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Mirror Lock Up

by Bob Atkins, 1998


With the exception of a couple of very special cameras (which I will deal with later), every SLR has a mirror which must be moved out of the optical path before a photograph can be taken. When this mirror moves (and especially when it stops moving!), it causes vibrations to be set up. These vibrations move the camera (and attached lens) around and can lead to a loss of image sharpness. This is especially the case when using long telephoto lenses or when doing closeup (macro) photography.

The loss of image shapness is worst at intermediate shutter speeds, say between 1/60 and 1/2 second. At very fast speeds the shutter is only open for a small part of a vibrational cycle, while at long shutter speeds the vibrations can die out, so only a small part of the total exposure is taken while the camera is shaking. Note that an flimsy tripod can make vibrations worse, but even the biggest, heaviest tripod can't eliminate vibrations completely.

In general, for lenses of 300mm and over (and macro work), users should try to avoid using shutter speeds between 1/30 and 1/4 second for optimal sharpness. For "normal" work with lenses of 100mm or less, sharpness loss due to mirror induced vibrations does not seem to be an issue.

The solution to this problem is Mirror Lock Up (MLU), where the SLR mirror can be locked in the "up" position, vibrations can be allowed to die out, then the shutter fired. Not many current SLRs have this function (the Nikon F4 and F5 do, as does the Canon EOS-1n), which is a pity. Some cameras do have what is called "mirror pre-fire" though. This is a mode in which the SLR mirror moves normally, but the camera delays the firing of the shutter by a couple of seconds, so the mirror induced vibrations have a chance to die out before the shutter fires. Most Canon EOS bodies have this function, for example.

Nature photographers planning on using long telephoto or macro lenses might want to look for MLU (or mirror prefire) on any camera bodies they plan to purchase. If a body doen't have MLU and you must use speeds around 1/15 with a telephoto lens, tricks such as putting one tripod under the lens and a second tripod under the camera can help, as can laying a sandbag, beanbag or even a hand on the lens above the tripod support point.

A few cameras have a fixed, semi-transparent mirror, rather than a conventional moving mirror. Obviously these cameras don't need MLU! The only current camera of this type is the Canon EOS-1n RS, though the Canon EOS RT can be readily found on the used market. The downside of these "fixed mirror" (pellicle) designs is that they cost about 2/3 stop of light at the film, and 1 1/3 stops in the viewfinder. The upside is that you can see through the viewfinder in real time. With a locked up mirror, the viewfinder is blacked out.

The figure below shows a typical vibration plot which illustrates most of the points made above. I made the measurements based on the deflection of a laser beam reflected from a camera, and it is part of an article I wrote for George Lepp's "Natural Image" newsletter.

[] | [ Q&A Forum ]


Article created 1998

Readers' Comments


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Alec Pytlowany , February 17, 1997; 09:56 P.M.

I enjoyed and learned from your ideas on mirror lockup. I use long lenses very often and have found even with mirror lock up that the tripod or tripod legs are also a significant problem with vibration. My experience is that even adding weight to the tripod is not a very good solution, but rather dampening the legs by wrapping my fanny pack or by laying weighted packs against the legs significantly reduces vibration, almost to nil. This isn't scientific, but try it. I used an EOS RT with several long lenses and just having the shutter fire was enough to cause lens shake. The same happened to almost the same level with weight from the center post. There was virtually no visible shake when the tripod legs were dampned by my weighted fanny pack and straps wrapped around all three legs. This displaced?, removed the vibration travelling through the tripod legs and thereby any camera or lens shake. I don't use long lenses without as much dampening as I can get. Try it an let me know what you think.

Bob Atkins , February 24, 1997; 02:10 P.M.

I certainly agree that the situation surrounding when MLU is needed is complex. It depends a great deal on the camera. Some models have much better mirror damping than others. It also depends on the tripod stability, the type of head used and the lens (some telephoto lenses have better tripod mounts than others). If you have MLU, then the best bet is to run tests with the equipment you use and see where it makes a difference. As a general rule, unless I knew otherwise, I'd always use MLU at speeds of 1/60 or slower when using lenses of 300mm or longer. Of course MLU isn't always an option and sometimes you just get lucky, so then I just shoot without MLU and hope for the best!

Adding weight to the tripod, or damping the legs can't hurt and can only help. It's always worth a try. Note that even the RT does have a small sub mirror (for the AF) which moves before the shutter fires. If you 1/2 depress the shutter release (in RT mode), the sub mirror drops. You can then wait for any small vibrations to die out before firing the shutter. The shutter itself does cause small vibrations when it fires, but much less vibration than an SLR mirror in an equivalent body (like a 630).

