[Darcy]

I am looking at Tamron 90mm macro lens. It looks like the Di version is the exact same except for the di glass coating and in-lens focus mechanics.
Are there pros/cons to the screw focus vs. the in-lens focus?

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Last edited by Darcy; 04-11-2016 at 04:11 PM.

[FantasticMrFox]

Screw-drive is noisy, in-lens is (near) silent. With modern Pentax cameras screw-drive is not always slower than in-lens, it can actually be faster at times. With the competition in-lens is usually far faster, e.g. Canon's USM.

[Adam]

I am looking at Tamron 90mm macro lens. It looks like the Di version is the exact same except for the dx glass coating and in-lens focus mechanics.
Are there pros/cons to the screw focus vs. the in-lens focus?

The version of that lens with in-lens focusing is not available in the Pentax mount.

Screwdrive can be faster than in-lens focusing, but micro-adjustments have the potential to be a little bit less accurate, plus there's the noise factor. Ultimately the real-world performance will depend on a combination of design factors such as focus throw, the camera body used, and the type of motor, so it's hard to generalize.

[starbase218]

Define "good". Screw-drive traditionally seems far less prone to failure than in-lens motors, so that's a plus. With regard to speed, the body can make a lot of difference, because the in-body motor has been upgraded a few times (K-7, K-5, K-3, etc). I don't think SDM lenses have benefited from an increase in speed with newer generation bodies, because in that case, upgrading the body does not upgrade the AF motor. Maybe newer bodies have faster AF, in the sense that they have better AF sensors, algorithms etc that get it right with fewer attempts. But in that case, that should again benefit both screw-driven lenses and SDM lenses.

Some people say that lenses with shorter focus throw focus faster than those with longer focus throw. That would be the case if the rotational speed (the number of degrees per second) was constant between all lenses, which it is not. It may very well be that a lot of lenses with a long focus throw focus slower than those with a short focus throw, which could lead to that conclusion. But that's the same thing as dismissing the existence of yellow cars because you only see grey and blue ones.

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Last edited by starbase218; 04-11-2016 at 03:07 PM.

[stevebrot]

As with lenses having a built-in motor, how well it works depends ultimately on build quality and mechanical precision.

Steve

[Dipsoid]

The main benefit to in-lens focusing motors is subject tracking, something that screw-drive isn't the best at. If you just generally use AF-S, screw-drive can be even faster to focus than good in-lens focusing motors and the only downside will be the noise.

[Darcy]

Ok, Thanks for the info!! Very informative.

So the only real difference is the glass coating for Di, in my example.