FTM lenses and how to use the FTM?

Hi All,

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I have been puzzled about how I can use the FT-M focusing on my 28-105 USM lens. According to the manual that comes with the lens it says one should not turn the rear focusing ring when it is moving. But without turning that how could I do the full-time manual focus?

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I have seen several fuzzy answers for this question on the web and it seems that FT-M is only recommended in shooting modes other than the "One Shot" mode. Is that true?

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If anyone could give me an example on how to use the FT-M feature without damaging the lens I will be very interested to know.

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Thanks for listening.

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Cheung =)

It is indeed true that you should use FTM in "One-Shot" mode only

because in "AI-servo" the camera would immediately try to counteract

your correction in order to find its primary AF target.

So the principal steps are (0. use "One Shot"), 1. use AF as a rough

focus till it indicates that it has found something, 2. use FTM to

fine-tune the setting based on your preferences. You have either to

keep the shutter half-pressed or use a custom-function to (de)activate

AF via a rear button. I've never heard that FTM can damage the motor -

finally there're no mechanical gears with USM. FTM just hasn't much

sense DURING AF.

Hi Klaus,

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Thanks for your reply. I have tried using the FTM function as you

suggested and it seems to work to some degree. But now it leads to

2 more questions:

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1. In the case where an AF has achieved focus (with one of the red

square lids up - I am using the eye control feature in the 50E),

turning the rear focusing ring may cause the "in focus indicator" to

go away in the view finder. And in one shot mode if the "in focus"

indicator goes away even though I have depressed the shutter button

fully it would not allow me to take the picture. And that leads to

the question - how would such FTM adjustment help if I cannot take a

pic?

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2. In the case where no initial AF can be achieved (due to lack of

contrast or whatsoever), would it be able to use FTM to try to assist

the camera to focus?

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Thank you once again for listening.

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Cheung

Quite surprising because this works just fine at least on the EOS 1, 5

and 100. In principal "one shot" means focus priority but IMO this

gets disabled once the camera achieved focus. What program mode did

you use ?

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In principal you could use FTM to prefocus in low-light situations but

even if the camera can lock on after that it is probably not too

accurate anymore.

Hi Klaus,

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The method that you were describing previously seems to be working

fine now (I must have done something silly with the shotting mode

stuff). Thanks again for your help.

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Cheung

In his first answer here, Klaus makes a key point about using

the FTM feature--that most of us initially use autofocus, and then if

we don't quite agree with the result, we then touch it up manually,

BUT the shutter button must be kept partially depressed until it is

finally tripped, or the camera will re-adjust focus as it sees fit if

the shutter button is again partially or fully depressed. Because of

this, I don't use FTM much, but in many instances I prefer instead to

simply switch the lens to manual focus when I need to touch up focus.

With the 1n, for example, custom fxn CF4 allow for metering, shutter

release and autofocus to be controlled by separate buttons rather than

together, but getting used to this can seem counter-intuitive.