Catch-in Focus



Pentax DSLRs have a wonderful feature called "Catch-in Focus" (CIF), sometimes also called "Focus Trap". Don't ask me about other brands, because I have not been able to find much references. Anyway, here goes my story:


Quite a few of us Pentaxians gravitate towards our brand because of its Pentax K-mount backward compatibility - and even further to the old 42 mm Asahi Pentax Takumars, using a simple adapter that Pentax introduced together with their K-mount. The in-body camera shake reduction further adds to the attraction for those of us who are fond of using the old MF-lenses.


This compatibility also means built-in focus confirmation in Pentax autofocus camera bodies. Normally then, one would shift the autofocus lever to manual mode and focus by eye- and ear"sight", having an audible beep together with a luminous, red central focus point, once the subject is in focus in the centre of the field of view.


But, here I stand with my old, fairly slow Tamron telephoto lens (SP 300 mm, f/5.6 - Adaptall-2 system, Model 54B) and would like to capture birds in flight with it.


That poses several challenges: 300 mm isn't in awful lot (as seen from a bird-in-flight-perspective) and if I want to see much detail, my targets have to come pretty close. In-flight means constant movement and the problem is not as much keeping the bird within the field of view but rather that a flying bird moves quickly in and out of focus due to the proximity and the relatively large speed at which everything happen.


Here comes Catch-in Focus, if not to the rescue then at least to much appreciated and valuable assistance:


Pentax K200D + Tamron  300 mm Model 54B  @  f/9 and ISO 320

Exposure times 1/800 s (left) and 1/1000 s (right)

In Catch-in focus you do not set the AF-lever to manual but to autofocus mode. In that event, the shutter will block unless the subject is in focus in the centre of the field of view. You will not be dead-sure that your subject is in focus each and every time your shutter is activated, as there is a little delay from detection to action - and those nasty birds the do move!!!  - but Catch-in Focus may and will indeed increase your chances of bringe home a couple of decent pictures.

And as always: Practice makes Master.

How to set CIF may vary from model to model. In my *ist DL the procedure is simple: Just switch the lever to AF and you are there. With my K200D I further have to allow CIF in the Custom Menu setting. Again, as always: Do read the manual.........
And one final example. Here the bird was not moving away from me, but it surely moved and CIF help me capture some action:





Copyright 2011 - Steen G. Bruun