[erluko]

I just picked up a Sigma 100-300 f4 EX (non-DG). It's been working great except for one annoying thing, and I'd like to know if there's a real problem or if the lens is operating as intended and my expectations were off.

If you own or have owned this lens, please respond.

When you slide the focus ring into the MF position, does your lens disconnect from the body's screw drive or do you also find that you have to set the body switch to MF?

If you've used this lens with the Sigma 1.4x TC or another autofocus TC:

When you slide the focus ring into the MF position, does your lens disconnect from the TC's autofocus screw drive?

Mine does not disconnect. When the lens is in MF mode, I'm fighting the camera screwdrive unless I put the body in MF mode. If I use Sigma's 1.4 TC, the AF works great ,but going to MF keeps the TC's autofocus system engaged making it very hard to manually focus even if the body is in MF mode. I want to know if this is normal or not. If it's not, I'll need to find out what a repair would cost.


Thank you!

[Digitalis]

As a long time owner of this lens, I'm qualified to answer your questions...

When you slide the focus ring into the MF position, does your lens disconnect from the body's screw drive or do you also find that you have to set the body switch to MF?

The lens is incapable of disengaging the Screw drive AF mechanism. Only the camera body has control over the connection of the AF mechanism, hence the need for the AF switch on the camera*.

When you slide the focus ring into the MF position, does your lens disconnect from the TC's autofocus screw drive?

No.

When the lens is in MF mode, I'm fighting the camera screwdrive unless I put the body in MF mode.

Doing this runs the risk of damaging the internal AF motor in the camera. Do not do this. AF speed is improved when the lens is left AF mode: when left in MF mode, the lenses AF will be considerably slower.

If I use Sigma's 1.4 TC, the AF works great ,but going to MF keeps the TC's autofocus system engaged making it very hard to manually focus even if the body is in MF mode.

This is odd, with all of my Pentax camera bodies MF mode disengages the screw drive mechanism, with the switch turned to MF the AF drive shaft retracts into the lens mount disabling the AF drive. The TC should not be overriding this, unless the gears in the TC are producing additional resistance and making the focus ring hard to turn - in which case there is the possibly of a mechanical fault with your TC.



* you can depress the Lens release button to disengage the AF mechanism for a pseudo quick shift, though this requires you to switch between AF and MF on the lens itself. Though be careful while doing this as the lens can become inadvertently detached.

[erluko]

As a long time owner of this lens, I'm qualified to answer your questions...

Perfect! Thank you for taking the time to help me out.

When you slide the focus ring into the MF position, does your lens disconnect from the body's screw drive or do you also find that you have to set the body switch to MF?

The lens is incapable of disengaging the Screw drive AF mechanism. Only the camera body has control over the connection of the AF mechanism, hence the need for the AF switch on the camera*.

When you slide the focus ring into the MF position, does your lens disconnect from the TC's autofocus screw drive?

No.

Oh. Ok. My other lenses (DA* 50-135, Pentax-F 100 Macro, Sigma 17-50) with AF/MF controls do somehow disengage regardless of the setting of the on-body AF switch. I'd assumed this one would too. Thank you for letting me know this lens doesn't behave like the others.

When the lens is in MF mode, I'm fighting the camera screwdrive unless I put the body in MF mode.

Doing this runs the risk of damaging the internal AF motor in the camera. Do not do this. AF speed is improved when the lens is left AF mode: when left in MF mode, the lenses AF will be considerably slower.

It seemed bad. I stopped as soon as I realized this lens wouldn't act like my others with an on-lens MF mode.

If I use Sigma's 1.4 TC, the AF works great ,but going to MF keeps the TC's autofocus system engaged making it very hard to manually focus even if the body is in MF mode.

This is odd, with all of my Pentax camera bodies MF mode disengages the screw drive mechanism, with the switch turned to MF the AF drive shaft retracts into the lens mount disabling the AF drive. The TC should not be overriding this, unless the gears in the TC are producing additional resistance and making the focus ring hard to turn - in which case there is the possibly of a mechanical fault with your TC.

I wonder if something is wrong with my TC. It's the only AF one that I own and the screw is spring-mounted. I wonder if it is sticking.

* you can depress the Lens release button to disengage the AF mechanism for a pseudo quick shift, though this requires you to switch between AF and MF on the lens itself. Though be careful while doing this as the lens can become inadvertently detached.

Neat trick! Thanks!

[jeallen01]

I "might" want to "disagree" with @Digitalis about NOT setting the lens to MF and the body to AF!

Been doing that for quite a few years with a K-5, K-3 & K-3 II because that allows far quicker "AF-override" which is rather like Pentax "Quick shift", and there's been no damage to the lens or bodys' screwdrive mechanisms - although I did have to have the lens AF PCB/PWB board replaced several years ago..

In fact, and often with the dedicated Sigma 1.4X TC, that is my standard setup for shooting at airshows and the like

PS: I have not found the lens to focus any faster when set to AF, and then there is the BIG downside that it takes far longer to re-establish AF lock, especially when the target is moving quickly towards to camera.

PPS: you need an extra option on the Poll to address "my" approach!

---

Last edited by jeallen01; 12-23-2018 at 01:32 PM.

[Digitalis]

I "might" want to "disagree" with @Digitalis about NOT setting the lens to MF and the body to AF!

You can disagree if you want: it doesn't alter the fact that failing to switch the lens from MF mode when using screwdrive AF puts more strain on the cameras AF motor, more torque is needed to move the focusing group because the motor is being forced to move more mass* - slowing down AF, and damaging internal components in both the lens and camera. Those small AF gears aren't supposed to move more mass than the focusing group.

* and pointlessly turning the focusing ring which is simply wasting energy, and reducing camera stability as you can no longer hold the focus ring to support the lens properly.

[kypfer]

I don't have this specific lens but I do have the 70-200 f/2.8 + EX 2x and can confirm that the OP's original description seems to be the default operation mode, both the lens and the camera have to be set to MF, or both to AF, for things to work smoothly.


I spent some time (years?) not changing both switches, unaware that there was any issue and kicked myself quite considerably when I found out how much faster the focussing was! I shudder to think how many shots I'd managed to miss because the camera/lens just didn't focus fast enough, fortunately no harm seems to have resulted

[jeallen01]

You can disagree if you want: it doesn't alter the fact that failing to switch the lens from MF mode when using screwdrive AF puts more strain on the cameras AF motor, more torque is needed to move the focusing group because the motor is being forced to move more mass* - slowing down AF, and damaging internal components in both the lens and camera. Those small AF gears aren't supposed to move more mass than the focusing group.

* and pointlessly turning the focusing ring which is simply wasting energy, and reducing camera stability as you can no longer hold the focus ring to support the lens properly.

On the first point we will have to "agree to disagree" - "my way" works better for me, and, as I said, there's never been a sign of damage to either the lens or the bodies (and the K-3 bodies have a much stronger focus motor than the K-5, and have no trouble driving the lens quickly in this mode).

On the 2nd point, I keep the tripod adapter/"foot" on the lens and under it - I can then both support the lens with the palm of my left hand under the foot/adapter and still easily turn the focus ring either way with the fingers of the same hand! Maybe I have somewhat large - but not huge - hands, but that "works" and is quite comfortable

---

Last edited by jeallen01; 12-24-2018 at 02:11 AM.