Corner sharpness: Four Thirds vs 35mm (bandwidth warning)

Started Oct 27, 2007 | Discussions
Ominous Veteran Member • Posts: 4,304
Re: FF corner test using my primes

Amin Sabet wrote:

Ominous wrote:

I lack any wider prime lenses, plan on adding a 35 and 24 before too
long (sold a 24 a while back and miss having a wide prime). I'll
have to try my 16-35, but I need to find a target that is large
enough, flat enough, and that I can light evenly, to test.

Yes, my normal and tele lenses have always had sharp corners when
stopped down on the 5D. The most common knock on the Canon 35mm
system is the lack of sharp corners on wide angle lenses. They
designed the 16-35 II and 14 II in large part to beat this rap. They
have in part succeeded. Some nice work evaluating wide angle lenses
for the Canon 35mm system has been done here ->
http://www.16-9.net/lens_tests/ . You may have seen it. If not,
check it out. You'll be happy to see that Mark used a tripod for
each test ;).

As for your future testing of wide primes, I'm personally not so
interested in seeing flat near targets. Many lenses behave
differently on close targets than far ones, and for this application,
it's generally the far ones that count. Of course that's just my
preference.

But why the fascination with corner sharpness?

For landscapes...often 50% of the corners is nothing but sky.

If you are shooting people....I would hope you are not putting someones face in the corner....talk about distortions!

If I'm shooting wide open...the corners are going to be out of focus in nearly any shot....if I'm shooting stopped down...I don't seem to have a problem keeping the corners sharp enough for anything I have printed.

My largest is only 20x24, but I have some panos that are several feet long, and don't have problems with the corners of them.
--
http://www.pbase.com/ewhalen

Ominous Veteran Member • Posts: 4,304
it wouldn't be as wide though.

You could simply crop the 5D shot to archive the same effect.

-- hide signature --
Danny Yee Senior Member • Posts: 1,276
but hardly wide angle

I think the original poster is interested in wide angle performance.

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Amin Sabet
OP Amin Sabet Veteran Member • Posts: 6,763
Re: Effective f stops on 4/3rds

fldspringer wrote:

This DOF equiv thing is nothing of any value to my photography.
Seems as no one outside of 35mm FF players seem to give it a second
thought.

That's not true. Do a search over at Photo dot net. Photographers have always cared about what f-stop is needed to get a certain depth of field, which is very much dependent on format size. There wouldn't have been an f/64 club for 35mm photography, right? The cultural imperialism and frequently misleading wording (eg calling fast lenses "effectively slow") are the new parts of a topic which has been of practical interest for decades.

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OP Amin Sabet Veteran Member • Posts: 6,763
I really wish Charles hadn't opened that can of worms.

I suppose it was inevitable. This is why I almost didn't start this thread. Bleh.

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Stu 5 Veteran Member • Posts: 3,277
Re: The test is OK (obviously)

pidera wrote:

If anything, I would like to see more of these tests. Even without
tripod. The results are indeed of more interest to people who (like
me) often do handheld shooting in not so good available light. Thats
when you have to do the shake - noise - DOF trade-offs.

You cannot test any lens handheld. What if one shot suffers from more camera shake than the other? Part of my photographic training was to test lenses and the method used here would have been laughed at. It is completely pointless but worse than that there is a real danger it will give people the wrong impression of a lenses performance.

YellowBullet Senior Member • Posts: 1,374
Re: Corner sharpness: Four Thirds vs 35mm (bandwidth warning)

Without tesing them at the same aperture setting the test is a
complete waste of time.

Couldn't disagree more. Testing them at the same f-stop would be a complete waste of time, since these are two completely different systems. DOF would be different, noise or shutter speed would be different.

I think Amin did a great job here. 2 stops smaller aperture for the FF system, 2 stops higher ISO for the FF system is the only way to compare equivalent setups.

Lens choice should perhaps have been different though. Tamron 28-75 2.8 would be my choice for the Canon system.

fldspringer Senior Member • Posts: 1,427
Re: Effective f stops on 4/3rds

Amin Sabet wrote:

fldspringer wrote:

This DOF equiv thing is nothing of any value to my photography.
Seems as no one outside of 35mm FF players seem to give it a second
thought.

That's not true. Do a search over at Photo dot net. Photographers
have always cared about what f-stop is needed to get a certain depth
of field, which is very much dependent on format size. There
wouldn't have been an f/64 club for 35mm photography, right? The
cultural imperialism and frequently misleading wording (eg calling
fast lenses "effectively slow") are the new parts of a topic which
has been of practical interest for decades.

I believe DOF has always been important. Its important to know for what system you happen to be using. You get no argument from me there.

The only place that DOF Equiv would have is if you had DOF charts for a different format and need a conversion.

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joe mama Forum Pro • Posts: 12,623
No need to be careful -- I'll accept the results.

