Ophrys Photography

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Effects of mirror slap and vibration

Background

I was carrying out some tests on a couple of new lenses on a dull day and my shutter speed was fairly low at around 1/80th sec. Despite focussing carefully and using a good tripod and wireless remote shutter release I was disappointed to find that most of my shots were very soft. I had not used mirror lock- up as I thought that my shutterspeeds were sufficiently far out of the 1/10-1/20 sec danger zone that is often cited. At these shutterspeeds vibrations resulting from the camera's mirror rising and falling are known to produce vibration that can cause blurring of detail. In order to see what was going in my case, I decided to set up some tests to investigate a bit further.

The first set of tests were done with the Canon 5D mkII camera and 100mm f2.8L IS macro with tripod collar fitted. I wanted to see how much mirror slap affected the images as shutterspeed was progressively reduced. I figured that as the 5DmkII has a fairly soft-sounding shutter it would not be causing too much vibration. Also a 100mm lens is fairly short and would probably not amplify vibration to the extent that a longer telephoto lens would. So I started with this combination.

Everything was done identically with tripod, cable release, IS off, camera in One shot (centre point only focussed on the centre of the banknote).
I allowed 5 secs between each shot for the camera vibrations to settle down, lens was micro- calibrated and identical processing.
ISO used was 400.In the first test I let the camera focus each time (a slight mistake as it has introduced a little variation between shots) but in the second test with the 1DmkIV and 70-200 f2.8 L IS mkII, I switched to manual focus to prevent refocussing errors creeping in.

Test 1 Starting image

The target was a banknote with an engraving of a mandolin on it. I focussed on the centre of the frame - on the curved portion of the instrument.

100% crops of the banknote.


Results

From test one some interesting things emerged:

Firstly, before I get onto mirror slap, there is a nice demonstration of the effects of diffraction here as it can be seen to progressively creep in as the aperture size is reduced. Just take a look down the right hand column of the mirror lockup series, you can see that the first hint of softening due to diffraction creeps in at f11 and gets increasingly worse as the aperture gets smaller. F16 is still fine - and is the aperture usually recommended for macro work. I would still use f22 if pushed and just increase the sharpening a little.But f32 is decidedly soft. No surprises there but this reinforces the need to be wary of using very small apertures.

The non mirror-lockup series will also have this diffraction superimposed upon the effects of any mirror slap/vibration. What surprised me was that I could see the effects of mirror slap so much earlier than I would have expected. Unfortunately the first non-MLU shot at 1/320 sec is a bit soft - presumably due to a slight focusing error as the next 1/160 shot is a bit sharper. However, if I was generous and said that the 1/320 shot was probably still unaffected, I can still see the beginnings of softness at 1/160 vs the MLU version. This softness is present all the way down to 1/40 vs the MLU version but at 1/20, 1/10th and 1/5th it gets quite a bit worse.
This is the well-documented zone of shutterspeed where MLU is usually recommended. By 1/5 to 0.4 sec the mirror slap has passed again and the non-MLU version matches the MLU version which is also soft due to diffraction.

Test 2.

This was performed exactly as before but with a longer lens, the 70-200 f2.8L IS MkII.
This time I was shooting from a greater distance of course to get a similar fiedl of view and being a physically longer lens, I suspected it could be more prone to amplifying mirror slap. I mounted a 1DmkIV camera onto the lens this time as I was wondering if my 5DmkII could be faulty in some way. The 1DmkIV in common with all 1 series cameras has a noisy and rattly sounding shutter (presumably as it has to be more robust and can perform at a higher 10fps frame rate.) and I wouldn't have been surprised if it fared even worse than the 5DII in terms of mirror slap.

Once focussed, I locked the Autofocus into manual which I hoped would remove one more variable. I also increased the ISO to 1250 as I wanted to start at a higher initial shutterspeed than before. Here are the results:

Results

These results appear a little more consistant than the first set as there is no refocussing between shots. As expected, diffraction was present from f16 onwards even in the MLU series - f32 being very bad.

I think that you can see that mirror lock up has a signicantly beneficial effect at 1/125 and below
and from 1/60th sec to 1/8 sec, mirror slap is very significant without it and this explains why I was getting poor results befoer conducting these tests.

Conclusions

I think that these shutterspeeds are much higher than you would normally expect to see the effect of mirror slap and should consider using MLU or Liveview shooting (when the mirror is already raised) when shooting off a tripod with remote shutter release at 1/125th sec or below - particualrly when using a 1 series camera.

I would also allow around 5 sec for vibrations to subside between shots when shooting in this way. When shooting with the camera tethered to a computer and viewing on the screen at 200% I could clearly see oscilating movement of the image on the screen for at least 3 secs after remotely closing the shutter with the computer.

The effect of mirror slap is definitely worse with the longer lens/1DmkIV combination but the effect was still present in the macro lens/5DII combination. I have not proven that one camera body is worse than the other (although I suspect that the 1 series is worse in this regard) - this would take more investigation, but the overall message here is the same.

It should be said that this is a very stringent test as the cameras are 21Mp and 16Mp respectively and the 100% image size is very large when seen on the computer screen and we are looking very critically at a very small part of the image. However, if we want top quality images from our high-resolution cameras, we must consider resorting to stricter vibration control when working off of a tripod.

In the case of the 70-200 f2.8 L IS, results would probably have been better handholding down to 1/30 sec thanks to the lens's great 4-stop IS system and the photographer's hands damping the camera vibrations.

Summary

The effects of mirror slap appear to be encountered at much faster shutterspeeds than is usually suggested. The reason for this is not revealed by these tests, but one can hypothesise as to whether thismay be because later cameras are producing more vibrations than previous models or whether high megapixel camera sensors are responsible for revealing the effects much earlier than before.

When shooting on a tripod with a cable release, I would now want to use MLU or shoot in Liveview mode or at least try to damp the lens vibrations with a beanbag placed on top of the lens/camera at shutterspeeds of 1/125th sec or less. In the past I would not have resorted to this before I hit 1/10- 1/20th second !

When using very long lenses such as the 500mm f4 off of a tripod I will continue to shun using a cable or wireless release but continue to recommend using "good long lens technique" which is described in part 5 of my article on photographing wild birds.