How to use Trap-focus or Catch-in focus

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.

[Adam]

Article approved and moved into the DSLR article section. Thanks a lot for your submission!

[eurostar]

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.

[Berned]

Originally Posted by eurostar

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

[MrApollinax]

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:

[Berned]

Originally Posted by MrApollinax

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...

[eurostar]

You must focus with AF selector on M, then put it back to AF-S for catch-in focus

[stu49]

Originally Posted by MrApollinax

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.)

:-)

[eurostar]

No, I mean DATA pin. It's the one to make blind so the camera believes an AF lens is a manual A one.