D700 vs df Viewfinder - Ease of focusing with manual focus lenses

[q.g._de_bakker]

<i>"[...] accepted wisdom that a Fresnel lens doesn't show you [etc.]"</i>? What accepted wisdom would that be?<br>All a Fresnel lens does is create a more evenly illuminated finder image. There is nothing it does to hide differences between two arbitrarily chosen apertures.<br>There is nothing it does to produce an image that we can inspect. We still need a matte screen for that, so whether Fresnel or not there is always a <i>"genuine ground glass"</i> in the finder.<br>Basic optics.<br><br>You will see the difference between f/1.4 and f/2 in the finder. If that difference isn't big enough for you to see, it would also be too small to see when going from f/4 to f/5.6. It has nothing to do with large apertures. Nothing to do with Fresnels and 'modern' finders. And since there's also nothing else that could explain such a supernatural phenomenon, It must be you. ,-)

[jose_angel]

<p>Andrew, I performed similar tests with an old film MF camera and a 50/1.2 with really confusing results. The blur difference between say f1.2 and f1.4 or even with f2 is minimal, so in my experience I found that I have to guess a difference between them.</p>

<p>In the best (cleanest) of my tests, I placed the background (printed paper) a bit closer to have less blur, tried to be absolutely steady, to get a much closer exposure, and this time I found very slight differences between half stops, from f1.2 to f5.6 (I stopped the test at f5.6). Sincerely, I cannot get absolutely clear results, so I cannot use them to prove anything. I assume Q.G. is right, it makes sense. I have no clue on this, and my experience is also unclear.</p>

<p>It was also my assumption that AF cameras are even more difficult to focus by eye; what Rodeo said. Time ago, I tried to find MF differences between F3, F6 and D700 screens. I think I wrote something in this forum, but I cannot recall it correctly. But for sure there were very slight differences, if any, between them. It is something very difficult to distinguish, and I`m not qualified to say anything because my eyesight is really bad. Only the split prism works for me under not so sharp conditions; it works perfectly with all my f1.2 or f1.4 lenses in all conditions.</p>

<p>I wonder if the quality of the ground glass (I`m referring to the smoothness of the surface) make that differences. <br /> In my experience with LF screens, the smoother ones are darker but with a more "precise focus" feel, with them I can use stronger loupes, while the coarser ones maybe give a "sharper feel" but not as precise... and focusing loupes have to be less powered.</p>

[Andrew Garrard]

<p>At the risk of diverting the thread, but I hope of some interest to people, my professional pride requires that I try to be convincing to QG. If I was a real professional, I'd have brought two tripods and a macro rail with me to work rather than trying to hold my RX100 steady with one hand and press the DoF preview button with another, while engaging manual focus mode on the RX100 (painful one-handed) and fiddling with the D810's finder diopter. I resorted to standing my D810 on an ash-covered bin (the grey thing bottom right) - I don't smoke. Things I do for this forum... :-)<br />

<br />

Firstly, consecutive shots within a few seconds of each other. I'll report the aperture and the averaged pixel colours of the bench for each shot. Apologies for the run of posts, but it seems cleaner than trying to squeeze everything in.</p><div></div>

[Andrew Garrard]

<p>Now to start stopping down...</p><div></div>

[Andrew Garrard]

<p>Now to start seeing differences - f/2.8.</p><div></div>

[Andrew Garrard]

<p>And to be more obvious - f/4.</p><div></div>

[Andrew Garrard]

<p>And finally, f/5.6.</p><div></div>

[ShunCheung]

<p>Of course the difference between the depth of field for f1.4 and f1.8 is small, as shown on this thread: http://www.photo.net/nikon-camera-forum/00b5BR</p>

[Andrew Garrard]

<p>Thank you for the prompt, Shun. Just to show you that this really is an f/1.4 lens, here's the f/2 shot from my D810's perspective.</p><div></div>

[Andrew Garrard]

<p>And now at f/1.4, to prove you can see the difference.</p><div></div>

[Andrew Garrard]

