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03-13-2010, 12:41 AM   #31
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QuoteOriginally posted by WMBP Quote
So I've mounted the Sigma 28 f/1.8 EX DC on my K20D. Pulled the barrel sleeve in to the MF position. Put the camera into MF, too, so I could rotate the lens to set the focus distance. Returned the camera to AF.S. Plugged in the remote cable release. I'd set the focus for a distance of 5 ft. Covered the lens hood with my hand and clicked the shutter release. The camera tried to auto-focus, then took a picture. In other words, it didn't work.

What am I doing wrong? Won't work with this lens? Something else?

Will
Hi Will,

AFAIK, Sigma lenses don't disengage from the screw drive shaft when you move the focus collar like my FA* 300/4. The only difference between MF and AF on the Sigmas is that the collar is disengaged from the focusing mechanism in AF position. I believe that shorting the pin is the only solution for Sigma AF lenses. I have 4 -- an EX 300/2.8, 17-70/2.8-4.5, Ex 180 Macro, and EX 100-300/4, and all of them behave alike.

Scott

03-13-2010, 02:55 AM   #32
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QuoteOriginally posted by snostorm Quote
AFAIK, Sigma lenses don't disengage from the screw drive shaft when you move the focus collar like my FA* 300/4. The only difference between MF and AF on the Sigmas is that the collar is disengaged from the focusing mechanism in AF position. I believe that shorting the pin is the only solution for Sigma AF lenses. I have 4 -- an EX 300/2.8, 17-70/2.8-4.5, Ex 180 Macro, and EX 100-300/4, and all of them behave alike.
I'm not discounting what you're saying since I don't have any Sigma lenses, but that sounds super silly. If we set aside catch-in focus for a second, under normal circumstances with a proper lens mounted, the camera will refuse to take a picture in AF.S mode unless focus has been achieved. What you're saying is that putting the lens in MF mode would essentially make the camera hunt on purpose and then give up, and then you would be unable to take a picture unless you focused manually... and then the moment you half-pressed the shutter button, the camera might once again try to auto-focus because it doesn't agree with your focus (I have auto-focus set to shutter half-press). This sounds like a terrible system.

With a DA* lens, if I have catch-in focus disabled, when I put the lens in MF mode, the camera switches to MF mode regardless of what the switch on the body is set to. So I can take pictures regardless of whether focus is achieved.

I find it bizarre (and unfortunate) that the body wouldn't keep track of whether a lens was set to AF/MF.
03-13-2010, 05:37 AM   #33
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QuoteOriginally posted by GoremanX Quote
. What you're saying is that putting the lens in MF mode would essentially make the camera hunt on purpose and then give up, and then you would be unable to take a picture unless you focused manually... and then the moment you half-pressed the shutter button, the camera might once again try to auto-focus because it doesn't agree with your focus (I have auto-focus set to shutter half-press). This sounds like a terrible system.

With a DA* lens, if I have catch-in focus disabled, when I put the lens in MF mode, the camera switches to MF mode regardless of what the switch on the body is set to. So I can take pictures regardless of whether focus is achieved.

I find it bizarre (and unfortunate) that the body wouldn't keep track of whether a lens was set to AF/MF.
Hi GmX,

That's not at all what I was saying -- When the focus ring is shifted to the MF position, AF still works and will lock normally, but the ring rotates during AF. When the focus ring is shifted to the AF position, it's disengaged, so it doesn't rotate. In either position, the screw drive motor is still engaged with the lens' AF system, and the chip in the lens is telling the body that an AF lens is attached, so in either AF mode of the body switch, the body will attempt to AF, so Focus Trap won't work. Don't forget, just eliminating the focus ring rotation during AF was, at the time noteworthy, and that was the purpose of this feature. There was really no good reason for the lens to "tell" the body that the lens focus ring was set to MF in this first generation of the focus clutch.

On all of my FA, F, and third party (Sigma, Tamron, or Tokina) screw drive AF lenses which don't have the two position focus rings (focus clutch), the focus ring is always engaged (and turns during AF). The AF screw drive shaft is always engaged with the AF motor in both AF modes. Manual focus is not feasible unless the body is switched to MF.

My FA* 300 (4.5 & 2.8) work differently, and both disengage the screw drive shaft and switch the focus mode to manual when the focus ring is shifted to the MF position, so the body does not have to be switched to the MF position in order to manually focus (and Focus Trap works with these). This was an advance of the focus clutch feature from the F* 300/4.5 where both the focus ring and the body have to be switched to MF for manual focusing, and Focus Trap is not possible without shorting the Data Pin. Quick Shift on the DA series lenses is the next advance of this feature, and the best implementation is on those models that also have the AF/MF switch on the lens in addition to QS (as far as Focus Trap or shutter priority capability is concerned at least).

