Sensors and Depth of Field

Olympus OM1, Zuiko 24mm f2 Kodak ASA200

I’ve been playing around with 35mm film and full frame sensor DSLR since the last post whilst I pondered the Depth of Field effects which are so much easier to get on cameras with large sensors. There’s some mathematics about calculating the near focus(NF) point, the far focus(FF) point and the consequent Depth of Field(DOF) in between. There is also the extra point called the Hyperfocal(H) point where from half that distance to infinity is in focus.

Why mention all of this? Mainly because just understanding that the points exist helps inform some types of photography. Its is less relevant when using auto focus or auto everything, but can provide some creative adjustments when wanting to throw background or foreground in or out of focus or to have a piece of the picture in focus alone.

I also noticed that it is easier to achieve with the larger format sensors and (less surprisingly) with wider aperture lenses. Quite interesting because there are a few commercial points to consider too:

1: most compact cameras have really small sensors – to keep down costs and to keep the camera small and slim. Neither point helps provide depth of field.

2: most DSLRs come with a zoom kit lens and many people don’t go beyond it. Many kit lenses stop down to around f3.8 and some of the really pronounced depth effects would typically be at larger apertures. The kit zoom is a pragmatic solution because the camera manufacturers know that changing lenses on digital is more dust prone than with film.

3: the sensors on most DSLRs are bigger than compact cameras, but still not as big as 35mm film, so the effect of the field is less pronounced for the previous mathematical reasons.

I guess it illustrates that the pixel race isn’t the only consideration with digital cameras although sensor size gets far less ‘publicity’.
Olympus OM1, Zuiko 24mm f2 Kodak ASA200


~ by rashbre on Saturday, 18 October, 2008.

One Response to “Sensors and Depth of Field”

  1. Quite right. Pixels are definitely not the whole picture (no pun iontended) as I have been trying to explain to a friend who seems to think it’s everything.

    I love playing with DOF but have had precious little time to do so recently. I have found that getting it correct with macro work is absolutely crucial!

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