Visual360 wrote:
Just bought myself a 135L. Can't wait when it gets here, so I can join the 135L club.
Given that you already have a 100mm f/2.8 Macro, I think you made the right choice. The 100L is a very nice lens, but a relatively minor update to the non-L version. The 135L on the other hand is a magnificent piece of glass. Happy shooting
denoir wrote:
It may be the lens or the camera. When it comes to the lens it's a question of the precision of the motor. The camera tells the lens to move, it does and the camera measures focus again and corrects for the error by issuing new move commands. The first sets of movements by the USM wil be an order of magnitude larger than the subsequent minor corrections so the chances are much bigger of the motor overshooting or undershooting.
Well, you seem to have more detail on the subject than I do, however, my understanding has always been that Canon AF in a single shot mode is an open loop (feedforward) type of control. The camera moves the lens once and that's the end of one focusing action, as initiated by the photographer. No residual focus error measurement, and no ensuing control action aimed at reducing the measured error.
However, please give me your references so that I can learn more.
PetKal wrote:
Well, you seem to have more detail on the subject than I do, however, my understanding has always been that Canon AF in a single shot mode is an open loop (feedforward) type of control. The camera moves the lens once and that's the end of one focusing action, as initiated by the photographer. No residual focus error measurement, and no ensuing control action aimed at reducing the measured error.
However, please give me your references so that I can learn more.
Oh, I know absolutely nothing about it - just speculating. Sorry that I didn't make that clear. I would guess that in order to increase the speed of the focus it would do an iterative focusing i.e first a large jump into the right direction and then smaller corrections. But as I said, pure speculation, I have nothing to back it up.
Assuming you are right, I'd still guess that it's the lens motor that is the cause of it. How else would one explain that it happens more often on one lens compared to another?
denoir wrote:
Oh, I know absolutely nothing about it - just speculating. Sorry that I didn't make that clear. I would guess that in order to increase the speed of the focus it would do an iterative focusing i.e first a large jump into the right direction and then smaller corrections. But as I said, pure speculation, I have nothing to back it up.
Assuming you are right, I'd still guess that it's the lens motor that is the cause of it. How else would one explain that it happens more often on one lens compared to another?
It is very educating conversation. I think Peter is right on Single-Shot AF.
Back to your 135 issue, I think that it may caused by loose/improper coupling between focus mechanism and lens housing or group. The motor rotates properly based on the camera's command, however, the actual distance moved is not what the camera AF system indicates. Did you hear any wobbling sound when you gently shake your lens? If so, then it could be the reason I just mentioned above.
denoir wrote:
Assuming you are right, I'd still guess that it's the lens motor that is the cause of it. How else would one explain that it happens more often on one lens compared to another?
My guess is that USM itself doesn't fail as often as the associated control and power circuitry does. In fact, the overall AF drive in today's lenses is quite complex.....only god knows in how many ways it can fail.
I'd have Canon check the lens as well as the camera together......and try to reproduce the erratic behaviour.
I had the 100L IS MAcro and decided to sell it for the 135 f/2. I need the extra stop of speed at times and I prefer the blurr at f/2 ; also and I think the 135mm length suites me better than 100mm. I dont find the IS to be all that helpful, except when doing a few macro shots I thought it might be helping since my hand was not steady at the angle i had to work with. This is a rare thing tho so to me it was not worth keeping over the 135f/2. I think it's possible the AF is faster in the 135 but it could be my imagination.
PetKal wrote:
My guess is that USM itself doesn't fail as often as the associated control and power circuitry does. In fact, the overall AF drive in today's lenses is quite complex.....only god knows in how many ways it can fail.
I'd have Canon check the lens as well as the camera together......and try to reproduce the erratic behaviour.
Yes, I'm currently considering getting a 5DMk2 as a secondary camera. If I do, I'll send in the 7D and the 135 for a checkup. I don't want to be without a good camera right now. Anyway, before I do send it in I'll do some systematic testing and I'll post a thread here to see if my results are within the margins of normal camera/lens behavior or if there is a real problem. Right now I'm almost exclusively using the new 70-200 which includes the 135mm range, so I'm not in a hurry.
There are a couple of other small issues with the 7D that I'd like to get checked out anyway (I got a shutter failure error a couple of times and the live view contrast auto focus consistently focuses incorrectly), so I'll take care of all those things in one go.
Visual360 wrote:
We should end this discussion now.
Just bought myself a 135L. Can't wait when it gets here, so I can join the 135L club.
You'll love it.
At one point I owned the 100mm macro (non-L) and the 135 f/2 (I now own the Sigma 105 macro and the 135 f/2). I love macro lenses, but the macro has nothing on the 135L's bokeh. And keep in mind that I'm a huge fan of macro lenses for all purproses.
Peter Kotsa wrote:
If you are after a macro, which i doubt you are, seeing that you already own the 100 mm f2.8, you will find that the new model is exactly as the one you have only with the advantage of IS.
Agreed, I tested the 2 macro 100 lenses on a tripod and didn't find much IQ difference between them at medium distances other than the Version II L IS was always 1/3 stop darker in exposure. Hand held is a different story of course. At strictly macro distances, reviews seem to favor the version II lens as well.
Now the 135 is the closest thing to a Zeiss lens that I own, other than the Zeiss lenses I own. The 135/2 seems to have greater contrast than other Canon lenses and is very sharp across the frame.
Mike K
