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Old Oct 24, 2010, 1:12 PM   #61
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But the end result is a sharper photo, given you a end result of a in focus photo.

And when we are talking about the sig, they sometime completely miss focus, not just that little oof that a editing program can find a work around.
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Old Oct 24, 2010, 1:20 PM   #62
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But the end result is a sharper photo, given you a end result of a in focus photo.

And when we are talking about the sig, they sometime completely miss focus, not just that little oof that a editing program can find a work around.
TacV and Shoturtle -- thanks for following up, for the photo samples, and for the great discussion. Peripatetic, any comment? NHL?

What do you think about the 1.2? I have never -- before Peripatetic's comment -- heard that it was hard to focus, much less "insanely" so.

As regards the Sigma, it has FTMF, right? So maybe that's how to adjust from wacky AF. The focus-shift issue (especially when stopped down) seems more pernicious.
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Old Oct 24, 2010, 1:28 PM   #63
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The "Focus Shift" problem is that the camera focuses with the lens at its maximum aperture, but when the exposure is made with the lens stopped down a little (such that the depth of field is still quite shallow) things that were in focus aren't any longer, and things that weren't in focus suddenly are. If you'll always shoot with the aperture wide open, or with the aperture small enough to give a large enough depth of field to include the object(s) you originally focused on, then "Focus Shift" isn't a problem. You just need to recognize it when it rears its ugly head.

And if you want to try fixing images in post processing, while I don't endorse the overuse of "sharpening", you may be comfortable with the results, whether the source of the problem is "softness" or "oof".
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Old Oct 24, 2010, 2:17 PM   #64
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The "Focus Shift" problem is that the camera focuses with the lens at its maximum aperture, but when the exposure is made with the lens stopped down a little (such that the depth of field is still quite shallow) things that were in focus aren't any longer, and things that weren't in focus suddenly are. If you'll always shoot with the aperture wide open, or with the aperture small enough to give a large enough depth of field to include the object(s) you originally focused on, then "Focus Shift" isn't a problem. You just need to recognize it when it rears its ugly head.
So, first, does that mean there is no problem with focus shift where you set the aperture before auto-focusing? For example, if I am in AV mode and stop down from 1.4 to 1.8, then auto-focus, I will see no "focus-shift" problem? (My understanding: There is no focus-shift problem when the camera does not change aperture after autofocusing.)

Second, am I correct that this is different from the spherical aberrations photozone suggests are apparent when the Sigma 1.4 is stopped down? (My understanding: The Sigma is known to have minor spherical aberrations when stopped down.)

Third, does the Sigma 1.4 have trouble auto-focusing -- i.e., does it "hunt" more than the Canon lenses -- and does it auto-focus less well? (My understanding: Yes. The Canon lenses have quicker and better AF.)

If my understanding on all three fronts is correct, my basic question is this: How is the performance of the Sigma 50mm 1.4 at f/1.4 compared with the Canon 50mm 1.2 at f/1.4?

Thanks for your patience with my amateurish questions. I'm learning so much from you -- all of you. This is much appreciated.
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Old Oct 24, 2010, 3:07 PM   #65
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So, first, does that mean there is no problem with focus shift where you set the aperture before auto-focusing? For example, if I am in AV mode and stop down from 1.4 to 1.8, then auto-focus, I will see no "focus-shift" problem? (My understanding: There is no focus-shift problem when the camera does not change aperture after autofocusing.)
dSLRs always focus with the aperture wide open. When you select a smaller aperture, that is only for when the exposure is made, not for when the camera focuses (which happens continuoulsy until the exposure is made.) "Focus Shift" is when the focus distance changes when the aperture closes during the exposure. Focus Shift is caused by spherical aberration.

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Second, am I correct that this is different from the spherical aberrations photozone suggests are apparent when the Sigma 1.4 is stopped down? (My understanding: The Sigma is known to have minor spherical aberrations when stopped down.)
Yes, the Sigma 50/1.4 suffers from spherical aberration, but so does the Canon 50/1.2. In fact, the Canon is the lens that was used to create the examples of Focus Shift in the article I linked to.

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Third, does the Sigma 1.4 have trouble auto-focusing -- i.e., does it "hunt" more than the Canon lenses -- and does it auto-focus less well? (My understanding: Yes. The Canon lenses have quicker and better AF.)


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If my understanding on all three fronts is correct, my basic question is this: How is the performance of the Sigma 50mm 1.4 at f/1.4 compared with the Canon 50mm 1.2 at f/1.4?
See:

Canon EF 50mm f/1.2L USM (Tested)
Sigma 50mm f/1.4 EX DG HSM (Tested)

If you want to avoid the problem of Focus Shift, get a lens that doesn't have as large an aperture. Something like the Canon 50/1.8, for instance. It's 2/3 stop slower than f/1.4 and a full stop slower than f/1.2, but it doesn't have nearly as much of a problem. (... and it's a lot cheaper.)
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Old Oct 24, 2010, 3:44 PM   #66
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No you cannot "set" the aperture before focussing. The lens is ALWAYS wide open when you focus. If you stop it down to say f11 there isn't enough light for the AF system (or you in MF for that matter) to accurately focus.

