Back focusing SL1

Mike - wrote:

PADF ?

PDAF - phase detection auto focus. Strictly speaking this describes the measurement method used to determine correct focus, and initially in DSLRs (and AF film-based SLRs) the only system they used was a separate PDAF array, whereby a bank of dedicated phase detection sensors in the base of the mirror box receive light, via the lens, which passes first through a semi-silvered portion of the reflex mirror and then is reflected down to them via a sub-mirror assembly mounted on the back of the main mirror. Obviously that somewhat convoluted optical path does have some inherent possibility of deviating from being exactly matched to the light path directly to the image sensor when the mirrors are up for an exposure, either via an adjustment issue during manufacture (any almost-microscopic deviation could have a visible effect on the results) or perhaps in the course of use, for example if some kind of impact befalls the camera. And that's where front- or back-focusing could occur.  This system is always used, including on the latest DSLRs, when the DSLR is being used in its native eye-level optical reflex mode.

I've never used Live View in any of my cameras. Well...I guess my point and shoot/pocket cameras are really Live View based, so in reality, I guess I have used...Live View.

Yes, they are, effectively.  The image preview being fed through the lens and displayed on the rear monitor prior to the shot is live view.  These days it's an (optional, activated by a button or switch) feature on any current DSLR, and the inherent, normal operational mode of mirrorless interchangeable lens cameras.  DSLRs are a lot better at it than they used to be, but its use still causes the eye-level optical reflex finder to be blocked and forces you to use the LCD monitor as your only viewfinder, whereas mirrorless cameras also have the option of retaining eye level use if they possess an electronic viewfinder.

I should try my two current APS-C lenses on my old 40D and see what happens. I guess I should see if I have a usable battery for it first..?! My 40D was my favorite (of many Canon bodies) until I went with full frame bodies (6D and 5D IV). Neither of these required any focus adjustment with the lenses that I use with them. Same exact test as done with my SL1. Distance, time of day, body and lens settings, everything.

Your comment about the 6D and 5D IV reinforces a facet of "Murphy's Law" that often strikes me - I haven't double-checked, but I bet both models have micro-adjust facilities.  It often seems to be the case that the cameras which don't need it doing are the ones that have the ability, whilst those where it needs doing (like, perhaps your erstwhile SL1) are the ones that don't have it and would require a trip back to the manufacturer!  Such is life... (it is perhaps because the more expensive models are built in smaller numbers and perhaps checked and calibrated more carefully than cheaper, large-production models which are additionally probably anticipated to be mainly used with smaller maximum aperture kit zoom lenses, which maybe won't show AF errors so readily as large-aperture prime lenses anyway).

I just familiarised myself with the EOS 40D by reading the DPR review of it.  If I read it correctly, the 40D does have an early iteration of live view, but unfortunately it wouldn't fully answer the question for you (obviously if it doesn't show a problem with any of the problematic lenses anyway, then it has no issue itself, and neither do the lenses, most likely).  The thing is, however, that the 40D achieved autofocus in live view by momentarily switching back to the DSLR separate PDAF array anyway - a brief mirror-drop occurs (cutting off live view for its duration and reinstating the view through the optical reflex viewfinder as a side effect, before returning to live view once AF lock is achieved).  Therefore results would be the same, regarding the AF system, whether in live view or not, as the same system is used for both modes of use.  Later DSLRs started to give the choice between this form of mirror-drop AF operation in live view or providing an uninterrupted live view AF operation by using the image sensor itself to achieve AF (in the way that all mirrorless interchangeable lens cameras always do).  Initially this was using the slow but precise contrast detection AF method (CDAF) but as sensors have evolved, a way of providing PDAF on the sensor itself has been developed - many brands use both on-sensor methods, switching between them as required or combining them.  Whichever method (PDAF or CDAF) is used, as long as it's on-sensor (the image sensor, that is) there should be no front- or back-focus in most circumstances.  Canon now uses the confusingly-named DPAF system on its latest models, which is a form of on-sensor PDAF named for its dual-pixel AF arrays.  The quick mirror-flip type of live view AF that reverts to the separate SLR-style PDAF array (as in the EOS 40D) is largely a thing of the past these days.

So, it's only the newer uninterrupted-AF in live view style (via AF measurements done by the imaging sensor itself) that show up for sure if there is an adjustment issue with the separate SLR-style PDAF system used when the DSLR is not in live view mode - soft results in normal eye-level operation, but perfect results in live view with all other settings the same are the telltale sign of this - but unfortunately it's a difference the EOS 40D's live view AF setup is not able to demonstrate since it uses the same measurement array as when it's not in live view.  Sorry that's rather long-winded but I hope it helps!

Mike