D700 Underexposure Puzzle

<p>Now we will look at f/4. Still with Center-weighted. Note how the vignetting clears up, doing away with much of the underexposure.</p><div></div>

<p>Next is at f/8. Everything else is still the same. Camera on tripod for all shots, as requested.</p><div></div>

<p>You would think the center weighted metering would notice the dark, vignetted corners and respond by lightening the picture a tad. Well, maybe it did. But wait: maybe matrix metering is the answer. Let's see if it will notice those dark corners and do something about it. Back to f/2, with matrix metering:</p><div></div>

<p>Gee, not so good, eh? Center-weighted was better. Let's save Photo.net a little disk space and just skip to f/8:</p><div></div>

<p>Oh, I almost forgot--just one more thing (Lt. Columbo). Let's go back to f/2, and center-weighted metering, and this time bump the vignetting control up to maximum:</p><div></div>

<p>Does it look any better than on normal vignetting control? Maybe a little.</p>

<p>In this series vignetting seems to explain a lot of the underexposure. That's got to be part of what is going on. But in the previous series of the fire station, when I used the 35/2 AF, which does not vignette so much, I still had this effect of underexposure at wider apertures. It just wasn't as pronounced. I wonder if I should try with a different lens now? Maybe the 35/2 AF, or the normal 50/1.4, or the 50/1.8? But first, does anyone want to see that?</p>

<p>Rob, <strong>M</strong>anual means <strong>No Metering, inc No Vignette Control! </strong>Still don't know if it's a lens or metering issue.....?</p>

<blockquote>

<p>Rob, <strong>M</strong>anual means <strong>No Metering, inc No Vignette Control!</strong></p>

</blockquote>

<p>I don't agree. I see no reason why you can't use the meter during manual exposure. I've been doing it for years--since I got my FE2. Before that, I did it with a Weston Master IV, with Leica M2 and Nikon F. You need a meter reading, for goodness sake.</p>

<p>Rob, you completely miss the point of my post. Use the meter ONCE to get a generic exposure and then take a separate picture with each of the different aperture/shutter speed combos of the same exposure to see if the variation is the lens' aperture. They should all be of identical brightness with a very similar histogram position.<br>

You do get that <a href="mailto:125th@f8">125th@f8</a> should give exactly the same exposure 'brightness' as <a href="mailto:250th@f5.6">250th@f5.6</a> right ?<br>

If this makes no sense.... :-(</p>

<blockquote>

<p>No sun today</p>

</blockquote>

<p>Unfortunately, overcast conditions are a poor choice to do controlled tests. Of course there there is sun today. It's above the overcast. If there are scattered clouds between the overcast and the sun, you will have variable lighting conditions.</p>

<p>When using aperture priority mode, you should still pay attention to the shutter speed selected by the camera. Close down the lens a stop and you should see the shutter speed slow down a stop.</p>

<p>You don't even need to take a picture to see if the metering system is working sanely. Put the camera on a tripod and watch the shutter speed change as you change the aperture.</p>

<p>In the three photos above with center weighted metering at f/2, f/4, and f/8, the camera chose the following shutter speeds</p>

<ul>

<li>f/2 - 1/2500</li>

<li>f/4 - 1/640</li>

<li>f/8 - 1/125</li>

</ul>

<p>In aperture priority mode, the displayed shutter speeds might be rounded from the actual shutter speed selected by the meter. f/8 @ 1/125 will collect about 1/3 stop more light than f/2 @ 1/2500. <br /> <br />But the two samples show way more variation than 1/3 stop. The most likely explanation for this is that the ambient lighting changed.<br /> <br />If the ambient lighting were consistent, then one explanation for the brighter image at the small apertures is that the aperture blades are sticky and aren't stopping down properly. A problem with the stop down lever could be another explanation.</p>

<p>What you should do first is to confirm that the camera is working correctly when using manual exposures. Pick an indoor scene with constant lighting. Manually meter to set correct exposure then take a series stopping down the lens one stop each time the shutter speed is reduced one stop. All the photos should be consistent and the RGB histograms should be nearly identical.</p>

<p>After doing the manual exposure test, you can proceed to aperture priority with matrix metering. Changing the aperture one stop should result in a shutter speed change of one stop. All the images should be consistent and have nearly identical histograms.</p>

<p>After passing each of the above tests independent, you can begin to wonder why matrix metering isn't giving the same image as as with center weighted metering. For an average indoor scene, I think matrix metering will give similar results.</p>

