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Photo Forum / Digital Photography / DSLR Cameras / October 2006Canon 100-400 IS EF Zoom...
I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens is in like new condition except for dust inside the lens...and some large specks that are troubleing. Is there any way I can get to thei inside of this lens without screwing things up? If I need to send it out to have it cleaned, who should it go to? I live in the far northern end of California. Thansk BArry > I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens is in > like new condition except for dust inside the lens...and some large specks > that are troubleing. Is there any way I can get to thei inside of this lens > without screwing things up? If I need to send it out to have it cleaned, > who should it go to? I live in the far northern end of California. Never done it mind you, but I can imagine it'd be something you coudl very easily screw up. I'd probably send it in to an authorized Canon servicer. Their website should have a link to find such. -- Todd H. http://www.toddh.net/ > I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens is in > like new condition except for dust inside the lens...and some large specks [quoted text clipped - 4 lines] > Thansk > BArry The dust is probably not as troubling as you think it is. Is it on the edge of the glass where the cropped 20D sensor never sees it? Can you see it if you stop the lens all the way down at 100mm and 400mm? Are you using the lens hood? No you probably can not get inside the lens with out messing it up. Send it to Canon; with any luck they will replace the dust seals too. So I guess you don't make it down to the Marin Headlands too much then? Mine was dusty with in the first month and that was almost three years ago, unless you can clearly see it is messing your pictures up don't bother with it. Jim >> I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens is in >> like new condition except for dust inside the lens...and some large specks [quoted text clipped - 7 lines] >The dust is probably not as troubling as you think it is. Is it on the >edge of the glass where the cropped 20D sensor never sees it? It is a myth that smaller sensors do not "see" the edge of the glass. Every bit of the glass passes light to every bit of the image (well, that's a slight simplification, but nearer the truth than the "lens edge passes light only to edge of image" myth). Why else would a wider-aperture lens make the image brighter all over? However, for the reasons in my other post, I agree that Barry should leave well alone. David  SignatureDavid Littlewood > It is a myth that smaller sensors do not "see" the edge of the glass. > Every bit of the glass passes light to every bit of the image (well, > that's a slight simplification, but nearer the truth than the "lens edge > passes light only to edge of image" myth). > > Why else would a wider-aperture lens make the image brighter all over? Um, good question. I'd never thought about that before. The followup question would be why is vignetting less of a problem with smaller sensors if the edges of the glass are seen just like with full size sensors? So how does it work? >> It is a myth that smaller sensors do not "see" the edge of the glass. >>Every bit of the glass passes light to every bit of the image (well, [quoted text clipped - 9 lines] > >So how does it work? First, illumination follows an inverse square law, i.e. is proportional to d^-2, where d is the distance from source to image. Light at the edge of an image has to travel much further than light to the centre, so its brightness is reduced. Second, at the edge the light is illuminating the image obliquely. Thus the same solid angle of light has to spread over a larger area, thus illuminance (light per unit area) is reduced. Third, there is likely to be some mechanical vignetting caused by bits of the lens getting in the way. With all of these factors, the remarkable thing is that wide angle lenses are usable at all. It takes a lot of effort in design to correct these effects to give reasonably even illuminance across the image. David SignatureDavid Littlewood >>> It is a myth that smaller sensors do not "see" the edge of the glass. >>> Every bit of the glass passes light to every bit of the image (well, [quoted text clipped - 23 lines] > are usable at all. It takes a lot of effort in design to correct these > effects to give reasonably even illuminance across the image. that would explain biiiig price of those lenses :-(( >It is a myth that smaller sensors do not "see" the edge of the glass. >David The edge of the glass is not relevant. It is the edge of the circle of light projected by glass designed to cover 35mm format that a 1.5 or 1.6 "crop" size sensor does not "see". Changing the f stop on a lens only changes the amount of light passed, not the size of the circle projected. JPB >>It is a myth that smaller sensors do not "see" the edge of the glass. > [quoted text clipped - 7 lines] > >JPB Oh dear, another spectacularly missed point. I must be losing my touch... I suggest you read what I said, and then you will (should) see that what you wrote in "response" is non-responsive, being a different point altogether. BTW, what you say is quite correct, it's just not the issue I was describing. David SignatureDavid Littlewood Call canon factory service in Irvine: 1-949-753-4200. I always schedule three weeks to be without the equipment and it's never exceeded that. I last shipped from NorCal, too. >I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens is in >like new condition except for dust inside the lens...and some large specks [quoted text clipped - 4 lines] >Thansk >BArry Barry, Don't even think about DIY disassembly. The lens elements need to be very precisely aligned, and the slightest bit awry on re-assembly will spoil the performance. Also, that lens in particular has a very large fluorite element as the second bit (behind a plain glass front protective element). This is rather delicate (hence the glass protector) and could easily be damaged by inexpert handling. It is 99% likely that the dust inside the lens will have no visible effect on your photos. It will be way, way out of focus, and the only slight risk (the other 1%) is that you get so much in there it reduces contrast slightly. You would need to compare the images produced with a known good specimen to check this. David SignatureDavid Littlewood > I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens > is in like new condition except for dust inside the lens...and some [quoted text clipped - 4 lines] > Thansk > BArry My 100-400 always had a bit of dust...largely because the push-pull zoom was like an accordian when it came to sucking/blowing air in & out. Dust NEVER showed up in an image. Never. Your reason for alarm in this case should be your images, rather than the specs you may see in side your lens. When you