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09-07-2015, 10:07 AM   #1
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AM/FM button on lens may harm the lens?

I bought a lens with a AF/MF switch on the lens body a few years ago. The dealer told me it was important I used that switch the right way, or I may harm the equipment. Now I have a lighter attention disorder that makes me sometimes not pay attention, so I didn't remember what he said.

Anyway; if I remember correctly, I should have the switch similar to as on the camera body. If I had camera on AF and lens on MF it could hurt the lens. Or the other way around. I don't really remember. Was it so? Is this important?

09-07-2015, 01:09 PM   #2
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QuoteOriginally posted by FilipWessman Quote
AM/FM button on lens may harm the lens?
Your lens is a radio?
09-07-2015, 01:23 PM   #3
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QuoteOriginally posted by dcshooter Quote
Basically what it boils down to is that manually turning a lens ring when the drive train is engaged can put stress on the motor in the lens or camera body or the various gearings between the two.

Usually the AF/MF switch activates some kind of clutch between the motor and the focusing mechanism, and flipping it back disengages it and allows the focus ring to spin freely. Trying to use AF with the lens switch in MF position may result in the motor spinning, but generally isn't going to cause damage to either lens or body; it's akin to revving your car engine in neutral.

Incidentally, quickshift designs have largely eliminated this danger.

I`ve heard this too, but I wondered what the actual incidence of any problems is. Anybody had real damage to a lens needing repair from not disengaging AF before touching the focus ring? I forgot to a number of times with a non-quick shift lens that seems not to mind. Is it just a small chance of strain to the motor and maybe manufacturer`s are being very cautious?
09-07-2015, 01:35 PM   #4
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Typically when there is an AF/MF switch on the lens and the lens is set to MF, the lens will still autofocus (if AF is set on the body), but the focus ring will turn as it does so. Which means there will be some extra drag during autofocus (which is probably ok), but it also means you want to make sure you're not gripping it (as it turns) or trying to turn it manually until you also turn the switch on the body to MF. And of course for many lenses without a switch this is the normal circumstance (focus ring turns as it autofocuses). When AF is set on the lens it will disengage the focus ring so it doesn't do anything (which means you must set AF on the body or you have no way to focus).

09-07-2015, 02:11 PM   #5
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On the first Sigma 100-300mm f4 I owned, I did not realize that the AF/MF switch is operated by sliding the focus ring forward/backward, and I believe I damaged the lens at some point while I was testing the lens, ignorant of the switch's existence and whether it was set to AF or MF. I sent it to Sigma and they repaired it, but I still don't like that type of AF switch.
09-07-2015, 02:31 PM   #6
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Absolutely not. The manual even tells you to set the switch to MF on the lens while the body is set to AF if you want to use Catch-In-Focus with an autofocus lens. (You can only use C-I-F with a manual focus lens, unless the autofocus lens has an AF/MF switch)
09-07-2015, 02:42 PM   #7
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QuoteOriginally posted by boriscleto Quote
Absolutely not. The manual even tells you to set the switch to MF on the lens while the body is set to AF if you want to use Catch-In-Focus with an autofocus lens. (You can only use C-I-F with a manual focus lens, unless the autofocus lens has an AF/MF switch)
Yeah, on the Sigma lenses I've used, switching to MF on the lens engages the focus ring, nothing more -- it remains autofocus as far as the body is concerned (and will in fact autofocus) until you switch the body to MF also. You don't want to be switching it while it is moving I'm pretty sure. But different function for different lenses and brands, probably, so just make sure you take a minute to figure it out...
09-07-2015, 02:49 PM - 1 Like   #8
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QuoteOriginally posted by vonBaloney Quote
Yeah, on the Sigma lenses I've used, switching to MF on the lens engages the focus ring, nothing more -- it remains autofocus as far as the body is concerned (and will in fact autofocus) until you switch the body to MF also. You don't want to be switching it while it is moving I'm pretty sure. But different function for different lenses and brands, probably, so just make sure you take a minute to figure it out...
On my Sigma 150-500 the focus ring is always engaged. Turning the focus ring while set to AF will focus the lens. If the lens is set to MF it will not autofocus.