Alway keep in mind that those tests are on a 1.6 crop sensor. The
tester included on the resolution section:

"As hinted above the EF 24-85mm f/3.5-4.5 USM received some rather
mediocre reviews during the mid ´90s. However, all these reviews were
based on full frame analysis. When looking at the original Canon MTF
figures the lens is very good except at the borders. On APS-C DSLRs
the borders reside way beyond the cropping factor and this also shows
up in the Imatest measurements. On the EOS 350D the lens is capable
to deliver a very good to even excellent center performance combined
with marginally worse borders. Very impressive and basically as good
as the pro-grade EF 24-70mm f/2.8 USM L (again: just on APS-C DSLRs).

It would be surprising to me to find that the 24-85 / 3.5-4.5 performed better than the 28 / 2.8 in the "corners" of 1.6x but worse in the corners of 35mm FF. I can't think of any reason why the prime should be sharper in the center, softer in the mid (corners of 1.6x), and then sharper in the edges again. I know of no lens that exhibits such behavior.

In any event, I would certainly wecome a test of zoom vs zoom: the 14-42 on 4/3 vs the 24-85 on FF. I think that's an ideal comparison.

Remember, I have no agenda except the facts. If the facts invalidate my theory, then I will change the theory to fit the facts. However, as I see it, this test is exactly in line with what I would have predicted. No surprises to me.

So much thanks to Amin for an excellent comparison. I would welcome further comparisons of this sort.

Amin Sabet
OP Amin Sabet Veteran Member • Posts: 6,763
Re: FF corner test using my primes

Ominous wrote:

But why the fascination with corner sharpness?

I have no fascination with corner sharpness. In fact, I don't give a damn about sharpness in the extreme corners. I just got sick of reading discussion over 35mm vs Four Thirds system corner sharpness with no examples, so I posted an example.

As for why some people care so much about corner sharpness, there were a couple threads on this in the Canon SLR Lens forum. Those with that obsession, more prevalent amongst landscapers, start to notice a difference in sharpness based on zones of distance from the center, analogous to what we see in MTFs. People see a critically sharp center surrounded by a zone which is disappointing by comparison, followed by the smearing in the extreme corners. Really expensive lenses start to disappoint, and really really expensive lenses become "necessities." I'm happily oblivious to that particular obsession.

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joe mama Forum Pro • Posts: 12,623
Yes, f / 1.4 is f / 1.4, and f / 2.8 is f / 2.8...

Ah jeez the whole f1.4 is really f2.8... Repeat after me... f1.4 is
always f1.4 the exposure will be the same no matter what system
whether 4:3 or 30x40 sheet film. The only difference is a 35mm lens
will expose 4x the area of a 4:3 sensor and will have less noise as a
result but otherwise the images will be the SAME and shooting at low
iso when there really isn't any noise at all the images will be
pretty much the same too.

...but the DOFs are not the same. If you're comparing corners, wouldn't you want to compare at the same DOF, rather than the same f-ratio? I mean, sharpness aside, just the fact that at f / 5.6 the corners would be further from the plane of ciritical focus would already make them soft.

Why compare corners at different DOFs?

pidera Contributing Member • Posts: 926
Chromatic Aberration

CA is something that worries me more than sharpness as it looks weird and is not at all that easy to correct. That's why I'm interested in the tests, particularly UWA. Rgds Pieter

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Amin Sabet
OP Amin Sabet Veteran Member • Posts: 6,763
Something along those lines is possible.

I wonder what kind of extreme corners the 16-35L II gives at 17.5mm and f/8 on a 40D.

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fldspringer Senior Member • Posts: 1,427
Re: No need to be careful -- I'll accept the results.

joe mama wrote:

Alway keep in mind that those tests are on a 1.6 crop sensor. The
tester included on the resolution section:

"As hinted above the EF 24-85mm f/3.5-4.5 USM received some rather
mediocre reviews during the mid ´90s. However, all these reviews were
based on full frame analysis. When looking at the original Canon MTF
figures the lens is very good except at the borders. On APS-C DSLRs
the borders reside way beyond the cropping factor and this also shows
up in the Imatest measurements. On the EOS 350D the lens is capable
to deliver a very good to even excellent center performance combined
with marginally worse borders. Very impressive and basically as good
as the pro-grade EF 24-70mm f/2.8 USM L (again: just on APS-C DSLRs).

It would be surprising to me to find that the 24-85 / 3.5-4.5
performed better than the 28 / 2.8 in the "corners" of 1.6x but worse
in the corners of 35mm FF. I can't think of any reason why the prime
should be sharper in the center, softer in the mid (corners of 1.6x),
and then sharper in the edges again. I know of no lens that exhibits
such behavior.

Such would be the behavior if a lens cast an image circle that was marginal for the format. When I read the paragraph, that's what came to mind.

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pidera Contributing Member • Posts: 926
Re: The test is OK (obviously)

I understand your point but this is not a lens test but a system (body + lens) test, and if you wish a user + body + lens test. It's all clear in the OP really so I wouldn't worry to much about people being mislead. These kind of comparisons are really quite rare and are not at all without interest. Rgds, Pieter

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fldspringer Senior Member • Posts: 1,427
Re: Something along those lines is possible.

Amin Sabet wrote:

I wonder what kind of extreme corners the 16-35L II gives at 17.5mm
and f/8 on a 40D.