<p> </p>

<p>Any chance the settings on this menu item were changed:</p>

<p><strong>b6 Fine tune optimal exposure</strong></p>

<p>I mention this only because A) this will not be recorded in the exif as exposure compensation B) spot, center-weighted, and matrix can be changed independently (causing greater that expected variations between the 3 types), and C) neither the 2-finger reset nor the other menu reset option will restore these values if they were changed.</p>

<p>Just a WAG. Be a shame to do all this testing if it was something you or someone else set and forgot about.</p>

<p>Sounds as good as anything else, Steve. It might explain why the multi-pattern metering didn't do what I thought it should. I'll check it out.</p>

<blockquote>

<p>Rob, you completely miss the point of my post. Use the meter ONCE to get a generic exposure and then take a separate picture with each of the different aperture/shutter speed combos of the same exposure to see if the variation is the lens' aperture. They should all be of identical brightness with a very similar histogram position.<br />You do get that <a href="mailto:125th@f8" rel="nofollow">125th@f8</a> should give exactly the same exposure 'brightness' as <a href="mailto:250th@f5.6" rel="nofollow">250th@f5.6</a> right ?<br />If this makes no sense.... :-(</p>

 

</blockquote>

<p>Umm . . . I understood the reciprocity of shutter speed and aperture by the time I was 12. My dad explained it and I grasped it instantly. That's when I started shooting with his Leica II and Weston Meter. I'm 71 now and still have the M2 that I bought at 19 with my savings out of my USAF paycheck(s).</p>

<p>Right, I didn't do it your way. Not yet. Doesn't mean I won't. But I wanted to demonstrate what the camera is doing under actual shooting conditions. One does not expect, in the normal course of things, to set shutter speeds by mental calculation when using such a sophisticated camera. With a manual Leica, I do it all the time. So far I am just trying to demonstrate that the D700--my D700--makes the picture darker when you would think that, if anything, at a wider aperture, it would make it lighter. Or hopefully give the same exposure.</p>

<p>At this particular point, I looking at vignetting as a contributing factor. we'll see.</p>

<blockquote>

<p>If the ambient lighting were consistent, then one explanation for the brighter image at the small apertures is that the aperture blades are sticky and aren't stopping down properly. A problem with the stop down lever could be another explanation.</p>

 

</blockquote>

<p>The outdoor light was pretty consistent, especially on the cloudless days of the first series. We can rule that out. As to the possibility of mechanical stickiness, I did get the same effect with three lenses, which would seem to rule out the lenses. As to the stop-down lever, well I got pretty normal exposures--I think--with those three lenses plus a fourth, at f/8 and f/11 yesterday. That seems to rule out the stop-down lever (seems that way to me at the moment). However I am going to go ahead now with the fully manual experiment, and we will see what happens.</p>

<p>Good night, everyone. Thanks for the pointers.</p>

When you do the "full manual" experiment, set the aperture with the aperture ring, instead of electronically. That should

help you isolate whether aperture control issues are part of your problem.

 

Also, you mentioned that the camera might meter differently near wide open because it sees vignetting. Since the camera

always meters with the lens wide open, this should make no difference.

<p>OK. Here we go. Camera on tripod, set to manual. Sunny day, cloudless sky. By Sunny 16, exposure should be 1/200 at 16. Spectra Professional meter confirms: 1/200 at 16. D700 set to 200, f/16; exposure indicator zeroes out at 1/160. So be it, we will use 1/1/60. here's what I got at f/2:</p>

<p>Well, the picture didn't upload. What I got was severely underexposed at f/2. Stopdown mechanisms shouldn't matter, since the diaphragm is wide open for both metering and exposure. I'll try again:</p><div></div>

<p>Vignette control was still set to "high" since I forgot to turn it off. Here's what I got at F/16. Looks good to me. I can skip the in-between pictures. The exposure increased with each successive stop, until f/11, which is nearly the same as f/16.</p>

<p>Vignette control was still set to "high" since I forgot to turn it off. Here's what I got at F/16. Looks good to me. I can skip the in-between pictures. The exposure increased with each successive stop, until f/11, which is nearly the same as f/16.</p><div></div>

<p>The problem is the shutter is not accurate at higher shutter speeds. The camera needs to be serviced.</p>

 

<p>You began the series above with a manual camera setting of 1/8000 @ f/2, so the series of photos you should have taken was:</p>

<p>1/8000 @ f/2<br>

1/4000 @ f/2.8<br>

1/2000 @ f/4<br>

1/1000 @ f/5.6<br>

1/500 @ f/8<br>

1/250 @ f/11<br>

1/125 @ f/16</p>

<p>I'm not sure whether you understand that the metering mode is irrelevant since you pointed out you were using center-weighted metering.</p>

<p>Whether or not the exposure is even accurate doesn't really matter for the above series.</p>