<p>Looking through the finder, I see no difference between f/1.4 and f/2. None. If the camera hadn't gone "chunk", I wouldn't know it had happened. An optical illusion might make the change look small, or allow me to compensate, but not completely hide a change while looking straight at the image - I should see <i>something</i> if the difference was visible in the finder. Even if it were an optical illusion, the point and shoot that was looking through the finder (on manual mode) would see a change in values. It doesn't. (1/255 is measurement error.) It didn't with my previous experiment either. Obviously this isn't perfect - all I could do is wedge the compact against the back of the finder, I wasn't equipped to keep the RX100 perfectly stationary compared with the D810. That would allow a scientific experiment of how large a difference is present, but almost exactly identical numbers on two separate attempts (do check yourself on the above images) does suggest I didn't mess it up completely.<br />

<br />

A figure often quoted on this forum is that faster than around f/2.2 or maybe f/2.5, no difference is visible. I didn't try to find the exact point where that's true for the D810, but I'd say the above does strongly suggest that f/2 is above the "no difference" point and f/2.8 is below it.<br />

<br />

I'm no expert in fresnel lenses, the exact optical path that's going on here, or Nikon's parts list - I'm fully prepared to believe that different cameras behave differently. But experimentally, I'd absolutely claim that the finder screen is hiding depth of field at larger apertures. With a pure ground-glass (non-fresnel) screen, I would not expect this to be the case. Forgive me for not trying to take photos of the live view image as well!<br />

<br />

Remind me not to try to do this again. Way more painful than it's worth. :-) If I do need to, I'll have to bring a longer lens - I only brought the 35mm Sigma because we're due thunderstorms and I was optimistic for prettiness. The depth of field would have been much more obvious with something longer, but I hope it's visible enough.</p>

[q.g._de_bakker]

Andrew, i appreciate the effort you put in, but you're not going to convince me. There are no optical illusions at play. There is no magic involved. Fresnel lenses and such can only do what they can do. It's really all basic optics.<br><br>I think Jose is right, pointing us towards the origin of the myth you are trying to prove. As so often with photo-myths, it is a solid bit of reality, but misunderstood and turnied into something it really is not.<br>Yes, compared to many old cameras, the viewfinders of present day DSLRs are bad. Not as easy to use for anything but framing purposes as viewfinders once were. That, because people relied (and still rely) on AF anyway, and are not very likely to switch to manualk focus (which appears to be seen as a defect nowadays), so why bother making a high quality viewfinder with expensive screen. So they do not, and the finders in my Nikon DSLRs are indeed not as good as those of older film cameras i have and have used.<br>Somehow that will have been turned into the "accepted wisdom" (though i never heard that one before) that there is something that these finders do that restricts their usability (so far so good: they're bad) by magically (oops) stopping being a regular optical device once the apertue of a lens gets beyond a certain limit (it would indeed be magic if they did).<br><br>And again, there is no such magic you think Fresnels are capable of, Andrew. They are just field lenses, that converge a diverging beam of light a bit. There is nothing to be found chasing after a "pure-ground-glass (non fresnel) screen" and a screen that sits above a Fresnel lens.<br><br>But i'm open minded, believe it or not. So let's see a decent explanation of how that would work, and i'll gladly change my mind.<br>Let's begin, Andrew, with how this "hiding depth of field at larger apertures" would work.

[jose_angel]

<p>Actually, this issue not that simple. Out of curiosity, I did it again, trying to be as clean as possible. Results are maybe enough to have an idea of this behaviour, but I still find it somewhat confusing. It is more complex than it could seem at a first sight.</p>

<p>FWIW, I have used a non-suspicious MF camera, a F3 with the HP finder. The lens is a 50/1.4 AiS, at half stop intervals, from f1.4 to f5.6. The images from the F3`s finder has been taken with a D700 and a 105/4 Micro @ f8 (with the second tripod and the macro rail Andrew was not willing to use :). The control of light has been done with the shutter speeds by adjusting the hystogram.<br /> The focus plane is on the "12" mark, check that the split image match the point. The crops are from the area below, around the "10" mark.</p>

<p>Yes, I`d say there are differences in all f-stops, from f1.4 (or f1.2 in my previous test), but they are not that clear. Check it by yourself (attached is a 100% crop).</p>

