Question about the Pentax DFA 100mm macro

I was having a go with a friends DFA 100mm macro the other day and thinking I'd probably buy one. I'd be happy to have the non WR version same as his because I don't wish to pay the extra premium when I never shoot in the rain anyway! And the aperture ring would be useful for my purposes also.

I noticed something on his though that I wanted to ask about: the focussing ring can still be turned beyond the two extremes of focus! Basically you can keep turning the thing as long as you want, albeit with a little more resistance. Also, the focus lock switch knocks out the auto focus in use, but again does not prevent you from turning the focus ring manually and altering the focus that way, even when the lock is engaged.

Is this normal for this lens?? I found it a little odd at first, but wondered if it's a by-product of the quickshift clutch.

Any advice would be welcomed before I go out and spend my money

What you describe is quite normal and locking the clamp does not stop the camera from continuing to autofocus the lens, at least on mine, maybe this can vary depending on the wear of the Clamp: which is there simply to prevent barrel creep if the lens is pointed up or down.

It's quite normal, it's a great lens as well.

Thanks for the advice
So am I to take it that the lock SHOULD stop the autofocus..?

As far as I can make out the going rate for a minty second hand DFA is around £280 - £300 and for the WR version £350 - £380. Would this be about what I should pay, or am I totally wrong here?

I agree John - from what I've seen so far it does indeed look like a great lens

Not sure about the lock offhand, I'll have to check. As far as I know it just stops creep when the lens is pointing downwards.

Like John, I don't know Mine doesn't so maybe it does depend on the wear on the clamp, maybe mine is worn, maybe your mates is faulty, I'd be interested to hear from anyone else that has one.

Your prices are probably about right if you buy from a dealer, privately I would think you could pick one up for around £200-£250

PS It is a superb bit of glass, my avatar was shot with mine (bigger pic in my portfolio)

The clamp stops the lens focussing either manually or in auto. At least it is meant to!

John

The clamp adds a little more friction to the focusing barrel to prevent lens creep when used vertically.

It's probable that different copies of the same lens behave slightly differently. On mine, when the clamp is on, the focus ring can be turned, but the focusing barrel (the one with the scale on it that you view through the window) does not move.

It would be unwise to use auto focus with the clamp on as it will introduce more strain on your camera's AF motor.

Be aware that the WR version does not have an aperture ring, but the non-WR version does. I love my non-WR version, by the way. Superb lens.

Also the WR version has rounded aperture blades which some people think gives nicer
boken.....

Interesting.... it seems that there's commonly a variation in the way these lenses behave - this would encourage me to feel concerned about build quality and manufacturing tolerances Consistency and identical operation of product is the quality control aim in manufacturing after all

I don't know how the clamp is implemented in the D-FA lens, but the FA lens has a little plastic pin about 1.5mm in diameter that is actuated by a rotating switch. All it does is contact the focusing barrel internally. Manufacturing tolerances dictate that any two lenses might behave slightly differently, but if they both have the same effect ie. stop the lens creeping, then I'd say that's OK.

I didn't realise it, but there is a Pentax-D FA instruction manual.

This is what it says about the clamp:
Hope that helps!

Thanks John

It sounds like the clamp is commonly damaged by people trying to manually turn the focus ring having forgotten they've engaged the lock. Wonder how much a repair costs, and whether this sort of damage breaks off anything inside the lens that might mess up the optics or focus travel. I might speak to a repair place and ask for future reference. I'll post what they say here.

I hardly ever use the clamp. Once in a blue moon, you'd say. Actually, I don't use autofocus all that much either. The chances of me causing damage to the lens is, I would say, negligible. I don't know what this worry is about, to be honest.

But if the clamp is "commonly damaged" I would, too, like to hear about it.