Camera 'swinging out' during animations

How can I stop the ‘camera’ from swinging out on a great arc during animations? If you look at my model in the warehouse ( Periscope animation ) you will see the animation zooms out wildly at the point where I switch from perspective to two-point.

Clearly, the aim here is to depict what actually happens with a real telescope, but this off-putting swooping effect is wrecking everything. BTW: it also does it at the start of the sequence, but that was easily rectified by deleting the scene. No such joy halfway through though.

Currently, what you are seeing is how SketchUp transitions from a model set in perspective to one in parallel projection.
If your eventual goal is to produce a video file, one solution is to use a video editing software to remove the unwanted frames.

CD

Is there any free software that would do this?

You could try windows movie maker (if your not on Mac).