I have not used the 50 f1.4 Sigma, but reports are that its AF accuracy is somewhat worse than Canon lenses, not so much that it hunts - it's USM motor doesn't hunt, but more that it thinks it has focus when it doesn't. Certainly the Sigma lenses I have used missed more than my Canon lenses. And there is also some focus shift.

The best description of the 50 1.2 that I saw was that it was "designed on the edge of disaster". Any slight defects in manufacturing, ones that normal L lenses would easily tolerate throw it out. It has no floating element to compensate for the focus shift. So quality control must be tighter. Hence the high price. My copy was slightly off in an odd way. It could give beautiful results, and a more lovely rendering than any lens I've ever seen except some Zeiss and Leica M lenses and various MF lenses. BUT I missed a lot of shots. Maybe 90% on my 5D2 at f1.2- f2 clearly missed critical focus. Some of that was just that if you are trying to shoot at f1.2 your DOF is often less than half an inch. That is way shallower than the accuracy of the AF systems on anything other than 1-series cameras, and even there... Also an slight movement of the subject or the photographer means your plane of focus is off. Focus - recompose? LOL forget it. Zero chance of getting your focus right using that method.

With the micro-AF adjustment I had 4 settings, at f1.2 and 3 meters. f2.8 and 3 meters. f1.2 and 5 meters. f2.8 and 5 meters. I had to switch settings constantly to try to compensate for desired effect and changing distance to the subject. For documentary style photography. Pah. Too much hard work for too little return. Though I really hated getting rid of it because of how it looked at f5.6. OMG it was beautiful. But sharp? No, not for me, not in the real world.

Here's the thing. Shooting that wide open you will never be getting close to the sharpness values you see in the charts. Not even close. You simply will miss focus most of the time.

[email protected] on a FF camera is very shallow DOF, shallow enough so that if the person's face is at an angle to the camera you usually can get one eye or the other in focus, but not both. For close work f2.8 is usually sufficient to throw the background very much OOF.

So the 50mm f1.4 from Canon is now my favoured lens. I shoot it at f2 - f11. Plenty shallow enough.

So here's the thing. Your camera doesn't have a good enough AF system to give you reliable results with a perfect copy of any f1.2 lens when shooting wide open. You don't have micro-AF adjustment in case you have slight back or front focus from an imperfect copy. You don't have live view to use with a tripod and nail it 100%. You almost certainly don't have good enough vision to use MF instead even with a viewfinder from a 7/5/1D, on a 40D? No chance.

Want a great "portrait" lens? Get yourself a 100mm f2.8 Macro instead. It also doubles as a Macro!

The reason I sold my 50 L (which I mostly used at f5.6) was simply that it was too big and heavy. The 1.4 is much easier to focus at f2-f4, and as sharp, if not as pretty in its rendering. I very much like that my 5D2 + 50 1.4 actually looks less fancy than many of the XXD cameras with their “standard zooms”. People don’t ask about my camera at all any more. With the L lenses they find it a lot more intimidating, and I find it a lot harder to carry around all day.
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Old Oct 24, 2010, 4:11 PM   #67
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Yes, the Sigma 50/1.4 suffers from spherical aberration, but so does the Canon 50/1.2. In fact, the Canon is the lens that was used to create the examples of Focus Shift in the article I linked to.

See:

Canon EF 50mm f/1.2L USM (Tested)
Sigma 50mm f/1.4 EX DG HSM (Tested)

If you want to avoid the problem of Focus Shift, get a lens that doesn't have as large an aperture. Something like the Canon 50/1.8, for instance. It's 2/3 stop slower than f/1.4 and a full stop slower than f/1.2, but it doesn't have nearly as much of a problem. (... and it's a lot cheaper.)
These two tests are terrific! Thanks TCav! The one about the Sigma does not (unfortunately) say anything about focus-shift/spherical aberrations, which appears to be the main concern about the lens. Also, the two tests do not directly address the question of whether AF is comparatively slow on the Sigma, although the Sigma review does say it takes 1 second to auto-focus. I'm not sure what that means in relative terms.

My main take-home points from the above reviews are that: (1) The 1.2 is not worth it; and (2) The Sigma does really well on an APS-C, in absolute terms as well as when compared with the Canon 1.4 or 1.2. The real question for me is how annoying the focus shift issue is going to be in the field -- as compared with the Canon 1.4 -- if I'm using the lens mainly wide open.

