Problems focusing Nikkor 50mm 1.4 AIS MF lens

<p>I inherited my brother's battered FM2 with a Nikkor 50mm 1.4 lens and was surprised to find that it worked. Now, having shot several rolls of film, I feel there may be a problem with the lens. Shots taken with larger apertures are often badly out of focus. I've chosen static subjects, focused carefully and kept a record of focus points. Often, objects in the foreground, well in front of the point of focus, are crisp and sharp, whereas the subject is not. There seems to be no problem with medium and smaller apertures.</p>

<p>I'm a relative novice, so there may be some error on my part.</p>

<p>Any ideas?</p>

<p>Screens for SLR cameras are often too transparent for good manual focusing. Your eye looks through them to focus on a virtual plane behind the ground surface. This causes the actual focusing plane to be short of the subject, as you have observed. The lens isn't very forgiving because you don't have much depth of field at f/1.4.</p>

<p>Make sure your eye is focused firmly on any grid or rangefinder outlines on the screen itself. These lines and the subject should be in simultaneous focus. </p>

<p>It is also possible that the screen is misplaced or even inverted. That's easy to do with replaceable screens, and easy to diagnose and fix. The ground surface should face downward, toward the mirror.</p>

<p>I've also found the screens on some of the consumer SLR's can be out of alignment in relation to the focal plane of the film. As well as the mirror may not be settling into it's proper position after each shot, which will throw off focus. </p>

<p>You mention you were surprised to find the camera still worked, is it in bad or beat up shape. Could be the lens flange is out of whack.</p>

<p>The Nikkor 50/1.4 AIS is a keeper. I find the center resolution does well on a A7ii at f/2.8 or smaller. It's okay at f/1.4, but the corners get a little fuzzy and the bokeh is a little rough.</p>

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<p>I've also found the screens on some of the consumer SLR's can be out of alignment in relation to the focal plane of the film. As well as the mirror may not be settling into it's proper position after each shot, which will throw off focus.</p>

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<p>I'd try to reseat the focusing screen first. The screen sits in a holder with a snap lock in the front. The operation is better done with a special tweezers like what comes with optional focusing screen package. If that tool is not available, you may have to impovise (difficulty level=quite easy).<br>

If the focusing screen reseating does not fix the problem, then the mirror adjustment can be an option (difficulty level= not easy, time consuming).</p>

<p>Rex: Misplaced focus is a common problem with large aperture lenses. Any lens of f/1.4 makes focussing very tricky, since these lenses tend to shift focus on stopping down and have some residual spherical aberration. The Spherical Aberration spreads the point of focus a little and makes it difficult to detect truly sharp focus with the naked eye. This is a common issue with most f/1.4 lenses, not just yours. It also affects the autofocus sensors in AF cameras.</p>

<p>Chances are that the screen is seated properly and doesn't need any tampering with. Especially not without the plastic tweezers made for the job. But it wouldn't hurt to push on the surrounding metal frame with something like a de-pointed wooden cocktail stick. If you hear a slight "click" then you'll know that the screen was slightly out of seating.</p>

<p>I believe the FM2 comes with a split image "K" type screen as standard. Using the split image <em>should </em>be fairly accurate, as should using the surrounding microprism ring. Using the remaining ground surface by eye alone makes focussing a bit hit-or-miss. If you have the K-type screen, then I'd recommend using the "focus and recompose" method. You simply focus on the subject using the central split-image or microprism and then recompose after focussing.</p>

<p>Edit: The issue will definitely be with the camera's focussing screen or your focussing technique and not the lens. Checking the camera viewing screen alignment requires another screen that you can place in the back of the camera and view with a magnifier. A makeshift screen can be made by taping a strip of Scotch "magic tape" over a microscope slide. The magic tape has a surface that acts exactly like a ground-glass screen.</p>

<p>I'm pleased with these responses, not least because it seems fairly clear from what is being said that I don't need to buy a new lens. I've also got a reason to take a closer look at the focus screen (a part of my camera that, as yet, I've not given much attention). Yes, it's a K-type screen.</p>

<p>I've just bought a Nikon F3-T. I love using it just for the feel, but I was starting to wonder what, in specific terms, what are the benefits of the 'pro' camera, and maybe there's an answer here; if focusing is easier and more reliable, that's a significant advantage.</p>

<p>As regards the condition of the camera, my brother worked as a photojournalist. The camera certainly saw plenty of service and took some knocks along the way.</p>

<p>I would suggest you remove the focusing screen and reinstall it. If it is battered as you say, it could have been knocked out of alignment. Removing the screen is easy and requires only a set of forceps</p>

<p>POSTSCRIPT</p>

<p>I had a look at the focusing screen and felt that there was no problem with its alignment. The mirror, on the other hand, looked a bit skewed. Bearing in mind Kari's comments about mirror adjustment, I took the camera to be looked over at a local shop. The guy, who is brilliant, realigned the mirror while I stood in the shop and charged me nothing. I've tested the camera out and all's well. And to think, I set out believing I was going to need to buy another lens.</p>

<p>That's a win for photo.net. Thanks for those suggestions.</p>