Tom Pfeiffer wrote:
> ----- Original Message -----
> From: "F. Craig Callahan" <[EMAIL PROTECTED]>
> >
> > Different optical formula. The IS versions of the
> >super-teles (at least the 300/2.8L) are said
> > to be *more* sharp than the non-IS versions.
>
>
> Is this true? I had heard (no facts, just unsubstantiated opinions) that it
> was just the reverse.
Well, it is true that "it is said" that the IS version of the 300/4L is less
sharp than its predecessor, and as you note the Photodo tests would appear to
bear this out. In addition, both Canon and other sources claim the IS
super-teles outperform their predecessors. I'm pretty sure the sources I've seen
that make these claims are fairly reliable, but I can't remember what they were
(George Lepp probably, and Chasseur d'Images for sure). As for Photodo, whatever
the shortcomings of their system of testing, I think it serves as a useful
comparative index of lens quality. And if you look at the actual Photodo info
sheets instead of just the Grade summary page, you'll notice a few things: 1)
the IS version of the 300/4L has a lot more glass-to-air surfaces than the
non-IS (15 elements in 11 groups compared to 8 elements in 7 groups), and 2) the
MTF charts show that sharpness falls off toward the edges more quickly in the IS
version than in the earlier lens. Yet, despite the extra glass, the IS version
actually weighs less, which suggests the possibility of a less-robust internal
construction. Now before anyone gets all lathered up over this remark, let me
say that I'm as aware as anyone that this is not the only possible explanation,
but at least neither the "L" lens brochure from 1999 nor the current EF lens
brochure say anything about magnesium construction in the 300/4L IS, whereas the
latter specifically mentions magnesium in the adjacent description of the
300/2.8L IS. Note too that the MTF graphs in the "L" lens brochure (Pub.
CT2-1505-004) for the two 300/4L lenses, while not the easiest to interpret (at
least for me) would appear to support Photodo's results.
> Photodo isn't much help, it ranks the 300/4 at 4.3,
> well ahead of the 300/4IS at 3.4, and the 75-300 IS just below the non-IS
> version (3.2 vs 2.9),
The difference in lens performance isn't IS per se: the optical formula of the
300/4L IS is significantly different from that of the non-IS version. You can't
simply assume that an IS version will offer a lesser optical performance (or a
greater one) than a non-IS version. Aside from IS, what are the design
differences, if any, between the two versions of 75-300 (for example)?
Interestingly, the two versions of the 400/2.8L score almost identically on
Photodo's MTF tests, although the older version, which has fewer elements, shows
significantly less distortion, and the charts suggest it has better edge
performance.
> other pairs. I'm hoping to spend some "slush" funds on the 300/4 one of
> these days soon, do I need to wait another year and save for the IS 300/4
> instead?
IMO, it all depends on what you need. Personally, I would only hand-hold a 300mm
lens out of necessity, and since the only advantages that the IS version offers
are weight (by a small margin), the IS itself, and a shorter close-focus
distance, I would choose to save some money and go for the optically-superior
lens. But if you intend to use the lens hand-held most of the time, then it
might make sense to go with the IS version, since with the older model any
advantage in raw optical performance is likely to be negated by camera shake.
Just because *I* use 300mm lenses almost exclusively on a support of some kind
doesn't mean that *you* work that way, so you need to make your decision based
on your own shooting style. But all things being equal, I think the non-IS lens
is a better value at current prices.
fcc
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