[Badger]

Hi guys, I know this may be a really stupid question, but here goes....
I have just bought one of these lenses (without instruction leaflet) and it is in mint condition (I think!) As I am not familiar with canon ef lenses (newbie ) Can someone please tell me if the AF/MF selector switch on the lens is supposed to stay at AF, for some reason this does not seem to budge.. (I told you this is a stupid question).. is it supposed to be like this? You can manually adjust the focus but Im not sure if doing this, while the lens is set to AF, might damage the lens.

[Skintt]

Originally Posted by Badger

Can someone please tell me if the AF/MF selector switch on the lens is supposed to stay at AF, for some reason this does not seem to budge.. (I told you this is a stupid question).. is it supposed to be like this? You can manually adjust the focus but Im not sure if doing this, while the lens is set to AF, might damage the lens.

I'm pretty sure you should be able to switch between manual and auto, otherwise whats the point of the switch? As for manually focusing while set at AF, this is a useful feature of certain canon lenses. I know I can do it on my 17-85mm IS USM, but not on the 50mm macro or 90-300mm USM. You won't break it!

[Badger]

Thanks for the reply. The lens is a real gem apart from the AF/MF selector problem. I'm really looking forward to using it at the weekend.

[Steve]

The switch should activate/deactivate auto focus. If it won't move from one setting to another than you have a defective lens, how much that effects you will depend on the price you paid and the guarantee you received, if any. If it is stuck in AF mode then it's probably of little concern as you should* still be able to manual focus when required by just rotating the focus ring, you will off course only be able to do that after half depressing your shutter release otherwise the AF will kick in and potentially alter the focus.

*you should check to see that altering the focus manually when in AF mode on this lens is not potentially damaging to the lens, some Canon lenses are designed to allow this and others are not. I do not know which it is for the EF 28-105 f3.5/4.5 USM although with it being USM you are likely to be ok.

[Skintt]

Originally Posted by Steve

*you should check to see that altering the focus manually when in AF mode on this lens is not potentially damaging to the lens, some Canon lenses are designed to allow this and others are not. I do not know which it is for the EF 28-105 f3.5/4.5 USM although with it being USM you are likely to be ok.

I presumed that the design of the lense itself would either alow it or not. If you can do it, and the lense wasn't designed to allow you to, then I would suggest the lens is FUBAR?

[Steve]

I have just done some checking for you...

Ring Ultrasonic Motor

Beginning in 1987 with the 300/2.8, Canon has been slowly equipping its best lenses with the ring ultrasonic motor, in which the rotor and stator are big circles around the optics. These are incredibly fast and silent. Even more important, they allow simultaneous use of autofocus and manual focus. You can leave the lens in AF mode all the time and override the camera's decision at any time (or move AF to a separate button as with the EOS 5 body).


Micro Ultrasonic Motor

If you were a big company and figured out how to make something for 1/3rd the cost but still sold under the same name, wouldn't you? Well, that's what Canon did. The micro ultrasonic motor is a tiny little motor that they stick in the lens and then connect with gears to the focus mechanism. It is tough to see how this is any better than the Minolta/Nikon AF method of driving the lens focus mechanism from a motor inside the lens mount.

A micro USM does not allow simultaneous AF and MF. Thus, the largest user-interface advantage of the ring USM is gone. Much of the noise of a standard motor is back too. The micro USM is noticeably quieter than a regular motor, but not silent like a ring USM.

Canon puts the micro-USM mostly into its new cheap zoom lenses.

So that’s an explanation of the two different types of USM and why with one you can use MF in AF mode but it still leaves you wondering if yours is ring or micro USM…

How to check if the lens has USM or not when you have the lens in hand?

First, all USM lens sold by Canon do have the "Ultrasonic" logo and trademark printed on it. But that does not mean it is a real USM ring motor inside.

Second: all USM ring motor do have a window were you can read the focusing distance. Some USM micro-motor have it too, like the 75-300 USM II (IS or not). But if it has not the window, then it is not a USM ring motor either. Usually on those lenses, the focusing ring is just on the front element and usually thin. Why? Because the user probably won't focus manually either. It is consumer lens after all...

Third: USM ring motor lenses, when commuted in AF mode (see the switch on the side of the lens, close to the mount), allow focusing manually. That means that if you turn the the focusing ring, the focusing distance you can read behind the small window will change accordingly. If it does not then you don't have a real USM ring motor on the lens.

That tells me that your lens is likely to be micro USM and thus should not be used to manual focus when in AF mode. From memory your lens does not have the clear window with the distance markings inside?

Sorry to be the bearer of bad news but better to know now before you do any damage.

Hope that helps?

[dod]

Steve's research is right, as usual

I've got the ring motor version, it's hardly ever mentioned which is a shame as it really is a very sharp lens for the money, good range as well.

[Badger]

Thanks Steve. I have checked my lens and it does indeed have "Ultrasonic" written on it. It does have the window you described for viewing the focusing distances and when adjusted manually you can see the changes in distance. So, I am assuming that I have a Ring USM lens. ... Right???
By the way what was the source of your research?

[SammyC]

Can you post a picture of it Badger?

[Steve]

Originally Posted by Badger

Thanks Steve. I have checked my lens and it does indeed have "Ultrasonic" written on it. It does have the window you described for viewing the focusing distances and when adjusted manually you can see the changes in distance. So, I am assuming that I have a Ring USM lens. ... Right???
By the way what was the source of your research?

From your description it does sound like you have the ring USM version ad should be ok. It is still faulty though so bear that in mind.

My research information came from the web.

[SammyC]

A bit of a dig on the ol' Canon interweb site:

EF 28-105mm f/4.0-5.6 USM





EF 28-105mm f/3.5-4.5 II USM





and from a differnet site I think this is the MKI ring USM one (notice different zoom grip):

[Badger]

Originally Posted by SammyC

Can you post a picture of it Badger?

I dont have the lens with me at the moment (at work ) I will bring it with me on Monday and let you know which one it is. .... By the way fellas, thanks for taking the time to be of help.

After studying the pictures, I do think it is the bottom one (98% sure) Its the picture of the little flower, instead of the word 'Macro' that makes me think that way... Highly technical stuff eh? :eyesup:

[SammyC]

Now there was another lens that had that as the only difference between a Mk 1 & 2, see if I can find it.....

[Badger]

Go for it !

[SammyC]

ok, after a while examining USM lenses on the interweb I have come to the conclusion that Ring USM lenses have the USM logo on the barrel and also a ring motif all around the barrel:




Whereas micro USM, i.e. not ring and therefore without full time manual, just have the USM logo:



This is not based on anything more scientific than browsing the web.

HTH.