Dr. Hans H. Siegrist -- , June 20, 1997; 08:21 A.M.

Fritz Pvlking from Germany recently published his test series comparing mirror lock-up (MLU) with other techniques reducing vibrations. He found that you will have the same effect as MLU when you hold your tripod-mounted camera body steady with your hands when you press the shutter. This seems to work even better than using MLU and a cable release and even in the critical range between 1/2 and 1/60 seconds. I have tried it out and I must admit that this is a valuable alternative when you have a body without MLU.

Bob Atkins , April 02, 1998; 02:52 P.M.

The measurements were taken on a vibration isolated optical bench. They are unlikely to be from any cause other than being induced by the mirror movement. Any 60Hz component could certainly be electrical in nature though as total isolation from AC line noise was probably not achieved, plus 60Hz flicker from fluorescent lights could have affected the detector (though it was shielded and filtered)

Joseph A Worrall MD RDMS -- , April 04, 1999; 04:58 P.M.

I have an old Nikon F that does have MLU. I do not have the instruction manual, but the MLU seems to work as follows: either before or after you compose the image through the viewfinder, turn the little control that causes the mirror to stay up. Then take the picture. The mirror will flip up and you will have taken a frame with vibrations induced by the mirror flipping up but not returning. Then advance the film (being careful not to move the camera, which of course is on a tripod). Since the mirror is now locked up, you see nothing in the viewfinder. Take as many "blinded" exposures as you wish, bracket if you wish, and all those exposures will be without mirror vibration. When you are ready to see through the viewfinder, return the control knob to the normal position and the mirror will clunk down.

Robin Smith , April 20, 1999; 11:45 A.M.

A trivial point: the Leica R6 and R6.2 have MLU operated by a seperate cable release. It is rather nice since taking a quick shot is easier (depress one cable release, and then the one to release the shutter) than having a fiddly button or switch.

Robin Smith

Erik H. Pronske , April 22, 1999; 11:07 P.M.

I just got the Minolta Maxxum 9 which has the 2 second mirror pre-fire type of mirror lock-up. I have been using my 300/4 lens with the 9 to shoot wildflowers here in Texas. I definitely can see the difference when using slower shutter speeds. I would like to echo Bob Atkins' endorsement of this wonderful feature.

Tom Trottier , May 29, 1999; 01:10 A.M.

The Olympus OM4 and OM4T also have MLU and auto diaphragm fire at the start of the 12 second self-timer. Recent threads in the Olympus mailing list ( http://Zuiko.sls.bc.ca/swright/olympuslist.html ) seem to point to resonances with particular lenses, connected to mirror or diaphragm movement.
Olympus suggests holding the camera body and pressing the shutter release with your hand. I imagine that adding weight to the lens/body combination, especially something that would absorb vibrations, like a mini sand bag, would help to damp all vibrations.
Look at the test of the Zuiko 250/2 at http://members.aol.com/olympusom/lenstests/default.htm to check the differences between the OM4T and OM1.

Horst Heller , June 17, 2000; 07:09 P.M.

Once, a mirror lock up was standard with every Nikkormat camera. If anybody questioned its usefulness - well, he just didn't have to use it. Now I'm waiting for more than10 years for a modern Nikon body of reasonable bulk and weight that gives me the mirror lock up (or pre release) I definitely want to have. No hope! Sometimes I wonder wether I'm the only Nikon user asking for this feature (they never answered my letters, by the way). Man, I hate Nikon, I really hate them!!!

Alfred Robinson , July 31, 2000; 05:01 P.M.

It seems to me that there is not a general understanding of what is going on when the mirror goes up. The mirror moves up rather rapidly. Conservation of angular momentum requires that the camera rotate downward, though by a much smaller amount, since the camera has a whole lot more moment of inertia than the mirror has. When the camera moves like this, what it does is compress the camera mount, (tripod, hand or whatever). As the shutter starts to open, this compression in the camera mount starts to release energy to the camera. If you view the camera mount as a spring, the camera and mount start oscillating at a frequency determined by the weight and size of the mount. The oscillation will die out in time, depending on the damping present in the camera mount, but it may not die out in time to do much good. The camera is oscillating about a horizontal axis during the exposure, causing a loss of resolution. Adding damping to the mount may help. Using a heavier tripod may help, it may hurt, it depends on the dynamics of the tripod/camera system. The noise you hear when the mirror hits the stop has nothing to do with the problem. It is the momentum exchange that does the damage. The use of a pellicle mirror has been mentioned in some of the comments above. This works. However, there is another way. If there is a mechanism inside the camera which is geared to the mirror, and rotates in the opposite direction, and if this mechanism has the proper size and weight, there will be no net momentum change as the mirror goes up, and no problem. I don't know for sure, but I bet this is done in the Leica reflexes. It is their style, and may be the reason they did not get into the SLR market for a long time. I think the Nikon F2E had this momentum balancer, and I believe I have seen ads for the newest wonder from Nikon that suggests they have it too. This is the best solution to the problem. BTW I don't use SLRs much, unless you call a view camera an SLR. In the early days I got burned with an old Nikon F which had a lens resolution of about 120 lines/mm, but only got 30 lines/mm at 1/30 second, on a heavy tripod. That is the best way to check out where you stand. Shoot resolution charts with and without lockup.

