richard_driscoll

Slide 52 - Live view/image review - raw histogram/highlights Perhaps the background could put things rather more strongly. AFAIK the JPEG histograms don't really tell you very much at all about how near saturation the sensor is do they? JPEG settings for white balance, contrast and saturation all have no affect on saturation but can affect the histograms.

Nikon's 'RGB' histogram is almost certainly a luminance histogram and it's possible for blue or red (green is unlikely) to blow without the luminance histogram or blinkies showing anything wrong. To check you need to look at blue and red in turn to ensure that neither has blown highlights. If you have red OR green OR blue blinkies rather than luminance then you can check in one step that nothing has blown out. (R or G or B) could be an option on both the highlight screen and on the histogram screen. If something has blown out then it's easy to check which channel is responsible, but the idea is that one can ensure all is well in just one step. You can see the RGB histograms all three at once but in bright light I find the blinkies easier to spot than a spike at the extreme RHS of a rather small histogram

A couple of issues with the matrix meter. Nikon published quite a lot of information on how the old FA matrix (or AMP) meter worked. It used the absolute scene brightness as a method of classifying the scene and it also ensured that parts of the scene brighter than LV 16 1/3 were given reduced weight or even ignored. Some of this persists to the present day since recent manuals state "values over 16 1/3 EV are reduced to 16 1/3 EV." Note that 16 1/3 LV is 16 1/3 EV at ISO 100. Another point is that if you put a lens on a bellows the exit pupil moves forward and it's my belief that short focal length lenses need a correction for matrix metering since an exit pupil close to the film/sensor plane will result in a significant cos^4 falloff in illumination. My guess is that the camera uses the supplied focal length and aperture as an index into a database, retrieving the exit pupil position. Only a rough index, of course, since the identification is not unique. If the exit pupil moves forward then the falloff will be reduced and any correction may be excessive. I believe that the above argument is supported by the statement in my manual that the accuracy of CW and spot metering is improved if both focal length and aperture are supplied. Nikon used to supply a BR-4 ring that worked the aperture stop down lever via a cable release. There was also a double cable release that worked the camera release and also the BR-4 aperture control or the aperture control part of the PB-6 bellows. I've not seen any of these things but imagine that the lens is stopped down in a slow relaxed fashion prior to releasing the shutter on the camera - so this doesn't really make any difference to the Df stop down issues.

Does this image review confirm your hypothesis that it's the 'helper' AF points that are responsible for the unexpected behaviour? Not having a D850 I don't know just what it shows. On my D7200 (CAM 3500) image review shows the focus point used for 9 point dynamic even though the viewfinder only ever show the initial selected point.

Thanks for that Ilkka. I was just able to confirm what you say using a picture frame on a blank wall (simulated eye) and a table lamp in the foreground just below (simulated Mexican hat). I focus on the edge of the frame and it's sharp. I shift to the blank wall to the right of the frame and the lamp underneath, in the foreground, is now in focus. I shift back to the picture frame but the lamp stays in focus with the frame out of focus. It seems therefore that after initial focus the selected starting focus point is treated just the same as the other 8. Interestingly on my D7200 if I turn display on of focus points I can see the expected behaviour as the focus point changes even though this isn't shown in the viewfinder. Can the D850 show the 'helper' focus points if you turn on this display? If so would that help Andrew discover what's going on? Capture NX-D can show the focus points too - I don't know about non-Nikon programs.

Not wishing to be a miserable old **** but I suspect that the force needed to engage 10 sprung contacts is going to exceed the force you can apply with double sided tape or whatever and even if you can won't the socket just pop back in again when you try fitting the plug? Wish I had a better idea.

Ilkka (or Andrew or Dieter perhaps), A little of topic, but I've been trying to get my head around this for a while. From what you wrote upthread is the following a fair description of 9-point dynamic on the CAM3500 with AF-C. 1. The chosen focus point is used and focus is adjusted until such time as the detector is unable to find anything it can focus on. 2. At this point the camera decides to try an alternative. 3. My guess is that out of the surrounding 8 points it chooses the one with the least focus error. Is that your understanding? 4. The new focus point is retained until such time as:- a) The original chosen point sees something to focus on at which point the camera switches to it. Goto 1. b) If not a) and the present point becomes unable to see something to focus on then another one of the remaining 7 is chosen using the criterion in 3. above. Goto 4.

