AF issues....

[Sheiky]

Or does it still FF & BF even if you manual focus them??

That would be up to you -Short answer: no it won't. Longer answer...if it does, it's not the camera nor the lens

So, you're saying that lens-sepcific front- or back-focus AF issues will not be a factor if you manually focus. Ok, that makes sense if you're relying on your eyeball view of the subject, or you've changed out your focusing screen for one that provides more visual assistance (if possible on your body, which it's not on my 7D).

Yes I do think so. I'm thinking about how I manually focus with my macro lens. You clearly see what is and what isn't in focus. Once you push the trigger, the part that you see in focus, will also be in focus on your photo. Nothing is going to change that, that's what I meant to say. I didn't change focussing screens either, that's also why I said that manual focussing isn't to hard at shorter distances, where you can easily separate the infocus parts from the out of focus parts. Once your subject gets further away from you (like more than 10feet/3m), I believe precise manual focus gets a lot harder. A different focus screen might help you out with that, I don't know, don't have that experience. Hope that clears my statement a bit?

But, whatsirhc_1 originally asked was:



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Just want to know if the AF inaccuracies on both OEM &amp; third party lenses can be overcome by manually focusing the lens thru focus confirmation?

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Yes I do think I misinterpreted this one. You're right about that. If your lens is inaccurate in AF, so FF or BF or both. I think it will also misinterpret thru focus confirmation when focussing manually.

'm not sure the answer there is the same, thatfront- or back-focus AF issues will have no effect.

Nope I guess you are very right about this one. Thanks for bringing that up. I don't know if I'm right about it, but I guess that if your lens has purely inconsistent AF, perhaps it will focus correctly from time to time using manual focus with focus confirmation. But is your lens inaccurate, your focus will always be off for a specific amount of back or frontfocussing, depending on your lens. This was the case with my Sigma 50mm 1.4 and this case is easily solvable with AF micro-adjustment. Inconsistent AF isn't I think.

Since the focus confirmation (i.e. the green dot in the VF) 'knows' that correct focus has been manually achieved by (passively) using the data from AF system, it may be that any FF or BF issues would also affect focus confirmation, right?

So yes I'm with you on this one John.

does the AF system 'know' the correct focus and the lens' motor just misses that mark, or is the AF system 'wrong' meaning focus confirmation would also be 'wrong'

Good question and it practically all depends on this one.


I know it's only wikipedia, but still it might have something:


[url="http://en.wikipedia.org/wiki/Autofocus]http://en.wikipedia.org/wiki/Autofocus[/url]


I read that there are multiple ways to achieve AF, so it's just the questions which type canon uses? Man this question is bigger than I thought [:P]


I guess this one is appliable, but I'm not 100% sure: quote from wikipedia


"
<h2><span id="Passive_autofocus" class="mw-headline"]Passive autofocus</h2>


Passive AF systems determine correct focus by performing passive analysis of the image that is entering the optical system. They generally do not direct any energy, such as ultrasonic sound or infrared light waves, toward the subject. (However, an[url="http://en.wikipedia.org/wiki/Autofocus_assist_beam]autofocus assist beam[/url]of usually infrared light is required when there is not enough light to take passive measurements.) Passive autofocusing can be achieved by[b]phase detection[/b]or[b]contrast measurement.[/b]
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<div class="thumbinner"][url="http://en.wikipedia.org/wiki/File:US_pat_5589909_fig_2.png][/url]
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<div class="magnify"][url="http://en.wikipedia.org/wiki/File:US_pat_5589909_fig_2.png][/url]</div>
Phase detection system</div>
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<h3><span id="Phase_detection" class="mw-headline"]Phase detection</h3>


Phase detection is achieved by dividing the incoming light into pairs of images and comparing them.SIR TTLpassive phase detection (secondary image registration,through the lens) is often used in film and digitalSLR cameras. The system uses abeam splitter(implemented as a small semi-transparent area of the main reflex mirror, coupled with a small secondary mirror) to direct light to an AF sensor at the bottom of the camera. Twooptical prismscapture the light rays coming from the opposite sides of the lens and divert it to the AF sensor, creating a simplerangefinderwith a base identical to the lens's diameter. The two images are then analysed for similar light intensity patterns (peaks and valleys) and the phase difference is calculated in order to find if the object is infront focusorback focusposition. This instantly gives the exact direction of focusing and amount of focus ring's movement.


Although AF sensors are typically one-dimensional photosensitive strips (only a few pixels high and a few dozen wide), some modern cameras (Canon EOS-1V,Canon EOS-1D,Nikon D2X) featureArea SIRsensors that are rectangular in shape and provide two-dimensional intensity patterns for a finer-grain analysis.Cross-type (CT)focus points have a pair of sensors oriented at 90&deg; to one another, although one sensor typically requires a larger aperture to operate than the other. Some cameras (Canon EOS-1V, Canon EOS-1D,Canon EOS 30D/40D) also have a few 'high precision' focus points with an additional set of prisms and sensors; they are only active with 'fast lenses' of certainfocal ratio. Extended precision comes from the increased diameter of such lenses, so the base of the 'range finder' can be wider."





So if this is the way, I believe it is true that the FF and BF also exist with focus confirmation, sincePassive AF systems determine correct focus by performing passive analysis of the image that is entering the optical system.


Thoughts?? [:P]