April 25, 2014, 12:21:30 AM

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Messages - neuroanatomist

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46
Lenses / Re: Review: Sigma 50mm f/1.4 DG HSM Art Lens
« on: April 22, 2014, 03:31:06 PM »
Is there a lens out there that never has occasional AF inconsistency?

Does a 40% miss rate really constitute occasional inconsistency?  I think not...

Compare this to Zeiss missing 100% of AF shots  ;)

This comparison is as pointless as comparing a Audi with (automatic) transmission problems to a stick-shift Ferrari.

I don't think Audi makes cars that 'occasionally' mis-shift, causing the car to lurch and hot coffee to spill all over the driver.  Just sayin'…   ;)

47
Canon General / Re: $10,000
« on: April 22, 2014, 01:42:00 PM »
you slowly start buying gear and one day your gear is more expensive than your first car.

…and then one day, you buy a single lens that is more expsnsive than your first car.   ;)

48
EOS Bodies - For Stills / Re: Focus indication with manual lenses
« on: April 22, 2014, 01:14:32 PM »
Then why not the camera:
1. Check the several sensors for the light coming in? If the wider sensors are not receiving light but the narrower ones are, then it could use the narrower ones. It would always use the wider ones receiving enough light. I must be missing something...
2. Allow max aperture to be set, one more parameter in some menu page, rather than forcing electronics on every lenses for such small (and constant) piece of info?
3. Assume some value (e.g 5.6), at least it would work in most cases, whereas like this it never works...

Why not?  Because Canon does not currently sell any lenses which do not report the max aperture to the camera electronically.

49
Lenses / Re: Review: Sigma 50mm f/1.4 DG HSM Art Lens
« on: April 22, 2014, 12:55:41 PM »
I don't disagree with what you are saying at all, but I understand the conundrum as a reviewer.  These days it seems like most reviews are published before retail copies are technically available.  Waiting until the lens launches to the public means that you lose the early momentum/hits that are so important to building a brand and a website.

Thus the suggestion to test additional lens(es) purchased through normal retail channels, once they become available.

I do appreciate the quandary, but I'd argue that merely adds another potential source of bias (and please note the use of the word potential).  If delivering an early review to gain momentum/hits is that important (and I'm sure it is), what if the review is negative?  It seems possible that a negative review would result in the reviewer not getting an advance copy of the next lens from that manufacturer, and thus losing out on the momentum/hits for the next round.

The full text of the review indicates a 40% AF miss rate in formal testing, and includes statements like, "...the longer I focus tested this lens, the less sure I was about its focus accuracy," and, "Sometimes, most images are properly focused and when my shots counted, this lens delivered. But sometimes, more images are out of focus than I am comfortable with."  To me, that does not equate to, "...occasional AF inconsistency."  Which of those statements made it into the concluding paragraph of the review, which is the part most likely to be picked up and quoted, as it was in this post by CRguy?

50
EOS Bodies - For Stills / Re: Focus indication with manual lenses
« on: April 22, 2014, 12:37:00 PM »
Why does the camera need to know the aperture settings of the lens?

The aperture setting is irrelevant, but the max aperture of the lens must be communicated to the camera.

51
Lenses / Re: Review: Sigma 50mm f/1.4 DG HSM Art Lens
« on: April 22, 2014, 11:40:09 AM »
Is there a lens out there that never has occasional AF inconsistency?

Does a 40% miss rate really constitute occasional inconsistency?  I think not...

52
Blasphemy!!  Do these testers not comprehend the paramount importance of dynamic range?  WTF?!? 



Oh, wait…you said they compared cameras, not just the sensors in them.  How very DRoll.   ;)

53
Lenses / Re: Review: Sigma 50mm f/1.4 DG HSM Art Lens
« on: April 22, 2014, 11:26:36 AM »
Quote from: Bryan @ TDP
Below I share ten 100% crops from one of the more-formal focus tests I performed. The subject is a large book properly aligned with the camera at a relatively close focus distance. Starting with a slightly defocused lens, each shot was autofocused using the center AF point that was very comfortably and completely covered by the book. The first 5 and last 5 images from this particular test are presented below and are representative of the larger test group. … The camera was a tripod-mounted EOS 5D Mark III with mirror lockup and the 2-sec self-timer in use.

Of those 10 shots, 4 are sufficiently OOF as to be unusable (3, 4, 6, 10).  A 60% hit rate with a static subject and a tripod-mounted camera, particularly one with an excellent AF system, does not inspire confidence. 


Also, this is a departure from the norm for Bryan's lens tests (and one, frankly, with which I'm not too pleased):

Quote from: Bryan @ TDP
My evaluation lens was a short term loan from Sigma, as they offered the production-grade lens before it was commercially available.

Any time a manufacturer supplies a product to a well-known reviewer, a big unanswered question is whether the provided copy is truly representative of units purchased retail.  Clearly, it would be in Sigma's best interest to pre-test a batch of them and pick the best copy they can find for review (in fact, they are supposed to generate measured MTFs for every lens they produce, so they have the data already).

