petrescu wrote:
Looking at the 50/1.2 block diagram, it seems to me there is little freedom of movement of the rear elements (between diaphragm and the right end). But it could be...
Sorry, it could be that the 50/1.2 does rear-focusing (or any other inner focusing); I don't want to conflict with any expert oppinion. I can't really say any other than there is little freedom of movement of the rear elements, and there seems to me more freedom to the front elements, _if_ the diaphragm stays put. It's also difficult to say because, AFAIK, all 85/1.2's elements move or "float" (except the rearmost aspherical element), together with the diaphragm.
That's OK, the only subject matter experts would be folks who design and build lenses......not many of those around , I'd say.
Mostly based on the front placement of the manual focus ring, my guess would be that the lens is front focusing with an extending inner barrel.
I'd also guess it's an electronic manual focusing lens.
However, not having seen any data on it, nor a block diagram, nor having the lens in my hands, that's as good a guess as anyone else's.
On second thought, for electronic manual focus, the positioner ring frontal (or any) location on the barrel does not have much significance....theoretically, it could be placed even on the lens hood.
Edited by handheld on Aug 26, 2006 at 02:18 PM GMT
Sorry, I thought I've posted the block diagram of the EF 50/1.2. It's from the Canon Japanese website. The green color means "aspherical element", google translated.
Sorry, I thought I've posted the block diagram of the EF 50/1.2. It's from the Canon Japanese website. The green color means "aspherical element", google translated.
Thanx, I think your reasoning was OK, looks like a front focusing/extending group.
By google translating the Japanese text, it seems to be a floating system:
"The lens is designed in order generally, the photographing distance whose use frequency is high for each aberration revision to be done in standard. Because of this, distance other than that, with especially short-range photographing each aberration to occur is tend to become easy. CANON to develop the floating system in order to avoid this, adoption. By the fact that being linked to photographing distance, it makes the portion of the lens move, it has succeeded in holding down aberrations to minimum photographing distance all over."
EFLWIII (EF Lens Works III) says: "floating system employed in 50/1.0 and 85/1.2 differs from that [floating] of wa lenses, in that it leaves the rear lens group fixed and extends the remainder of the lens system during focusing". It pictures an 85/1.2 where all elements move except the rearmost element (not group).
It may be that several elements move in 50/1.2, and not the rightmost lens or group.
Also, I think one mentioned "IF", I think that stands for Internal Focusing. EFLWIII says that internal focusing is a lens or group moving between fixed frontmost and rearmost elements. 70-200/2.8/is is given as an example, a zoom.
Interesting, thank you for taking the trouble to translate that. Another question is about manual focusing.......is it electronic (like 85L and 50 f/1.0) or mechanical (conventional).
ranmandx wrote:
What is the DW-R and the CA logo on the bottom of canon usa's lens description?
I know what the other ones are FT-M is full time Manual AL is aspherical element. U is usm. I/R is internal rear focusing, CaF2 is fluorite.
I think DW-R stands for Dust and Water Resistance, after googling it. Note though it doesn't appear on any lens logo on the Canon USA site, although some _are_ sealed, like the 17-40.
CA stands for Circular Aperture (in Canon speak). This logo is present on other lenses too, like the recent 85/1.2II or even the earlier 17-40. Sometimes I've seen CA for Chromatic Abberation, something to complain.
handheld wrote:
Interesting, thank you for taking the trouble to translate that. Another question is about manual focusing.......is it electronic (like 85L and 50 f/1.0) or mechanical (conventional).
Well, I don't quite understand this. Logo-wise 50/1.2 has FT-M (full-time manual focus).
EFLWIII says "full-time manual focusing originally employed an electronic focusing method for the 85/1.2L and other early EF lenses, but today uses a mechanical system in almost all USM lenses equipped with a manual focusing ring and a distance scale, such as 24-85/3.5-4.5, 16-35 and 300/2.8is." Then follows a detailed description of how works the full time mechanical manual focus mechanism, diagrams and photo of "focus unit".
