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First, for those who might not be familiar with the term, mirror lock-up (MLU) is a function on many SLR cameras which helps reduce vibration inside the camera. In the sequence that follows pressing the shutter release (mirror moves up out of the way, second curtain activates, first curtain exposes, second curtain closeses, mirror returns to original position) the activity of the mirror springing out of the way, intended to be an extremely fast action, can cause this vibration as it comes to a stop inside the camera. Under normal circumstances this activity produces a very minimal effect, often not noticed.
Under certain circumstances, such as macro photography or long zooms, the effect can be more noticeable. How noticeable is dependent on a number of factors, such as the camera model, quality of build, shutter speed, etc…
With my hands on a Canon EF 100mm f/2.8L IS Macro USM, thanks to BorrowLenses.com, I decided to experiement a bit. My first shots of fungus in the woods seemed to show a big difference between no mirror lock-up and mirror lock-up, with mirror lock-up being sharper. Back at home, where it was warm and not windy, I decided to experiment a bit more with something more two dimensional.
Below are the results of my experiment so you can see the difference yourself. I decided introduce one other variable some people don’t consider when taking macro shots and that is the effect the act of pressing the shutter release has on the image.
The images go in this order:
You can click on the main images for a full size file (NOTE: 11mb file sizes per image). Below each image is a 100% crop which can also be clicked for full size as the width of this column is just 600px. Those second images are only 400KB.
Rather than tell you my opinion, the only one that matters in this case is your own. I did my best to insure there was no skewing of shots or movement that wasn’t induced by the act of taking the photos themselves (opting to throw the dogs outside and not even play any music, I’m that dedicated :)) The shots were taken with the subject taped in place, no wind, tripod mount for the camera with no use of center post. Lighting was kept constant and all shots are at ISO 100, 100mm, f/2.8 and 1/160.
In response to the comments below that the shutter speed of 1/160 was not of a sufficient speed to highlight any movement from mirror bump, I have run another test at various shutter speeds. Below I show the best example out of the bunch. I ran the test at 1/15, 1/4 and 1/2 and in all cases the results looked inconclusive. As the lens used in the original post above has gone back to BorrowLenses (true to their name, they want their stuff back) I used my Canon 7D with Canon 28-300mm L, extended to 300mm, with the Canon 500D close-up lens. I tripod mounted the lens with its supplied collar and set the focus to manual, image stabilization off, fixed the white balance and manually set the shutter and aperture to 1/4 and f/11. In this test I only used the 2 second self timer as reasoned below (most every camera has one). Click on each image for a larger version. I did not modify the images in post.
To my eye, the results do not show ample blurring without the MLU activated. My original intent with this test was to see if there was any, while not attempting to prove there was with this setup. That is why I originally withheld my impression. I want to present what actually came out of my camera. It seems with this setup, mirror bump is not as evident as it is for others. Mind you, this is just one camera and lens combination and I can’t test them all. I suggest you test it for yourself as many noted in the comments that they have seen positive results while using MLU. They do not, however, state the type of equipment being used.