<p>First the whole image,</p><div></div>

[jose_angel]

<p>Now, below are the crops starting from 1.4 to 2.8, and in a second row from 2.8 to f5.6. Notice that the pics are in focus, the ring portion at top is the outer side of the microprism image:</p>

[jose_angel]

<p> </p><div></div>

[jose_angel]

<p>And below there should be a link for the 100% crop:</p><div></div>

[Andrew Garrard]

<p>(Way of topic, but I hope still interesting to some...)</p>

<p>Thanks Jose - and interesting. I'm actually struggling to see much DoF difference between f/1.4 and even f4. I'd claim you can just see it on my images (with apologies again for only having a 35mm lens to hand) but not between f/1.4 and f/2, except in the actual shots from the D810, where the background is clearly softer wide open.</p>

 

<blockquote>

<p>Notice that the pics are in focus</p>

</blockquote>

<p>Show-off. :-)</p>

<p>Firstly, apologies for missing your previous post - I was too busy pasting my own sequence and just missed yours until QG brought my attention to it. For the record, quoting the Mir.com.my Nikon pages:</p>

 

<blockquote>

<p><strong>Other than the Nikon F3AF model, the standard focusing screen used on any F3 camera is the Type K screen</strong>: It is a combination of Type A and J screens. It has a Matte/Fresnel field with 3 mm split image rangefinder spot surrounded by 1 mm-wide microprism doughnut.</p>

</blockquote>

<p> <br>

I assume that's your screen. We may mainly be proving how hard this kind of thing is to photograph - though commendable effort. Sadly, taking two cameras into my office (where we're not really supposed to have any - hence shooting outside) was one thing; taking my tripods in was another. I should try some day - I've never actually used my macro rail...<br>

<br>

QG: I'm very prepared to believe that cameras are different. The assertion that larger apertures are indistinguishable has been common on this forum, and certainly wasn't started by me. I don't claim to know the mechanism, but I really stand by my measurements: there are clear pixel value differences as stops change (and I changed by a whole stop each time - not having an f/1.2 lens in my arsenal) except between f/1.4 and f/2. The sensor absolutely sees a very visible difference both in depth of field and in brightness between f/1.4 and f/2. Through the finder, I can clearly see differences at smaller apertures, but not at the f/1.4 and f/2 pair. As noted above, the bench, as shot through the finder with the aperture at f/1.4, had pixel value 147, 157, 160; by f/2, it was 146, 156, 159. That's easily within rounding error (I was averaging several pixels within the bench, but obviously my RX100 wasn't completely stationary). There really is no visible difference between the two fastest apertures, and no measurable difference as recorded by my RX100. The difference between, say, f/2.8 and f/4, or f/4 and f/5.6, is extremely visible and measurable. Actually taking a shot with the camera shows that f/1.4 and f/2 are just as differentiated - it's not that my Sigma is "lying" and actually only f/1.9. Irrespective of the optical design of the viewfinder and why this should be so, it really is a verifiable fact that, at least with this camera, you won't see the difference between the f/1.4 an f/2 apertures - it's not magic, whatever it is. I believe I've confirmed the same behaviour with a D700 in the past.<br>

<br>

I <em>am</em> interested to know how this works - but the measurements indicate that it is so, and the lack of explanation doesn't invalidate them. From this point on, I'll try some conjecture on the "why", in the hope of educating myself or inspiring others to do so. I'm expecting someone to tell me that at least some of the following is wrong...</p>

<p>To try to see what was going on, I just had a go with my F5. Firstly, again, I can see absolutely no difference when stopping the aperture down from f/1.4 to f/2.2. By f/2.5, I can see a slight reduction in brightness. I'm prepared to believe that the f/2.2 view is also slightly darker but by a small enough amount that I can't see it, but I'm not prepared to believe that it's a whole stop darker than f/1.4 before I notice anything at all. What I couldn't try on my F5, and couldn't quite be bothered to get my D810 out to prove, is how visible the aperture changes are. The D810, like the D800, D3 and D4 series (and D750 I think), drives its aperture motor separately from the mirror so you can hold down DoF preview and adjust the aperture while looking through the finder. I'd have run out of hands to try this earlier.</p>

