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05-01-2009, 07:30 AM   #1
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Focus Trapping-What am I doing Right?

Odd question I know. Since acquiring some M42's, I wanted to try focus trapping on my K10d. I read on another site that to do such I needed to shoot in manual mode, single shot AF, and short the contacts with aluminum foil. I tried this and it works. However, last night I tried to go back to regular focus shooting. I changed to Av mode, removed the foil unmounted and remounted my Supertak 50 and it still focus traps. Changing to AF-C did stop the trapping.

That made me think of times when I am trying to catch some shots of my kids with my 77 mm or DA35. I get everything set up (great never-to-be-seen-again expressions) and press the shutter and the camera freezes up. This is so frustrating. It is just like focus trap but with an AF lens in Av mode and AF-S.

Is this due to dirty electrical contacts? If so how does one clean them?

Is it due to AF-S? The reason that I have been using AF-S is that I like to use the center af point to lock my focus and exposure then recompose. I set this thru the custom menu. (I know that I can use the AE lock button, but that is another step and it locks the same exposure until pressed again.) This custom feature doesn't work with the camera set to AF-C. So, I lock AF/AE to the center point and recompose (at which point the center point is often no longer in focus but now over the background) press the shutter and get nothing just like I am focus trapping. In fact if I hold the shutter down eventually it will fire as I move the camera or the kids move.

Hence my original question: What am I doing 'right' to get this focus trap effect with AF lenses when I don't want it?

Thanks and I am sorry for the long question.

05-01-2009, 07:54 AM   #2
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Dup thread. Mods close?
05-01-2009, 08:00 AM   #3
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Huh - that's a weird one... here's how I think my K20D logic on focus trap works.
  • First of course, you must have "Catch In Focus" or whatever it's called enabled in the custom menu (which you obviously do).
  • Then, the camera needs to "see" the lens as MF - because it's getting no indications of it's AF abilities through it's electrical contacts. This could be a MF lens like an M42, or something like a DA* with the switch set to MF.
  • The camera needs to be set in AF.S (I think).
  • Now it should "catch in focus" when the shutter release is held in.

Auto focus in AF.S using the center AF point (as you said you prefer) should work this way...You focus via AF button or a half-press of the shutter release and when the camera determines the focus is correct, it displays the green hexagon, and maybe beeps... You can now recompose and shoot, but however you activate the AF system (the default setting would be half-press of the shutter release), you'll need to keep the system engaged (half depressed shutter button or keep the AF button in) to keep the focus lock while recomposing or the next time you press the button - to take the picture, the camera will re-evaluate focus, determine it doesn't have a subject in focus under the center AF point, and it will start to focus again and refuse to shoot since in AF.S, it won't fire until it has a focus lock on something (similar to catch in focus, but not related to that menu option).

Keep that green focus confirmation indicator lit and it should fire whenever you fully depress the shutter. If you're doing that and it still won't fire - I'm stumped...
05-01-2009, 08:11 AM   #4
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On a K10D trap focus should not work with AF lenses. From what I understand only the K20D can trap focus with AF lenses that have a true on/off AF switch as this is the "Catch In Focus" feature. Does this happen with ALL of your AF lenses or just certain ones?

05-01-2009, 10:13 AM   #5
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Not sure where you heard to short the focus contacts, from an electrical engineering stand point I definitely wouldn't do that.
For focus trapping on MF lenses I just tell the camera to not take a picture until it has a focus lock and then hold down the shutter release and focus or move, thats it. I don't know how it is for a k10d though, I use an *ist D
05-01-2009, 12:12 PM   #6
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So you're sure the camera has locked focus? You're seeing the solid green hexagon before you recompose, and it doesn't go away?

Sometimes I can't get focus and I hit the OK button to cancel auto-focus (that's how mine's set up) so I can just take a damn picture!
05-01-2009, 01:00 PM   #7
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QuoteOriginally posted by MrApollinax Quote
On a K10D trap focus should not work with AF lenses. From what I understand only the K20D can trap focus with AF lenses that have a true on/off AF switch as this is the "Catch In Focus" feature. Does this happen with ALL of your AF lenses or just certain ones?
This sounds about right. I haven't look at the K10D/K20D manuals, but I'm pretty sure Catch-In-Focus will only work with the DA* zooms and maybe the DA*55mm. The lens has to have the AF/MF switch on the lens itself. The K200D also has this capability with M42 lenses as long as they have the A/M switch and the contacts are shorted.
05-01-2009, 01:21 PM   #8
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Sorry for the duplicate thread- my bad.

