On Thu, 03 Sep 1998 13:37:36 GMT, pchefurka@plaintree.com (Paul Chefurka) wrote:
>On Thu, 3 Sep 1998 07:59:49 +0200, patrick@multiweb.nl (Patrick
>Hudepohl) wrote:
>>Neuman-Ruether (d_ruether@hotmail.com) wrote:

>>> It is one of Nikon's best (you may find my Nikkor evaluation
>>> list, on my web page under "I babble", interesting...;-),

>>Yes, interesting indeed. The AF-D gets a score of 4.3, whereas
>>the AIS gets an 4.8, a subtle difference of 0.5 point. Not quite
>>sure if that justifies a doubled prices for the AIS.

>The AIS has a lot going for it, mechanically and optically. It's
>built *much* better than the AF, and it has CRC which makes it *much*
>better close up. And it focusses to 0.2m - that looks to me like
>enough of a list to justify the higher price.
>
>Remember that no lens can be described by a single number.
>Let's try a thought experiment to see why this is so:
>
>Say you have a perfect lens, and gave it a "5.0". Then you have three
>other lenses, each of which has only one flaw, but the flaws were
>different. One has a bit of flare, one has some barrel distortion,
>and one has low resolution wide open. All these three lenses rate a
>"4.5" (one flaw costs half a point).
>
>If the "5.0" lens costs too much, how do you decide which of the "4.5"
>lenses is best for you? Not by looking at that single number, that's
>for sure. For someone who shoots a lot of "contre-jour" the first one
>is unacceptable, the other two are fine. For someone who shoots a lot
>of architecture the second one is unacceptable, the other two are
>fine. For someone who shoots a lot of available light, the third one
>is unacceptable and the other two are fine.
>
>But they all got a "4.5", so they must be fundamentally equal in
>quality, right? I think not.

You make good points (though the AF-D 28 does have CRC...;-).
I point out the inadequacy of a one-number rating system in
my Nikkor evaluation list, but it is better than nothing if
you know what is being evaluated by the rating. I base my
ratings mostly on wide stop (or, more particularly, the
widest reasonable stop at which to expect good performance
with a particular type of lens...) edge and corner sharpness.
Issues like flare and distortion are not considered in the
rating, but if they are unusual, they are noted. My list
makes assumptions (listed in the paragraphs that preceed the
list, and before each catagory) when asigning a rating
number, and if those assumptions are not met, that is noted
with the rating numbers in the list. (This is why I would
like to discourage the use of just the numbers...) For me,
the "without which, nothing" is sharpness (which means
reasonably good sharpness out to the corners). A low flare,
low-distortion lens that is not reasonably crisp everywhere
in the frame at a useful stop would be given a low score in
my list - and a lens that has high flare and considerable
distortion, but was very sharp, would be given a high score,
with the faults noted... I find it useful to evaluate
lenses by judging the most important characteristic only,
and then noting the exceptions to good performance in other
areas of lesser importance to me. Most lenses, no matter
how poor, are often fairly decent in the center at wide
stops, and OK in the corners by f16 - and they can be used
for most photography where f16 is practical, even if they
show high flare and distortion. What separates out the
really good lenses is how sharp they are at (relatively...)
wide stops. (BTW, I evaluate mostly Nikkors on my list,
and low distortion and flare are common characteristics
of most Nikkors...;-)