<p>The reason I wheeled out the F5 is partly that I know what kind of screen Nikon claims it has - the standard EC-B "fine-ground matte field" shown with fresnel circles in the F5 manual - and I can also take it out and look at it (the first time I've done this - and it appears my F5 still works, so yay). Nikon do specifically make a type C with no Fresnel, and the type U screen is a fresnel "good for lenses longer than 200mm", which might be a clue to what's going on.</p>

<p>Unfortunately, the EC-B is quite a complex bit of kit, and I still can't quite see what's going on (and I'm not prepared to unscrew it). Shining a light on the prism-facing side of the screen shows a completely smooth surface - other than fine traces for the LCD wiring - that's appreciably convex (the lens on the back of the finder screen is either not fresnel or not <em>entirely</em> fresnel). Shining a light off the mirror side produces diffraction patterns - but regular ones without an obvious circular component. Shining a light <em>through</em> the screen clearly shows the circular fresnel pattern. Without a couple of hours with a macro lens and a lot more lighting than my phone, reproducing that will be difficult, so I'm afraid verbal description is what you get.</p>

<p>What's going on? Well, it looks a bit like there's a non-fresnel screen on the mirror side, a fresnel <em>inside</em> the screen arrangement, and a conventional lens on the back. But that could be rubbish.</p>

<p>The way I had always thought a fresnel screen helped was by capturing the light cone from the exit pupil. As QG says, a fresnel is just a (thin) lens, so I'd assumed there was more to the arrangement than that. I'm prepared to believe that the behaviour I've been prescribing to the fresnel in terms of whether light hitting the screen at an acute angle is captured should in fact have been blamed on the microstructure of the screen - though if in fact there is still appreciable scattering at the back of the finder, maybe the fresnel still cannot capture all of it and is still partly to blame!</p>

<p>I notice there was a brief discussion on the topic on <a href="/medium-format-photography-forum/00WS6F">this</a> thread (including QG!) - and this confirms my report of a fresnel "inside" the screen with an additional lens on the back.</p>

<p>The discussion <a href="https://luminous-landscape.com/understanding-viewfinders/">here</a> on Luminous Landscape says the following:</p>

 

<blockquote>

<p>Similarly, “focusing snap” and viewfinder brightness don’t exactly go hand in hand. The super-bright screens are essentially bundles of very small fiberoptic cables, sliced crosswise, or miniature fresnel (flattened) simple lenses. While they transmit a ton of light, they can be very difficult to focus on. Everything looks pretty sharp; it’s not very obvious what’s in focus and what’s not. (The effect is worse with wide-angle lenses, which have more depth-of-field.) Old-fashioned ground-glass screens had better focusing snap the coarser the grind (surface texture) was. But, the coarser the surface, the dimmer the finder.</p>

</blockquote>

<p> <br>

To me, that doesn't quite explain the situation, but it's interesting.<br>

<br>

Anyway. Very wide apertures, not distinguishable in the finder of a D810, F5, or probably anything in between (the Df <em>may</em> be a little different; the Df and D810 finder views are supposed to be improved, but I thought that was down to prism coatings improving brightness - the Df may or many not additionally have a different screen). I'm interested in more details of why, though.<br>

<br>

As for whether the finder of a DSLR is as good as that on a film camera, that's another matter. Technology indubitably improves, but at least from the multicam-3500 generation, the entire finder screen is seen through an LCD - which is why everything goes dark and blurry if you take the battery out and look through the finder, although also how the active AF points get to go away when you're not using them. This is definitely not true of the F5, and obviously can't be true of manual cameras. How much effect the LCD has on the finder view I can't say, but I doubt it can <em>improve</em> visibility (and I'm kind of guessing there must be a polariser in there somewhere for the LCD to work, so there'd be some light loss). However, I don't remember a huge outcry when these LCD designs were launched, so I guess the effect can't be enormous. (My Eos 300D certainly doesn't do this - it just has LEDs that light up at the focus points - but being a pentamirror it doesn't really inform me about relative brightness in finders...)<br>

<br>

Fun evening. I think I'm zeroing in on an education. :-)</p>

[Dieter Schaefer]