<p>What matters is that the above series should give images with approximately the same density (film) or histogram (digital). They could all be underexposed (by the same amount) or overexposed (by the same amount) or even perfectly exposed. What matters is that each of them should be pretty much the same.</p>

<p>All of the other camera settings are taken out of the equation. You don't have to puzzle about how matrix metering magically decides what exposure to use. You don't have to wonder whether you spot metered off a good spot. It won't matter whether vignette control is on or off as long as it is at the same setting for all shots.</p>

<p>You did make a minor mistake on your f/16 image as it was shot at 1/160" instead of 1/125" which is what was needed to get the same exposure as at f/2. But the f/16 image would have been even brighter which would still indicate the problem at high shutter speeds.</p>

<p>I've heard that replacing a shutter isn't terribly expensive but if you're lucky, maybe there's a calibration procedure that can be done.</p>

<p>Good luck.</p>

 

<p><em>'So far I am just trying to demonstrate that the D700--my D700--makes the picture darker when you would think that, if anything, at a wider aperture, it would make it lighter'</em></p>

<p>I suspect the entity, known as your D700, is NOT doing anything of the sort. It's telling the shutter to stay open for X, and the aperture to shut down to Y. Full stop. However, one or the other, or possibly both, are NOT doing as they are told. The D700 won't know a thing about it.</p>

<p>Metering is done wide open, so any failure to close quickly enough is an aperture error and usually results in overly bright or erratic exposures.</p>

<p>Shutters are <em>usually </em>very reliable, but when beginning to fail, the very top end and the very bottom tend to suffer first.</p>

<p>Usually the way of differentiating is to see if it effects all lenses the same = shutter<br>

or one lens, maybe 2 if old lenses, = sluggish apertures.</p>

<p>Tom: Although the series was presented with f/2 first and f/16 last, I actually shot the other way, beginning at f/16 and 1/160. Then it went: f/11, 1/320; f/8, 1/640; f/5.6, 1/1250; f/4, 1/2500; f/2.8, 1/5000; and f/2, 1/8000. Note that the final speed should be 1/10,000, but the camera only goes to 1/8000. That error, however, ought to be on the plus side. It should have made the picture 1/3 stop more exposed.</p>

<p>The points about the metering mode, vignette control, etc are well taken--all we really care about is that the exposures are either consistent, or else they are not. And they are not.</p>

<p>Mike, I see you have reached the same conclusion, concerning the shutter. One thing bothers me, though: Let's note that the correct shutter speed would have been 1/10,000 at f/2. And the picture at f/2 was, just offhand, maybe 3 to 4 stops underexposed. To be even 3 stops under, the shutter would have to be operating at 1/80,000. For 4 stops, it would take 1/160,000. That's a pretty fast shutter, guys! The D700 only goes to 1/8000. Problem there: how can it be the shutter?</p>

<p>This makes me think more along the lines of some sort of reciprocity failure of the sensor. It's not putting out the full quota of electrons when the exposure is that brief. Does that make sense?</p><div></div>

<p>I guess those are <em>indicated</em> speeds. If the first blind is 'late' or the second 'early', it would act like a faster shutter.</p>

<p>However, I still favour the lazy apertures.</p>

<p>Borrow a new(ish) G lens and do a <strong>M</strong>anual Series (once only metering to set a basis) series of shots. If they are <strong>not</strong> near identical, I'd think Shutter. However, if they are very close, it's sticky old Apertures in the <em><strong>other</strong></em> lenses. </p>

<p>It's not a question of lazy apertures. The meter reading on the scene was 1/160 at f/16 and that image was exposed properly. A lazy aperture would have caused a shot at f/16 to be overexposed while the shot at f/2 would have been correctly exposed. Instead the opposite happened.</p>

<p>The posted example labeled f/4 at 1/2500 is actually the same file as f/16 at 1/160. Rob - you said "I can skip the in-between pictures." Did you even bother to look at them? You should have noticed the progressive underexposure as you moved form 1/160 to 1/8000.<br>

<br /><br>

And your comments about shutter speeds of 1/80,000" and 1/160,000" suggest you don't understand how a focal plane shutter works. <br>

<br /><br>

The curtains of a focal plane shutter move at the same speed irregardless of shutter speed. Exposure is controlled by varying the delay between the first curtain opening and the second curtain closing. At speeds above 1/250" (flash sync speed), the second curtain begins closing before the first curtain is fully open. As the exposure time decreases ("faster" shutter speed is really a misnomer), a progressively smaller slit moves across the frame. For more detail, search on something like "How does a focal plane shutter work".</p>

<p>Your shutter isn't working right. Send it in for a repair.</p>