What is your standard prime?

Started 3 months ago | Discussions thread
Bender79ita Senior Member • Posts: 1,164
Re: What is your standard prime?

DutchMM wrote:

You ask why FF lenses could have faster AF than crop lenses. First of all, I don't know whether this is true. Thus far, all my e-mount lenses are crop.

That said, I have a theory that the faster the lens, the faster the AF. Because the AF systems in (at least) Sony bodies perform the AF with the aperture wide open. So faster lens = more light = faster focus.

Although both FF and crop lenses project the same image on a crop sensor, the FF lenses have to let in enough light to avoid severe vignetting in the corners of an FF sensor. Hence most of the FF lens makers are hard chargers for fast lenses. I except Sigma from this remark, since there is a triad of F1.4 lenses for crop sensors. But has anyone ever offered you a crop lens with a max aperture of 1.2, leave alone 0.95?

I believe the AF speed depends on the focus motor assuming the lenses are used on the same body...

More recent, faster focus motors will perform better than older, slower motors.

As the FF lenses are updated more often it might explain why they generally have newer, faster motors... but not because they are FF lenses, they are simply more recent.

In example, the 70-350 has the same kind of linear XD motor that's in the Sony 50 mil f1.2 lens for FF. The Tamron 17-70 for aps-c also has the same RXD motor that's in the 70-300 for FF (stepping motor).

The 70-180 is VXD which is a linear motor. I have no clue which is better but I think that's where one should look for differences.

 Bender79ita's gear list:Bender79ita's gear list
Sony RX100 III Nikon D810 Nikon D5600 Sony a6400 Tamron SP 24-70mm F2.8 Di VC USD +8 more
Post (hide subjects) Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark MMy threads
Color scheme? Blue / Yellow