Nikon F3 DOF Button Issue

<p>Ok, so I just happened to be playing with my new to me F3 this afternoon and I noticed something I don't recall seeing before.<br>

When I press the DOF button the meter reading drops by 1 stop. When I let go of the button it returns. It occurs for all f-stops except wide open. The indicated meter reading for each f-stop prior to DOF button push is spot on with my two other cameras. I have used several lenses and the same thing occurs on each. These same lenses used on my FA and F100 don't exhibit the same issue. Not sure if this will effect my exposures or not.<br>

Otherwise camera is in good shape. shutter speeds appear correct and meter readings are good. Camera has new light seals.</p>

<p>It should drop by the number of stops your lens is set at from maximum aperture. For example if you have the f/1.4 lens mounted and you set the aperture to f/2 it should drop 1 stop. If you set the aperture to f/2.8 it should drop 2 stops and so on. </p>

<p>It is called "stop down metering" :)</p>

<p>Not sure for a FA, but if I recall well, a F100 will not exhibit this, as it 'electronically' knows that DoF preview is bing used. The F3 however doesn't; it only knows how much stops a lens is from its max. aperture, and calculates exposure that way based on the light falling in through the lens. When you use DoF preview, the aperture actually is stopped down, the F3 lightmeter perceives less light, and corrects accordingly. As Bebu said, it should drop by the number of stops, but at very low light levels, the lightmeter becomes more erratic so it may become less accurate at very small apertures and/or in dim light.</p>

<p>Your F3 seems to be functioning normal. Tested my F100 as I was packing it (or FE2) for backup. F100 cancels exposure metering when the dof preveiw button is pressed.<br>

When you stop down a lot, then the not darkened eye piece may let in enough light to confuse the light meter. The more closed aperture in the lens the more light relatively via the eye piece. Maybe that happened in the O.P's case.</p>

<p>A drop in the indicated shutter speed is normal when the DOF preview is used, but as Bebu says, it shouldn't be a fixed one stop and should vary with the aperture set.</p>

<p>In any case the DOF preview is a near useless function, and I would just forget the thing even exists - except as a lock for the MU lever.</p>

<p>Thank you everyone for your responses. The light meter definitely drops a stop as I stop down on each fstop which is correct. I just would have thought that the DOF preview button would bring the aperture down to the area that would produce the same meter reading not less. Hence my concern about exposure. But maybe it is really just a light meter sensitivity issue then as mentioned and the original reading based on the wide open setting is more accurate. Time to run a roll through it along side my FA. Thanks again everyone as usual!</p>

<p>I'm actually pretty annoyed that this approach doen't work for stop-down metering on DSLRs - and I'm not quite sure why it doesn't (since manually stopping down a lens without an aperture lever works just fine). At least, it would allow pre-AI lenses to meter (and, indeed, AI lenses to meter on cameras without aperture rings) - if you could just use DoF preview and then press AE-Lock, I don't see why that wouldn't work, at least without the matrix meter. I suspect it would also be less painful than the "dial the aperture in twice" mechanism that the Df uses on pre-AI lenses (as I understand it).<br />

<br />

It's one of the little mysteries like why you can't control the aperture of an AI-s lens from the camera (seriously, why?) - and, perhaps, even why cameras with independent aperture levers (D3/D4/D8x0/D750) can't support AI lenses through open-loop metering... Of course, I may be misunderstanding something complex about the mechanicals.</p>

<p><em>the original reading based on the wide open setting is more accurate</em><br>

It most certainly is; if you use Ai/AiS lenses, you should not use stop-down metering, but just use the value presented without DoF Preview pressed. That will give the correct shutterspeed for the aperture set on the lens and ISO set on the dial. The reading with DoF pressed will be off.</p>

<p>Wouter: Why? After all, in stop-down mode, you've got the actually selected aperture, not what the lens claims it is.</p>

<p>When there is more light entering the light meter, the more accurate the meter reading is going to be. That was why we stopped using stop-down metering some half a century?? ago. By the same token, AF is more accurate when more light hits the AF module, so is manual focus.</p>