QuoteOriginally posted by heliphoto Quote
Huh - that's a weird one... here's how I think my K20D logic on focus trap works.

I agree.

Auto focus in AF.S using the center AF point (as you said you prefer) should work this way...You focus via AF button or a half-press of the shutter release and when the camera determines the focus is correct, it displays the green hexagon, and maybe beeps... You can now recompose and shoot, but however you activate the AF system (the default setting would be half-press of the shutter release), you'll need to keep the system engaged (half depressed shutter button or keep the AF button in) to keep the focus lock while recomposing or the next time you press the button - to take the picture, the camera will re-evaluate focus, determine it doesn't have a subject in focus under the center AF point, and it will start to focus again and refuse to shoot since in AF.S, it won't fire until it has a focus lock on something (similar to catch in focus, but not related to that menu option).

Keep that green focus confirmation indicator lit and it should fire whenever you fully depress the shutter. If you're doing that and it still won't fire - I'm stumped...

Honestly, I can't remember if it lit or not. I do know that the center focus light lit and the lens stopped hunting for focus as if it was locked in on a face in good light I might add.


QuoteOriginally posted by MrApollinax Quote
On a K10D trap focus should not work with AF lenses. From what I understand only the K20D can trap focus with AF lenses that have a true on/off AF switch as this is the "Catch In Focus" feature. Does this happen with ALL of your AF lenses or just certain ones?
It has happened with my 35 and 77 mm. Not often, though. I too thought that it should not work with the AF lenses. What stumps me is that I have plenty of pictorial evidence that my camera will fire without my subject in focus.


QuoteOriginally posted by zplus Quote
Not sure where you heard to short the focus contacts, from an electrical engineering stand point I definitely wouldn't do that.
For focus trapping on MF lenses I just tell the camera to not take a picture until it has a focus lock and then hold down the shutter release and focus or move, thats it. I don't know how it is for a k10d though, I use an *ist D
You are right. It doesn't sound like a great idea. I have heard it here particularly in threads regarding M42 lens. Some say that it helps improve the camera's metering. Here is a link to the focus trap recommendation:
Focus Trap or Catch In Focus |Photography Rulez



QuoteOriginally posted by farfisa Quote
So you're sure the camera has locked focus? You're seeing the solid green hexagon before you recompose, and it doesn't go away?

Sometimes I can't get focus and I hit the OK button to cancel auto-focus (that's how mine's set up) so I can just take a damn picture!
I need to go back and try it out.

Thanks for the replies.

Maybe it is just the AF-S and the focus lock not setting. Any other thoughts on it ?


05-02-2009, 05:49 AM   #9
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In AF-S the shutter won’t fire unless the camera has focus, no matter what type of lens. (If you have AF on shutter button that is.) Therefore you manually have to turn the focus ring to fire or move the subject into focus ( focus trap) with a manual lens.

With a modern lens the AF-motor will turn the ring into focus and then fire. If there is fast action the AF might fail to get focus in time and you will miss the shot.

Things might get confusing if you have moved AF to the AF button though, it is still logical but you have to think a little.
05-02-2009, 06:30 AM   #10
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QuoteOriginally posted by zplus Quote
Not sure where you heard to short the focus contacts, from an electrical engineering stand point I definitely wouldn't do that.....
I'm not sure what "Focus Contacts" are being referred to, but shorting the contacts on the lens mount must be OK from an electronics standpoint as these mounts are designed to support K type lenses which short all contacts (except maybe the "A" contact - but a closed "A" contact appears to be a dead short.)

Iowa Dave
05-02-2009, 11:00 AM   #11
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QuoteOriginally posted by newarts Quote
I'm not sure what "Focus Contacts" are being referred to, but shorting the contacts on the lens mount must be OK from an electronics standpoint as these mounts are designed to support K type lenses which short all contacts (except maybe the "A" contact - but a closed "A" contact appears to be a dead short.)

