Road Train !!!!!!!!!!

by Russell McMahon

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I got mugged a few days ago, but got my camera back in the end. Bonus: I got some sand too. I now have the camera in pieces, cleaning them as I go along, and the lens barrel extends and retracts smoothly again.

But there's a flex PCB ribbon (4 conductors) going into the barrel that worries me: what if there's another motor and gearbox hidden in there? If there is, I'd rather open this thing up some more and make sure there's no sand in it. If not, if maybe it's just a end stop optocoupler, I don't think I'll bother.

So far I've found the lens barrel extend/retract motor, mounted on the outside of the lens assembly, and another, smaller, motor inside the assembly, that drives a lens along a leadscrew just in front of the CCD. Are there likely to be more than just these two moving elements in this zoom lens?

Extended lens barrel with 4-conductor flex PCB going inside

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1 Answer 1

up vote 2 down vote accepted

This is only very rough guessing as I haven't dismantled the Canon A490 before myself but here is what I think it is. Where I have circled Auto-focus drive/gears, were there gears and a lens element attached to a spiral rod? If so, then that's the auto-focus mechanism. If not, I'm not 100% what it is.

I TAKE NO RESPONSIBILITY FOR ANY DAMAGE DONE.

If you want to look further, it looks like all you need to do is rotate the most outer barrel, past the home position and time it so it pops out. It should have teeth visible where I've circled Zoom drive. Keep turning the teeth so the barrel comes towards you but be vary careful not to break or damage the flex.

enter image description here It was found that the auto-focus mechanism was fixed to the CCD frame and not viewable in the original image

If the zoom and auto-focus gears move freely, I'd consider that OK and reassemble it. There shouldn't be any other flexes, unless the auto-focus mechanism is done more internally (which I doubt), but I can not see where it is.

The apreture and shutter should be OK. The actual blinds/aperture ring is under the element where I have pointed but not circled.

Report back if you'd like just by commenting.

EDIT: So, there will be more moving parts, but not gears. Just arms that sit in the grooves/tracks.


And here is the flip side of the moving piece:

enter image description here Thanks to Bernd Jendrissek for the image

One might notice that the aperture is only one hole and not made up of blades to change the size of it. That is because most compact cameras have a fixed aperture. If you find that you get different aperture values in the EXIF data, that's due to zooming. As the hole moves away from the sensor, it appears bigger, creating a kind of "pseudo" aperture.

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Thanks! Although the zoom and auto-focus are a bit different, just your pointing out that the flex going in might be for the aperture, is enormously helpful. –  Bernd Jendrissek Oct 29 '12 at 11:45
    
Ok, thanks for that. I'll edit that picture. –  BBking Oct 29 '12 at 20:47
    
Couldn't help myself, opened the lens barrel further. Your ID is confirmed: the flex goes to a solenoid. I guess that's your aperture drive! –  Bernd Jendrissek Oct 30 '12 at 23:32
    
Great! It's more likely to be the shutter. Most compact cameras have a fixed aperture. They might have, say a secondary aperture. It will move out of the way for more light/less DoF to focus but will move back in place for the actual shot. Are the any moving arms? Other compacts may have a moving filter, typically ND, but not all. I'm willing to guess there is a second moving part where the shutter is but as I said, haven't worked on this model before. Could just be the shutter alone. I've got to fix up that image too! God, photo.stack is hard work! :P –  BBking Oct 31 '12 at 2:10
    
I later saw there were two solenoids. As you predicted, one controls the shutter (I didn't know digital cameras had or needed these!) and the other a secondary aperture. Image for the curious. –  Bernd Jendrissek Oct 31 '12 at 19:35

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