It is an interesting lens. Its built for wide open performance at wide angle. Its ment to overcome the 35mm FF issues in that area. They have seemingly succeeded. There is a test/writeup at:

http://www.slrgear.com/reviews/showproduct.php/product/1082/cat/11

You can click on the full frame tab to get a wonderful plot. Click on that and you can adjust f-stop. There is a HUGE surprise in stopping down the first stop at when it at its widest setting in the crop camera.

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Amin Sabet
OP Amin Sabet Veteran Member • Posts: 6,763
Re: No need to be careful -- I'll accept the results.

joe mama wrote:

I can't think of any reason why the prime
should be sharper in the center, softer in the mid (corners of 1.6x),
and then sharper in the edges again. I know of no lens that exhibits
such behavior.

Do you know a lens that has it's best center sharpness wide open and gets worse stopped down one stop? PZ says their 28/2.8 does this. Also, look at the MTFs from Canon. 24-85 at 24mm takes a huge hit at the edges.

28/1.8 does the double dip - gets worse moving out from the center, then better again a little further out before taking the big dive at the edge:

28/2.8 does a similar double dip though less pronounced. Based on MTF, it would be expected to have the best f/8 corners of the three.

At f/11, my 28/2.8 had better extreme corners than my 24-105L. Here's someone else's comparison against 13 other lenses at 28mm tested on a 5D -> http://www.shiftlenses.com/Shop/Application/OwnWebPage.php?Id=17

In any event, I would certainly wecome a test of zoom vs zoom: the
14-42 on 4/3 vs the 24-85 on FF. I think that's an ideal
comparison.

I think an even more ideal comparison would be the 14-42 on 4/3 vs 28-105 on 35mm or better yet, 28-90 II on 35mm.

Remember, I have no agenda except the facts. If the facts invalidate
my theory, then I will change the theory to fit the facts. However,
as I see it, this test is exactly in line with what I would have
predicted. No surprises to me.

Do you agree that there is an appreciable sudden dropoff in the 5D system image extreme corners relative to the rest of that photo whereas the E-410 system shows worse global quality without the same degree of dropoff in the corners relative to the rest of the photo? I thought that your predictions were at odds with that outcome.

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joe mama Forum Pro • Posts: 12,623
Re: No need to be careful -- I'll accept the results.

It would be surprising to me to find that the 24-85 / 3.5-4.5
performed better than the 28 / 2.8 in the "corners" of 1.6x but worse
in the corners of 35mm FF. I can't think of any reason why the prime
should be sharper in the center, softer in the mid (corners of 1.6x),
and then sharper in the edges again. I know of no lens that exhibits
such behavior.

Such would be the behavior if a lens cast an image circle that was
marginal for the format. When I read the paragraph, that's what came
to mind.

I'm afraid I don't understand. Are you saying that it's possibly that the 28 / 2.8 might have a much larger image circle than the 24-85 / 3.5-4.5? That would be surprising for sure. I guess it could be possible, but, it doesn't matter regardless.

I don't cherry pick examples between formats. If the 24-85 is at a disadvantage, so be it, let the pics speak for themselves. Of course, if the 24-85 did suck, I would suggest that we might not compare the Tamron 28-75 / 2.8 instead (basically the same range and price). But I wouldn't discount the 24-85 test, either.

My agenda, as always, is the facts. By "facts" I mean comparison pics like Amin has so excellently done. The more of these we have, the more people can make choices for themselves, rather than merely having to take someone else's word for it.

For example, when someone says "soft corners", what, exactly, do they mean? Well, just show the pics. Now you know, right? No more of this "he said, she said" BS.

Amin Sabet
OP Amin Sabet Veteran Member • Posts: 6,763
Re: Corner sharpness: Four Thirds vs 35mm (bandwidth warning)

YellowBullet wrote:

I think Amin did a great job here.

Thanks.

Lens choice should perhaps have been different though. Tamron 28-75
2.8 would be my choice for the Canon system.

Extreme corner sharpness at 28mm is a known weakness for the Tamron 28-75 versus the 24-70L or 28-70L, is it not? In the following comparison, the 28/2.8 soundly beat the Tamron in border sharpness without even looking at the extreme corners -> http://www.shiftlenses.com/Shop/Application/OwnWebPage.php?Id=17

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Amin Sabet
OP Amin Sabet Veteran Member • Posts: 6,763
Re: No need to be careful -- I'll accept the results.

joe mama wrote:

I don't cherry pick examples between formats. If the 24-85 is at a
disadvantage, so be it, let the pics speak for themselves. Of
course, if the 24-85 did suck, I would suggest that we might not
compare the Tamron 28-75 / 2.8 instead (basically the same range and
price). But I wouldn't discount the 24-85 test, either.

If the Oly lens sucked in the corners, would you suggest an alternative or just add it to your essay? That's a rhetorical question, as I'm pretty confident I know the real answer. Incidentally the Tamron is not strong at 28mm in the extreme corners. IIRC you have a test gallery with the Tamron, so I suspect you can verify this.

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