I've always felt that one of the strengths of Bryan's reviews (in addition to their thoroughness and readability) is that he purchases review copies through standard retail channels (B&H may put him near the top of the preorder queue, but that's fine), and therefore avoids the potential confound of bias introduced by testing a 'hand-picked' lens from the manufacturer.  I hope Bryan chooses to test one or more copies of the lens purchased retail to see if the results align with the copy provided by Sigma. 

54
Canon General / Re: Canon Hong Kong Announcement April 24, 2014
« on: April 22, 2014, 07:56:08 AM »
shadow and light created by objects...
Reminds me about a flash or something. May be some EX-440-RT.

Probably not a 4x0EX-RT, that would be a pretty significant (global) announcement.  However, a while back there was a rumor of a new flash coming for the EOS M system, sitting above the 90EX in the lineup.  The light/shadow thing, coupled with an announcement in a prominent Asian market, are consistent with that.

Regardless, it seems like we don't have long to wait.

55
EOS Bodies - For Stills / Re: Stranege "rendering" 5D3
« on: April 22, 2014, 07:49:21 AM »
I'd still consider replacing the card.  Many card manufacturers offer a lifetime warranty with free replacement for defective products.   What if the next time it happens, the shot that gets ruined is the once-in-a-lifetime shot of a unicorn flying over your head?  ;)

56
Canon General / Re: Canon Hong Kong Announcement April 24, 2014
« on: April 22, 2014, 07:36:47 AM »
or you could say it will not be earth shattering because canonrumors had no clue about an "annoucement" prior to the teaser... but then.... that´s always the case isn´t it?   8)

The point is, if there is information (official or unofficial) from only one location in the world, it is unlikely to be an announcement of global significance.

57
Software & Accessories / Re: Unidentified Object on big lens
« on: April 21, 2014, 08:58:24 PM »
The AoV of a long lens can make it hard to locate a subject in the viewfinder, and a red-dot sight can help.  I got one of these after getting my 600 II, along with a Weaver hotshoe adapter to mount it to the camera.   

It's a little like training wheels - after using it for a while, finding the subject became second nature.

One tip to help, short of a red-dot aid.  When you mount the hood of a supertele, put the mounting screw on top, at 12 o'clock.  Then you can line up the hotshoe and the mounting screw as a crude sight to get you in the ballpark.

58
Consider that we are imaging three-dimensional space, and compare the XY dimension (FoV) to the Z dimension (DoF).  When magnification is low, the DoF is relatively large compared to the FoV.  For example, with a 50mm lens and 8 m distance, Z/X is ~0.4.  At higher mag, e.g., a close up of the dog with the 50mm lens at <2 m, Z/X is <0.1. 

Basically, misfocus is less obvious with a lower magnification.


Interesting, this explains why with longer lenses AF accuracy can be problematic even though there is a relatively large dof.

All I have tried to show is that the outer points on the 6D give infinitely more accuracy than an f5.6 dof - because there has been confusion in this thread about the meaning of an 'f5.6 precision' AF point, and that the outer points are perfectly useable in many circumstances whether near or far.


Agreed, it's confusing.  It sure doesn't help that Canon's literature on the subject treats precision and accuracy as interchangeable terms when they're not...and the difference is relevant here.  For the average of a given set of tests, accuracy is 'closeness to true' and precision is 'closeness to each other'.  A single shot says nothing about AF performance.  A hundred shots says something.



An f/2.8 point has a wider baseline, therefore it's more accurate than an f/5.6 point.  Canon apparently does not specify accuracy values for their AF systems.  AFMA adjusts the global accuracy of the system.

The center point of many bodies is a 'high precision' point, that can be either f/2.8 or f/5.6 in terms of baseline.  Canon does specify precision, albeit incompletely.  It's specified as depth of focus, which is the sensor-side equivalent of DoF, but distances are in microns.   High precision means 'within 1/3 the depth of focus', standard precision is 'within one depth of focus'. In both cases, that's the depth of focus for the attached lens' max aperture.  So, with the 50/1.4 attached, an f/5.6 point is precise to within one depth of focus at f/1.4.  We still don't know exactly what that means – will 95% of shots fall within that zone, or 99%, or 99.99% (that's what I mean about Canon's incomplete specification of precision). 

Personally, I found the 5DII's outer points to be ok in good light, but with close subjects and fast lenses they'd miss critical focus with noticeable frequency.  If I took 2-3 shots of the same subject, if be reasonably sure if getting a keeper. 

59
Consider that we are imaging three-dimensional space, and compare the XY dimension (FoV) to the Z dimension (DoF).  When magnification is low, the DoF is relatively large compared to the FoV.  For example, with a 50mm lens and 8 m distance, Z/X is ~0.4.  At higher mag, e.g., a close up of the dog with the 50mm lens at <2 m, Z/X is <0.1. 

Basically, misfocus is less obvious with a lower magnification.

60
I've made them fit the page but have included a magnification in each one where you can see that the very narrow dof has been achieved over the focus point.

Not to be argumentative, but that isn't a particularly narrow dof. How far away is the dog?

Narrow to me means if you hit eyelashes, the retina is OOF.

+1

@ Sporgon, your 'very narrow DoF' looks to be over 2 m deep, distant subjects aren't as taxing for an AF system.

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