Summary: Full-frame sensors only have an advantage in landscape photography if longer exposure times can be used.
OK, that's a little simplistic and only really applies when you need to maximise depth of field but it captures the essence of my point.
I was having a little rootle around the Net today in an effort to discover a definitive text discussing the pros and cons of full-frame vs cropped sensors for landscape photography and came up with very little. Maybe my search strings were poor or maybe the answer is considered so obvious that nobody has bothered to write about it.
Recently, over in this thread
, I tried to explore the technical advantages, or otherwise, of full-frame sensors compared with cropped sensors. For sensors with the same pixel count, the main points were that:
- Full-frame sensors have better dynamic range.
- Full-frame sensors give better image quality.
- Full-frame sensors can work at higher ISO numbers.
- Full frame sensors can be less demanding on lenses.
- Full-frame sensors can more easily offer a shallower Depth of Field but they don't have to.
So it would seem to be game, set and match to full-frame sensors. After all, even without considering the above bullet points we know that many of the best landscape photographers use 5x4 inch film cameras so a larger digital sensor must also be better.
I'm not sure it's completely clear-cut though. The big deal with film is that if you double the size of the film you double the resolution while essentially leaving all the other characteristics unchanged. When considering digital sensors with the same pixel count, in order to obtain the largest depth of field while still avoiding diffraction issues, it turns out that the full-frame camera has to be stopped down further when using a lens giving the same angle of view as a given lens on a cropped sensor camera. As an example, if 20mm and f/8 gives best DoF on a 1.5x crop factor sensor then 30mm and f/12 (1.5 x 20 and 1.5 x 8 ) gives the equivalent DoF and sharpness on a full-frame sensor with the same number of pixels. The problem then is that the rate at which light is gathered by the lens on the full frame camera is exactly the same as the rate at which it is gathered by the shorter lens on the cropped one. In the example above, both lenses have an entrance pupil of 2.5 millimetres. So each of those big fat full-frame pixels actually has exactly the same amount of light falling on it as the smaller pixels on the cropped sensor.
As mentioned, a full-frame sensor isn't having to work it's lens so hard. But when operating near f/8 (cropped) or f/12 (full-frame) you don't necessarily need mega-expensive glass to obtain sharp results. Of course, for the same wide angle of view, full-frame cameras can use lenses with longer focal lengths and those lenses are likely to be cheaper but that has to be set against the increased cost of the camera. In this context, I am not suggesting that the tiny sensors on compact cameras are as good for landscape work as those in DSLRs because the demands on the lenses become extreme as diffraction limited apertures of the order of f/2 are needed (in the example above a 1/8" sensor would need a diffraction limited lens of 6mm focal length working at f/2.3).
I have come to the conclusion that, with the same pixel count, a full-frame camera has only one
advantage over a cropped sensor camera when shooting landscapes where depth of field must be maximised. It has to work with the same amount of light entering its lens as diffraction limited best DoF demands the same entrance pupil but, using the same ISO number, that light is integrated over a longer time (smaller f-numbers mean longer shutter times). That can be done on a full-frame sensor without blowing the highlights because of the deeper wells so we gain reduced image noise and/or better dynamic range. The longer exposures aren't usually an issue with landscapes though they probably indicate a greater need to use a tripod. If the subject demands the same short exposure time as would be needed on a cropped sensor camera then the advantage of the full-frame sensor disappears (increased ISO and the same f-number means increased sensor noise).
So much for my theoretical ramblings. Would any forum members fortunate enough to have shot landscapes with both full-frame and cropped sensor cameras care to comment? Then, of course, there is the added complication of the higher pixel counts usually associated with full-frame sensors!