You seem to present electronic ft-m employed in 85/1.2 as more advanced and mechanical ft-m to be conventional. EFLWIII seems to say mechanical ft-m to be more advanced.
50/1.4 has ft-m too, EFLWIII: "thanks to a differential mechanism built into the gear unit".
Japanese translation on 50/1.2: "As for the automatic focusing mechanism of OS all body side ranges, lens inside drive motor system. The ultrasonic motor which CANON utilizes for the first time in the world =USM (Ultrasonic Motor), the quite high torque high response. In order to convert the ultrasonic vibration to rotational energy, almost silent. You can call ideal as a motor for lens drive. By the fact that the motor which is optimum to each lens is loaded, ideal high-speed high accuracy AF is achieved e.g., ring USM, micro USM is adopted to the small-sized lens in the large aperture lens."
It may mean that 50/1.2 has micro USM (instead of ring USM), it may mean that only the mechanical manual part of micro-USM (from 50/1.4) is used in the ring-USM. It may also be that the Japanese Canon text is simply wrong to mention micro USM, or the translation could be completely wrong.
I can't find anything more on that. Someone with the lens could try to compare the feeling of turning the focus ring, between 50/1.2, 50/1.4 and 85/1.2.
Petrescu, you'd make a stellar researcher at a university !
No, I did not mean to imply that the electronic (remote) manual focus control is more advanced than the mechanical (direct coupled) one. In fact, Canon deployed such electronic manual focusing in the early EF days on several lenses out of which 2-3 are now obsolete. The obvious side-effect of such control scheme is that focus controls need to be powered up (the camera turned ON) in order to be able to focus manually. When deenergized, the manual focus control ring (positioner) spins idle.
I appologize if I am writing about things you are familiar with.
The 50 f/1.2 will employ the ring USM as well as FTM, electronic or not, we'll find out soon enough for sure.
The 200 f/1.8 has manual focus-by-wire, does it not? And its AF speed may be the best on the planet. If the 50 f/1.2's AF performance is anywhere near that of the 200 f/1.8, I will be very happy indeed.
Nill Toulme wrote:
The 200 f/1.8 has manual focus-by-wire, does it not? And its AF speed may be the best on the planet. If the 50 f/1.2's AF performance is anywhere near that of the 200 f/1.8, I will be very happy indeed.
Nill
~~
www.toulme.net
Yes, agreed. I have one of the new 85 1.2s and made a deal with the store, if the new 50mm has the AF speed I'm hoping for, the 85 will go back and will get the 50 1.2 instead. Would be nice to have both but....
For sports, the AF on the 85 is barely fast enough, few keepers and lots of deleted shots...but it is a beautiful performer otherwise and the compression on the 85 is great . A fast AF 50 1.2 would really help in many of the very lowlight venues. Even a half a stop can make or break an indoor track shot or a cross country shot deep woods, or maybe get the ISO down a bit.
Nill Toulme wrote:
The 200 f/1.8 has manual focus-by-wire, does it not? And its AF speed may be the best on the planet. If the 50 f/1.2's AF performance is anywhere near that of the 200 f/1.8, I will be very happy indeed.
Nill
~~
www.toulme.net
The 400/2.8 II (not the IS, I don't know about it) had focus-by-wire manual, as does the 85/1.2 original. Not sure on the new version.
I agree - if the 50/1.2's AF is very good (along with the image quality), it will sell well. It won't be a hot seller like the 17-55 EF-S, but it's not a high-volume lens either.
I'll contemplate it in the future, but I have see how it tests, and see if the price settles a few months down the road.
I do not think the type of manual focus control scheme employed in a lens has much to do with the lens AF speed. Some electronic manual focus lenses have a high AF speed (200 f/1.8), some others are slow (85L MkI and II).
The brief swedish hands-on report apparently stated the 50 f/1.2 AF was faster than the 85L AF.
Either way, not a concern to me at all.
I believe that the 85/1.2's AF has quite a large load of glass to move when focusing, and that is why it's slow. In the automotive sense, it's "geared down" to multiply torque. The smooth MF is a plus, electronic or not.
