Screwdrive AF = Mechanically coupled?

[connloyalist]

Hi All,

Am I correct in thinking that screwdrive AF lenses by definition have mechanically coupled focus rings and can therefore always be manually focused?

My experience so far with manually focusing screwdrive lenses is that this is ergonomically an unpleasant experience because of the often narrow focus ring and short throw. And that they don't always / often don't have an aperture ring requiring an adapter that includes a mechanism to do this. But I have found that sometimes in a pinch a screwdrive AF lens can be useful.

Regards, C.

[D1N0]

Yes it's gears in the lens driven by a screwdriver in the camera. Always put the camera in manual mode when manually focussing (or the lens if it has an AF/MF switch to decouple the gears from the camera), or you will harm your in camera AF motor by forcing it's gears.

[connloyalist]

In my case I have a "dumb" adapter between the lens and the camera, so no risk of damaging gears.

Thanks for the answer

Regards, C.

[KEO]

[connloyalist]

[RokkorDoctor]

Indeed, the short rotation of the focus grip on autofocus lenses in general makes me avoid them.

Even the slightest rotation of the focus ring takes you from focusing far too long to focusing far too short. It makes finding the "sweet spot" using focus rocking, circle-of-confusion symmetry and muscle memory nigh impossible (assuming live focus and not use of a focus wedge).

Too many AF lenses have their entire focus throw allocated in only a 45 to 90 degree turn or so. The most pleasant of my MF lenses give 180 to almost 330 degrees of turn for the same focus throw; much more precise...

If focus precision is your priority, I would stick with older MF lenses.

(It can be taken too far though; a very long rotation combined with too much dampening makes finding the sweet spot using focus rocking & muscle memory also difficult to achieve).

Referring to your original post, the lack of an aperture control on the lens is a complete non-starter for me when adapting legacy lenses.

[cooltouch]

When it comes to AF lenses, I'm old school. I want an aperture ring. I don't care much about the screw drive, but an aperture ring and a well-damped focusing collar are important. The AF lenses that exhibit these qualities the best are Nikon's D Series AF lenses. All the ones I've tried, and own, have adequately large, and well-damped focusing collars. They all have aperture rings with crisp click stops. And they all focus plenty fast for my needs. So, I'm content with these lenses. Perhaps best of all, because they are older tech, you can pick up nice examples for cheap. One example I can think of off-hand is the 70-300mm ED zoom, which can often be found for well below $100. I own two. One came with an F3 kit I bought (go figure) and the seller was basically just tossing in the lens because he had no use for it, and another came as a body cap for another camera I was after. So I paid little to nothing for the two I own. I also own a "nifty fifty" D-series 50mm f/1.8, and a 28-105mm D-Series zoom.

[paulhofseth]

Early screwdriver lenses probably were existing designs modified with the necessary cogwheels. My Angenieux zooms optics were recalculated from its earlier wide limit of 35mm to 28, when issued as autofocus, but maintained the large and easily grippable , entirely mechanically coupled focus control ring.

p.

[D1N0]

For screw drive AF the focus throw needed to be short and light in order to be fast enough, so manual focus is not ideal. If it were dampened the focus motor would have to work too hard. I have a Pentax FA AF 100mm 1:2.8 macro that does have a long throw and therefore slow focussing. It has a focus limiter to help with that a bit and a manual mode with a clamp that ads some resistance to to focus ring to help with accurately focussing manually. Most older AF lenses still have an aperture ring. At least Pentax (and probably Nikon) kept them in the film AF era. Canon and Minolta were sooner to ditch them.

[KEO]

[stevemark]