<p>Yep. Makes sense.<br>

Also, just tried the DOF again this time outside in bright light. Def. eratic and much more so as I stopped the aperture down. My FA seems much less effected...wonder it that is becuase it just had the Gus CLA treatment so the sensors are clean whereas my F3 is in need of one and the sensors might be a bit dirty causing them to be more effected by the lower light levels. I'll say that us the case so I have a good reason to send it off to Gus for his treatment :)</p>

<p>Andrew, apart from Shun's point, on the F3, it seems like the lighmeter only takes the set aperture into account, *not* whether DoF preview is engaged or not.<br /> How I reason it works (I might be wrong on details, it is the disney version): let's say I have my lens stopped down 2 stops, and the ISO selected correctly for the film I am using. The F3 meter measures an amount of light, calculates the matching shutterspeed, and divides by 4 because of the 2 stop of aperture difference. End result is displayed as the 'correct' shutterspeed.<br /> When you press DoF, the same calculation still happens, only now the light hitting the light meter is already 4 times less. So, shutterspeed will be 1/16th instead of 1/4th - 2 stops slower than it ought to be.<br /> This is why I believe - at least on my F3 with Ai and AiS lenses - you shouldn't be stop-down metering. With pre-AI lenses, things probably change, but I don't have unconverted lenses of that vintage.</p>

<p>Edit: And I might be vastly wrong, by the way, but it is the behaviour I see with my F3 in A-mode.</p>

<p>There is a step on the aperture ring of AIS lenses (or a slotted tab on AI lenses) which engages the F3 lens mount, which conveys the aperture setting to the camera. The reading should be about the same whether the DOF button is engaged or not. Since the F3 uses center-weighted metering with a sensor behind the mirror, which has a perforated coating to allow some light to pass, the pattern will change with the aperture, so the reading may change depending on light distribution in the subject.</p>

<p>While stopped down metering was largely abandoned with the advent of SLRs with automatic diaphrams, the reason was not necessarily for greater sensitivity. It is easier to see the image if the lens is wide open, and the focus point is more sharply defined. Automatic metering, which came along about 10 years later, had to accommodate this mechanism.</p>

<p>Times have changed, and many mirrorless (and the few remaining rangefinders) use stopped down metering almost exclusively, because that's the way the lenses work. While less light reaches the meter, it is the same light which ultimately strikes the sensor or film, without errors subject to mechanical or electronic coupling with the diaphram. While rangefinders use a pop-up sensor, or read light reflected from the front of the shutter, modern mirrorless cameras use the image sensor itself, as does the electronic viewfinder (100% live view).</p>

<p>If the lens is stopped down, less will reach the sensor. However in dim light, you usually open the lens, so in practice stopped down metering suffers no disadvantage. Furthermore, the sensitivity is intrinsicallyproportional to the current ISO setting, unlike DSLR sensors, which are fixed.</p>

<p>(Since the sensor is also used for focusing, any focusing shift with aperture is automatically taken into account. You can actually use the lens wide open without fussy calibration procedures, and the lenses themselves are nearly as sharp as when stopped down, unlike most SLR lenses.)</p>

<p>Shun: Okay, I buy that. Although in good light I'd still claim it was a toss-up between the meter accuracy and the accuracy of the lens's aperture stops!<br />

<br />

Wouter: Agreed that the F3 doesn't appear to know it's stop-down metering. With pre-AI lenses on an F3 (or anything more recent), it doesn't know what aperture is selected, so it would treat the stopped-down meter value as though it were wide open, which would be the right thing to do. I'm just annoyed that - unless I'm very confused - you can't do the same thing on a DSLR.<br />

<br />

Edward: Metering stopped down does not imply that you need to focus stopped down - hence my AE lock suggestion. I'm surprised to hear that mirrorless cameras run with the lens stopped down - this would provide much less light to the autofocus system. I'll have to check my GF2, but I really didn't think it did this (as usual, I could be wrong); I'd have thought small apertures would at least break on-sensor phase detect systems. Live view on a DSLR certainly doesn't stop down unless you specifically ask it to. Of course, rangefinders can stay stopped down, but that's not relevant to their focus mechanisms because they're not TTL. It's true that the meter in my Bessa R (and I believe the M5 and later) do work on a stopped-down lens, but they're not amazingly sophisticated systems.</p>

