Manual focus

<p>Hi,</p>

<p>Recently I noticed that I get a lot of out of focus images using my Zeiss 100/2 ZF lens on a D80 body. Therefore I put the camera on a tripod, carefully adjusted the diopter and focused on a bunch of flowers some 5 m away, diaphragm wide open. I found that I often front focus. Then I tried the same procedure with my left eye, now with perfect focus. I wear contact lenses. Should not the diopter settings should fix any not optimal correction on my contacts?</p>

<p>Anyone who has any idea what the problem might be?</p>

<p>Thanks,</p>

<p>JonasF</p>

<p><em>Should not the diopter settings should fix any not optimal correction on my contacts?</em></p>

<p>Well, yes............and no! Depends on your prescription! If you have astigmatism and don't have toric contacts, then NO, the diopter correction won't help. Astigmatism is an optical pain, in that it's non-spherical, meaning that up>down and left>right are different 'power', the straight lines etc of the focussing screens aren't easy to use effectively.</p>

<p>AFAIK, the diopter correction in the viewfinder eyepiece doesn't change anything to do with the 'real' lens focus, it just changes your ability to focus your eye on the focussing screen. It doesn't shift the correct focus point. If it's wrongly set for your eye, you'll just find it much more difficult to know when it 'pops' into focus as you rotate the focus ring.</p>

<p>If you get any difference between your left and right eye, then your contact prescription needs changing or account needs to be taken for astigmatism. No single diopter adjustment on the camera will work for both eyes if they're of different prescription.<br /> Sounds like your right lens needs adjusting somewhat.</p>

<p>I nearly returned an expensive telescope eyepiece as I couldn't get it to look even satisfactory, certainly not good enough to justify the £££s. Because of it's complex optical design it really showed up how astigmatic my right eye had become, a mildly more expensive set of toric contacts was a revelation!</p>

<p>I think the D80 has a focus confirmation beep indicator, which would probably help a lot in this situation.</p>

<p>Unfortunately, modern DSLR viewfinder screens are designed solely for image brightness, and not with manual focusing in mind. The "ground glass" surface isn't really rough enough to properly focus on and is a bit too transparent. This lets your eye partly see through the screen to another plane of focus, thus fooling the eye into thinking the image is in focus when it isn't. To put it more simply and bluntly, the viewing (you can't call them focusing) screens fitted in most DSLRs are rubbish. You might want to see if any replacement screens are available from a 3rd party supplier.</p>

<p>Another solution might be to fit your Zeiss lens with a Dandelion chip. This fools the camera into thinking your lens is AF and can enable shutter focus-lockout. When this is enabled the shutter refuses to fire until focus is acquired. Now you can simply hold the shutter button down and slowly rotate the lens into focus; when the camera detects the lens is in focus, the shutter fires. Works well on the lenses that I've Dandelioned, including an f/1.8 105mm Ai-S Nikkor, which is very picky about focus.</p>

<p> Could it be you adjusted the diopter on the subject instead of the little lighted square on the focus screen. But at any rate the left and right eye many times will take a slightly different diopter setting. </p>

<blockquote>

<p>Another solution might be to fit your Zeiss lens with a Dandelion chip. This fools the camera into thinking your lens is AF and can enable shutter focus-lockout. When this is enabled the shutter refuses to fire until focus is acquired. Now you can simply hold the shutter button down and slowly rotate the lens into focus; when the camera detects the lens is in focus, the shutter fires. Works well on the lenses that I've Dandelioned, including an f/1.8 105mm Ai-S Nikkor, which is very picky about focus.</p>

</blockquote>

<p>Joe, is this working as well on the lenses that are factory chipped? I tried on D7000 with my Nikon 45/2.8 AI-P and with Zeiss Distagon 35/2 ZF.2 and I was unable to figure out how to make it work this way... Maybe I have a dumb setting on the camera that is disable this feature.... I dunno... I'd appreciate if you can elaborate a bit more.</p>

<p>I don't think the factory chips are the same, but I may be wrong. The Dandelions can definitely be programmed to activate AF lockout or not. I know that AF shutter-lock doesn't work with my factory chipped MF Samyang 35mm f/1.4, but as I said, it works a treat with Dandelion chipped Nikkors.</p>

<p>I'm not sure if the Samyang chip is reprogrammable or not. Haven't dared try to put it into program mode to be honest. I have a working lens with superb IQ and don't want to jeopardise that situation.</p>

<p>Thanks Joe! What you say about Dandelions feeds my motivation to chip ASAP my MF Nikkors!</p>

