DOF preview doesn't get darker in smaller aperture

[shiang_wang1]

<p>I have a Voigtlander 58mm f/1.4, when I use it on FM2, DOF preview works as expected on all apertures.<br>

But when I use it on F100, DOF preview doesn't get darker until I step down to f/2.2. I don't have other Nikon lenses that are as bright as this one, so I can't verify if it is a problem with this third party lens or F100 DOF preview button can't handle aperture below f/2.2.<br>

At first I thought the electronic DOF preview doesn't push the lever all the way, but it does. Does anyone know why?<br>

Thanks</p>

[Jerry_]

<p>Electronic connections in a Nikkor lens were designed by the same engineers that constructed your Nikon camera body. Using a Voightlander lens that may or may not have <strong>the best-guess electronic understanding</strong> of what a F100 requires for good communication between a lens and the camera. It should work well, but if the only problem issue is DOF preview and that is <em>a important feature</em> for you, you need to find a Nikkor lens.</p>

<p> </p>

[ilkka_nissila]

<p>The OP's observation is correct and normal. Typical included focusing screens of autofocus cameras do not show noticeable differences at the widest apertures (i.e. f/2.5 or wider).</p>

[hans_janssen]

<p>Look into the front lens when you push the DOF button, so you can see if the aperture is closing.</p>

[CvhKaar]

<blockquote>

<p>Electronic connections in a Nikkor lens were designed by the same engineers that constructed your Nikon camera body</p>

</blockquote>

<p>I do not understand this statement in this context, since the aperture control (and also the DOF Preview) are mechanical aren't they ?</p>

[Peter_in_PA]

<blockquote>

<p>The OP's observation is correct and normal. Typical included focusing screens of autofocus cameras do not show noticeable differences at the widest apertures (i.e. f/2.5 or wider).</p>

</blockquote>

<p>This is the fact. I've also tested and seen it on my DSLRs (although I wasn't aware that even the F100 was affected.. Not only that, but you can't tell the difference, I'll bet, in DOF through the DOF preview between f2.2 and f1.4, can you? The viewfinder is designed and built for brightness with slow lenses, and this is what's sacrificed. The good news is that when you put a slower lens on the camera, you can perhaps see better through the viewfinder than you can with an older camera like your FM2.</p>

<p>It's normal, and it has nothing to do with Nikkor or non-Nikkor lenses (although that can occasionally be an issue in other ways, especially AF).</p>

[joseph_wisniewski]

<p>To elaborate on what Ilkka said:</p>

<p>Bright screens don't scatter much light, that's why they're bright. 50 of the light hitting a bright screen stays within a cone of about 10 degrees. 10 degrees is f5.6. You see basically the f4 DOF on a wide open f1.4 or f2 lens. f4 is actually a 14 degree cone, but like I said, the normal screen puts 50% of the light in the 10 degree f5.6 cone, the other 50% is distributed over the f4 and f2.8 cones. Nothing outside f2.8, its "extinction angles" is around 20 degrees.</p>

<p>The discrepancy in brightness and bokeh decreases as you stop down: what you see at f1.4 is 3 stops "wrong", what you see at f4 is only about 1 stop wrong, and by f8, you're all caught up. Then you start getting too dim to judge DOF. So, basically, the DOF preview button lets you preview DOF at any aperture you want, as long as it's f8. Henry Ford would have been so proud...</p>

<p>There's a second, unexpected side effect. You cannot see harsh bokeh on the focusing screen. Because the screen "rolls off" the sharp edge of the light cone, bokeh always looks better on the screen than it does in the print.</p>

[johnw63]

<p>How far back do you have to go, to see the difference, down to , say, f1.4 ? The F2 ? The F3 ? Probably not the F4.</p>

[photo5]

<p>The F3 will show the difference, as it has a high quality ground glass (as do the F and F2, don't know about the F4), not just a thin plastic focusing screen. I know the F100 has just the focusing screen.</p>

[johnw63]

<p>The F4 has plastic screens, I think. I changed mine, and it didn't feel heavy, like glass would.</p>

<p> </p>

[joseph_wisniewski]

<blockquote>

<p>How far back do you have to go, to see the difference, down to , say, f1.4 ? The F2 ? The F3 ? Probably not the F4.</p>

</blockquote>

<p>F5, actually. Not with the default EC screen, which has the sort of scattering characteristics I described earlier, about a 10 degree cone. The D was the ultra wide scattering screen that you used with the fastest lenses. Use an F4 D in an F5. Which brings us to...</p>

<blockquote>

<p>The F3 will show the difference, as it has a high quality ground glass (as do the F and F2, don't know about the F4), not just a thin plastic focusing screen.</p>

</blockquote>

<p>That's totally wrong. But it's an interesting, Luddite kind of wrong. The basic, easy wrongness of it is that F, F2, and F3 have plastic screens, the heavy glass thing in the frame with them is the condenser lens. By making that part of the screen assembly, you get the ability to view directly looking down on the camera without a prism finder in place. Of course, you get an optical mismatch between condenser and the lenses in the prism finder, but hey, you get to act like a Blad shooter and contemplate your navel. What more do you want? Ground glass is for view cameras. F4 introduced condensers in the prism finder, so they matched each finder, giving a less distorted view than earlier Fs.</p>

<p>And the second level of wrong is that there is nothing, at all, about a ground glass screen that makes it either "high quality" compared to plastic, or more capable of showing the DOF and relative brightness of fast lenses. In fact, reality is exactly the opposite.</p>

<p>As I explained earlier, it is the angle at which a focusing screen scatters light that controls the DOF and relative aperture brightness of a screen. For a glass screen, this is dependent on how coarse the glass is ground (actually, sandblasted, but "blasted glass" doesn't sound like something a Luddite can brag about) and then how the glass is acid dipped, heat treated, or lacquered. A plastic (or hybrid plastic over glass) screen has a molded pattern, and the master is cut, like a old fashioned vinyl record, with a diamond tooled machine. The designer can precisely cut any deflection angle, he doesn't have to hope that this week, one certain combination of blasting grit and lacquer comes close to the Nikon spec for a G4 screen...</p>

<p>So, as zooms caught on more and more (not AF, not digital, put the blame where it really belongs, photographers' desire to have more zoom range, at the expense of speed) the camera companies lowered the scattering angles for their default screens to accommodate. But they still made the coarser screens for people who wanted them.</p>

<p>It's a pity, although Nikon stopped making wide scattering screens, Canon still does. Their EFS screen is a classic high scattering screen.</p>

<p>wizfaq focusing screens.</p>

[photo5]

<p>Joseph, "Luddite" is one who fears technology. I don't know why you would say my comment was a "luddite kind of wrong." I certainly appreciate the correction, I forgot that the F3 and older F bodies had the plastic screen on top of the glass condenser lens. But please watch yourself and be respectful of other forum members, even when they are not entirely correct, as in this case.</p>

[joseph_wisniewski]

<p>Dave, I was reacting to your whole "a high quality ground glass" vs. "just a thin plastic" comment.</p>

<p>There are few people who love glass more than I. My wife and I are well known in the local art glass community, we collect paperweights, depression glass, modern art glass, etc.</p>

<p>But I stand beside my original stance, to state that there are any quality implications in the use of "just plastic" for a focusing screen is a technophobic point of view.</p>

[shiang_wang1]

<p>Thanks for all the responses. f/1.4 is very difficult to focus, now I need to keep in mind even if I see it is focus on the view finder, it might appear out of focus on the final image as I learn it in the hard way.</p>