<p>It's my understanding that the issue of inaccurate DOF representation of modern AF screen has to do with the fact that they are optimized for maximum brightness - a feat achieved by using microlenses that focus gather light and focus it upward into the prism. The viewing area does not consist of "ground glass" but an array of microlenses. The fresnel portion is embedded and serves to even out light distribution - it is not responsible for the appearance of "too much DOF". That's caused by the microlenses "seeing" only the center portion of the lens - and depending on their characteristics, they do not "see" an increase in aperture beyond a certain value - usually somewhere around f/2.8 or a little larger. So, on the viewfinder, f/1.2, f/1.4, and f/2 all look pretty much the same.</p>

<p>IIRC, Canon has some different focusing screens that are optimized for manual focusing - those screens sacrifice brightness for the sake of "pop" - the image "springs" into focus like one was used to see with the screens in many film cameras. Which is the effect may not appear in the viewfinder of an F3 but does show in a D810 - they do not use the same type of focusing screen. MF film camera screen: "ground glass" not optimized for brightness, AF screen, optimized for brightness, sacrifices DOF preview (and thus focusing) accuracy at large apertures.</p>

<p>Edit: Andrew cross-posted - didn't see his post while writing mine.</p>

[Dieter Schaefer]

<p>Some image comparisons: actual image recorded vs image seen in viewfinder: http://www.jayandwanda.com/photography/dslr_man_focus/man_focus.html<br>

Viewfinder brightness as a function of aperture (Olympus E-1 and E-500): http://www.jayandwanda.com/photography/dslr_man_focus/ViewBright-3c.jpg</p>

[keith_b1]

<p>This link will show you what is IMO the most recent, and conclusive, evidence that the "light pipe" sliced fiber optic based modern screens in Nikons create an optical limit of about f/2.8 in terms of how it processes the aerial image from the lens into the appearance of the illusion of depth of field. No supernatural here.<br>

http://nikongear.net/revival/index.php?topic=539.0</p>

 

[jose_angel]

<p><em>"I assume that's your screen."</em><br /> Right. I haven`t checked it but I think it`s the "newer" ("red dot"), K type screen. (BTW, I also used a Beattie Intenscreen on the F3, but for whatever the reason I promptly returned to the Nikon original).<br /> <br /> My point is that even on a F3HP, which (I think) is considered amongst the best cameras to use with MF lenses, the DoF preview is not that sharp as I could expect. On AF cameras, we should expect it to be better. I can made a similar test with a good AF camera screen... (with my wife`s permission, obviously... ) :D<br /> <br /> At the Zeiss site (-manufacturer of the "premium" Zeiss ZF lenses-), I read that users should pay attention to the screen they are using. If I recall it correctly, they say AF screens are not optimized for MF just because they lack focusing aids like the split image and microprism things. They don`t even mention the GG type or quality in a first approach. <br /> <br /> After that, they mention some AF screens (cameras) are better than others. The good ones (which also lack that MF focusing aids), are the D and F one-digit pro series. They don`t mention any other "consumer" model (the site is somewhat outdated right now).<br /> <br /> DoF is also extremely subjective or dependant, sometimes it looks even an absurd concept. I`d say the "DoF preview" could be a silly idea, even more silly on a focusing screen where also happen the typical wide open softness, a possible focus shift, the roughness of the GG, the "true" speed of the less, the linearity of the aperture ring at the widest apertures, the light distribution (or whatever it is) when stopping down... etc. etc... the only thing I get from it is a more or less (rough) conclusion that the image looks sharper or not at the widest aperture. I assume it will be the same on AF cameras (with priority on the brightness of the screen).</p>

<p>Maybe the real myth is about the "reality" of the "DoF preview" in such small viewfinders.</p>

[jose_angel]

<p>Link to the Zeiss site; <a href="http://www.zeiss.com/camera-lenses/en_de/website/photography/what_makes_the_difference/focusing_screens.html">here</a>.<br /> ---<br /> I knew Dieter`s linked site; it also remind me the "electronic rangefinder aid" issue (also mentioned at the Zeiss`site).<br /> Keith`s link make me think again on the LF screens. They are made in almost every form, with all fresnel position choices. No problem here, but I still tend to think that main differences are due to the ground glass type, not to the fresnel position. Again, I´ll ask to my wife`s permission... ;D<br /> --- <br /> And a typo above: "<em>On AF cameras, we should expect it to be better... </em>". Obviously, we <strong>should`t.</strong></p>

[pete_s.]

