More D800 autofocus observations

After a couple more days of testing, I’ve got more observations on the D800’s autofocus system:

1. I think we’re reaching the limits of accuracy for CAM3500FX, and in fact, any phase detect based AF system. There are just too many parts that have to be precisely perpendicular and in exact alignment to achieve focus accuracy – the AF sub mirror assembly, the AF sensor itself, and the main imaging sensor. If any of these is out of plane by a few microns, then you’re going to see some softness. We’re now getting enough resolution that the planarity of the lens mount relative to the sensor becomes an issue – to say nothing of perfect alignment of optical elements. I believe there was an article posted a while back on the Luminous Landscape about shimming a sensor and how much resolution improved by both on-center and especially in the corners of the frame.

2. Future AF systems will have to be hybrid – i.e. use some form of contrast detect or phase detect embedded into the imaging sensor in order to work around these limitations. It doesn’t however solve the problem of mount planarity or lens element alignment.

3. There are some things you can do as a photographer to counter these limitations, chief of which is use live view for critical focusing, or stop down – or better yet, both. Live view eliminates problems of AF sensor/ sub mirror alignment. Stopping down covers slight sensor misalignment with depth of field.

4. AF fine tune is an absolute must to get the most out of the AF system.

5. Bad news for manual focus fans. I did my mirror alignment and calibration this morning – it was almost perfect from factory, which is a first; however, my joy died after removing the focusing screen. The focusing screen in the D800 is a different size to anything Nikon has yet produced. Worse still, it’s the largest one I’ve ever seen, so you can’t even cut something down to fit – it’ll just drop out. This is a real shame; I can only hope a third party produces replacement screens for MF aficionados.

6. Finally, lenses you thought were fantastic on the previous 12MP FX cameras may now only be mediocre or average on the D800 – you have been warned. MT

Comments

  1. Hello, Ming! Thank you for the very detailed and generous blog posts on D800!

    I was just wandering whether you could post a screenshot or something similar of the manual focus issue – i.e. the ‘dropping out’ when ‘cutting something to fit’?

    When you say you’re ‘long past the point of pixel sufficiency’, what else, or which features exactly, made you in the end choose D800 instead of D800E?

    Thank you!

    • Hi Dinora, my pleasure. What I meant with the ‘manual focus issue’ is that in the past, I’ve always been able to find an existing Nikon manual focusing screen (micro prisms, split image, both etc) to modify – i.e. cut or file down – to fit the camera. The D800’s focusing screen is larger than any I’ve seen in the past, which means we can no longer modify legacy screens to replace the stock one; it’s held in place by a thin wire frame that runs around the edges of the focusing screen. Other screens, which are narrower, won’t catch the edges of the frame and simply fall out.

      I think 12 clean MP is more than sufficient for the vast majority of uses, and that includes commercial work. However, I went with the D800 because a) my D700 is aging and high mileage, and throwing the occasional black frame (sticky shutter?); b) I had upcoming commercial work that would both require reliability (i.e. a new camera) and where the client thought additional resolution might be an advantage. Hence the D800. I originally ordered the E, but due to timing issues of the aforementioned jobs, I elected to take a regular D800.

      Ironically, it seems that I will get the D800E in the end – due to the autofocus issue, NPS have offered to replace my camera with another unit once they receive a new batch – I was also offered the option to upgrade to the E (pay the difference). Having seen how quickly diffraction kicks in on the D800, I’m inclined to do whatever I can to get back every bit of pixel level sharpness, otherwise I might as well just continue using the D700 for extreme macro work (where I need large depth of field and very small apertures on occasion). Hence the eventual switch (back) to the E version. It will also give me a chance to review it thoroughly for my readers :)

  2. I had my D800 delivered today. I have the 14-24, 24-70, 70-200 VRII and 85 1.4.

    You are right on about the focus. All my lenses are all over the board. Never seen anything like this. Fine tuning is a MUST!

    • I’m starting to suspect the AF sensor of my camera is misaligned, too. It works fine with telephoto lenses, but is consistently off on one side only with every wide-angle I’ve tried – especially bad with the 24/1.4, which is wide, IF design (small lens movement increments) AND shallow DOF to top it off…

  3. Lot of bad news today :(
    Plenty of issues appeared with growing user base and more D800 bodies out there:
    http://nikonrumors.com/2012/03/27/nikon-d800-issues.aspx/
    Live view USELESS for critical manual focusing? read here: http://forums.dpreview.com/forums/read.asp?forum=1021&message=41042567
    I do not believe any FW update can fix bad LCD screen, I had such issue on Samsung Galaxy S2 screen (yellowish tint)…
    Ming Thein, does your D800 reproduce any of these issues? I hope not… because some people report so and then any problem should be covered by warranty as individual fault.