<p>I believe the F3 (and any other Nikon SLR that allows the mounting of pre-Ai lenses) allows stop-down metering via the DOF preview button; the lightmeter just measures whatever light falls on it (it has no idea whether it's bright outside and the lens is stopped down or the aperture is fully open and its dark outside - it's the same EV for it in either case) - with pre-Ai lenses it has no way of knowing what the maximum aperture of the lens attached actually is. It was never intended to allow stop-down metering with Ai/Ai-S lenses - because that feature is not needed there. It just provides a means to meter without knowing anything about the lens that's attached.</p>

<p>Can't answer Andrew's question why Nikon chooses to cripple (all) DSLR as to not allow metering with non-CPU lenses (or the need to enter the information) - my Sony A7 has no issue metering any lens I put on it via an adapter - not knowing anything about the lens at all.</p>

<p> </p>

<p>So after reading these recent excellent posts I tried a little experiment. I put my AI-S lens on the F3 and stopped down to f22 and took a reading. Then I removed the lens and pushed the little coupling prong out of the way. Now when I stop down to f22 the meter reading stays constant as the camera doesn't know I moved the aperture ring. Then I pushed the DOF button and took the reading. This reading matched the original AI-S f22 reading. Now it makes more sense to me.<br>

Again thank you all for your very detailed and thoughtful answers. Whenever I post here I always leave with more knowledge and so far no one ridiculing my question. Great forum.</p>

<p>Andrew,<br /> I have only one auto-focus lens for the Sony A7, a Sony 70-200 f/4. There is no aperture ring, but I was surprised to find that using the control wheel for the aperture actually closed the lens down. There is no auto-aperture, even though it probably wouldn't be hard to implement at the expense of greater size and complexity of the lens.</p>

<p>In the A7, the AF sensors, both phase and contrast detectors, are embedded in the sensor. They work differently than the prism mounted sensors in a Nikon DSLR, and are not dependent on the size of the incident cone of light. For other reasons, the Sony doesn't focus as well as a DSLR in dim light, but that may resolved with further development, even firmware. For more details, see (http://www.dpreview.com/articles/1652088044/sony-an-eye-on-focus?utm_campaign=internal-link&utm_source=features-default&utm_medium=homepage-block&ref=features-default) and (http://www.dpreview.com/articles/7945517371/opinion-did-sony-just-do-the-impossible)</p>

<p>Most lenses have some degree of focus shift with aperture, and in some (e.g., Leica Summitar) it is excessive. It is for this reason that Nikon DSLRs and others have provisions for focus fine tuning. With mirrorless cameras, it is a non-issue. It is so easy to achieve precise focus with the A7ii, for example, that anything less is almost disappointing when viewed at the pixel level. You learn to accept that OOF in the second row of faces in a group at f/5.6 is still good enough to print, and is equivalent to "in focus" with my D3.</p>

<p>Not all DSLRs disable metering in non-chipped lenses. I have several older lenses which work just fine on my D2x and D3. If you program for the lens, the correct f/stop is displayed and logged. The single-digit Nikons retain the aperture coupling ring on the mount. On the F3, F4 and F5, the coupling tab folds out of the way for pre-AIS lenses.</p>

<blockquote>

<p>Of course, rangefinders can stay stopped down, but that's not relevant to their focus mechanisms because they're not TTL.</p>

</blockquote>

<p>Certainly wasn't with film, but now that the M has live view, it does become an issue. And M-mount lenses don't have an automatic diaphragm.</p>

 

<blockquote>

<p>Sony A7 ...t here is no aperture ring, but I was surprised to find that using the control wheel for the aperture actually closed the lens down.</p>

