Full Frame and Cropped Sensors

When it comes to the topic of full frame or cropped camera sensors, there are two particular Wetpixel discussions which I draw your attention to. They are:



They both discuss (and argue) the advantages and disadvantages between the two. At this time I have yet to use a full frame camera in a housing and I'm unable to comment on either performance so if you are looking to purchase a system then it would be wise to visit these two reviews/discussions. If the concept of full frame and cropped sensors is unfamiliar to you then read on.

During the film era the format which captured an image on a 35 mm (film) SLR camera had the dimensions of 24 mm x 36 mm. Period! In digital photography, there are sensors which vary in size. We refer to a camera sensor by its 'crop factor'. If a sensor is 24 mm x 36 mm in size, then there is no crop factor and it is referred to as 'full frame'. This term is often abbreviated to FX.

Nikon has two different sensor sizes: full frame (FX) and 1.5x abbreviated as (DX).

Canon has three sensor sizes: Full frame, 1.3x and 1.6x. Other manufacturers are similar with only Olympus being the notable exception, at 2x.

fig. 3.28 Sensor Size Fan Coral, Bali. Crop Factors Explained

Black - Full Frame

HI - 1.3x Crop Factor

Yellow - 1.5x Crop Factor

- 1.6x Crop Factor

Taken from camera reviews, I will compare my own Nikon D300 and it's full frame big brother the D700.

Reviews indicate the Nikon D300 to be a good performer in low light, but nowhere near to the D700. A Nikon D700 provides at least two stops (+2 EV) of useable ISO when compared with the Nikon D300. The upshot of this is whilst I am content to use my D300 up to and including 400 ISO, on a Nikon D700 one could use ISO 1600 and higher. This performance is all to do with the size of the sensor. Both cameras have 12 megapixels, but the individual photo sites (pixels) on the D700 are farther apart, which results in a reduction of the amplification of noise when high ISO settings are used.

The downside is that full frame bodies are more expensive and there are situations where the crop factor is an advantage. For the underwater photographer this is most noticable with the longer lenses used for macro photography, i.e a Nikon 60 mm macro with a crop factor of 1 x 5 equates to a 90 mm lens. Many photographers including myself prefer this extra 30 mm of free focal length.

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