eeprete wrote:
Nice job playing both sides of the fence.
Are you talking to me? I'm playing both sides of the fence? And how is that exactly? I want to see this issue get resolved just like everyone else, Ed. Don't get it all confused. My comment was made in jest and wasn't meant to suggest that these guys making these claims don't know their ass from their elbow. I have acknowledged that there may in fact be an issue here, but also question whether or not it may be paranoia in some cases. And as far as I know this is the ONLY forum where this discussion taking place. And the guys reporting the problem here represent a fraction of the overall photogrpahic community world-wide. I might be wrong, but that's what I know. Time will tell if there is a large percentage of these lenses having problems, or if it's just a few pixel peepers noticing this. Let's wait for an official response from Canon, yes? Playing both sides of the fence indeed!
I've got very little time between this afternoon's shoot and tonight's party, so I don't really have time to respond to dcmiller in detail. However, it is pretty clear this thread has reached a new low and instead of going back over all the stuff I've presented for everyone's benefit and rehashing the same old debates, I'm simply going to bow out until I get my lens back from Canon (again).
I'm a new comer to this thread which Ď've been following with care fora while.
Despite the nuisance of dcmiller which I prefer to ignore, it's pretty interesting.
I received mine two days ago and you can imagine who many tests I've been running...
My first test in poor conditions, in my basement, under tungsten light, at ISO 800 etc... showed that my lense is affected by this weird backfocusing issue (not as badly as some of you though...).
I ran another set of tests in abundant natural lighting (let's say enough to allow 1/800 at ISO 100 full open). The results are much, much better.
It's still gradually backfocusing when stopped down, but never enough to get out of focus.
Just for what it's worth...
Got one from the recent batch at B&H, and it arrived on Friday. Here are a couple of photos at 1.2; despite the razor thin dof performance is great! I did a comparison with my old 1.4 and the results are also below. Make your own conclusions. =] I am happy, it will be a useful lens.
irieweasel wrote:
Got one from the recent batch at B&H, and it arrived on Friday. Here are a couple of photos at 1.2; despite the razor thin dof performance is great! I did a comparison with my old 1.4 and the results are also below. Make your own conclusions. =] I am happy, it will be a useful lens.
Looks great to me with the exception of f/4 and f/5.6, where it appears the f/1.4 has better sharpness. Did focus remain constant for all tests?
jcbenner said: Looks great to me with the exception of f/4 and f/5.6, where it appears the f/1.4 has better sharpness.
To be more precise, at f/5.6 50 f/1.4 has MUCH better sharpness but I would attribute this to some focusing mistakes. One think is certain, even this test confirms that the f/1.2 lens is not better than the old (cheap) one for f > 2.8.
mfurman wrote:
To be more precise, at f/5.6 50 f/1.4 has MUCH better sharpness but I would attribute this to some focusing mistakes. One think is certain, even this test confirms that the f/1.2 lens is not better than the old (cheap) one for f > 2.8.
Actually, I was thinking his test indicates that his lens may be misfocusing like some of us have been seeing. The test also echoes William Castleman's test results. The lens reaches its maximum sharpness at f/2, then it drops off at f/2.8 and doesn't really regain sharpness until the DoF is deep enough to compensate for the misfocusing around f/8.
I've said it once, and I'll say it again... doing sharpness tests with this lens without having some way to judge focus accuracy is going to be a really incomplete test at this point.
Sam Bennett wrote:
Actually, I was thinking his test indicates that his lens may be misfocusing like some of us have been seeing. The test also echoes William Castleman's test results. The lens reaches its maximum sharpness at f/2, then it drops off at f/2.8 and doesn't really regain sharpness until the DoF is deep enough to compensate for the misfocusing around f/8.
I've said it once, and I'll say it again... doing sharpness tests with this lens without having some way to judge focus accuracy is going to be a really incomplete test at this point.
I agree completely with what Sam and Roy see here. It is definitely a focusing issue. Mine is impressively sharp at f/2, but it is significantly sharper still at f/2.8.
All photos were on a tripod w/ mirror lockup. I haven't completed forward / back-focus testing, but could try to include those tests at some point -- it could definitely be the case.
In general, I plan to shoot the lens most at the extreme < f/2.8, and for that it will suit my purposes perfectly. =] I am building a gallery on Flickr, PM me if you're interested in seeing more shots.
I've set up a Jackson focus chart, and run a series of tests with three bodies, the 50/1.2L, 50/1.4, and some other lenses for comparison.
The most interesting new finding, I think, came from focusing the L only once (with aperture set wide open),
and shooting the series at all fractional f/stops through f/4:
The lens backfocuses slightly when wide open - call it ~6mm at a focused distance of ~75cm.
As the lens is stopped down (without refocusing), the plane of sharpest focus very smoothly and gradually
shifts to the rear, settling at what I'd estimate at 12mm backfocus at f/3.5 and beyond. After that it's harder
to determine the exact focal plane, and it doesn't matter anyway.
This seems to demonstrate that something like spherical aberration is causing focus shift with stopping down.
It also fits with the gradual increase in acutance when stopping down. In "more typical" use,
say portraits from a meter or further, fudge factors seem to have hidden some of this from me.
For example, the very closest eyelashes may be chosen as the focus point, resulting in the iris falling in the region of
sharpest focus. Or, a wisp of hair that's closer than the eyes might "capture" the focus, which technically is a
mistake but can lead to an effective result of perfect eyes.
If this sounds like making excuses for a defective lens, it is!
I don't want it to behave this way, but I'm not sure if sending it to Canon service would likely resolve the problem at this stage.
It seems to me that if a bit of focus shift is inherent in the optical design (and it would probably be
greater for close focusing distances than far), then a firmware fix could make a difference.
Also, even the tiny amount of backfocusing that I've measured is highly undesirable when we add focus shift in the same direction.
I've not been one of the major complainers about this lens, but I have to add myself to the negative side
of the list at this point. Perhaps Canon should recall the lenses when they work out the solution.
In the meantime, I plan to keep using it, armed with knowledge of where it requires compensation.
Sam Bennett wrote:
So you're saying the 50/1.4 didn't behave similarly when you did the same thing?
That's correct. The 50/1.4 very slightly front-focused, but showed no focus shift at all when stopped down.
I observed slight variations in back-focusing with the 50L on different bodies. It was greater on my 1Ds than on the 1D or 1DMk2. The 1Ds seems to be slightly back-focusing with all my primes (or those I've tested), so it would seem the body is due for calibration. The other two bodies very nearly nailed the focus with the 50/1.4, and definitely hit the mark with some other primes.
