ID zooms with no increased length

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drs@canby.com - 30 Oct 2004 05:00 GMT

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?

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Alan Browne - 30 Oct 2004 15:35 GMT

> 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.

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Mark M - 30 Oct 2004 21:24 GMT

> > Is there an easy way to identify zoom lenses that have all individual
> > lens elements contained inside so that when increasing the
[quoted text clipped - 6 lines]
>
> 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.

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Alan Browne - 31 Oct 2004 15:33 GMT

> "Alan Browne" <alan.browne@FreeLunchVideotron.ca> wrote in message
>>
[quoted text clipped - 4 lines]
> 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.

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-- rec.photo.equipment.35mm user resource:
-- http://www.aliasimages.com/rpe35mmur.htm
-- e-meil: there's no such thing as a FreeLunch.--

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brian - 31 Oct 2004 03:10 GMT

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

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drs@canby.com - 31 Oct 2004 17:05 GMT

>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
[quoted text clipped - 7 lines]
>
>Brian

That sounds like most new premium zooms have a moving front group so I
guess the next question is this: Regarding dust and moisture in harsh
conditions, is there any way to determine which lenses offer the most
protection?

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