downloading from 70D

[thomashead]

I am shooting with a 70D and one or more 600 EX-RTs. When I look at my photos on the LCD monitor, they look fine. When I download them to the computer (OS X 10.10.3), they are very dim, as if the flash hasn't fired. I've downloaded them both to Aperture and directly to the computer from the card and the result is the same.  Results are the same in RAW and JPG. Suggestions appreciated.

[RobertTheFat]

You probably have the brightness of the LCD turned way up, and that fools you into thinking the picture is brighter than it is.

And remember that the dynamic range of the human eye is far greater than that of any camera. IOW, you can't trust your lyin' eyes.

[TCampbell · Accepted solution]

Don't feel too bad... the very first time I used a DSLR (having shot film for years) I too was fooled by the appearance of the image on the LCD.  The problem is, as Rob says, the brightness setting can trick you into thinking the exposure is either higher or lower than it really is.

The better way to check is to use the "histogram".

Display the image on the rear LCD screen of your camera, then press the "Info" button (perhaps a few times).  Each time you press "Info" the camera changes the type of info displayed (it has a limited number of options and eventually just circles back to the first option.  On my 5D III you can press the Info button four times and it circles back to the first screen.)

There's a screen that displays the combined "luminance" histogram.  There's also a screen that will show the histogram for each color channel (red, green, and blue) as well as the combined histogram.

What it means:

The histogram is a graph that sort of resembles the silhouette of a mountain range.  From left to right it represents the darkest possible tonality that the camera can capture (blackest blacks) and the right edge represents the brightest tonalities (whitest whites) -- and the middle is everything in between.  The hight of the graph at each level of tonality represents the quantity of pixels that have that specific tonality.  

Ideally you'd want the extreme left edge and extreme right edge of your graph to make it all the way back down to the ground. If it looks like you've got a hill building up (either at the right or left of the graph) and it's simply cut off... that means you've either over-exposed or under-exposed the image.  

I'd like to say that all the mounts should be "in the middle" but that's misleading.  If I take a photo that is supposed to be very dark (e.g. a starry night sky) then most of the data SHOULD be over on the left.  If I take a high-key photo of a very white snowy scene... most of the data SHOULD be over on the right.  So the data doesn't need to in "in the middle" to be correct... you just want to make sure your histogram isn't building up a hill that gets chopped off at the edges (either left or right) of the graph.  That implies that there should have been more data beyond the edge but our camera couldn't capture it because it was beyond the limits of the sensor's range.

Here are a couple of articles that may help:

http://www.learn.usa.canon.com/resources/articles/2012/understanding_histograms.shtml

http://www.cambridgeincolour.com/tutorials/histograms1.htm

https://luminous-landscape.com/understanding-histograms/

Another option (not everyone likes this) is to turn on something we call "the blinkies" (highlight alert).  This mode causes over-exposed highlight pixels to blink black/white and underexposed pixels to blink black/blue.  

[thomashead]

Thanks very much, Tim. The histograms do show the images to be seriously underexposed. Let this be a lesson to me.

And the articles are very helpful.

Tom Head