4/24    Dear motd photo gurus:  I have a Canon EFS 17-85mm lens that's got a
        ca. 1cm, thin and shallow scratch in the front lens.  Can this be
        replaced or ground out, or do I need to buy a new lens if I want to
        get rid of it? -John
        \_ holy crap that a long psb response..  anyway short answer..
           small scratch on front lens not bad and usually not at all
           noticable. scratch on rear glass is bad. dont let it happen.
           i agree w/ psb tho, buy a cheap UV filter and leave it on 100%
           of the time. look on ebay. try to search for Hoya 67mm HMC UV
           and expect to pay ~$60 -shac
           \- i doubt you'll save that much money on ebay rather than
              bhphoto. i'd start with bhphoto to get a sense of the
              "standard price" and the primiums for various brands
              and see what your options are. in fact you might just
              call them on the phone and have them recommend a reasonable
              protection filter for your lens. of course if you are
              international that might change the calculations a bit. --psb
        \- Um if you have dirt/smudging on a lens, that's generally not
           too bad of a problem ... you can keep shooting in the field and
           you can get a shop to clean that, but if you actually have a
           scratch substantial enough to cause diffraction problems, i
           you can get a shop to clean that, but IF YOU ACTUALLY HAVE A
           SCRATCH SUBSTANTIAL ENOUGH TO CAUSE DIFFRACTION PROBLEMS, i
           think you may be hosed in terms of the resale value [that is a
           $500 lens, no?] since obviously that is the part of the lens people
           are going to care about the most ... and a scratch could potentially
           totally ruin a picture with an artifact rather than just cause a
           subtle amount of distortion. I've occasionally shot with my 52mm
           subtle amount of distortion. I've occasionally used my 52mm
           lenses without a skylight/uv filter but for my large front element
           lenses I keep some filter on them 100% of he time. [although
           somewhat ironically, the only filter i've cracked was a 52mm one,
           http://home.lbl.gov:8080/~psb/PSB_MISC/PSB_Nikon6.jpg but it saved
           a $350 lens]. it is possible the lens is in ok shape but i dont
           know how on the one hand you do full disclosure to the seller
           without totally killing the lens value. are you that chile fellow?
           if you wre in the BA area i'd suggest getting the opinion of the
           if you wre in the SFBA i'd suggest getting the opinion of the
           HORIZON ELECTRONICS people. if you havent done so already, buy a UV
           or skylight filter for all of your lenses. even the cheep ones...
           ... for the cheep lenses you can get the cheep $15
           filters. different people will give you different advice about how
           much to spend on a protective filter for a nice lens. ok tnx.
           for the cheep lenses you can get the cheep $15 filters. different
           people will give you different advice about how much to spend on a
           protective filter for a nice lens. ok tnx.
           protective filter for a nice lens. if you buy filter, either get
           them used in person or buy over the net. the markup on filters
           is often huge. ok tnx.
           \_ Thanks, good tips.  I don't think it's causing smudging (I
              thought it was resulting in some ugly blotches.)  As I don't
              intend to sell it anytime soon (great lens) it's not so much of
              an issue, I guess.  I've been using mainly a polarization filter,
              but I should probably get something protective for that.  -John
              \- You want to keep the UV/skylight filter on when you are
                 NOT using the CP. on a wide lens you may get vignetting
                 if you put two filters on [although "digital" lenses
                 may be more forgiving there]. the problem wont be
                 "smudging" but more of a flare-like problem or some
                 chromatic problem because of the scratch acting like a
                 diffraction grating. lenses,  especially like this one,
                 can take quite a bit of the kind of of dirtiness you
                 might think may cause a smudge on a picture. in fact
                 some people clean their lenses too much.
                 \_ I use microfiber towels I get from the optician where I
                    buy my shades--I have gotten quite a lot of smudging from
                    not-serious-looking dirt.  In fact, I thought the shadow
                    I asked about removing from large series of images in an
                    earlier post is something I thought stemmed from the
                    scratch on the lens.  I need to play with the UV filter;
                    I have found that the polarization filter lets me take
                    pictures with far nicer light, with effects that I haven't
                    managed just with camera settings (EOS 350D.)  -John
                    \- carry a blower/brush then. i'm not saying cleaning is
                       never necessary, just that a lot of people over clean
                       by rubbing. if you want to figure out if the "shadow"
                       is a "bug", i guess you are going to have to treat
                       this as a "debugging problem" ... maybe you can find
                       somebody else with that lens ... which should be pretty
                       common i think. the UV/skylight filter wont really do
                       that much for you ... there isnt really much to "play"
                       with. it is "lens insurance" ... to protect your $500
                       glass with $50 glass, rather than a functional filter
                       like your CP. i love my wildly expensive CP. yes, there
                       are definitely things you cannot do otherwise:
                    \_ circular polarizer!
                    \- you should get a blower brush and use that instead of
                       wiping mostly. sometimes wipe cleaning is needed but
                       a lot of people over do it. whether or not the scratch
                       is causing the shadow is a "debugging" problem you
                       probably will need to figure out by swapping the lens...
                       i'd think that would be a pretty common lens and should
                       be simple to analyze with a digital camera. there really
                       isnt much to "play with" with the UV filter ... it's
                       really $50 "lens insurance" for your $500 glass, not a
                       much of a functional component of your lens array.
                       i like CPs alot for use in the mountains ... you can
                       definitely get some dramatic exposures you cannot
                       otherwise although sometimes what you really need are
                       things like graded filters. this is a decent example of
                       very heavy pol:
           http://home.lbl.gov:8080/~psb/ANNAPURNA_01/AnnapurnaI-SWFace+ASG.jpg
           \_ Nice picture.  I need to wipe the lens a lot, it's a pretty
              dirty country.  And what sort of iso/WB/polarization do you use
              for those colors?  For example, GlacialStream-AnpSanctuary.jpg
              is a lot darker and more vibrant than the colors (esp. sky) I
              usually get.  -John
              \- all of the annapurna pix were either Fuji Velvia or
                 Kodak E-100 VS? [i havent taken a digital camera on a
                 serious mountain trip. used n90 and f4 and only shoot
                 slide film]. the big problem with mountain shots
                 is how to deal with snow on teh mnt but get detail of
                 the darker foreground ... e.g. by using graded filters,
                 but i think those are a little hard to use. the glacial-stream
                 picture i actually think is pretty boring. that's more
                 "documentary". i am not too fond of most of the digital
                 pictures i've taken.
        \_ it depends upon the scratch.  The scratch CAN BE cosmetic
           (in a realistic term).  If the scratch didn't really ruin your
           picture quality as far as you can tell, then, don't worry about it.
                                kngharv