Lens came off the camera in my backpack

I was carrying my 400mm f5.6 (attached to a 20D) in a backpack while mountain biking. It worked fine on the first day while I had an extra fleece in the bag as well. Unfortunately the weather was colder on the second day so I decided to wear the fleece and left the camera by itself in the bag.

As we neared our camp I heard a "click" and another strange noise. Since I was going downhill on slightly rough terrain I concentrated on the bike and did not worry too much since it was all in one piece. When I finally opened the backpack, I was horrified to see the lens standing upright without the camera attached. The camera was of course sitting on the bottom of the backpack minding its own business.

I found a a few bits of dust on the camera sensor as well as the lens. After cursing quietly for a few minutes (no tools to solve the problem), I started to relav and went back to taking pictures. I have looked a few images and don't see any obvious defects (dust spots).

Now I have a few questions:
1) How can I best evaluate the pictures for dust particles?
2) What is the best way to remove dust particles from a 400 f5.6 lens?

thanks,

John

You shouldn't get much if any dust on the sensor from having the lens off.. It has to get around the mirror and through the shutter blades which are closed and covering the sensor.

I carry a bulb blower and in a case like this I'd just gently blow out the mirror box. Don't blow too hard or you can force dust up under your focus screen.

You can blow out your lens with the bulb blower too.

To check for sensor dust, take a picture of the sky in Av mode with the aperture set to f/22.

Take a pic of the clear sky at f22 and do autolevels in ps.

As for cleaning the outside lens, I use the nikon lenspen. Dunno if much can be done about the dust *inside* the lens short of sending it back to canon.

yup...boost your f-stop as high as it'll go and shoot at the sky/white wall while moving the camera around a bit (to eliminate spots on the wall looking like spots on your sensor)

give the inside of your camera a couple good shots of air with a rocket blower and see what you've got.

you don't have to use a noink lenspen...many other companies make them.

Thanks for the suggestions. However I already used that method to confirm that the dust particles are on the sensor. I agree that it is surprising this happened if the shutter was closed. I was really asking how I can try and evaluate the final results of pictures taken when there are dust particles on the sensor.

John

You shouldn't have any issues with dust in the lens. Make sure you blow off, then wipe the rear element of the lens (that's the most criticial piece of glass), but it's unlikely that any more dust got in the lens that would happen in normal use.

With regard to dust on the sensor, only you can determine what is acceptible to you. If you've shot the sky at f/22 and then done an auto-levels on the photo, you'll see any dust particles on the sensor. You can then either opt to clean them off with a dust blower or use a more aggressive method of cleaning. If you don't shoot at small apertures, you may opt to wait as it's unlikely the dust will show up a larger apertures. The only way to tell if there are issues is to use your camera like you would normally use it. If you can see dust (especially in the sky or other light areas) then you'll need to clean again.

Mark