Going squirrely with depth of field.

Depth of field is affected by many different factors. The main ones that concern most photographers include focal length, aperture, and point of focus.

Depth of field is the region in focus perpendicular to the front of a lens. Lower focal lengths (wide angles) have more depth of field than longer focal lengths (telephotos). Smaller apertures (f/16) have more depth of field than larger apertures (f/2.8). The further your point of focus is away from the camera the more depth of field there will be. Those factors can be combined in such a way as to obtain a very large depth of field or a very narrow depth of field. Each extreme is desirable in specific circumstances. Landscapes tend to benefit from a large depth of field while portraits improve with a narrower depth of field.

Since I use long lenses to photograph wildlife and require fast shutter speeds to do so the amount of depth of field is very limited. In the above photograph of the squirrel, the aperture was wide open at f/5.6 and the focal length was 500 mm. The point of focus was relatively close; the three factors combined to produce a very narrow depth of field. If you look at the leaves at the top and bottom of the image you will see that they are significantly blurred. Only the leaves immediately around the subject are in focus. You will also notice that the leaves to the left and right of the squirrel are also in focus; that is because depth of field runs perpendicular to the direction that the lens faces.

To freeze the action of the squirrel I used a shutter speed of 1/125th of a second. In order to get that speed, an ISO of 640 was required. The shutter speed would have been too slow if the lens did not have vibration reduction, but the VR allows the photographer to shoot at lower shutter speeds without causing blur due to camera motion. Although VR improves minimum hand-held shutter speed it does not compensate for subject motion. I find 1/125th of a second a bit on the slow side but suitable if the organism is not flitting around. In those circumstances, I use 1/250th or higher and consequently need higher ISO values to compensate. This is where larger sensors come in handy as the resulting images have less noise and produce much better images. I prefer the APS-C sized sensor as it improves focal length (1.5x crop factor) and reduces noise at higher ISO values.

Overall, I quite like the effect of the increasing blur moving away from the squirrel. It helps to draw your eye and the mixed colours are very pleasing. It would be nice if the beast was a little more cooperative though. It didn't pose for me at all and there was no hint of a smile.

Thanks for reading.     Ericspix     Eric Svendsen

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