have an image problem, then you may wish to send it in. Until then, I wouldn't worry about it (though I understand the annoyance part). -Mark² SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson > > I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens > > is in like new condition except for dust inside the lens...and some [quoted text clipped - 11 lines] > have an image problem, then you may wish to send it in. Until then, I > wouldn't worry about it (though I understand the annoyance part). This is exactly what I was told by the largest photo rental outfit in my state when I went to rent this very lens, looked through it, and saw all the dust and asked whether they were planning on having it cleaned before I rented it (they had already told me that it had just come back that morning from another rental - I was scheduling the rental for a week later). And they were right. > My 100-400 always had a bit of dust...largely because the > push-pull zoom was like an accordian when it came to > sucking/blowing air in & out. [snip] Does a push-pull zoom suck in more air than a rotating-ring zoom? Either way, the volume of the lens is changing, which means that air is getting sucked in or blown out. SignatureRay (remove the Xs to reply) >> My 100-400 always had a bit of dust...largely because the >> push-pull zoom was like an accordian when it came to [quoted text clipped - 4 lines] >Either way, the volume of the lens is changing, which means that air is >getting sucked in or blown out. I think he's comparing the push/pull zoom of the 100-400 with the interior zoom mechanism of the 70-200 which doesn't exchange air with the outside when it zooms the lens elements internally.. jc Signature"The nice thing about a mare is you get to ride a lot of different horses without having to own that many." ~ Eileen Morgan of The Mare's Nest, PA >>> My 100-400 always had a bit of dust...largely because the >>> push-pull zoom was like an accordian when it came to [quoted text clipped - 8 lines] > interior zoom mechanism of the 70-200 which doesn't exchange air with > the outside when it zooms the lens elements internally.. That's also true, but here was my response to him...which proposes that there may be additional dust issues with a push-pull: "...in practice, I think it [a push-pull]may, simply because one is able to extend the lens with such speed and gusto on a push-pull that it can SUCK air, rather than merely transfer air...so it might actually pick up dust that is at rest on the outer lens surface in addition to floating dust. -I don't think that's the only factor though. -This lens also happens to change its length in a HUGE way. Most lenses don't DOUBLE in length, but this one comes pretty close." YMMV... SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson >> My 100-400 always had a bit of dust...largely because the >> push-pull zoom was like an accordian when it came to [quoted text clipped - 4 lines] > Either way, the volume of the lens is changing, which means that air > is getting sucked in or blown out. Not technically...necessarily. But in practice, I think it may, simply because one is able to extend the lens with such speed and gusto on a push-pull that it can SUCK air, rather than merely transfer air...so it might actually pick up dust that is at rest on the outer lens surface in addition to floating dust. -I don't think that's the only factor though. -This lens also happens to change its length in a HUGE way. Most lenses don't DOUBLE in length, but this one comes pretty close. SignatureImages (Plus Snaps & Grabs) by Mark² at: www.pbase.com/markuson >> Does a push-pull zoom suck in more air than a rotating-ring zoom? >> Either way, the volume of the lens is changing, which means that >> air is getting sucked in or blown out. > Not technically...necessarily. But in practice, I think it may, > simply because one is able to extend the lens with such speed and > gusto on a push-pull that it can SUCK air, rather than merely > transfer air...so it might actually pick up dust that is at rest > on the outer lens surface in addition to floating dust. I suppose the sliding action might also carry surface dust into the interior, independent of air movement. When you zoom out, part of the barrel that was outside is now inside, though I have no idea how easily dust could get from there to the lenses. Presumably there's some kind of sliding seal to minimize this. > -I don't think that's the only factor though. -This lens also > happens to change its length in a HUGE way. Most lenses don't > DOUBLE in length, but this one comes pretty close. I looked for a list of specs that gives the maximum length, but couldn't find anything. Is that published anywhere, or could an owner measure it and post it? Enquiring minds want to know. From pictures I've seen, it does look to be close to doubling. <http://www.mercadolibre.cl/jm/img?s=MLC&f=4620598_2236.jpg&v=P> SignatureRay (remove the Xs to reply) SNIP > I looked for a list of specs that gives the maximum length, but > couldn't find anything. Is that published anywhere, or could an owner [quoted text clipped - 5 lines] > Ray > (remove the Xs to reply) With the caps on and the hood off 8 1/4" to 11 3/8" >> I looked for a list of specs that gives the maximum length, but >> couldn't find anything. Is that published anywhere, or could an >> owner measure it and post it? Enquiring minds want to know. >> From pictures I've seen, it does look to be close to doubling. >> <http://www.mercadolibre.cl/jm/img?s=MLC&f=4620598_2236.jpg&v=P> > With the caps on and the hood off 8 1/4" to 11 3/8" Thanks. Not as big a change as I expected from the pictures. Canon specs the length as 7.4", so they probably measure from the mounting surface. And without the caps ;) SignatureRay (remove the Xs to reply) >I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens is in >like new condition except for dust inside the lens...and some large specks >that are troubleing. Is there any way I can get to thei inside of this lens >without screwing things up? If I need to send it out to have it cleaned, >who should it go to? I live in the far northern end of California. Unless you have real evidence that it is affecting your images, just leave it. Lenses are for looking with, not looking at! > I acquired a Canon 100-400 IS zoom lens for my Canon 20 D. The lens is in > like new condition except for dust inside the lens...and some large specks > that are troubleing. Is there any way I can get to thei inside of this lens > without screwing things up? If I need to send it out to have it cleaned, > who should it go to? I live in the far northern end of California. Unless you see the spots in pictures, don't worry about it. The lens is mechanically very complex (lots of little ball bearings!). If the dirt is really a problem in images, I would send it to Canon in So Calif and let them clean it. Phil |
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