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#1
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ID zooms with no increased length
Is there an easy way to identify zoom lenses that have all individual
lens elements contained inside so that when increasing the magnification the front element doesn't extend the total length of the lens? Is there a name for that design? And wouldn't such a lens be more water- and dust-resistant than the ones that have extending barrels? Or am I missing something? |
#3
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"Alan Browne" wrote in message . .. wrote: Is there an easy way to identify zoom lenses that have all individual lens elements contained inside so that when increasing the magnification the front element doesn't extend the total length of the lens? Is there a name for that design? And wouldn't such a lens be more water- and dust-resistant than the ones that have extending barrels? Or am I missing something? Not sure about the name ... just that they're nice to have. They will 'breathe' less, but they do breathe just the same. But wouldn't they "breathe" predominantly their internally contained air--recirculating it, rather than pulling in outside air which necessarily happens with those that externally extend? I would think that INternal "extension" would create far fewer dust problems. |
#4
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wrote in message . ..
Is there an easy way to identify zoom lenses that have all individual lens elements contained inside so that when increasing the magnification the front element doesn't extend the total length of the lens? Is there a name for that design? And wouldn't such a lens be more water- and dust-resistant than the ones that have extending barrels? Or am I missing something? I would call such zooms "old fashioned" or "classic", since that's the way they were almost universally designed in the 1950's through the early 1980's. Not that old-fashioned is bad in this case, mind you. A few longer zooms are still made that way, mainly for reasons of mechanical stability. Such designs are mechanically simple (relatively speaking), and they naturally tend to have a constant f/# through the zoom range. Allowing the front group to move during zooming is typically done to help increase the field of view at the wide end, make the system more compact, or both. Brian www.caldwellphotographic.com |
#5
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Mark M wrote:
"Alan Browne" wrote in message They will 'breathe' less, but they do breathe just the same. But wouldn't they "breathe" predominantly their internally contained air--recirculating it, rather than pulling in outside air which necessarily happens with those that externally extend? I would think that INternal "extension" would create far fewer dust problems. Yes, it is betterm which is why I said "They will 'breathe' less" but as they are not sealed (not even remotely close), air will move in and out and will carry dust and worse in and out. As pressure changes (weather, riding in the car up and down hills, the odd air trip), wind, etc. will cause air to move. Cherrs, Alan. -- -- rec.photo.equipment.35mm user resource: -- http://www.aliasimages.com/rpe35mmur.htm -- e-meil: there's no such thing as a FreeLunch.-- |
#6
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