photog11 Loc: San Francisco

I splurged $100 on an old Nikkor Ai 300mm 4.5 lens. It is a manual focus lens used on D750, and I am missing focus, also some chromatic aberration I think. Please take a look at these photos. Is the lens ok? Why do I miss focus at less than infinity? Any tips? These shots were handheld.

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CHG_CANON Loc: the Windy City

You're probably heard all the hype about mirrorless cameras? One of the reasons is how they enable / enhance manual focus lenses. Take your coot for an example. We can download the image and click to the 1:1 details and see the missed focus.

Now imagine if that 1:1 detail had been available in your view finder for you to 'see' and accurately focus the manual lens on the bird's head in passing. Imagine too if you could confidently shoot at a slower shutter knowing the in-body stabilization will handle any camera shake.

Imagine if you could zoom to the details in the EVF (Electronic View Finder) of those far buildings at Point Richmond and focus exactly on those houses and capture a sharply focused image? If you had set-up a tripod and used the zoom display on the DSLR's rear LiveView, you'd have a similar ability to see and focus on those small-in-frame details.

Finally, imagine if the EVF also highlighted with a yellow (or white or red) shimmering color telling you where the camera was focused. That shimmer is most useful when you can't zoom to the 10x details in the EVF for a moving subject. As these pelicans flew by, you could use that shimmering color to help judge the plane of focus and help to adjust to a bird as it passed. Although, BIF is a challenge even with an AF lens.

Quixdraw Loc: x

So it is all technology - maybe so, maybe not. Happenstance, I have the same lens. Hasn't been much around lately, but I'll mount it on one of my "obsolete" DSLRs and see what I can come up with to post.

a6k Loc: Detroit & Sanibel

FWIW, I tried that lens with Metabones dumb adapter on my a6500 and did not find it to my liking. I sold it.

Many modern cameras will correct chromatic aberration but they can only do it if they "know" the lens.

The gent who bought it was having some trouble getting good focus at first but either tried a different camera or got it adjusted. I don't recall which. But in the end he was happy with it.

flip1948 Loc: Hamden, CT

Have you tried using the focus confirmation that your D750 has built in?

It may work differently on your camera, but I still shoot film on my Nikon F100 (sweet camera) and it has it. On the F100 there are two arrows in the lower left corner of the viewfinder, one points left and the other points right. There is a dot between the arrows. If one of the arrows is lit then that indicates the direction you must turn the focus ring to achieve focus. When focus is achieved, the dot between the arrows will light. On your D750 I believe there will also be a "beep" when you're in focus.

Check your manual and give it a try.

I think it should work with AI lenses, but all mine are AI-S so I'm not positive.

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The LED focus guide depends on the SLR AF module and therefore is likely to be inaccurate. Last time I used that lens (recently) it was to time and measure star trails. Focus by the Sony magnifier was acoarst perfect even for stars. If you’re stuck with an SLR, accurate focus is available by the live view option.

Pre-AF SLRs have excellent focusing screens but focusing an AF SLR by eye is barely possible and seldom perfect.

Quixdraw Loc: x

Skill might work as well. Just a thought.

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But not an especially useful thought. Skill won’t help with seriously inadequate or inappropriate tools. A live view focusing magnifier allows exercise of your MF skill. The view screen of an AF SLR is not intended as a focusing screen.

photog11 Loc: San Francisco

Thank you CHG Canon. Everything you said is undoubtedly correct. At this stage of my life, changing to a mirrorless system is not really an option. Of course, a tripod and live view magnification is a possibility. All these shots, however, were handheld. Focussing at infinity is always easier... and my request for tips related to whether the lens is bad or whether my technique for focussing at less than infinity is lacking. (Probably both).

photog11 Loc: San Francisco

Thanks quixdaw. I look forward to your results.

photog11 Loc: San Francisco

Thanks flip1948. Focus confirmation on the D750 is (.)... but it doesn't really work with an Ai lens.

photog11 Loc: San Francisco

Yes quixdraw. My skill is obviously less then what is needed at this point.

flip1948 Loc: Hamden, CT

I believe, since the AI lens doesn't have the electrical contacts to let the camera know that it is mounted, that you have to program the lens into the camera.

I believe you do this in the camera's settings. You give the lens a number from 1 thru 9, tell the camera the focal length and aperture and then select that lens number when you mount the lens on the camera...at least from what I've read. As I said I use a film camera right now, hope to eventually get a D750 as I consider it to be a fantastic camera, so I am not exactly sure. Perhaps someone with experience with a D750 can point you in the right direction. I believe an AI lens should work fine with a D750.

LWW Loc: Banana Republic of America

Yep.

camerapapi Loc: Miami, Fl.

Let me give you my take on this. The Nikon 300 mm f4.5 AI is a good lens. As has been discussed already it has to be programmed in the camera menu so that the camera will recognize it since it has no electronic contacts to communicate with the camera.
You should know that a majority of focus errors are the fault of the operator and not the lens. A manual focus lens today is aided in the digital camera with a confirmation green light, like the one in your D750. When that light is on the subject is in focus. I am assuming that there is no front or back focus but in my humble experience those issues do not really apply to manual focus lenses.

If you bought the lens for birds in flight do not expect great shots although your shot of the pelicans looks to me acceptably sharp. It is very possible that you will loose many opportunities because of the lack of AF. The first image is totally out of focus and your last hardly has any contrast. Weather conditions and slight movement will effect the sharpness of the lens. Your lens is better used with a tripod and good tripod techniques.

Chromatic aberrations are common even with modern lenses. If they are not controlled with software you will need another lens. Lenses of the past were designed for film cameras, they have excellent resolution but many of them suffer of chromatic aberrations. I have a set of old lenses and I use them all the time, some are single coated lenses from the 60's and early 70's.