Good Lens/Bad Lens?

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the_niner_nation - 29 Jun 2007 18:18 GMT

I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my
canon 400d and read a lot of favourable reviews.
A lot of the reviews, however are very excited about having a 'good copy' of
this lens.

As a newbie, i am confused...arn't ** all** these lenses made to the exact
same specification and manufacturing processes?

And how can you tell a 'good' copy' of this lens from a 'bad copy' ?
Just how much *worse* can a bad copy can be from a 'good copy' ?
And again, I am staggered that there are discrepencies that are pretty
important on somrthing I believed was manufactured in a mass production
system..it's not like buying a hand made silk suite etc.
I am thinking of buying this online, what sort of test can i do with this
lens to ensure it's a 'good copy' and can I legally return it to the seller
if it turns out to be a 'bad copy'?

Thanks in advance!

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Jim - 29 Jun 2007 19:00 GMT

>I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my
>canon 400d and read a lot of favourable reviews.
[quoted text clipped - 3 lines]
> As a newbie, i am confused...arn't ** all** these lenses made to the exact
> same specification and manufacturing processes?

Yes, but also there is a tolerance on all dimensions and all glass. So,
there will be a
difference between lenses. As none of the manufacturers tell us how close
their lenses
come to the specifications, there is no way for us to judge how well a
particular lens
will perform without actually using it.

Jim

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Tony Hwang - 29 Jun 2007 19:25 GMT

> I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my
> canon 400d and read a lot of favourable reviews.
[quoted text clipped - 14 lines]
>
> Thanks in advance!

Hi,
Copying 100% is not a hard thing to do but legal matters.

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Frank - 29 Jun 2007 19:35 GMT

I'm skeptical to be honest. I have never had a problem with Canon lenses,
therefore I wonder if maybe it is operator error.

I do remember reading something recently though (regarding back focus if I
remember correctly) that says that lenses have a tolerance for 5 for
example, so it could be anywhere from -5 to +5. The bodies also have a
similar tolerance. Therefore, it could be possible that if the body was at
one end of the specification tolerance, and the lens was the other, then
even both are within spec, they could not be working optimally.

I can't find the article.

>I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my
>canon 400d and read a lot of favourable reviews.
[quoted text clipped - 14 lines]
>
> Thanks in advance!

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Eatmorepies - 29 Jun 2007 21:51 GMT

>I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my
>canon 400d and read a lot of favourable reviews.
[quoted text clipped - 6 lines]
> And how can you tell a 'good' copy' of this lens from a 'bad copy' ?
> Just how much *worse* can a bad copy can be from a 'good copy' ?

Hello again

It's true that manufacturing tolerances will produce variation in
lenses/bodies. Modern manufacturing techniques make those variations quite
small.

Canon sell L lenses to the pros. Canon can't afford to have poor build
quality on L lenses and will not be supplying seconds to eBay sellers. Look
at the problems they are facing with the current MK III - they have to have
their pro equipment up to scratch or lose sales.

John

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David Ruether - 29 Jun 2007 22:06 GMT

"the_niner_nation" <the_niner_nation@sf49ers.com> wrote in message news:4685326b$0$16315$88260bb3@free.teranews.com...

>I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my canon 400d and read a lot of favourable reviews.
> A lot of the reviews, however are very excited about having a 'good copy' of this lens.
>
> As a newbie, i am confused...arn't ** all** these lenses made to the exact same specification and manufacturing processes?

In theory, yes - but it is my impression that the manufacturers
in practice may check relatively few samples, mostly early in
the production runs - and some lens designs are more difficult
than others to get right consistently. Even with producers like
Nikon, that has a generally good reputation both for high image
quality in the lenses across its line, and for good sample-to-sample
consistency, small variations are common - and there is the very
occasional "dud" (for more, see my extensive lens comparisons,
including multiple samples of the same lens, at:
www.donferrario.com/ruether/slemn.html ).

> And how can you tell a 'good' copy' of this lens from a 'bad copy' ?

I test using detailed and familiar infinity-distance targets to
establish that all four corners are equally sharp (or possibly
unsharp at wide stops...;-), as are opposite sides of the frame
(with all camera controls locked down) at the widest stop, f5.6,
and f11. There is more to it than this, but this can get you
started - but just don't become preoccupied with it(!). For
digital, adding newspaper targets can be useful if you are not
shooting too close, since this can show asymmetrical CA problems.
Have reasonable expectations for the performance of the tested lens
(which should be very high for the lens you mentioned - it should
check out as quite sharp in all corners and edges wide open if
properly focused and the sample is good).

> Just how much *worse* can a bad copy can be from a 'good copy' ?

With some lenses, very much worse. For instance, many people
like the Nikkor 35-200mm f3.5-4.5 MF, but two samples I had
were very soft. Nikon's 35-105mm f3.5-4.5 MF also varied,
but not quite so much (from so-so to superb) - but these were
the only two Nikkors I found much sample variation with. In other
brands, I have seen many more...

> And again, I am staggered that there are discrepencies that are pretty important on somrthing I believed was manufactured in a
> mass production system..it's not like buying a hand made silk suite etc.

This is why I ALWAYS recommend that new gear be checked
IMMEDIATELY! I'm amazed when pro acquaintances buy gear,
don't bother to check it out, then later discover the problems when
it is too late for an exchange/refund. I've found that warranties on
lenses are nearly useless - repair people often cannot correct lens
manufacturing faults (just possibly the damage from accidents).

> I am thinking of buying this online, what sort of test can i do with this lens to ensure it's a 'good copy' and can I legally
> return it to the seller if it turns out to be a 'bad copy'?

See above - but establish in advance the seller's return/exchange
policy. (BTW, I like dealing with the no-nonsense people at
B&H Photo (www.bhphotovideo.com). Just don't expect them to
hold your hand...;-)

Signature

David Ruether
d_ruether@hotmail.com
http://www.donferrario.com/ruether

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Chuck Olson - 29 Jun 2007 23:55 GMT

> I am thinking of splashing out on the Canon 70-200 mm f4 USM L lens for my
> canon 400d and read a lot of favourable reviews.
[quoted text clipped - 14 lines]
>
> Thanks in advance!

Others have addressed the lens testing and production tolerance issues of
your long lens. Going to L-Class, I feel, is the best you can do to minimize
the likelihood your lens will not perform as you want it to. Even more
important than getting the L-class would be Image Stabilization. When You
buy a lens that has excellent sharpness, you need every trick you can muster
to make sure that its great sharpness will be present in your final images.
The IS, IMHO is a must-have for any long lens. The sharper the lens, the
more important is Image Stabilization.

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