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Messages - neuroanatomist

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EOS Bodies / Re: 5D MkIII instructions - Rant !!
« on: December 06, 2012, 12:01:29 PM »
I believe the how, the why, the when and the what (and possibly others) go together. I believe manuals need to morf into a compendium of "How to...".

Oh, that's simple.  Canon covers that in the Quick Start guide, right up front.  Insert battery and card, mount lens with AF switch set to on, turn on camera, set green square/A+ mode, point, and shoot.   ::)

EOS Bodies / Re: 5D MkIII instructions - Rant !!
« on: December 06, 2012, 11:40:08 AM »
It is amazing how one can be lost in the "I need to explain what happens when I use this option" rather than why and where the F^@* would I use this function...

Should documentation for a cell phone tell you who to call, and when?  Is it Canon's job to teach us how to use the camera itself, or to teach us how to take good pictures?  The why and where seem much more aligned with the latter, and I'd argue that's out of scope for a manual. 

Technical Support / Re: Autofocus working conditions
« on: December 06, 2012, 11:17:10 AM »
It's a question of the 'baseline' - the narrower the max aperture of the lens (or TC combo), the less the phase difference between two points in an image that the phase-detect AF system needs to determine the focus calculation. It's not a hard line, there is some flexibility (obviously, else Canon couldn't change from f/5.6 to f/8 with a firmware update, nor would the Kenko TC or pin taping tricks work).  But the issue is reliability and speed at the edges of performance.

The wider the baseline, the more accurate the focus calculation - that's an advantage for the Canon f/2.8-sensitive AF points.

See http://www.the-digital-picture.com/Photography-Tips/Canon-EOS-DSLR-Autofocus-Explained.aspx.

Lighting / Re: Help with lighting for portraits...
« on: December 06, 2012, 10:59:11 AM »
indoor/outdoor photo shoots

One key question - would you have access to AC power in your outdoor location, or need battery packs?

I don't have access to the standard...

In any case, it has no bearing on this discussion.

I do, but you're right.  However, we're talking about small (one stop or in most cases, much less) differences.  My point is that even though it's a relative measurement, labeling the test results as "-7 EV" is pretty darn misleading in light of the specified performance of the cameras being tested.  The difference between -2 EV and -7 EV is a 32-fold difference in light intensity.

EOS Bodies / Re: 5D MkIII instructions - Rant !!
« on: December 06, 2012, 10:51:55 AM »
Wait, let's go over this again. I turn the camera on, press the shutter button and it takes a picture. Ok thanks.
I'll try it.

You didn't put in a memory card and attach a lens as instructed on p.16.  Therefore, no picture will be taken.  RTFM, dammit!


Then EV is amusingly useless since there are varying definitions of ISO 100.

LOL...now that's amusing.  "ISO 100" is defined unequivocally by ISO 12232:2006 as published by the International Standards Organization (which is why we call it ISO). 

But you're point is valid.  In actuality, when set to ISO 100 the cameras in question are really at a sensitivity of ISO 73 - 80 based on the actual standard.  That's one of the things that DxOMark measures.

Given the point was to do a relative comparison and not an absolute measurement, I don't see much of a problem. Especially when he cited his definition of 'EV'. As neuro pointed out, it might add to the confusion a bit but it doesn't really invalidate anything.

No, but now that I've looked at the methodology, there are other holes to be poked in the 'analysis'.  He's testing targets illuminated to different light levels, yes, but they seem to be different targets shot from different angles, therefore they may not be comparable for the same camera (and shooting an orthogonally-shaped target from an angle isn't the best way to test AF performance). 

The better way to have done this test would be to have pointed the cameras straight at the same target, and vary the light levels only.  I'd have set the illumination at 2 EV, then stepped down the illumination to -4 EV in 1-stop increments using ND filters on the lens.

Having said that, a generic conclusion that the 6D center point AF performs very well in low light is quite reasonable.

Lenses / Re: 300MM lens advice
« on: December 06, 2012, 09:47:59 AM »
All the bad reviews of sigma products usually come from people who use canon or Nikon pro lenses.

Ok, but the OP has a Canon 500mm f/4L IS II.  Do you think he'll be happy with a Sigma?

