Lock Up Your Mirror When Stacking

When it comes to focus stacking with high magnification objectives, anything that can reduce vibration counts. Among all the other things, one common factor well known by many experienced stacking experts, is the mirror lockup mode of camera when using flash to light the subject.

ssmw01This image is done at 30x magnification, it would be impossible to do without mirror lockup.

What is mirror lockup? Well, before we get into this, we need to understand how modern DSLR (or SLR for that matter) camera works. DSLR or SLR camera has a mirror that redirects light from lens to the view finder eye piece. This mirror normally is situated between the lens and view finder and is blocking light from reaching the sensor when not taking a picture. This mechanism allows you to see what camera sensor would see (or most of it, like 95% to 98%, depends on camera). So when you finish focusing and are ready to take a picture, here is what happens: camera first lifts up the mirror, to get it out of the way of sensor, then takes a picture. Of course, this is super simplified way to explain it, but for detailed information, Wikipedia is our friend – Single Lens Reflex Camera

Why is this a problem for high magnification focus stacking? Vibration it causes! Normally, when you take a picture with regular lens or even a low magnification macro lens, vibration caused by lifting mirror up is not a major issue and it might not pose serious effect on image quality. But when you are using a high magnification lens or microscope objective, slight vibration can cause major issues. The vibration caused by lifting up the mirror not only affects camera itself, but also affects lens, which at high magnification, the lens is very long, thus a minute vibration will cause the lens to bounce around, further reduce image quality.

Here is one comparision: the top image was stacked with images captured using mirror lockup and the bottom one is without. Magnification is not very high, at 13.89x and there are two strobes on each side. The result is clear.

mirrorlockup

How do we turn on the mirror lockup mode of camera? Most modern DSLRs have this mode of operation although terminology might be different by different manufacturer or even different camera model of same brand. However, google is our friend by searching for the term “mirror lockup” for the particular camera model.

One example here is my Canon 550D and 600D, a quick googling yields this: How to Enable Mirror Lockup on a Canon EOS Rebel T3i Essentially, you set camera in one of the operation modes that supports mirror lockup, then set a custom function, in my case custom function #8, to either enable or disable mirror lockup. When mirror lockup is enabled, if you press shutter button once, the mirror will be raised and stay that way until your press shutter button again. This might not be what we want because very likely, camera activation is done via some electronic control module. Fortunately, this can be resolved by using self timer for this particular camera. The self timer is roughly 2 seconds and when camera is activated, the self-timer starts counting and then tripping the camera the second time which takes a picture.

I also happen to have a Nikon D5200, though if you search for “mirror lockup”, you might end up sensor cleaning. For Nikon D5200, the actual term for mirror lockup is called “exposure delay” and you can turn this feature on in the menu.

Conclusion: if you are using flash to light subject and doing high magnification work, be sure to turn on mirror lockup feature of your camera!

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