Practice.
I don't do this anymore but I did before the first time and it helped build confidence without being scared
The sensor cover is glass so cleaning a glass filter will give you a feel for what you are doing.
Put the filter flat on the table and drip one drop of eclipse fluid in the middle of it. Watch the eclipse spread out then start to evaporate. In theory eclipse is so pure there will be no residue. In practice there is a visible tide mark at the edges where it dried.
With that in mind although we need the eclipse to dissolve any stickyness in the dust we don't want too much that could leave residue.
Now to clean the filter. Put 2 drops
** of eclipse on the swab near the front edge but not right on the edge. I aim for the thicker bits where it is folded. Pic below I'm pointing with the tweezers as i can't get a pic of the drop with my p&s camera.
Now put 2 drops
** on a second swab and put it down. The first swab should now be ready to use and the second can be used immediately afterwards.
Using the first swab which has had a few moments to soak press it into the egde of the filter at an angle with pressure like you would on a biro. Draw it back towards the middle and once central lean your hand to reverse the angle of the swab to the glass and then push the swab to the other side and lift off. You should have a clean stripe across the glass. Notice as you work there may be a slight hint of evaporating fluid on the glass following the swab. Any more than a hint and you are using too much fluid - or using the swab too soon after applying the eclipse drops.
Once you have used the swab once on the sensor you don't want to use it again. pull the tape off and re-wrap it if you need more....don't be lazy and try to re-use it. Practicing on a filter though I wouldn't worry to just get the feel of it. A well used swab won't clean so well though.
Camera setup.
You are going to be making test shots at f22 so you need a lens that can do this and is not too big. The kit lens is ideal.
You don't want to be messing about with RAW conversions so set it to large jpeg.
Test shots will be of nothing so set the lens to manual focus.
Make sure the battery is freshly charged - you don't want the mirror dropping down on you because the power ran out.
Longer exposures are not a problem so use 100 iso. Aperture priority set at f22.
Point the camera at the sky so that nothing but sky is in the shot. Wave the camera about a bit as you take the shot so nothing could possibly be in focus (like a passing bird).
View the image on a computer screen. You should see marks as it is if your sensor badly needs cleaning. If you want to feel worse try auto levels on it. So now you see the problem
If you don't have any sky then a plain white wall will work too - the more out of focus the better.
Cleaning.
The actual process you have already practiced above. The only real difference doing the actual sensor is that you are working semi blind down a deep recess and it is smaller. So this is really just a few pointers to help solve problems.
Select the sensor clean on the camera menu and highlight OK but don't do it yet. Put drops on 2 swabs. Ok the camera to cleaning position and remove the lens. Lay the camera on its back in front of you and swipe it with the first swab.If the swab is too narrow then swipe one side from end to end, lift off and repeat in the same direction but along the other side. Repeat with the second swab but in the opposite direction. Refit the lens and turn the camera off to end cleaning mode.
Take another test shot and view it as before. Don't panic if it is worse than it started out. Assuming it is better than it was,it is now a judgement call how many times you remake your swabs with new pec pads and repeat the process. Again going back to my first clean it took 7 goes with the first being worse before it got better.
The first time I cleaned my sensor I also had a bit of stubborn dirt stuck to the sensor (sensor cover glass to be more accurate). In that situation it OK to scrub the offending point with a swab to free it. Then use a new swab for a full swipe afterwards.
If you can see eclipse evaporating behind the swab as it passes over the sensor you have too much fluid on it. Just means doing it again with less as the micro droplets will leave drying marks. They look like dust on test pictures but are translucent. Just like dust they don't show at normal aperture settings usually.
I would expect to do it twice - which is why I start out with 4 swabs.
If you do have a stubborn spot say top left in the picture remember it will be bottom right on the sensor (as seen from behind the camera - bottom left once you turn it over to look at the sensor face).
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If you read this far I'm amazed. If there are not a few mistakes above I'll be even more amazed. Feel free to post corrections, questions and downright disagreements
** 30.08.07 Just wanted to add a comment with regard to E2 - the sensor cleaning fluid. I've just bought some and done a clean on the 5D. E2 fluid dries much more slowly than eclipse. One drop is all that is required or you will be into drying problems and watermarks. I found it best to allow a longer standing time after applying the fluid to the swab or it is still too wet.