On any of these AF screw drive lenses (except for the FA*s mentioned,and possibly a few other FA models) and even the DA lenses that don't have an MF/AF switch on the lens, you need to fool the camera into thinking that the lens is a manual focus lens in order to use Focus Trap, and the only way I know to do it is to short the data pin.

Scott
03-13-2010, 06:35 AM   #34
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I have tried catch-in focus just few minutes ago.
1. Put my 50mm 1.7M lens on.
2. Enabled catch-in focus.
3. MF/AF switch was set to AF
4. Focused somewhere while holding shutter button fully pressed and tried to move object to camera. As object approached focused zone camera took a picture by itself. Picture was sharp.
5.This function is ok for slowly moving objects as long as fast moving objects are not captured.
6. It's a pity that object should be placed in the centre of frame otherwise camera does not "see" it.

03-13-2010, 08:48 AM   #35
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QuoteOriginally posted by kent Quote
4. Focused somewhere while holding shutter button fully pressed and tried to move object to camera. As object approached focused zone camera took a picture by itself. Picture was sharp.
5.This function is ok for slowly moving objects as long as fast moving objects are not captured.
There are two applications (that I see) of trap-focus. The primary, as documented in the manual, is to prefocus on a point where you expect the subject to be, and let its in-focus appearance trip the shutter. This lends itself to continuous-mode shooting. The other is handheld and hand-focused shooting, especially in less-than-perfect conditions. This is slower than autofocus; but faster than manually hunting for focus confirmation and then pressing the shutter.

QuoteQuote:
6. It's a pity that object should be placed in the centre of frame otherwise camera does not "see" it.
I rather miss the functionality of my Sony DSC-V1, with its Selected Frame Priority AF, which lets the user select the focus point within the frame: center, left, right, top, or bottom. With the K20D the best to be done is to capture the image, then crop for composition.
03-13-2010, 02:50 PM   #36
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QuoteOriginally posted by snostorm Quote
That's not at all what I was saying -- When the focus ring is shifted to the MF position, AF still works and will lock normally, but the ring rotates during AF. When the focus ring is shifted to the AF position, it's disengaged, so it doesn't rotate. In either position, the screw drive motor is still engaged with the lens' AF system, and the chip in the lens is telling the body that an AF lens is attached, so in either AF mode of the body switch, the body will attempt to AF, so Focus Trap won't work.
Ah hah! Now I get it. All these different AF/MF/ring disengage options are too much for my tiny mind o absorb.
03-14-2010, 04:21 AM   #37
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I use catch-in focus for macro shots with my Pentax A 4/100 macro lens, works great and helps a lot with very thin DOF.
03-14-2010, 07:23 PM   #38
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QuoteOriginally posted by simico Quote
I use catch-in focus for macro shots with my Pentax A 4/100 macro lens, works great and helps a lot with very thin DOF.
I use it with my M 100/4 macro. It works better for me than a tripod when chasing bugs.

03-15-2010, 04:07 AM   #39
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QuoteOriginally posted by kent Quote
It's a pity that object should be placed in the centre of frame otherwise camera does not "see" it.
With debug mode you can use catch in focus with any focus point: https://www.pentaxforums.com/forums/pentax-dslr-discussion/88186-off-center-m...bug-k100d.html
03-15-2010, 11:30 AM   #40
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QuoteOriginally posted by Radix Quote
With debug mode you can use catch in focus with any focus point: https://www.pentaxforums.com/forums/pentax-dslr-discussion/88186-off-center-m...bug-k100d.html
Before I try the K100D debug mode trick on my K20D, I'd better ask: does the K20D *have* an accessible debug mode? Is it non-toxic? I don't wanna brick the camera.

I know that with SEL the focus point (for AF or confirmation) can be selected -- but only for AF lenses, whether in AF or MF. If I mount an AF lens, SEL an off-center point, then mount a manual lens, the focus point goes back to center. Then when I re-mount the AF lens, the point I SEL'd is still active, whether on not I've power-cycled the cam. Would a DEBUG trick (or any other trick) allow off-center catch-in-focus on the K20D?
03-15-2010, 05:02 PM   #41
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QuoteOriginally posted by RioRico Quote
Before I try the K100D debug mode trick on my K20D, I'd better ask: does the K20D *have* an accessible debug mode? Is it non-toxic? I don't wanna brick the camera.

I know that with SEL the focus point (for AF or confirmation) can be selected -- but only for AF lenses, whether in AF or MF. If I mount an AF lens, SEL an off-center point, then mount a manual lens, the focus point goes back to center. Then when I re-mount the AF lens, the point I SEL'd is still active, whether on not I've power-cycled the cam. Would a DEBUG trick (or any other trick) allow off-center catch-in-focus on the K20D?
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