</blockquote>

<p>Don't have an AF lens for my A7, so I can't check. On my Ricoh GR, which has an f/2.8 lens, it is obvious that the lens focuses at f/4 and then opens or closes to the selected f-stop. In other words, the lens is always at f/4 and only goes to the selected value when AF has finished its job. I will see if I can borrow an AF lens for the A7 to check if it behaves that way too.</p>

 

<p>Too late to edit the above: it appears that the behavior of the diaphragm on the "A7 lenses" depends on whether or not the live view effects are turned on or off. If off, then the lens will focus wide open and then stop down to the set aperture. If the live view effect is on, then the lens will start stopped down, but open up depending on overall scene brightness (though usually not to fully open) during AF operation. You probably want that effect set to on in order to get the full benefits of using live view - with it set to off you want get WYSIWYG.</p>

<p>Whether or not pre-AF is enabled could make a difference as to being able to observe that behavior - the camera may already have acquired focus before you look at the iris behavior.</p>

<p>The Leica M6 (film) has TTL auto exposure.</p>

<p>I had forgotten about "Live Effects ON/OFF" in the Sony A7ii. It's not explained very well in the manual, and only slightly better in the camera help site. It affects a wide range of option settings, including image stabilization, so I generally leave it on.</p>

<p>There's always a final focus even with pre-focus enabled, whereupon the green focusing points appear. I suspect that occurs after the aperture closes, but things happen too quickly to tell for sure. I generally use "aperture priority", in fact there's little choice with manual lenses, which I use most of the time. The viewfinder automatically adjusts to constant brightness with exposure changes, according to the ambient light level.</p>

<p>For the information of others in the forum, "pre-focus" is an option wherein auto focus is engaged continuously, based on the selected focus area. Focus finalizes when you press (half-press) the shutter release. In single mode, focus then locks, or in continuous mode it tracks that object in three dimensions. In addition to the normal patterns (center, closest object, etc.), the camera can recognize faces (eyes), even smiles, and can be trained to recognize up to 10 separate people.</p>

<p>If the A7 sounds like a video game with a shutter, you have it about right. There are a LOT of options in a D3 too, which most people never visit. You find which settings work, then keep them until something doesn't work the way you want. I learned something new today.</p>

<p>James: Glad we helped. I'm still learning here too!<br />

<br />

Edward/Dieter: Thanks for clarifying. It makes sense that the Sony, like the Nikons in live view mode, have the option of stopping down to give you a faithful impression of the shooting aperture. The GR behaviour is fascinating - presumably the f/2.8 performance is such that the optical aberrations could confuse the AF.<br />

<br />

I believe on-sensor phase-detect AF <i>does</i> still depend on the cone of light - it effectively blocks light from one side of the lens for some of the sensor sites, and I believe that mask has to be "aimed" at one side of the lens. I'm prepared to believe it's got fairly wide coverage, just as even a D700 will <i>usually</i> focus at f/6.3, even though f/5.6 is quoted. I could also be entirely wrong about how this works - obviously there's less optical difference available than on an SLR.<br />

<br />

Dieter: Good point with the live view rangefinder - but in my defence, if you're using live view, the rangefinder is incidental. :-) Very interesting about the A7.</p>

 

<blockquote>Most lenses have some degree of focus shift with aperture, and in some (e.g., Leica Summitar) it is excessive. It is for this reason that Nikon DSLRs and others have provisions for focus fine tuning.</blockquote>

 

<p>Well, I <i>wish</i> it was possible to do aperture-dependent fine tuning on Nikon DSLRs! And, indeed, zoom length dependency. Or different settings for different ends of the focus distance range. Sigma offer the latter two, but only via a really clunky mechanism of "try a shot, take the lens off, put it on the dock, upload, put it back on the camera, iterate". Why they couldn't just put a micro-USB port on the side of the lens so you could update it on the camera I don't know. And why Nikon have taken so long to put this kind of functionality in the body (and why the entire process couldn't be automated in calibration against images from the sensor) is a mystery too; I guess someone has a patent that we're all suffering for.</p>

 

