A quick trick for, primarily, multi-second shots from your camera to remove blur

Happy new year! Here's a quick trick for those long exposure pictures you are taking since you stayed up late at night and want to get a great night-shot.

I'm going to assume you know WHY you are taking a multi-second shot. And really, this will work down to about a 1/4 second shot if you are willing to take a few tries to get it right, but it works best with several second shots.

I'm going to assume you are using a tripod and not hand holding your camera. So if the purpose of taking a long shot is to get a blur, then you can stop reading, this trick won't help you!

But if you are taking landscape or sunset/sunrise photos and you are taking shots that are a few seconds, this trick is for you!

Update 2018: If you have a mirrorless camera with electronic release, then this trick is also of no value to you. The electronic release and lack of a mirror completely solves the problem for you. But if you have a DSLR, or you have to manually push a button, then this trick is still relevant for you.

A little bit of why you need this trick first:

When you press the button on your camera, your finger is going to move the camera.

Then, even if you use an electronic shutter so your finger doesn't move the camera, there is a mirror in your camera that slams up when you start to take the picture and that causes a small amount of jiggle at the beginning of your picture.

With shots that are slower than 1/mm of your lens (so a 100mm effective lens that would be 1/100th of a second, on a 50mm lens 1/50th of a second, on a 600mm that's 1/500th of a second) and less than let's arbitrarily say 30 seconds, the amount of movement caused by your finger and the mirror can drastically or even just annoyingly cause a blur in the image.

The longer the mm of the lens - the worse this little (or a lot) of blur will be because a little movement on a 600mm lens is a LOT of movement on the image, but the same amount of movement on a 16mm lens is only a little bit of movement on the image.

The shorter the time of the shot - the worse this will be - because it will be for a greater percentage of the total light gathered.

Now the trick:

Get a piece of black construction paper (rough texture is what you are going for) or a fuzzy black cloth that will block most or all of the light.

Calculate how much time the shot should be for.
Set the camera to 'bulb' (open all the time) or to a time that is several seconds longer than you want the shot to be, if possible, 3 or more. Let's say you picked 3 seconds. Better to not be too long because of possible light leakage, but long enough that any movement from your finger and the mirror will be gone. 3 seconds for me seems to be a number that has always worked.
Hold the paper or cloth directly in front of the lens, making sure you can remove it with jostling the camera.
Press the button to take the picture.
Wait the number of 'extra' seconds you set it to - 3 seconds
Remove the paper.
Wait until the camera finishes taking the picture - do NOT touch the camera until you hear the shutter close and/or the mirror drop back down. Note that the dropping back down of the mirror happens AFTER the shutter has closed, so the mirror dropping back down does NOT affect the quality of the image, there is no light coming in starting just before the mirror drops. It is only going up that causes problems because the camera keeps shaking a bit after the lens 'slams' up.
Check your image

Then repeat several times, perhaps changing the number of seconds for the exposure up and down.

The longer the exposure time, the less quickly you have to remove the paper - but still do it quickly - and the less critical your timing has to be to get it right. But also, the longer the exposure time, the less the initial jiggle is going to affect the final outcome. The issue here is, as you are removing your paper, some of the sensor is going to start getting light, so some parts of the sensor will be exposed longer. On a long exposure, this fraction of a second more light will make no visible difference, but on a shorter exposure time - it will. But the faster you remove the paper, the less effect it will have as well. I could be wrong, but I think when I do it, it is less that 1/15th of a second from when the 1st part of the sensor gets light to when the last part does.

If you are unsure or just want to test - set something up for lets say a 1 second picture, taking a picture of a white or grey wall that is evenly lit - then take away the paper and check the result - if you see it is noticeably brighter on the side that first gets the light, then obviously you are not taking it away fast enough. You can do this test once by removing the paper 'slowly' so you can be sure that you are seeing the effect.

Certainly if you are taking pictures that are a minute or longer, you are very unlikely going to need this trick, because even 2 seconds movement at the beginning is only 1/30th of the total light falling on the image. So even if you are really picky - a picture of 3 or more minutes would never need this trick.

If you are taking pictures less than, oh I don't know, let's say 2 seconds, you may want to make these adjustments to the trick above:

Set the time for the exposure to perhaps 5 seconds longer than you want (4 if you are talking a sub 1 second exposure. Why? because you don't want light leakage so you don't want it 'taking the picture' for longer than necessary after you bring the paper back.)
Wait the 3 seconds as above
Remove the paper for the time (down to about 1/4 second exposure with practice)
Bring the paper back in to cover it again - and now it is safe to use your hand to hold it against the lens - movement won't matter now.
Wait until the camera stops taking the picture.
Remove the paper and your hand from the front of the lens
Check your image

If you can, take the paper away from one side and bring it back from the other side. Think of it this way, you are counting the exposure time in your head, you pull the paper away and start counting in your head (or out loud), the paper moves in a circle above the lens and you come back in as soon as the exposure time is up - but from the other side. That way all the film will get the same amount of exposure. I'm not sure how short a time you can do this, but you are unlikely to be able to do this circle in a shot of less than 1/2 second. Try a few times to see how quickly you can do it. And try it both ways - in a circle and in a 'tick/tock' fashion to see what, with your skill and speed, gives the best final shot.

Note that on shots longer than several seconds, unless you are very slow removing the paper, the difference in the amount of light from one side to the other is not going to, percentage of the full shot, be enough different to bother with this add-on trick. But on your less than 1 second shots - it definitely is going to.

When will this not work?

When the time for the exposure is too short. For most purposes, anything less than 1 second is going to be really difficult to time it perfect as to when to remove the paper - and the shorter the exposure time you want, the more quickly you are going to have to remove the paper so that you don't have some portions of the image with a lot more light than others. You are likely going to have to try a lot more times for a 1/4 second shot (to get the timing correct) or even a 4 or 5 second shot than with a 30 or 60 or 120 second shot.

When you are using 'fill flash' at the beginning of the image. This is where your flash goes off to light something, typically a human, and then the many second exposure is to give the background enough light. Obviously this will fail because your paper will be in front of the lens when the flash goes off. If you are using fill flash at the end of the image exposure, then this trick will still work fine.

Alternate trick:

If your camera has an electronic shutter (so you can make it take the picture without touching the camera) AND your camera has a mirror 'lockup' mode. You can do this by locking the mirror up, waiting a few seconds, then taking the picture using the electronic switch.

And a bonus set of tricks for long exposures:

If you are taking the picture in a windy environment, put some beanbags on the tripod and or camera to minimize the movement.

Stand upwind when doing all of this to block as much of the wind as you can with your body.

Put the camera in a tent or directly downwind of a vehicle, building, large rock - all with the idea of blocking the wind. If you are too far downwind, you will have the camera and lens in the place where the wind turbulence makes it even worse than just being out in the wind.

If your subject is being blown around by the wind (flowers for example) just forget it if you aren't making an 'impressionist' picture - or make the picture a multi-minute picture to see if the flower spends 'most' of it's time in one place - you might get a nice creative effect from the movement.