<p>It's much too hard to use DOF to try and determine effective aperture. It also too hard to use apparent brightness to measure effective aperture.</p>

<p>What you should do instead is to measure the size of out-of-focus point spread function.</p>

<p>So find a point source light and shoot an out of focus image like the one below. Then shoot an image of the viewfinder. Then resize the images and compare the size of the "blobs".</p>

<p>An f1.2 or f1.4 lens would be best. Make the blobs as big as possible.</p>

<p> </p><div></div>

[Andrew Garrard]

<p>Thanks, everyone. Interesting threads.<br />

<br />

I'm prepared to believe that the issue with the screen not showing wider apertures is to do with another aspect of the microstructure of the screen (microlens or not) rather than with the fresnel. My apologies for conflating the two, especially if I was the first to do so - my confusion is based partly on Nikon's list of screens for the F5, for which most but not all of the screens show stylised fresnel rings.<br />

<br />

I'm also interested, but not enormously surprised, at the reports in Keith's post that the D5100 screen doesn't show aperture above f/5.6. (Actually, that's not quite what it says, but I'll go with that interpretation.) If the trade-off is brightness at a given aperture vs whether changes in aperture are visible at larger apertures, it makes sense that the D5100, which is expected to be used with f/5.6 (sometimes) kit zoom lenses, should be optimised for the brightness of those. I'd always assumed the same reasoning was true of the ~f/2.8 alleged limit on the pro bodies.</p>

<br />

<blockquote>I`d say the "DoF preview" could be a silly idea, even more silly on a focusing screen where also happen the typical wide open softness, a possible focus shift, the roughness of the GG, the "true" speed of the less, the linearity of the aperture ring at the widest apertures, the light distribution (or whatever it is) when stopping down... etc. etc... the only thing I get from it is a more or less (rough) conclusion that the image looks sharper or not at the widest aperture.</blockquote>

<p>I'm not so sure. I would find it useful to know how out-of-focus the background is. I don't care so much about trying to judge the depth of the sharp region optically (it's always a plane, anything else is only "in focus" with caveats), but I would like to have a better idea of whether I've hidden a hideous background, sometimes.<br />

<br />

Pete: Agreed. Unfortunately I had the wrong lens - you can compare branch thickness in the images I shot, but they're a bit hard to see, even in the full-size versions. These are, for the record, a PiTA to shoot. I'll see if I can give it another go this evening - I was deliberately going for outdoor shots earlier because I didn't want to confuse matters with light strobing, but that isn't an issue if I'm just pointing at an LED. My turn to try two tripods and a macro rail. I'll give my D810 + macro lens and an F5 a go rather than the RX100. It will go down well with my wife - we have an anniversary this evening...</p>

[jose_angel]

<p>Andrew, I agree that to make an idea the DoF preview works; but my point is that it is very relative. The idea it gives is very rough.<br /> (BTW, hope you have had a nice soiree... congrats. :)</p>

<p>Again, if there is still anyone interested, below I`m posting similar shots to those above with the F3, this time they belong to a D700 screen, half stop intervals from f1.4 to f4 (50/1.4AFS). Due to technical limitations the quality is not the same, but again, it could work to have an idea. <br /> Notice that the last frame is f1.4 again (red characters), to make easier a comparison with the f4 shot. I`d say there is a very slight difference between them (f4 and f1.4), so there will be also diferences between all steps, although they are extremely small to be noticed. This could be the reason to think that "below f2.8" the screen is not capable of showing the "real" DoF... I`d say it is less capable to show DoF than others (the F3 is much better in this respect). We need a "jump" from f1.4 to f2.8 (or to f4) to see a difference.<br /> <br /> According to Zeiss, the F6 is a good one; I also tested it, but I cannot see a substantial difference with the D700.</p><div></div>