David G72: Rishi, thank you for your detailed investigation on the D750. Nasim at Photography Life also wrote an article on the flare issue and categorized it as a non-issue, giving examples from a number of Nikon and Canon cameras that showed similar problems. These issues are not just isolated to Nikon and Canon and I'm sure any DSLR will most likely be prone to such internal reflections. That's an important point to be aware of.
My only recommendation is to remove references to lenses front-back focusing because of the mirror differences: those two are not related. A visible difference in mirrors being lower or higher would result in huge discrepancies in AF performance, not just+20 or -20 in the AF scale. The main reason is that manufacturers actually calibrate each camera's AF sensor position after the camera is built (it is a setting in the camera, which the manufacturer has access to). So please do not make it sound like the AF sensor being out of place will also screw up autofocus!
Rishi, hopefully people will be smart enough not to be tied up in the AF thing...
I know a bit about the calibration procedure. There are things that have to be done manually by adjusting the secondary mirror or the AF phase detect sensors when software thresholds don't work anymore (too big of an angle, for instance) and things that are done purely via software. Once the hardware is within the QA threshold, proprietary software is used to calibrate each focus point. Distance values are dialed into each focus point, so some focus points might have different values than others, particularly towards the edges of the frame. The software automatically determines the values and dials them in for each camera, then saves them into camera's memory. This is done after the camera leaves the assembly line, during the QA process. If you determine that a focus point is inaccurate, the manufacturer can fix it by re-running the software and realigning the focus points.
Hope this helps!
David G72: One more thing, to anyone who wants to send their D750 for updating:
The fix to move the AF sensors down is complex and requires opening the camera, moving the phase detect sensors and re-calibrating the camera. When your camera comes back from Nikon service center, you might end up with it being worse than it was in terms of AF accuracy and reliability. If this flare issue does not bother you and your D750 is in excellent working condition, just forget about this and keep on clicking!!!
Rishi, there are two separate adjustments that are made by the manufacturer, in two different places:
1) In camera: after the camera is assembled, the phase detection / AF sensor is calibrated for that distance. If there is a variance in distance (and there usually is), that value is programmed into the camera. This one needs to be very precise, down to micrometer.2) In lens: lenses also need to be adjusted and calibrated for AF to be precise.
Either one could get out of whack and create AF accuracy issues. Sometimes it is the camera, sometimes it is the lens and sometimes it is both. That's why Nikon and Canon often want you to send both for inspection. If they re-calibrate your body to their standard and your lens is the problem, then you will still have issues.
In regards to Canon 1D X, there are many folks out there that own that camera and know how to use it. If the body was at fault for AF problems, by now people would have figured it out...
Plastek, are you serious? I am the one defending the brands here! I am telling DPR that adding their autofocus tests is misleading, because it is a separate issue that has nothing to do with the flare issue. Please re-read my post.
It is not any "more" of an issue. Flare issue has nothing to do with phase detection sensor calibration. Those two are completely separate. If what you said was true, then the Canon 1D X and other cameras would have all kinds of problems with out of whack phase detection placement and variance. From what I have seen from DPR, IR and Photography Life, many cameras have their sensors placed differently. It does not mean that all of the ones that have them higher up have issues with AF.
Now in regards to always fine tuning lenses, you might need to read up on fine tuning here: https://photographylife.com/how-to-calibrate-lenses
Specifically, read #9, where it is stated that calibration is done for working distance. In some cases, it is best not to deal with calibrating lenses at all, irrespective of their type (fixed or zoom). I personally find calibration to be useful to determine if things are bad. If they are, it is best to send the lens to the manufacturer.
Rishi, but mentioning AF accuracy might introduce confusion to current D750 owners, who now might think that if they don't send their cameras to Nikon, that they are likely to have focus issues. That's certainly NOT the case! My D750 has the flare issue, but its AF is nearly perfect. Pretty much every lens I own works beautifully with the body and only a couple of lenses had to be calibrated to small values under +-10. And I tested all lenses using LensAlign too.
So in my humble opinion, it is wrong to associate this particular issue with phase detect sensor misplacement.
If the optical path was grossly different, no AF Fine tuning would have helped. Even a fraction of a millimeter can play a vital role here, which is why manufacturer calibration is important. I bet if you were to take a few more D750 bodies that had the flare issue and compared them, they most likely would vary in AF accuracy. Some would be spot on, while others would have the slight deviation.
One more thing, to anyone who wants to send their D750 for updating:
Rishi, thank you for your detailed investigation on the D750. Nasim at Photography Life also wrote an article on the flare issue and categorized it as a non-issue, giving examples from a number of Nikon and Canon cameras that showed similar problems. These issues are not just isolated to Nikon and Canon and I'm sure any DSLR will most likely be prone to such internal reflections. That's an important point to be aware of.
To anyone who seems to be dissatisfied with this lens, you have no idea what you are talking about. This 300mm f/4 lens is a breakthrough and many Nikon shooters will go crazy about it. 755 grams, barrel size of the 70-300mm and VR will let wildlife photographers hand-hold this thing tirelessly and capture shots they have never been able to before.
Nasim at Photography Life wrote about these and other benefits in his article, which I highly recommend reading for everyone:
Nasim just posted his 58mm f/1.4G review with some delicious photos:
This lens is not about sharp optics, but the result is stunning.
Severely disappointed by DPReview for posting this crap. Why are you playing catch up games with Engadget? Who gives a damn if those guys are wrong?
Seriously guys, please go back to being a great site you once were...
Duh, this is just stupid...this article is pretty much meaningless - I agree with what everybody said here.