Originally posted by Giklab The first review of the new HD AW TC has been posted and it seems people still think teleconverters somehow increase AF speed.
AF speed is determined by the lens and the body only, the sole function of the TC is to increase the focal length of the lens and to relay data and AF to and from the lens. Unless the TC unlocks a hidden software AF speed limit, there is no way for a conventional TC to increase the AF speed. The only impact on AF speed might be negative, due to the lower effective aperture.
If a native lens requires 10 turns to move from 5ft focus to 7ft focus then providing there is no reduction in gearing the same lens with a 2 x converter attached wiil require 5 turns to move from 5 ft to 7ft.
ergo the AF will be twice as fast with a converter atached.
Traditionally to make a converter function you add a reuction gear as in the above the camera would under PD move ten turns and miss the target before the next lock check, So you reduce the gearing by 2 so for a traditional converter you still require 10 turns to move from 5ft to 7ft but now take twice as long to go from min to infiinty i.e the AF is 1/2 speed but focal length is doubled so relative speed is constant.
It appears with the SDM focusing rather than reduce the SDM speed (not an easy task) the converter reports true focal length to the camera so stepping remains consistant and the relative speed is increased by 40% (for a 1.4 converter)
So reports of faster AF for SDM lens on the new converter are in all proabablilty true.
It is incredibly easy to establish if what I'm saying is true , take any screw converter and count turns of the key side to turns on the slot side if what I'm saying is true it will never be 1:1
And as none are 1:1 then this is obviously wrong and based on some complete misconception of how Converters maintinian AF compatability....
Originally posted by Giklab AF speed is determined by the lens and the body only, the sole function of the TC is to increase the focal length of the lens and to relay data and AF to and from the lens..
When a true statment would be the fucntion of a TC is to increase the focal length whilst mainitaining consistent AF ratio with the convertered focal length.
---------- Post added 17-03-14 at 01:04 PM ----------
Originally posted by y0chang Those are wonderful images and that is a testament to Pentax's optical design if you can get that kind of results with a teleconverter. I'm not saying that a well engineered teliconverter wont give great images, and in fact if it does give those results its well worth the money. If you have enough contrast with a great lens and that particular day's lighting adding a TC will not affect anything because the camera can see contrast and still focus on it. What I'm trying to state is there is no way a TC can make your camera focus faster.
LensRentals.com - Teleconverters 101 There is nothing in rogers paper to back up your claim "there is no way a TC can make your camera focus faster."
He doesn't mention AF gearing or any other methods to adapt PD to the new focal length.
So let me summerise , It can be easily tested
1 if end to end Focus speed remains constant then relative AF speed is increased by the Focal multiplier
2 if end to end focus speed is reduced by the focal multiplier the relative AF speed remains constant
In the case of all pre HD 1.4 AW converters clause 2 applied
The HD 1.4 AW seems to apply clause 1 to SDM focusing by correcting focal length reported to the camera.
This is also why currently HSM lens are broken on this converter as no corrected focal length is reported to the camera the PD af system overshoots the targets repeatedly leading to the 'hesitant no lock'