Iowa Dave
After visiting the site where he got the information, I would have to agree with you, its not as big as a deal that I thought it was. At first I thought he was shorting the SDM focusing contacts, which I still think wouldn't be a good idea.
05-04-2009, 06:38 PM   #12
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I've done trap focus with my K100D and posted my steps awhile back. For an autofocus lens I put insulating tape over the contacts, not foil. Reading the url MSM posted that person said tape as well. He only mentioned foil for non-AF lenses which as newarts mentioned the lens would short the contacts anyway. The camera must be short circuit proof since I've mounted many old K1000 lenses already.

As to why the camera did not recover afterward I'd look for something you set and forgot to unset. Perhaps try the camera total reset. My post-trap problem was I forgot to remove the tape from my Pentax Macro and thought I broke it for about 20 minutes.

Last edited by LeoTaylor; 05-04-2009 at 06:43 PM. Reason: Added paragraph
05-05-2009, 06:23 AM   #13
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QuoteOriginally posted by heliphoto Quote
Huh - that's a weird one... here's how I think my K20D logic on focus trap works.
  • First of course, you must have "Catch In Focus" or whatever it's called enabled in the custom menu (which you obviously do).
  • Then, the camera needs to "see" the lens as MF - because it's getting no indications of it's AF abilities through it's electrical contacts. This could be a MF lens like an M42, or something like a DA* with the switch set to MF.
  • The camera needs to be set in AF.S (I think).
  • Now it should "catch in focus" when the shutter release is held in.
Thanks. That explains what I did not understand described in the manual for my K-m. On Catch-in Focus, the manual states (the following quote is a copy&paste from page 118):
'How to Take Pictures
1 Attach a proper lens to the camera.
2 Set the focus mode lever to AF.
3 Set AF Mode to AF.A or AF.S.
4 Set focus on a position the subject will pass.
5 Press the shutter release button fully.
The shutter is released automatically when the subject comes into focus in the set position.'

I think the manual is either wrong or confusing. I had taken the step to 'Press the shutter release button fully' to mean press it all the way down as opposed to half way. You explain that the button has to be held down until the subject comes into focus, at which point the camera will take the shot. I'm not sure what step 2 means. I have writtet to Pentax asking for a clarification.
05-05-2009, 01:33 PM   #14
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The K10D has no special Catch-In-Focus mode. (The OP has a K10D). It uses Snap-In-Focus which was introduced with the SF-1. Snap-In-Focus requires no special techniques. All it needs is a manual focus lens mounted on the camera, and the camera's AF set to AF.S. The camera won't take a picture until things are in focus. So here are the instructions for using a manual focus lens on the camera in Snap-In-Focus mode.
1. Mount a manual focus lens (or cheat with silver foil)
2. Set the camera to AF.S
3. Set the lens' focus to where you want to trap
4. Press and hold the shutter button until the camera takes the picture.

Catch-In-Focus, first introduced on the K20D, allows you to use an autofocus lens with a MF/AF switch the same as a manual focus lens, if the appropriate menu option is enabled, the camera is in AF.S and the lens is in MF. Personally, I was disappointed that I could not CIF with the K10 and DA* 50-135.

PS - the users that use the tin foil system cannot damage anything as long as the foil stays on the lens mount only and does not fall into the camera.
05-05-2009, 01:55 PM   #15
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QuoteOriginally posted by Canada_Rockies Quote
1. Mount a manual focus lens (or cheat with silver foil)
2. Set the camera to AF.S
3. Set the lens' focus to where you want to trap
4. Press and hold the shutter button until the camera takes the picture.
The instructions I came up with for a K100D for taking photos with a manual lens as long as an object is in focus have a few more steps:

------------
Mode Dial > M
Record Menu > AF Mode > AF-S
Record Menu > Swtch dst msr pt > Center Spot (may be greyed out)
Setup Menu > Auto Power Off > OFF
Custom Menu > Using Aperture Ring > Permitted
Fn Button Menu > Drive Mode > Continuous
Front of camera slide switch > AF
Rear of camera slide switch > SR Off
I used external power since the camera was left on for over an hour.

Focus camera at desired distance.
Aim camera slightly away from any background objects at the focus distance.
Lock shutter with remote shutter cable or shorting plug.
Test by passing your hand slowly through focus point.
-----------

I used this procedure when aiming the camera to one side of a squirrel feeder. I came back later and had 900 photos and most had a squirrel in focus.
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