09-07-2015, 03:01 PM   #9
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QuoteOriginally posted by boriscleto Quote
On my Sigma 150-500 the focus ring is always engaged. Turning the focus ring while set to AF will focus the lens. If the lens is set to MF it will not autofocus.
Yeah, does not apply to SDM/HSM lenses (I believe that is one?) since they are never engaged with the motor drive on the body -- with standard screw-drive there is no way to disengage autofocus from the lens side with Sigma, Tokina, etc I've used. There are a few Pentax screw-drive lenses with such a switch, aren't there? Not sure how they work...
09-07-2015, 03:14 PM   #10
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QuoteOriginally posted by boriscleto Quote
Absolutely not. The manual even tells you to set the switch to MF on the lens while the body is set to AF if you want to use Catch-In-Focus with an autofocus lens. (You can only use C-I-F with a manual focus lens, unless the autofocus lens has an AF/MF switch)
Oh........never knew that. Cool. Now I can use CIF on my DA*50-135 and DA*200
09-07-2015, 03:21 PM   #11
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QuoteOriginally posted by FilipWessman Quote
I bought a lens with a AF/MF switch on the lens body a few years ago. The dealer told me it was important I used that switch the right way, or I may harm the equipment. Now I have a lighter attention disorder that makes me sometimes not pay attention, so I didn't remember what he said.

Anyway; if I remember correctly, I should have the switch similar to as on the camera body. If I had camera on AF and lens on MF it could hurt the lens. Or the other way around. I don't really remember. Was it so? Is this important?



If it's an early lens with no "Manual Override" , if you try to focus manually while the AF is engaged then yes you will damage the lens. Happened to me with my brand new Sigma 35-70mm lens on the first day I used it. I swore off Sigma for years since that day, but now most AF lenses have Manual Override, you have to check the Specs.
09-07-2015, 04:15 PM   #12
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QuoteOriginally posted by From1980 Quote
I`ve heard this too, but I wondered what the actual incidence of any problems is. Anybody had real damage to a lens needing repair from not disengaging AF before touching the focus ring? I forgot to a number of times with a non-quick shift lens that seems not to mind. Is it just a small chance of strain to the motor and maybe manufacturer`s are being very cautious?
I don't know about lenses, but I've seen a lot of things that have a "mechanical fuse", i.e. something inexpensive/easy to repair that breaks before damage may occur to more critical parts of a system. It would certainly make sense to design an AF lens like this, and also for the manufacturer to urge caution when operating the lens in MF because of this very reason.

My Sigma 30/1.4 (screwdrive/non-HSM) has a focus ring that is always engaged with the AF motor. At some point, the focus mechanism locked up, evidently a mechanical fault. My memory is foggy as to whether this happened before or after someone at a party tried to zoom the lens with the focus ring, though it didn't break immediately after the mishandling.
09-07-2015, 07:04 PM   #13
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It seems to be necessary on the Tamron 90mm macro to have MF/AF synchronised on lens and body. It's a pain, but I do it.
09-08-2015, 09:05 AM   #14
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The lens I bought in the shop is an SMC DA 16-50.
Shall I assume that there is no danger as long as I only manually focus while the body AF/MF switch is set to manual? Because this is what I generally do.

---------- Post added 09-08-15 at 09:05 AM ----------

QuoteOriginally posted by bxf Quote
Your lens is a radio?
He, got me there. Didn't proof read the title.
09-08-2015, 09:08 AM   #15
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QuoteOriginally posted by FilipWessman Quote
The lens I bought in the shop is an SMC DA 16-50.
Shall I assume that there is no danger as long as I only manually focus while the body AF/MF switch is set to manual? Because this is what I generally do.
No, that lens has "quick-shift" capability and is designed to allow for manual adjustments in AF mode. Don't flip any switches while the AF drive is actually engaged/moving -- other than that you are in no danger...
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