<p>To the OP: I think Joe is right regarding OEM screens being optimized for brightness, not manual focusing. I was also told (here) that there might be an effective limiting viewfinder f-stop. I'm not certain that those two statements (screen allows more forward light, not really re-scattering it; effective viewfinder f-stop) are describing the same fact. What I observe on my D70 with a Katzeye screen and a chipped 35/1.4 AI is the following: Visually I can not see a change in viewfinder brightness when stopping down from f/1.4 until I get to f/4. So it seems the viewfinder itself is limiting. I can't see a change in depth of focus until f/4 either, but the 35/1.4 might not be the best lens for that.<br /> Another question, regarding trap focus: to make trap focus work I have to switch my D70 to autofocus mode, which means the 'screwdriver' of the AF drive is poking out through the lens mount. Will this wear out the drive? It is spring loaded, but still, it's pushing against the lens.</p>

<blockquote>

<p>I tried on D7000 with my Nikon 45/2.8 AI-P and with Zeiss Distagon 35/2 ZF.2</p>

</blockquote>

<p>I tried the same lens Jonas had - ZF.2 100 to D700. Then I tried one of my Dandelion chipped lenses. They worked the same way. The focus does not affect the shutter tripping even at focus priority ( AF-single default).<br>

My Dandelions are programmed as Manual lenses. I think that Zeiss.2 are also at "manual"-mode.<br>

Then, camera settings as before, I tested one of my AF lenses. The shutter refuses to trip if the focus is not achieved (focus priority still).<br>

You CAN program Dandelion to pretend a AF-lens. Then you lose focus direction guiding arrows, BUT you gain the conditional shutter tripping when the in-focus condition fullfills.</p>

<blockquote>

<p>So it seems the viewfinder itself is limiting.</p>

</blockquote>

<p>Yes, the viewfinder in (D)SLR cameras tend to limit the aperture at around 2.5. You can not see any change in the viewfinder if you change settings between 1.4 to 2.5. The sensor does.<br>

Jonas, change the diopter correction according to your current viewing eye. What I have is a different color balance between left and right eye. To correct that would result in glasses or contact lenses of different colours. No so good solution.</p>

<p>The OP has differential focus problems left eye to right eye. Admittedly, the viewfinder screens are not great for manual focussing, but it's caused by an external problem, ie human rather than a camera problem.</p>

<p>Tech question, which focussing system does the little green dot work by? I'm guessing Contrast rather than Phase, but I'm guessing!!</p>

<p>Kari, I <em><strong>guess</strong></em> I'm slightly luckier, my eyes have the same colour balance but different saturation levels!</p>

<p>As others wrote the stock screen is way to transparent to provide accurate focusing, as the eye will see through the screen and judgement of manual focus depends on how the eye is focused. An answer to this problem is to replace the stock screen with one that is less transparent, like the KatzEye screens. I performed a test on how different type of screens affect the perceived viewfinder image here: <a href="http://otoien.zenfolio.com/p932719671">http://otoien.zenfolio.com/p932719671</a></p>

<p>your question about contacts has been misunderstood and misanswered. the purpose of the ground glass is to place an image focused by the lens at optical infinity for your eye. if you can see it well, you should be fine.</p>

<p><a href="../photodb/user?user_id=2403817">Rodeo Joe</a> is right. Modern focusing screens are no good for manual focus. too much of the light comes straight through without being scattered by the screen. your eye can adjust to make this light sharp, but it won't be sharp on the sensor. Sorry for my ignorance, but can you use live view?</p>

<p>Sadly, no Live View on the D80... :-(</p>

<p>Great reason for an UPGRADE!... :-)</p>

<p>The cheapest and best upgrade might be a better focusing screen: $105 at <a href="http://www.katzeyeoptics.com/cat--Nikon-DSLRs--cat_nikon.html">http://www.katzeyeoptics.com/cat--Nikon-DSLRs--cat_nikon.html</a>. The screen is not difficult to install (at least on a D70): If you can hold a camera steady enough to take pictures, you can do it. Trap focus with a 'Dandelion' chip works, but I find the AF 'in focus' zone a bit wide on my D70. (Both suggestions, screen and chip, were already made in the second answer to your post.)<br>

Adjusting the diopter: there is some latitude there, and it might help to keep your other eye open and focused on something distant to judge the optimal setting for the diopter.</p>

 

<p>I have a super-precision screen in my 5D1. I use it with a long lens, and it's great. for short lenses I use the 5D2 with live view. SLRs have never been great at focusing short lenses. rangefinders have always had the advantage. Try a screen. j</p>