergreen cedar tree that gives a green bokeh to the darker picture however all the background was some distance away. The subjects are in the middle of an open field.

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A darker object(tree) in the background can make a difference in the light intensity throughout the scene, perhaps requiring an adjustment in shutter speed which as you said, you didn't do..

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Originally Posted by HDNitehawk

The other explanation I can come up with is that the camera itself malfunctioned and did a faster shutter speed. It would take more than two full stops in post to make the back ground come out right.


My thought now is it was some kind of glitch in the camera.
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That could very well be.
How long have you had your camera, and what is the Shutter Curtain Count?

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Originally Posted by tkerr

That could very well be.
How long have you had your camera, and what is the Shutter Curtain Count?

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Shutter count is 2500. I bought the 7D in november to use with the 500mm. I probably should check to see if the firmware is up to date.

I compared the two fence posts side by side, just the shaded sides that face the camera, with no changes to the original exposure. This removed any 'optical illusion' about the brightness of the posts when compared to the background. The difference in brightness is only about 2/3 of one stop. I'm sure this is just due to a slight difference in the ambient lighting. The posts are leaning in different directions so the sides facing the camera may not be catching the light in the same way, and no compensation was made for this.

There's no way that a camera exposure glitch could turn a bright background into a black one, yet still get the two posts within 2/3 of one stop, so I stick with my assertion that the answer to the OP's original question is that the background was too dark to register at 1/1600s.