Originally posted by normhead Hopefully the FF will. But if the K-3 doesn't make full use of the new lenses, I would expect the lens to move so quickly that the lens moves past the focus point without registering that it was in focus, and then having to come back. You see this in old screw drive lenses that are 6.3 or slower, the speed of focus is geared up but there isn't enough light to look focus at that speed and the lens hunts.. SO, I'm wondering if you're seeing anything like that that would indicate the speed of focus is stressing the AF system?
I guess in the FF system they could bump the voltage to the new lenses to make them faster and have a recognition chip so the it doesn't fry the SDM lenses, but apart from more power to the motors, I'm not sure how the lens would focus faster than it does now. The only factor that could be different would be the camera's ability to recognize when the image is in focus. If it's not missing focus and hunting, I'm not sure how it could be any different. The .1 second focus speed on a D610 is based on a very short movement when focussing the lens. The .5 second focus speed on a K-3 is in part based on a much longer distance. There are only two ways around the slow focus speed. Move the lens element faster, or shorten the distance it has to move to get from close to infinity. Am I missing something?
In both cases the AF system has less time to recognize that the desired point is in focus. But just improving the AF focus lock system in the camera can't make up for slow focussing lenses.
Or in other words, unless Pentax starts making lenses designed with higher gearing or less distance to travel in focusing, I'm not sure how any improvement in the AF module is going to help. Most of the time, the AF system is waiting for the lens to get to the point where things are in focus. That's what I'd like to see improved i these lenses. If it takes the AF system a few years to catch up that's fine with me. To me, seeing a bit of hunting out the gate would be good thing. It would mean the lens focusses quickly.. and the cameras AF could be improved to make it lock focus more reliably in the future.
If the K-3 doesn't hunt, and you're still dealing with a slow focusing lens... how is there going to be improvement? It doesn't make any sense to me to release an "improved lens" that focusses at 1/5th the speed of the competition.
The whole point of PDAF is that you can detect directly where exactly the focus should be put on and give the order. There no need to reread the focus position. At the basic there no feedback loop where the AF check again and give a new correction order with hunting. That's why you can have back/front focussing: there play in the mechanics and so own and so in the end the focus is not exactly where it should be. The hunt is the camera that discover there was an error and try to correct... or even maybe that known that its initial computation was not very precise and try to correct it.
On advenced lenses, the lense monitor himself the execution of the new focus position. It is then able to detect that if there a "long move" to do it can accelerate at full speed... and slow down to stop exactly where needed. This feedback loop also help make the most advenced lenses much more precise. The concept is a bit like when you want to grab something with your hands: if you uses you eyes to track the movement you are much more precise than if you just given the order eyes closed and execute it. You can't correct any devition from it.
As for the power limitation, without knowing the protocol of the mount and it latest evolutions, it is simply impossible to conclude what the limitation is, how the negociation is made with the camera if the voltage stay always the same and the motor can just consume as much intensity as it needs. Anyway this is very basic eletricity. If a 5$ USB charger can plug to a power plug and give exactly the form of energy the USB device need including transforming the voltage I guess a 2000$ camera + 2000$+ lense should be able to solve the issue... The only limitation really would be battery power. And there even Pentax could use a more advenced model if needed. They just need to use the latest advencement made on battery gear for smartphone, laptops and other very power hungry mobile devices.
Last but not least, there almost never such a need to focus fast. To go from minimal focus distance to infinite instantly. Most often what is needed is to move slightly the focus. So the lense more than being fast, should be reactive, have minimal latency and be precise.
On the camera side the issue is that moving objects continue to move when the mirror is up to take the photo and so the AF-C doesn't work anymore. Advanced algorithms continuouly evaluate what is the object the photographer want to focus on by using both the AF sensor (to evaluate the distance and get a deph map) and also the metering sensor to get a low resolution picture of the scene. Using theses both information is it possible to follow the object moving lateraly or vertically in the frame and with AF sensor to follow the deph change. All of this finally allow to estimate the current speed, direction, trajectory of the object in focus an predict exactly where it will be when the photo will be taken and to ask the lense to move to this focus position just in due time.
This is by combining everything that you get the best results. A modern lense with advenced feedback look mechanism and very precise high quality mechanics. A powerfull enough motor, a good optical design that allow to move fast enough the focussing lenses, a good AF support from the camera and even machine learning and IA algortihms to recognize subject, predict trajectories, give the orders so that the focussing will be just fine at the time the picture is taken.