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09-10-2009, 07:24 PM   #1
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SMC-M 80-200mm

I've got two different copies of the SMC-M 80-200mm zoom lens.
One, will focus on a distant moving object (usually a ship) at infinity throughout the zoom range, requiring no adjustment. The other requires adjustment at and close to 200mm to maintain focus.

For example, the first can be kept constantly at infinity, and all I have to do is zoom and take my shots. The second must be focused at certain zoom levels, and can only be kept at infinity on the long end for very distant objects. So, as the vessel gets closer, it gets out of focus on this lens, but not on the other. (i.e. I must focus at 200mm, but I can keep it at infinity at around 80mm.)


Could anyone tell me what the problem may be, and which is actually proper operation?

Thanks

09-11-2009, 01:17 PM   #2
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zoom lenses should keep their proper focus during zooming, otherwise they are called varifocal lenses.
There is an adjustment in the zoom lens to calibrate this, probably one of your lenses got out of the right calibration. This can happen with a serious shock.

George
09-12-2009, 06:01 PM   #3
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Original Poster
Do you know what it would take, or how much it would cost to fix the problem?
Thanks
09-12-2009, 11:34 PM   #4
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QuoteOriginally posted by Halco Quote
Do you know what it would take, or how much it would cost to fix the problem?
Thanks
In general yes, for this particular lens, I do not think I have done that before.
It is an adjustment done at the end of the lens assembly, by shifting all lens groups forward/backward over a small distance.
Usually on these push/pull lenses you can remove 3 screws on the barrel with the focal length engravings, and then shift that part forward.
Then three sets of two screws become visible, which define this distance in combination with a V shaped ring in the part below it.

For some lenses this distance is calibrated with different thickness metal rings, then you must do more and different disassembly.

If you want to do it yourself, get proper fitting and high quality screwdrivers !
Not the cheap stuff, they will only damage the lens.

If you do not feel comfortable in doing it yourself, I do not expect it to be an expensive repair.

George

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