It's not so easy to compare the AF specs. of the DSLRs with the new Z cameras. My D7200 for example quotes AF down to -3 EV at ISO 100 without stating an aperture. The implication here is that it's f/5.6 or (even f/8 in the centre) since the design of the system means that the light from wider apertures is essentially lost. The Z cameras are different; IIRC they quote AF at an aperture of f/1.8, so that if the Z camera quoted AF at -3 EV ISO 100 with a f/1.8 lens then you are better of with the DSLR if your lens has an aperture slower than f/1.8.

That's what I used to think (they used to photozone.de). I'd been puzzled for sometime by the vertical scale on their MTF measurements - apparently line widths per picture height, in that they did seem a little high in some cases. Then I read an article on lenstip.com - Why the Lenstip reviews differ from others? - Where could the differences stem from? - LensTip.com ... which makes the observation that some of photozone's measuremenst exceed the resolution of the sensor! It turns out that photozone were using sharpening!!

Recently I found the service instructions for the Nikon 16-85 VR DX. I was surprised by the construction with bits and pieces hanging off the barrel along its length and even a fair bit of double sided tape. That 24-70 disassembled above looks more like I understand Canon have been doing it for some time with just one PCB and flexprint running out to the various electro-mechanical sub-assemblies. The 16-85 also uses metal brushes on the zoom encoder; not optical. You can tell it's an old design; part of the adjustment procedure uses a D200! It may be that the design reflects the evolutionary approach that Nikon have adopted. Canon EOS had the electric diaphragm and the focus motor from the first and IS pretty early too whereas with Nikon these were added later. http://ss-it.de/data/lens/AF-S%20DX%2016-85mm%20f3,5-5,6D%20G%20VR.pdf

I'm going down with a virus and feeling rough (so info. should be checked!) but you should be able to use Joe's original diag. Pins 1,2 and 3 become pins 1,2 and 3 (same) Pins 4,5 and 6 become pins 6,7 and 5 (the gate on the other side of the DIP. Pin 7 becomes pin 4 pin 14 becomes pin 8 The layout is the same except that there's only one device each side of the DIP package - you want the plastic E version. You will need a pull-up resistor on the output of the first gate (pin 3) going to Vcc (around 5.6k to 12k should do), so the saving in components is small though there is less wiring and a space saving. If you have any tantalum bead capacitors in the box it's good practice to put one across the supply, perhaps 10-50 microfarad. I do have a few concerns:- 1. Just how much current do you need to drive a white light LED sufficiently and what is the voltage across it at that current? 2. How much current can the 10 pin connector safely supply? 3. If the circuit develops a short is the camera protected internally from damage?

Probably too late if Mike has all the bits, but you could use a dual CMOS NAND buffer in an 8 pin DIP. These can sink 100mA so no transistor needed. http://www.ti.com/product/CD40107B

We are in the area I was highlighting with a fairly small difference between two large numbers. It would not take much of an increase in card write speed to remove the need for any more memory buffer! Have to wait and see. I must check my calcs. for my D7200 with the aid of those speed figures from cameramemoryspeed.com. IIRC the figures I got were inconsistent when comparing 12 bit, 14 bit compressed and not. Being a skinflint I was trying to estimate the impact of using a card a little slower than the Sandisk extreme Pro!

I don't think the relationship is quite like that is it? As the data rate from buffer to card gets close to the rate from sensor to buffer, the net buffer fill rate drops rapidly and the apparent buffer size grows rapidly. For example. Data rate from sensor 120 MB/s. Data rate to card 60 MB/s. Net fill rate 60 MB/s. Now increase the rate to the card by 50%. Data rate from sensor 120 MB/s. Data rate to card 90 MB/s. Net fill rate 30 MB/s. So a 50% faster card resulted in a doubling of apparent buffer size.

If it's not too late don't worry trying the experiment yet. I've just won a Lowepro 100aw at auction for a silly low price. Condition may not be too good but the idea is that I can give it a try and see if it will work for me. I'm hoping that the camera will fit in lens down across the width resting on the 'ears' of the internal dividers. Extra lenses may then fit in underneath, or if not at one side. Thanks again for the help.