Best Canon EF Adapter?
- Thread starter filmrebel13
- Start date
cuervo
Veteran
LOL...it's definitely the lens aperture actuator. You make an interesting point. Using these EOS lenses on my Canon 5D or 7D, they don't "cycle" as the exposure changes quite like they do with these 3rd party smart adapters. There is probably some "damping' or delay function Canon uses to keep the aperture from changing to slight variations in exposure. I am assuming that the Metabones adapter has zero damping/delay while the MTF doesn't seem to be quite as reactive to exposure changes. Anyone familiar with control theory should know that a control circuit like this, if too responsive, needs a damping or delay function.
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It is true that the servo loop must be tuned, but that is built in to the lens and not easily accessible to the outside. The commands sent to it can conflict with the hard coded servo loops. Obviously the Canon cameras are in sync with this. With that said, there was never really any effort put into making these lenses quiet since they were always much quieter than the release mechanism ;-)
Controlling these lenses for an application that they were never designed for is certainly not trivial especially since Canon will not help.
cuervo
Veteran
Agreed. I'm not knowledgeable enough to tell you if it's a digital or analog voltage signal sent to the lens controller. But, I can say that the time interval between signals could be modulated. But, perhaps asking too much from a 3rd party vendor. At any rate, you are quite right. And I'm grateful to have ANY kind of aperture control. I don't much care for AUTO anything, so setting the aperture control on manual works just fine for moi.
It is not a digital or analog signals at all. The motion controller is in the lenses, not the camera. This keeps the electromechanical differences between lenses from confusing the camera. It also makes life more of a challenge for 3rd party developers because it allows Canon to hide the details. These are the things that keep me at work on the weekends ;-)
cuervo
Veteran
D-AD-A
I'm not understanding. The mechanical actuator is in the lens, I get that. And the actuator is driven by a voltage supplied from the camera. Furthermore, the exposure is determined within the camera's processor. So, the camera must send a signal to the lens actuator to open or close the aperture to adjust the exposure. This is a closed loop feedback controller, isn't it? There has to be some kind of signal sent from the camera to the lens actuator. All I'm saying is that the response speed of this signal can be damped. If it's a digital command, there's not much that can be done.(this implies an D-A converter in the lens) If it's an analog signal, there's more possibilities.
I'm not understanding. The mechanical actuator is in the lens, I get that. And the actuator is driven by a voltage supplied from the camera. Furthermore, the exposure is determined within the camera's processor. So, the camera must send a signal to the lens actuator to open or close the aperture to adjust the exposure. This is a closed loop feedback controller, isn't it? There has to be some kind of signal sent from the camera to the lens actuator. All I'm saying is that the response speed of this signal can be damped. If it's a digital command, there's not much that can be done.(this implies an D-A converter in the lens) If it's an analog signal, there's more possibilities.
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The lens has a completely self-contained motion control system inside. What the camera feeds it are software based requests to do something. These requests are very high level compared to a voltage or pulse train. Essentially, the camera may send a request to go to an f2.8 and it is entirely up to the software embedded in the lens to figure out how to make the request happen. This would include low level things like acceleration and deceleration as well as velocity to make a controlled landing at the desired spot. If the lens was at a f1.4 when it gets a request for an F2.8 it knows to open the lens, again the camera does not really care if the lens needs to open or close or how much or how fast - all the camera cares about is that it wants an F2.8. The camera never takes direct control of the lens motors.
For still photo, this is all well and good. For folks like me that are accustomed to very expensive lenses that have smooth and continuous aperture control - it sucks. Essentially, we have to make tricks to get the software in the lenses (non-negotiable) to do something it was never designed to do. Even if there were access to the raw servo loops, it would create the problem that Canon has already solved. Each lens has differing capability and electromechanical performance nuances that we would have to calibrate and learn each time the lens goes on the camera. Yuk!
This should help everyone understand why these adapters take a long time to develop and they have had spotty performance. We have designed and manufactured incredibly complex electronic systems for high-end digital cinema and broadcast cameras so I am not guessing on this one. Making the lens move: easy. Making the lens move well: hard.
For still photo, this is all well and good. For folks like me that are accustomed to very expensive lenses that have smooth and continuous aperture control - it sucks. Essentially, we have to make tricks to get the software in the lenses (non-negotiable) to do something it was never designed to do. Even if there were access to the raw servo loops, it would create the problem that Canon has already solved. Each lens has differing capability and electromechanical performance nuances that we would have to calibrate and learn each time the lens goes on the camera. Yuk!
This should help everyone understand why these adapters take a long time to develop and they have had spotty performance. We have designed and manufactured incredibly complex electronic systems for high-end digital cinema and broadcast cameras so I am not guessing on this one. Making the lens move: easy. Making the lens move well: hard.
paulcurtis
Veteran
I remember seeing early demos of software control of EF lenses.
Each lens also has a different granularity of focus 'step', this manifested as some of the lenses not being as smooth to pull a rack focus for example. I presume based on what Carlos was explaining that the controlling software would have to continually request focus adjustments rather than telling the lens controller to go to X over Y steps. So that makes a controller more difficult. Also it was noted at the time (from memory this) that all the steps are relative, not absolute. So you can't say go to 1m focus, you'd have to know where you were and then step to 1m. So calibration is made even more difficult because the lenses don't have hard stops. This is probably why this first wave of controllers don't attempt to do electronic follow focus.
Aperture settings Carlos has already explained.
cheers
Paul
Each lens also has a different granularity of focus 'step', this manifested as some of the lenses not being as smooth to pull a rack focus for example. I presume based on what Carlos was explaining that the controlling software would have to continually request focus adjustments rather than telling the lens controller to go to X over Y steps. So that makes a controller more difficult. Also it was noted at the time (from memory this) that all the steps are relative, not absolute. So you can't say go to 1m focus, you'd have to know where you were and then step to 1m. So calibration is made even more difficult because the lenses don't have hard stops. This is probably why this first wave of controllers don't attempt to do electronic follow focus.
Aperture settings Carlos has already explained.
cheers
Paul