I will respond to Peripatetic's fantastically helpful post separately, but will ask this here too so TCav might be able to respond: Given that I will be using an APS-C camera, will the DOF at 1.4 be as horrendously shallow as described by Peripatetic? My understanding: The crop sensor will make my depth of field significantly deeper wide open. Given that I want to shoot with available light, both photo and video, and with the 60D, will I be using the 1.4 alot despite the shallower depth of field?
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Old Oct 24, 2010, 4:22 PM   #68
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Peripatetic,

Wonderfully detailed and helpful response! Thank you! Some questions:

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Here's the thing. Shooting that wide open you will never be getting close to the sharpness values you see in the charts. Not even close. You simply will miss focus most of the time.

[email protected] on a FF camera is very shallow DOF, shallow enough so that if the person's face is at an angle to the camera you usually can get one eye or the other in focus, but not both. For close work f2.8 is usually sufficient to throw the background very much OOF.
What about on an APS-C? The DOF focusing issue seems like less of an issue: http://www.dofmaster.com/dofjs.html

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So here's the thing. Your camera doesn't have a good enough AF system to give you reliable results with a perfect copy of any f1.2 lens when shooting wide open. You don't have micro-AF adjustment in case you have slight back or front focus from an imperfect copy. You don't have live view to use with a tripod and nail it 100%. You almost certainly don't have good enough vision to use MF instead even with a viewfinder from a 7/5/1D, on a 40D? No chance.
How about a 60D, which I plan to buy? (FYI: The 40D does have Live View, but your point is well-taken.)

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Want a great "portrait" lens? Get yourself a 100mm f2.8 Macro instead. It also doubles as a Macro!
Won't the 100 F/2.8 be too long for indoor shooting, and especially for video? And won't the DOF capability be undermined by my APS-C sensor? Also, I currently have the Sigma 17-70, and at 17mm 2.8 I still find it doesn't get enough light. Why would that be if not the max aperture?

If you are right, and 2.8 is wide enough for my needs, I'm tempted to put aside the Sigma and get a Canon EF-S 17-55 f/2.8 IS. That way my walkaround lens is also my "portrait" lens. Unfortunately, they don't make a 250D for 72mm threads, so I'd lose the Macro capability, but I would really pare down my needs. I just thought the 2.8 wouldn't be wide enough for low-light interviews at dawn/dusk.... but if 1.4 is going to be impossible to focus, why not just upgrade my walkaround?!

Quote:
Originally Posted by peripatetic View Post
I very much like that my 5D2 + 50 1.4 actually looks less fancy than many of the XXD cameras with their “standard zooms”. People don’t ask about my camera at all any more. With the L lenses they find it a lot more intimidating, and I find it a lot harder to carry around all day.
Duly noted. I like the low-profile look of the Canon 1.4 and will continue to consider it. Any further thoughts you may have -- or answers to my questions above -- would be greatly appreciated. Thanks again!

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Old Oct 24, 2010, 5:27 PM   #69
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... The real question for me is how annoying the focus shift issue is going to be ... if I'm using the lens mainly wide open.
If you'll be using the lens wide open, there's no focus shift. Focus shift only happens when you stop it down a little. If you leave it wide open at f/1.4, there's no problem. If you stop it down to f/2.0 or smaller, there will be a shift in the focus distance, but at smaller apertures the increased depth of field will encompass the original focus distance. So the problem only appears at f/2.0, sometimes at f/2.8, and rarely at f/4.0, depending on the actual focus distance.

If you'll be using a large aperture lens at short focusing distances, perhaps you'd be better off with a large aperture macro lens like the Tamron 60mm f/2.0. It won't have the focus shift problem, and it will focus even closer than the lenses you're considering, but it's a full stop slower.

Quote:
Originally Posted by yohy View Post
I will respond to Peripatetic's fantastically helpful post separately, but will ask this here too so TCav might be able to respond: Given that I will be using an APS-C camera, will the DOF at 1.4 be as horrendously shallow as described by Peripatetic? My understanding: The crop sensor will make my depth of field significantly deeper wide open. Given that I want to shoot with available light, both photo and video, and with the 60D, will I be using the 1.4 alot despite the shallower depth of field?
From DOFMaster's On-line Depth of Field Calculator I've been able to determine that, at a focus distance of 18 inches (the minimum focus distance of both the Sigma and Canon 50/1.4 lenses), the total depth of field is 0.16 inches. At 36 inches, the total DoF is 0.67 inches. At 54 inches, the DoF is 1.53 inches. And at 72 inches, the DoF is 2.75 inches.

With the Tamron 60/2.0, those DoFs are 0.15, 0.65, 1.50, and 2.69 inches, respectively. The slightly longer focal length gives you a slightly smaller DoF with the slightly smaller aperture, but it lets you avoid the focus shift problem, and it's a macro lens, so you can focus as close as 9 inches if you want to.
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Old Oct 24, 2010, 5:38 PM   #70
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If you are going to be shooting indoors a lot, isn't even 50mm too much?

How about the Canon 28mm f1.8 or Sigma 30mm f1.4? (Plus possibly a 50 or the 85mm f1.8?)

Or yes, simply the 17-55 f2.8 IS would seem to be the most sensible all-round option.
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