<blockquote>Not all DSLRs disable metering in non-chipped lenses. I have several older lenses which work just fine on my D2x and D3. If you program for the lens, the correct f/stop is displayed and logged. The single-digit Nikons retain the aperture coupling ring on the mount. On the F3, F4 and F5, the coupling tab folds out of the way for pre-AIS lenses.</blockquote>

 

<p>Pedantically, you need an adjusted coupling tab on the F5 (and F6) - it's not standard, and mine doesn't have it. I should really see if I can find someone who'll still fit one, just in case.<br />

<br />

I have some AI-S lenses that "work fine" too (on my F5 and D810) - but they need to be AI in order to meter; there is no DSLR which can stop-down meter, which ought to work perfectly well even with <i>non</i>-AI lenses, because the camera doesn't need to know the aperture difference (unlike metering wide open). Also, you have to use the lens's aperture ring to change the aperture, because the camera doesn't know that the aperture lever is linearised with respect to aperture, so the camera doesn't know where to move the lever to (unlike an AF lens). The FA and F4 know this by detecting the indent on the back of AI-s lenses, which no Nikon DSLR can detect. What frustrates me is that when you enter the maximum f-stop, you could also perfectly well tell the camera that the lens was AI-s, meaning that it could control the aperture via the lever - giving you aperture control via the camera dials and automatically in shutter priority or program mode. The F5 has the same functionality as the digital cameras with an aperture ring, except that you can't tell it the maximum lens aperture or focal length (you can on the F6) which means you're stuck with no matrix meter. The F5, of course, has an optical view of the aperture ring, so you can see what you've set anyway (in good light); the digital cameras lack this.<br />

<br />

The FA and to a lesser extent a few others (FG, F301, F501, EM, FG20, F4 - see <a href="https://www.graysofwestminster.co.uk/glossary/ai_ais_difference.php">here</a>) can pick up the maximum aperture from the mechanical indicator on AI lenses (<a href="http://www.photo.net/nikon-camera-forum/00ELD">more here</a> and my confusion <a href="http://www.photo.net/nikon-camera-forum/00biPA">here</a>), which is a trick that nothing recent can do. I'd still love to see Nikon make a DSLR will a fully-featured money-no-object F mount with full compatibility with everything - I don't believe any F-mount features are mutually-incompatible, except possibly the first AF prototypes. The Df isn't that camera - it can't even handle invasive fish-eyes fully.</p>

<p>Andrew! I know exactly how and why a camera like the F3 would work with stop down mode. In fact it would meter with anything you can mount in front of it. Like you I don't understand why modern cameras can't do stop down metering, I do understand why Nikon doesn't let the matrix metering work in stop down but I still don't understand why other modes don't work as well. </p>

<p>An important fact that the F3 doesn't know which aperture is selected. It only knows how many stops the lens is stopped down from maximum. Modern camera insist on knowing exactly what aperture number is selected because it wants to know the real scene brightness and not only what I sees through the lens. </p>

<p>...and the film cameras only <i>need</i> to know how many stops to stop down (which is what the AI follower ring does on cameras that have it, and what's missing from the low-end DSLRs) in order to meter wide open, so that it knows how much will change. The F3 (and 4, and 5) have a usability advantage that they have a hole in the finder so you can optically see the set aperture on the lens, which you can't on a DSLR; whether this matters in another issue. Still, I have non-AI lenses from third parties (Kiev, Hartblei, Peleng) which still mount on a DSLR, with manual stop-down functionality (like the Nikkor TS-E lenses only clunkier), and the metering has always been just fine - especially if you don't try to matrix. All I need a camera to do is drop its aperture lever before metering! On the high end DSLRs with the mirror and aperture lever independent, this shouldn't be a technical problem even to do automatically - though I can see that cameras with a mirror and aperture lever interlock (if I've got that right) there might be an issue; the AE-lock solution should solve it, though.<br />

<br />

Of course, while I appreciate the matrix meter does some things dependent on the apparent absolute brightness (such as trying to detect snow...) I really don't think it can matter all that much - otherwise anyone who screws an ND filter onto their lens would have metering problems.</p>