I’ve decided to break my D7000 vs 7D ambient exposure evaluation into separate articles/videos. First up is the age-old question, “Does the Nikon D7000 overexpose?” Well, age-old in terms of internet time anyway. There’s been lots of people complaining about this online, particularly for bright outdoor scenes, and many have blindingly-bright, flat, and washed-out photos to show for their troubles.
Some people agree with them. Some don’t. Some even tell these hapless photogs they don’t know how to use their camera, a response I’ve always found curious considering that the whole idea behind an evaluative/matrix metering system is to fully automate exposure decisions in as many situations as possible. It seems to me that landing short of this goal should be regarded as a shortfall in design rather than something the user is doing wrong. That’s not to say it’s reasonable to expect an AE system to nail exposure for every conceivable scene, particularly scenes where the dynamic range exceeds the camera’s abilities or when “proper” exposure is more of a subjective judgment call (those two are one in the same for many cases). But how about something simple, like a medium-contrast landscape? (simple, eh?)
In part one of this three part video, I start with a discussion of the basic methodology I used for comparing the exposure systems between the Canon 7D and Nikon D7000. Part two dives right into the overexposure issue, using differential analysis of some landscape photos taken with both cameras. I finish up with part three, an old-fashioned snow fight!
I have just released the first version of Rawshack, an open source utility that reports various statistics about image data in a raw file. I created this program as part of my D7000 vs 7D exposure evaluation effort, to help me fully evaluate the exposures that these (and other) cameras create. Click Here for more information and download links!
I’m still in the logistics/planning stage for my D7000 vs 7D exposure comparison. There are a maddeningly number of variables to account for in comparing the exposure between two completely different makes of camera. For starters, differing default tone curves, even within the same raw processing application! I’d prefer to use the same raw processor for both cameras and Lightroom is my first choice since that’s what most people use yet Lightroom’s default raw processing profile (Adobe Standard) produces drastically different output between the 7D and D7000. I get much closer results if I change Lightroom’s processing profile to each Camera’s default neutral profile.
Other thorny comparison variables include differing white balance, nominal ISO , color responses, lens t-stops, and on and on. Not to mention framing issues between lenses and AF point placement in the photo (since each camera heavily weights metering on the active autofocus point). This is going to take a while.
In the meantime here’s another teaser, a moderately-low contrast daytime landscape of Lake Tahoe. This D7000 exposure is hot, hot, hot, within shouting distance of the right edge of the histogram, yet all channels (red, green, blue) are below raw clipping levels. This image actually shows a hint of JPEG histogram clipping on the D7000’s LCD for the “neutral” picture control, but shows lots of sky clipping when processed using the camera’s “landscape” and “vivid” picture controls. This might explain why some D7000 owners have reported overexposure problems. Evaluation of photos like this one will come down to how you define overexposure. If you’re a raw shooter then this photo is deliciously exposed to the right, full of signal and a complete lack of blue-channel sky noise, ready for some serious post-processing. If you’re a JPEG shooter then things aren’t as rosy and the photo is probably overexposed if you were hoping to avoid any post processing. The 7D metered the same scene 1 2/3 stops below the D7000.
About 8 months ago I purchased a new Sigma 50-500mm f/4.5-6.3 DG OS HSM APO lens (that’s a mouthful). I bought it during the final heydays of Microsoft ‘s Bing Cash Back program, when they were giving away cash on pretty much anything you could find in a search engine. Ah, the good ‘ol days. I never actually opened the box because at the time I wasn’t sure whether I’d be using Canon or Nikon for my long focal length shooting and have since decided on Canon for the long stuff.
I finally got around to listing the lens for sale on fredmiranda.com and found a willing buyer who only asked that I test the lens out first to make sure it doesn’t suffer from any Sigma-esce focusing problems. Smart move. I mounted the lens on my D7000 and did some IQ tests first. Images looked great – sharp at 500mm @ f/6.3, sharper still at f/8.0. Not a light speed demon by any means but for the price and focal range I consider the Sigma a good deal. Then I did my focus tests and uh oh, the lens started bucking like a donkey at 200mm. Either it would refuse to focus, meaning nothing happened when I pressed the back-button focus on my D7000, or the lens would do a few jerks to humor me and then just sit there like a sad, graphite-colored puppy. For the few times it actually attempted to focus it would take about a second to shift through its non-focal-distance-limiter-support range (in other words, no focal length limiter switch like on Canon/Nikon telephotos) and then give me that comforting focus confirmation “beep” on my D7000, only to be greeted by great bokeh that covered the entire range of frame, including the subject I was attempting to focus on. In other words, it was completely out of focus. Same results at 300mm and 400mm, but better at 500mm.
Needless to say the sale is off, at least until I get the lens fixed. To Sigma’s credit I looked up my serial number and it does fall within the range of recalled copies for the 50-500mm OS line, a recall that was proactively announced by Sigma all the way back in July 2010. So Sigma knows about the issues and got in front of the problem so it’s up to me to do my part and send the lens in for an AF motor tuneup. I’ll reevaluate the AF when it arrives back and post my results. In the meantime here’s a video showing the AF problems I observed.
Next on deck is a comparison of the auto-exposure/metering of the Nikon D7000 vs Canon 7D. I’m only in the early planning stages of this effort and the more I plan the more I realize how big of a project this is going to be, if I really want to do the topic justice. Does the D7000 “over expose” like some review sites and users have claimed? Can the 7D’s new color metering sensor design keep up with the D7000’s more-mature color matrix metering, especially for scenes predominated by colors that would otherwise blow-out certain channels? Does the AF-sensor weighting of these metering systems make them smarter? Or just more stubborn? What is “proper exposure” anyway?
While I crunch on boring research and methodology planning, expect a few teasers over the course of the next week. Like this one:
Click on the above image for a larger version. Looks like Nikon has designed a metering sensor that finally understands white stuff falls from the sky sometimes.
One key Canon 7D Live View feature I forgot to mention in my video is its electronic 1st shutter curtain. Most DSLR sensors rely upon the light-blocking function of a closed shutter to help facilitate the clearing or “resetting” of the sensor’s pixels, so that all pixels start out as “black” for a new exposure. When a photograph is taken, the first of two shutter curtains is opened to expose the sensor to the light in your scene, followed by a second shutter curtain that again blocks light to the sensor, allowing the camera to then read the pixel values off the sensor and generate the photograph.
The 7D’s sensor (along with previous Canon models like the 40D and 50D) has a unique feature that allows it to completely reset its pixels without the need to block out light via the shutter. This feature is enabled in Live View whenever you use one of the 7D’s “quiet” modes (mode 1 or 2), which were originally designed to make the camera quieter by reducing the audible noise of the shutter’s first curtain. But this feature has the added benefit of eliminating the minor camera vibrations that can occur when the 1st shutter curtain is moving, which translates to sharper photographs for situations where the absolute minimum amount of camera vibration is essential. Such situations include using very long focal lengths like 400mm and also macro/microscopic photography.
Canon has designed its electronic 1st shutter curtain so that it can emulate the complete functionality of an actual mechanical 1st curtain, including the cases of high shutter speeds (above 1/250) where both the 1st and 2nd curtain are both “open” at the same time to form a “slit”, so that only a portion of the sensor is exposed to light at any given time. This is no small feat.
The Nikon D7000 has no electronic 1st shutter curtain, so to take a photograph the camera must first close the shutter (between photographs, the shutter is open in Live View so that the camera can display the scene on the LCD and also meter/focus). The camera then resets the pixel values on the sensor, which is aided by the blocking of light of the closed shutter, then begins the process of taking your photograph by opening the 1st mechanical shutter curtain.