(Note: Here "0" EV was an even exposure at 1/60, 2.8 ISO 400).

You're adding a lot of confusion here by arbitrarily defining your own zero.  It's like saying you're going to start counting everything from the number 4, so if there are of 2 of something on a table, you're telling everyone there are 6.  Makes no sense.

0 EV has a real, absolute definition - an exposure of 1 s, f/1.0, ISO 100.

Technically, your "0" EV is actually EV = 5.  That means your -7 EV is really -2 EV (and in fact, the 6D is spec'd to AF at -3 EV, but of course, that may not equate to real world numbers).

It would help avoid confusion if you restate your numbers according to the real definition of EV = 0, otherwise many people will read that you're testing at "EV = -7" and think you're spewing complete bullsh cow manure.

Sorry, but the fact that you don't seem to understand some of the basics, like the fundamental definition of the basis for the specification you are testing, makes me question what you're doing.  I definitely appreciate individual testing (and especially the fact that you did post your definition, so the error could be spotted), but post/blogs like this contribute to the vast and growing pool of bad and/or unreliable information out there. 

How can you not understand the interest in testing beyond the rated limit?  The light around you won't stay to the rated limit of your camera, right?   :)

See...this is my point.  He's not testing beyond the rated limit of the 6D, he hasn't even tested it as low as the rated limit.

EOS Bodies - For Stills / Re: Would switching to FF hurt my macro??
« on: December 06, 2012, 06:40:14 AM »
OK, so it has already been established that the crop factor doesn't help the 7D, but the pixel density does.

Now, say you're worried about depth of field: when you move to FF, it will be significantly narrower than on APS-C. Can you close the iris to compensate, or will diffraction be a problem if you do? I mean: if I'm shooting f/11 on APS-C because above that I get diffraction and the image comes out soft, when I move to FF, will I want to stay at f/11, or will f/16 suddenly be acceptable?
Is the diffraction limit the same for APS-C and for FF? I'm guessing it is, since it's a characteristic of the lens, but I'm too busy today to think this through myself  ;D

The 'diffraction limit' depends on pixel density, not sensor size.  But, DoF depends on sensor size (for equivalent framing).  In general, FF sensors have larger pixels, so narrower apertures for equivalent diffraction effect - in your example, yes, f/16 on FF would probably give you approximately the same amount of diffraction effect as f/11 on APS-C.  So, if you're talking about framing something identically (i.e. you're further away with APS-C), for the same DoF you'd have the same diffraction (approximately, with recent sensors). 

But...in the case where the lens magnificaiton is held constant (e.g. shooting at 1:1 on APS-C vs. FF, where the framing is not the same), the APS-C will actually have a slightly shallower DoF at the same aperture, and suffer more from diffraction at the same narrower aperture (assuming higher pixel density).  That's why, if you are planning to shoot at 1:1, FF has an advantage (and as mentioned, the disadvantage of putting fewer pixels on target).

Lenses / Re: 100mm macro VS 180mm macro
« on: December 05, 2012, 08:43:49 PM »
I plan on using whichever lens I get for food/product shots...I'm looking for piece of info that I might have not considered before making a final decision.

I'd really recommend considering the TS-E 90mm f/2.8 for food/product photography - it's really the lens of choice for that application.  The problem with a macro lens is DoF - it's either too thin, or you have to stop down well into apertures narrow enough to soften the image with diffraction.  The tilt feature of a TS-E lens gives you control over DoF, and allows you to get a deeper DoF at wider apertures.

I've never had the Kirk clamp loosen, even a little.  When mounted to the body, I have the knob under the lens, and when mounted to the lens plate, the knob is on the side swag from my body.

Lenses / Re: Canon 100mm f/2.0 for portraits
« on: December 05, 2012, 05:57:40 PM »
With what body (APS-C or FF) will you be using it?  It's a very good portrait lens on FF, IMO it's too long on APS-C, but good for indoor sports.

EOS Bodies - For Stills / Re: 5D MKIII - file size and low MPs question
« on: December 05, 2012, 01:07:29 PM »
When you read some things on the Internet, it's best to take them with a grain of salt.  When reading KR, you just need a few more grains.

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