DSLR vs Mirrorless thoughts

Martin Norden asked ( Inbox, AP 5 January 2019) for our views on whether full-frame mirrorless gear will be as heavy as DSLR kit. My opinion is that it will, because of the drive for quality, which requires bulk and weight. A basic Micro Four thirds (MFT) camera will be smaller and lighter than is practical for a larger format. But it will be rather small for stable handholding (particularly if, like me, you’re over 6ft tall), and there isn’t much room for direct controls. Panasonic addressed these limitations with its G9, and produced a MFT camera of much the same weight and size as current full frame (FF) mirrorless models!

FF lenses need twice the focal length, but only half the aperture ratio, to give the same light- gathering power, field of view and depth of field as a MFT lens. So a quality MFT 25mm f/1.4 would be matched by a FF 50mm f/2.8, for example. Optical aberrations become more severe at larger apertures, requiring more, and more complex, elements to correct them. If designed to the same weight and cost, these small-aperture FF lenses could probably be optically superior to the large-aperture MFT lenses. Also, to match a MFT 25mm f/1.4 shot at ISO 200, a FF sensor would use 50mm f/2.8 at ISO 800, and should give similar noise and dynamic range. But the FF sensor, being physically larger, could hold more charge representing photons captured; in stable conditions, an extra three stops of the shutter could give much better image quality at ISO 100.

A FF sensor is an expensive component, so interchangeable-lens budget cameras are built round smaller sensors, which still give good image quality. So, though possible, I guess companies don’t think there is a worthwhile market for small, budget FF lenses for high- end cameras.

For telephoto, small sensors have a real advantage, although in my opinion it’s much smaller than the 2:1 claimed for MFT over FF! Long lenses, for bird photography, etc, are rarely long enough, and the photographer is usually more concerned with the level of detail recorded when cropping in. With a good lens and good light, this depends on the ratio of the pixel pitch to the focal length. MFT sensors currently top out at 20MPs, but some FF sensors have much higher pixel counts. A 400mm lens on a Nikon D850 or Z7, if cropped to 20MP (or if the camera is set to APS- C), will give an almost identical field of view to a 300mm lens on MFT. If both lenses have the same aperture ratio, the larger photosites of the FF camera will gather more light, and so should give better image quality.

To answer Martin’s question directly, I think FF mirrorless could, in principle, save weight over DSLR kit, particularly with wideangle and mid-range lenses, but in practice I think manufacturers will aim for ever-higher quality, and smaller formats will be the way to reduce weight.

My kit is based on a Nikon D800 and 24-70mm zoom for great image quality for the majority of my shots, but some of my lenses are APS- C to save weight. I also have a Panasonic LX100 which I can carry in a jacket pocket, but in use I have to hold it between my fingertips. Chris Newman (Mr)