    • I think I’ve solved the live view issue, and yes, there’s a color difference but it’s not too bad (for me at least). If they had a calibration utility like Olympus did with its Pen cameras (all firmware), we’d be fine. I’ll be putting up another post in a minute.

  4. Thanks for the reply. With the D7000, it had become evident 1.5 times the focal length was needed for the shutter speed to get good results. I can totally relate to the micro contrast issue which I had noticed on the D7000 when viewing at 100%. My observation with that camera was the lack of consistency in the micro focus (for things really close to each other sometimes the focus would be on the wrong area) despite AF fine tuning and careful technique. For paid work, this was too much of a hazard to deal with. The D800 seems insanely good for situations where the shot can be reviewed thoroughly and redone if needed. Product/food photography, lanscapes, static portraits. Still wondering if it can deliver as consistently as the D700/D3S/D3 when it comes to impromptu shots that cannot be redone if missed. Time will tell.

    • Agree with you – it’s not the AF system is bad, I honestly think we’ve reached its limits because the size of one AF box is 200×300 pixels! And inside that area there can be a lot of possible subjects for the system to pick – this is the risk. I’m also using the D800 only for controlled situations. The D700 and M9-P remains for everything else.

  5. cpapenfuss says:

    Another super post! Thanks so much! Quick question about the lenses. I noticed that you posted a bunch of photos taken with the 28-300. How is that lense working out on the D800? (I am an avid amateur…)

    • Thank you. The 28-300 works surprisingly well on the high density sensors – better than you would expect. Overall contrast and sharpness is great, but micro contrast is lacking somewhat (so fine details aren’t as well delineated as we would like). It’s great from about 35-200mm, with the remainder of the range so-so wide open, improving a lot by one stop down, and peaking two stops down (but still not getting much better in the way of micro contrast). I’ll be posting a full review of this lens soon.

  6. Thank you for these exceptionally well presented reviews. I used a d7000 for over 1 year and have experienced the need to be very meticulous in technique. The margin of error is very low in order to get exceptional results. Based on Tom Hogan’s comments, it should be even harder with the D800. This camera is not for the faint of heart. I imagined it would frustrate a lot of people and challenge others to milk it’s potential to the max.
    Looking forward to the lens evaluations.

    • My pleasure, Andrei. I don’t think it’s harder with the D800 than the D7000 – if you follow the shutter speed vs focal length that’s comfortable for you on the D7000, you should be okay with the D800 (i.e. 50mm requires perhaps 1/75s or 1/100s rather than 1/50s).

  7. mvngtrck says:

    I have been enjoying your blog a great deal. Your inital review of the D800 is the best evaluation of the camera that I found anywhere on the web. I have a question about the AF Fine-Tune. How do you determine the value (+20 to -20) for each lens in AF Fine-Tune on the D800?

    • Thank you! I’ve had so many questions on this subject, I should really put up an article :) Bottom line: trial and error. The ‘increments’ are not really precise units of anything. Just try say +10 in one direction then -10 and see which looks better, and iterate.

      • Jeffrey Friedl has a ridiculously detailed explanation, i found it very helpful.
        http://regex.info/blog/photo-tech/focus-chart

        Early on, when i first bought my D7000, I knew that I would upgrade to the D800. So, I only purchased lenses that i though would stand up to it.
        Namely, the f/2.8’s 14-24,24-70 and 70-200. Hopefully, these will still be at the top of the class once your tests are done.

        • Sounds about right. In the center zone, the D7000 and D800 are about the same on lens requirements because the pixel density is the same. It’s at the edges of the full frame where the lenses really start to become challenged. The 24-70 and 70-200II are both great on the D800; the 14-24, less so I’m afraid.

  8. Hui Wang says:

    First of all, thank you for all the reviews. I have some questiones:
    About focus: only for pros of pros? and more time to focus when you photograph?
    About lenses: Nikon should upgrade lenses for the future to adapt large MPs? otherwise should we stay with cameras like D700 or D4?
    About manual lenses: when using a MF lense, will the liveview work?
    Thx in advance :)

    • No problem. To your questions: not necessarily, you just need to be careful that it’s focused on what you want. The focus boxes are small, but still big enough that there’s probably a 200×300 pixel area or so they cover, and inside that, many possible subjects and different areas.

      I think some lenses will definitely need upgrades. I’d like to do more testing before saying exactly which lenses, in case it’s a sample variation issue.

      Live view works fine with any lens.

  9. Scary-Any G Lenses that did not make the grade?

    • At the moment, yes. Some very, very bad surprises actually. However, I’d like to do more testing (and with several samples) before I say which lenses, because I haven’t completely ruled out sample variation yet – it could even be an issue with the AF sensor’s alignment on my particular D800 body.

Thoughts? Leave a comment here and I'll get back to you.

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 26,172 other followers

%d bloggers like this: