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>Date: Sat, 03 Apr 1999 19:12:35 +0800
>From: Jed Wee <[EMAIL PROTECTED]
>
>Just to clarify one thing... the original poster, BC, was talking about
>a HALO of light... NOT light fall-off.
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Actually, I was talking about both, but the fact that there is the halo
intensifies the drop-off considerably. In fact, if the halo weren't there,
and the drop-off into the corners was continual and gradual through that
region, the light drop-off into the corners might fall into the
"acceptable" range.
>>>>>>>>>>>>
>Or, well, it might be light fall off in the middle and at the corners,
>but missing a middle band, if you think about it...
>>>>>>>>>>>>>>>>>>>>>>>>>>>
Let me describe it in more detail. I can do that accurately, as I had the
slide in the files at my desk, and I am looking at it as I write this. It
was shot on Fujichorme 50.
The inner circle of proper exposure is approximately 24mm across, or enough
to fit within the short dimension of the frame (top-to-bottom, looking at
it in "landscape" mode). The "halo" of slightly lighter exposure is a band
about 3-5mm thick around that, and of course the edges are somewhat
gradual. The drop-off into the corners is *very* sharply dilenated because
of the halo, and there is some continuation of the drop-off into the middle
of the sides of the frame. This turns what should be common corner
drop-off into more of a center-circle of lightness. As I said, the "halo"
heightens the effect.
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>Light fall-off definitely exists, but I challenge anyone to find a zoom
>lens that exhibits no light fall-off
>>>>>>>>>>>>>>>>>>>>>>>
No doubt, but the question is how much is acceptable and how it compares to
others. More on that later.
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<With regards to the lens itself... I was immensely worried on two
<counts: One because I own it, and two because me tests revealed none of
<this. Also, never heard of it before. For example, it's never surfaced
<on the list for the year or so I've been here, and not in the newsgroups
<for the last half a year or so (I'm a regular poster/reader in that
<time), and for example Ruether doesn't note anything about it.
<
<Strange thing is, someone concurred, so I panicked. And when I saw
<someone questioning the reliability of independent lens testers... I had
<to go dig up my chromes and negs. I've tested FOUR samples of this lens,
<two of them with collars and two earlier push-pull versions. And try as
<I might, I can't find a halo of light... perhaps if BC would enlighten
<us as to how obvious this halo is? 1/2 stop, 5 stops, or would we need a
<densitometer to pick it up, which I don't have and don't use to view my
<slides with anyway. Yes, 80-200 lens at 80mm and 200mm, shot at f2.8...
l<ight fall off I CLEARLY see. An angelic halo no.
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The halo is about a half-stop up from the center exposure. The effect
versus the center of the image is subtle, but again, under normal use, its
effect would be to make the corner drop-off especially pronounced.
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<I use newspaper plastered to a more
<or less uniformly lit wall (incident meter tells me variance of no more
<than 2/10 stop from left to right), and I can't see anything... Unless
<you're telling me my newspapers have a halo of darkness which I don't
<notice... and I've done these tests on new newspapers everytime... I've
<tested on Velvia, Elite Chrome 100, Pan F Plus...
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As has been pointed out by other people in this forum, the blue-sky test is
the definitive exposure evenness test for telephotos that is available to
the average photographer. In fact, it would be hard to devise a superior
one. It would be extremely difficult to get an artificially-lit field to
be as even. And what MUST be kept in mind is that the effect is most
pronounced at infinity focus, which is somewhat impractical to reproduce
artificially. (Note- I am aware that the lens will focus past infinity,
and I determined infinity focus by focusing on a distant object manually
and leaving the focusing ring in that position when I pointed it at the
sky.)
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<If I don't get a satisfactory answer, I figure I'll take a picture of
<the sky... sigh what a waste of Velvia, what? I don't believe I'll find
<anything personally, because while I might concede that I might have
<been careless and missed it, I've got to be blind not to see it if I'm
<looking for it if it's at all obvious enough to matter...
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Well, Jed, I don't see how using up one frame of film to get a definitive
answer on an important aspect of lens performance is so much of a waste.
It seems you and I both shoot newspapers to get a handle on sharpness, and
I certainly don't consider that a waste of film.
Keep in mind that it only shows up beyond 180mm at apertures near wide open
while focusing on subjects that are somewhat distant. Now, I was shooting
some fast news the other day--a fire happened in my neighborhood, and I
decided to grab the cameras and run-- and I shot at f4 near the long end.
The shot ran on the front page of the next edition of the local daily, and
looking at the image printed in the newspaper (as I am right now), the
fall-off is not noticable. WHY? Several reasons. One, it is a vertical
shot, and the peak of the roof of the house is top center, which puts the
edges of the roof right about where the halo happens on the upper part of
the frame. In this case the corner drop-off it actually helps, as the sky
is white, and of course over-exposed. The bottom part of the frame is a
jumble of burned debris, and the variations of dark objects would certainly
keep anyone from noticing a difference of exposure there. Also, the image
is cropped, which would further reduce the effect.
Yes, you are going to get corner and edge drop-off in most lenses, the
question is, how much is acceptable? As James McDonald pointed out, he
could see the problem quite clearly in the image of a city skyline
published in Nikon World. I use both the Nikon and the Pentax systems, and
I moved to Nikon becuase the Pentax professional support is very close to
nil, and there are gaping holes in the system. I got the Nikon lens
because the Pentax version was almost $600 more, and no one had it in
stock. Several months after I bought the Nikon I tested the Pentax
version, and the difference was noticable. Yes, there is some drop-off
into the corners, but the drop-off is much more gradual, you have to get
very deeper into the corners to see it, and there is no halo. My Nikon is
only worth about $650 on the used market now, and I can't afford the $1000
difference for the Pentax version. I use it mainly for fast news and some
stock, and since I am aware of its limitations, I feel I can use it fairly
well. I also have some primes that cover the high end of that range that
don't exhibit the drop-off. But I sure wish I didn't have to work around
it.
Here are the relevent points:
1. Yes, all zooms and even most primes will exhibit fall-offs into the
corners, at least. The question is; how much is acceptable? This answer
will vary from photographer and from shot to shot. But I can tell you
that when the test images first came out of the processor, for a moment I
thought there might be a processing problem. The halo and edge drop-off
certainly detract from the overall performance of this lens.
2. There is at least one similar zoom I know of in the marketplace made by
a competitive manufacturer that is in some important ways optically
superior to the Nikon (the corner sharpness at the shorter focal lengths is
not as high, other than that they are very close sharpness-wise: the light
fall-off at 200mm is not nearly as pronounced, starting further away from
the center of the frame and being more gradual--and there is no halo),
albeit at a 50 percent higher price. There may be more, I have not tested
them all.
3. If the performance is acceptable to you, then the lens falls within
your needs. As I said in the original post, if you can live with this kind
of performance, then buy it. Just don't buy it thinking that there isn't a
better-performing 80-200 f2.8 among the other mid-range manufacturers
(Nikon, Canon, Pentax, Minolta, Olympus, etc.).
4. From the prices in the ads I have seen, the Nikon 80-200 f2.8 is the
least expensive among camera manufacturer-made lenses of its type. If you
can live with the limitations--and if you have a choice--that may be a
reason to purchase it. Just remember that you get what you pay for.
5. The lens in question is built very tough. If I was shooting wars
again--something I haven't done in years--that would be a huge
consideration.
6. Notwithstanding the exposure evenness problems, the lens is quite
sharp.
And finally, I have this offer: If anyone wants to see the effect and
judge for themselves, I have some slightly expired Fuji 50 that I would be
happy to shoot up on the blue sky test for my fellow Nikon Discussion Group
denizens. Just send me a stamped, self-addressed envelope at Image
Excellence Communications, P.O. Box 912, Greenbelt, MD 20768, and as soon
as I get a clear enough blue sky, I'll shoot it and soup it and send it
off, one to a customer (unmounted). Anybody out there with this lens
should be able to replicate the test, if they can get a perfectly clear
blue sky. I would very much like to see samples from other versions of
this lens, as well. -BC-