John Chiarotto , August 01, 2000; 08:21 A.M.

Here's a random thought on mirror lockup... given that the thump of the mirror against its stop causes vibrations of x frequency in a body weighing say 500grams.. what if the camera body weighed 5 kilos ? Perhaps the sand bag(s) should be on top of the camera body - thus making it heavier, with greater inertia to be overcome before it can begin vibrating.

John Chiarotto

Max de Hertelendy , August 14, 2000; 02:07 P.M.

Another idea on this subject: Many suggested holding your camera firmly with your hands. Also, if you're using a long lens, you should try holding it, on the front end. Y think the longer the lens, so is the lever action you are applying against the oscillation of the camera caused by the mirror going up. For sure, several times stronger than holding the body only. This is consistent with the idea previously presented of having two tripods, one for the lens and one for the body. The farther the lens tripod is from the body, the stronger it's effect on angular movement, which causes the greatest change on the image for a long lens.

Eric Anderson , August 15, 2000; 03:11 P.M.

As has been mentioned in passing above, you can often use the self-timer feature to help combat this problem. With many cameras, including my Nikon FM10, if you set the self-timer and press the shutter button the mirror will swing up when you press the button, and then the shutter will fire when the timer runs out. This introduces a delay of several seconds between when mirror swings and the exposure is made, which should allow vibrations to subside.

You can easily check whether your camera works this way: Set the self timer, depress the shutter release, and look through the viewfinder. If you can't see through the viewfinder while the timer is going, that means that the mirror has already swung up, which is what you want.

Joseph Albert , August 22, 2000; 11:01 P.M.

I didn't see it mentioned above, so I thought it would be well to add that not only is mirror lockup/prefire important but aperture prefire is highly desirable also if you are shooting macro or long telephotos.

My attention was first called to this point when looking at this web site that posts performance data for Olympus Zuiko lenses in which a difference between using an OM-1 with mirror lockup and an OM-2000 with mirror and aperture prefire was detected. I have since done my own comparisons using a Tamron 90/2.8 macro attached to both an OM-1 and OM-4T with the lens focused at 1:1 and find that the shots taken with mirror and aperture prefire are sharper.

Tommy Huynh , February 08, 2001; 12:32 A.M.

I'm glad somebody did a in depth review of the subject. Thanks Bob. The question now is why on earth does Nikon not put MLU on more of their bodies? That made a big impact on my decision on which system to choose.

Curtis Clegg , March 05, 2001; 12:43 P.M.

Mirror lockup is a wonderful and oft-neglected feature, but its use is not always practical in wildlife photography.

Moose Peterson's web page describing proper long lens technique is a good alternative for mirror lockup, and a prudent practice for all shots with long lenses.

Curtis

Staffan Johansson , March 14, 2002; 05:16 P.M.

Hello!

Mirror lock up is certainly a good idea in many cases, but don´t forget the shutter itself! It will also introduce vibrations. As a Leica M user I need to eliminate that type of vibration since there is no mirror but a focal plane shutter with a good deal of inertia.

Here is my tip: Use a sturdy tripod and make it even better by dampening the tripod leg vibrations. My simple method is to use a coarse bicycle rubber hose, fill it with sand, tighten the ends, tie it together and place it over the tripod legs, half-way between camera and ground. It will do a lot of difference. Especially at exposures around 1/15 or 1/30 of a second. You can test this by attaching a small mirror to the camera body, direct a laser pointer to the mirror and observe the reflected laser spot on the wall when releasing the shutter (using the self timer). Satisfaction guaranteed!

Kind Regards Staffan Johansson www.staffan.net

Alexey Kats , May 15, 2002; 04:52 P.M.

To Alfred Robinson.

