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How to use Trap-focus or Catch-in focus
Posted By: eurostar, 02-14-2009, 06:21 AM

Any Pentax DSLR allows the user to easily build a photographic trap to shot elusive birds and other animals. No need for infrared sensors and electronic do-it-yourself skills. Just a camera, a manual lens and a cable release with lock, and everyone can create a robot-camera that shot when the subject come on the spot. And the shot will be always in perfect focus.

You need: an AF Pentax reflex camera (a DSRL is preferable), a KA mount manual lens, an electrical cable release with lock and a tripod or similar camera support (pic 1).
Camera must be set on AF-S (pic 2), continuous shooting (pic 3), exposure mode on AV (pic 4). Aperture priority allows the use of a large aperture, with shallow DOF and fast shutter time to freeze movements.
Aim the central focus point to the place where your subject is expected to come, manual focus until focus aid (green hexagon) lit up, recompose to have the central focus point to aim at the point where subject head should be.
Now put viewfinder cap on, to avoid errors in exposure (pic 5)
Plug in the cable release (pic 6), push the release button and block it (pic 7).
Nothing will happens. Go to the place your subject will come, wave you hand in the focus point, and you will hear the shutter working.
Go away and allow subjects to come. After some hours come back and control if pictures counter advanced. If so, you can replay pictures on the LCD to see what species came.

With Pentax K20D, you can use not only the central AF point, but every one, allowing for a better placement of subject in the frame of the picture. This improvemetn has brought Pentax to rename the function catch-in focus.








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02-14-2009, 12:22 PM   #2
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Article approved and moved into the DSLR article section. Thanks a lot for your submission!

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02-16-2009, 02:40 AM   #3
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What I have written above is what I believe the easiest set up.

But you can also use K and M lenses at full aperture, to retain AV mode.

And you can also use AF lenses simply putting a tiny piece of aluminium foil blocked by adesive tape over the golden pin on the camera mount, tricking the camera to believe the lens is an A type.

Finally, cath-in focus on the K20D works directly with FA and DA lenses with a M-AF switch.
06-09-2009, 05:58 AM   #4
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QuoteOriginally posted by eurostar Quote
What I have written above is what I believe the easiest set up.

But you can also use K and M lenses at full aperture, to retain AV mode.

And you can also use AF lenses simply putting a tiny piece of aluminium foil blocked by adesive tape over the golden pin on the camera mount, tricking the camera to believe the lens is an A type.

Finally, cath-in focus on the K20D works directly with FA and DA lenses with a M-AF switch.
Hi eurostar,
I'd like to use Tamron's 90mm Macro als A-Type lense in order to work with catch-in focus on my K10D. Which pin do you prefer to connect or isolate??? Sorry I'm too stupid!

best berned

06-09-2009, 08:21 AM   #5
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I believe he is refering to the "data" pin on the camera lens mount. It is the gold pin found closest to the 6 o'clock position on the mount:



06-09-2009, 11:50 PM   #6
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QuoteOriginally posted by MrApollinax Quote
I believe he is refering to the "data" pin on the camera lens mount. It is the gold pin found closest to the 6 o'clock position on the mount:
Hi MrApollinax!
I think you'r right! Now the Tamron is behaving like an A-Lens, but I'm not able to disconnect the Lens and camera's drive... Moving the focus ring stirs the drive. That seem dangerours to me...
07-21-2009, 12:15 PM   #7
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You must focus with AF selector on M, then put it back to AF-S for catch-in focus
10-10-2009, 11:03 AM   #8
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QuoteOriginally posted by MrApollinax Quote
I believe he is refering to the "data" pin on the camera lens mount. It is the gold pin found closest to the 6 o'clock position on the mount:




I think he means the A pin, Data pin is for lense data (mft info. etc.)

:-)

11-10-2009, 05:18 AM   #9
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No, I mean DATA pin. It's the one to make blind so the camera believes an AF lens is a manual A one.
12-20-2009, 03:30 PM - 1 Like   #10
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There's a setting in the K200D which must be set called "Catch-in focus". Put the camera in AF mode and press the shutter release - the shutter won't fire until something comes into focus. Best used with a tripod. Works with my Chinon 50mm K mount lens but not with the mirror lens which has a plastic K-mount adapter.

Last edited by RobG; 12-22-2009 at 03:55 AM. Reason: found required info
04-19-2010, 11:37 PM   #11
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is there any way to do this without the cable?
05-17-2010, 05:19 PM   #12
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very informative - keep it up
08-13-2010, 04:01 AM   #13
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Clarification about Tamron 90mm and AF/MF

I am not sure if anyone will still reply to this tread, as it is a little old now, but...

Can anyone confirm that, with the Tamron SP AF 90mm 2.8, it is necessary to cover the pin?

Similarly, when eurostar commented that "catch-in focus on the K20D works directly with FA and DA lenses with a M-AF switch", can anyone confirm that this is specifically pentax FA and DA lenses, and that the same thing won't work with any lens that has an MF/AF switch.

Thanks

Rob
10-02-2011, 06:14 PM   #14
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Trap focus is a great way to get shots of things in motion from old lenses, that's how I've been using it the most. Specially my old SMC Pentax-K 300mm 1:4 lens. All the pictures here that are from the 300mm of things in motion are taken with trap focus. Some of those of things not moving as well. I framed the shot, focused until something came into focus and the picture was taken. Trap focus is a great invention This was with the K-x, but it works just as well with the K10D and K-5 (which I used to have, K10D, and now have, K-5)

Finnmarksl°pet 2010: Finnmarkslpet 2010
10-03-2011, 06:38 AM   #15
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QuoteOriginally posted by HoBykoYan Quote
is there any way to do this without the cable?
For CIF to work, the AF switch must be set to AF.C and the shutter must be held down somehow -- either by pressing the shutter button, or holding a wired or wireless remote button down.

QuoteOriginally posted by rob_k20d Quote
Can anyone confirm that, with the Tamron SP AF 90mm 2.8, it is necessary to cover the pin?
I don't know that lens, but in general, CIF can be used with any lens whose bare-metal base covers the mount contacts. If an AF lens has an MF switch, set it there. Or with any handheld AF lens, there is a trick: hold down the lens-lock button, then hit the shutter. Don't lose the lens!

QuoteOriginally posted by netrex Quote
Trap focus is a great way to get shots of things in motion from old lenses, that's how I've been using it the most.
I have delaminating eyeballs and 200 manual lenses. I *depend* on CIF with those lenses, unless I'm using zone-focus / hyperfocus techniques. The only lenses that don't benefit are some M42's whose bases are too narrow to cover the mount contacts. For those, I must use a bare-metal wide-flange no-infinity-focus M42-PK adapter to safely short the contacts, although the lenses can then only be used for close work. For long lenses, that's no problem; far-focus may still be over 100m
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