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09-21-2013, 07:29 AM   #1
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Just a newbie question...(in-body AF Motors)

Hi,

this is my first post here. My name is Bernhard, but friends call me Bernie.
I am german, so my english is far from perfect, please excuse the mistakes I'll make.

I bought a Pentax K-30 because of the fantastic features it has compared to the competitors in its class.
Indeed calling the K-30 "entry level" isn't doing it justice in my opinion.

My aunt is very dedicated to photography and donated me her "old" Canon EOS 1000D (she also has an EOS 50D and 5D Mk III). I wasn't much interested in this hobby, but this gift "infected" me quite a bit.

Now my question:

I am new to the in-body AF system as my previous camera didn't have this feature.

I learned that this system works by a pin that drives the zoom mechanism in the lens.
So I assume when switching from AF-S via AF-C to MF, that then this pin will be retracted - right?

I now ask myself if it is better to switch to MF before removing / changing the lens as the AF driving pin is then retracted, sitting in the bayonet.

I guess it doesn't make a difference how the AF switch is set prior to changing lens, but would like to understand why.

Best regards,

Bernie

09-21-2013, 07:56 AM   #2
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Good question, but the answer is 'no need'.

The drive pin is spring loaded and is designed to simply get pushed into the body as the lens is rotated.

I wish my German was even fractionally as good as your English!
09-21-2013, 08:21 AM   #3
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Good Morning, and Welcome to the Forum!

As John wrote, it is something that you need not worry about - at all. This design has been tried and proven for so long that it is pretty fool proof. It is a very mature design, and there has only been a very small handful of questions about the in body auto focus motor here over the years. Indeed, the other camera manufacturers have reserved the in body AF motor for their more expensive bodies, thereby making the entry level users purchase more expensive lenses (with a focus motor). Pentax, on the other hand puts the screw drive motor in every single body. It might be a bit slower and may be a tad noisier, but it works every time, and the lenses become much simpler and essentially a near pure combination of optics and mechanics that last forever.

Your English is much better than my German.

09-21-2013, 08:22 AM   #4
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QuoteOriginally posted by JohnX Quote
I wish my German was even fractionally as good as your English!
I wish my English was as good as yours, much less my German!

As noted "no need" the drive pin retracts automatically when the lens release button is pushed. Take the lens off and look at the mount, press the release button and you will see.

Also, please note that modern Pentax cameras have two separate AF drives. The "screw drive" for in body motors that works with all older and most newer lenses and the SDM contacts that drive the in lens focusing motors in newer lenses. Some lenses have both systems but only allow SDM if it is present in the camera and some new lenses only have SDM. This is mostly transparent to the user but something to be aware of.

And welcome, by the way.

09-21-2013, 08:36 AM   #5
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Original Poster
Thank you all for your quick and detailed answers, very helpful.
09-23-2013, 08:29 AM   #6
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QuoteOriginally posted by JohnX Quote
Good question, but the answer is 'no need'.

The drive pin is spring loaded and is designed to simply get pushed into the body as the lens is rotated.

I wish my German was even fractionally as good as your English!
Guten Tag! to our Menschen from German speaking countries!

The AF pin is "pushed into the body when the lens is rotated" only when a lens is mounted. It may sound picky, but this pin is retracted into the body under two conditions:
  • When the body is changed from AF to MF via the switch on the side of the lens box
  • When the lens release button is pressed in (the lens release pin is also retracted).

This knowledge is important because you never want to turn the in-body AF motor by turning the focus ring on the lens. Not only will it be difficult, but it will damage the in-body AF mechanism. Many DA lenses include a clutch that disengages the lens from the AF when you manually turn the focus ring - this feature is called Quick Shift. However, DA L and old AF lenses generally do not have this capability. However, you can simulate this capability using one of the above two methods to retract the AF pin.
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