Thank you very much - it was a thorough and accurate explanation of the problem. And I like your idea about dumpening mirror angular momentum inside of camera. Its implementation might be problematic though. Since most cameras do not have enough space to incorporate another moving part with size and weight comparable to the mirror there will be two ways essentially. One would have to make it smaller but heavier to gain extra moment of inertia to overcome available space limitation. Or one would have to make it smaller but rotating at higher speed to gain extra angular momentum. Either way, unless bith parts (mirror and its counter-part) can be started and stopped synchronously, engineer will have to deal with resulting net momentum gained from three parts - mirror, camera with support, and mirror counter-part. It will (if designed properly) reduce net angular momentum, but it won't eliminate it. Strictly speaking, MLU does not eliminate it either - it simply reduces amplitude of oscillation due to mirror movement to the level below one gained from surrounding environment.

By the way, does anybody have some information about what camera models (if any) did incorporate that kind of dumpening system opposing to MLU?

Thank you.

Victor Yushenko , November 25, 2003; 09:20 P.M.

Maybe there is no mirror slam. I mean if we imagine that mirror and camera body are two separate systems then when camera starts moving its mirror it (camera)gets acceleration X. When mirror hits camera, camera adds acceleration - (minus) X. X + (-X) = 0, so no acceleration at the end.

Gary Reese , February 05, 2004; 12:17 P.M.

I had this thread bookmarked for a few years just to see where it was headed. I'm the author of the above cited web site for Olympus OM lens tests.

I've read most of the popular articles on this subject which have been published in the last few decades. It is as if the authors mostly just rehashed what previous articles have said. Even a vibration chart like the one at the head of this thread was published by Minolta a few decades ago (and reprinted in a textbook by Norman Goldberg). Early on Herbert Keppler talked about sources of vibrations in rangefinder vs. SLR cameras and listed the automatic diaphragm mechanism as a source of vibration. In subsequent articles where vibration effects were tested he oddly ignored that source. Too bad.

It is my understanding that we are seeing digital cameras with optional 2 or 10 sec. self timers. That is akin to the benefit of mechanical self timers on cameras like the OM-2000, in which you can set a 2 sec. self timer action which prefires the mirror and the automatic diaphragm. The bottom line, which Olympus OM users have found out: if you want to coax the maximum performance out of your lenses and the situation allows it, then prefire the mirror and automatic diaphragm by using the self timer. It works on many other camera system bodies, also, albeit sometimes only on some classic designs, like a Canon EF or a Minolta SRT.

Steve Hovland , July 10, 2004; 11:52 A.M.

The graph also shows another way to beat the problem:

Where appropriate, you use shutter speeds of 1/4 or longer. That way most of the exposure occurs after the mirror vibration has damped.

Also, if you are using strobe for fill, set the camera so the strobe fires just before the rear curtain closes, not when the front curtain opens.

I am very dubious about putting your hand on the system to steady it. It seems to me that you are likely to add a source of movement. I prefer to trigger with the self timer when shooting non-moving subjects to avoid tripod vibrations.

Thakur Dalip Singh , September 05, 2006; 12:12 P.M.

I have read about this problem and solution from the one top nature photographer of Australia.He suggested using tripod under the camera not under long lens and use second support under the lens. My experience is mirror induces vibrations even with 80-200 lens and high shutter speeds also when camera is not on tripod and supported with lens' tripod collar. Thus the practical approach is to use two supports : main for camera and second for lens. If any doubt : test yourself at all speeds with and w/o MLU. Make big enlargements 30x40, or see at 200%. I also endorse the vierw that different cameras have different mirror vibrations, My nikon D2X is worse. Putting hand on camera or holding camera definitely reduces mirror induced vibration. Unfortunately most of the times in nature photography MLU is not practical.

Ian Rance , April 03, 2007; 06:38 A.M.

I have found that MLU does have a positive improvement on photo sharpness, and it has proved useful to me even when hand-holding the camera (such as pressed up against glass in a museum) and using slow speeds. What is lacking in many cases is that it is often poorly implimented which puts many people off using it. If it was more prominent and labeled as such, then it would be used alot more. Canon users need to access the custom functions which is a fiddle when on the go and Nikon have it linked to the self-timer (pre-fire) on the Manual bodies. The Nikon F6 seems to have improved on these systems by having it linked to the drive control, but few use this model.

If you have the MLU feature, do use it as often as possible to give your photos a greater chance of being sharp.

Charl Zacharyahs Mellin , August 09, 2011; 04:50 A.M.

Hello all!

Thank you for good advices and thoughts in this Mirror Lock Up thread!

I wonder if anyone uses the "Live view" to avoid unwanted mirror vibrations! I find MLU a bit tricky and not so convinient so I rather use Live View instead even if it consumes a bit more battery!

Do anyone else use Live view - with remote control - as I do?

I can see the differences  compared with normal way of exposure.

 

Best regards,

 

Charl Mellin

Sweden


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