I read a statement on a forum recently and it set me thinking…
The statement was about the image quality from different sized sensors (the thing that replaced film)
“bigger sensor better image quality, that is physics” which of course is correct…
..if there are no other variables.
So I set out to find if there are variables other than size.
The reason for my interest is that I am considering changing from a Full Frame camera to something smaller, lighter with great image quality, a camera that will allow me to more “agile” and sensor size is a big factor in my decision. The camera that I am considering is the Fuji XT1.
There are different sensor designs, I am going to look at the Bayer sensor and the Fuji X-trans because I have experience with them.
Note you may wish to also look at the Foveon X3 sensor which is very different offering high resolution but poor low light performance
Bayer sensor as used in my Full Frame Canon.
(21 mp, 35mm x 24mm sensor)
Bayer sensors are found in most digital cameras. In the image the grey blocks are the pixels (photo-sensors), laid over the pixels is the Bayer filter array. There are twice as many green filters than the red and blue filters. (to match the colour reception of our eyes) This means that the light has to travel through the filters, to get to the pixels.
But we do not photograph subjects only made of the three basic colours, a typical outdoor scene will have billions of colours. So the software has to make an educated guess at how to mix the three base colours Red Green and Blue (RGB) to make the other billions of colours, it does this by using demosaicing algorithms. This is called interpolation or as a friend of mine would say “guessing”.
Because of the layout of the RGB filters there is a risk of moiré in the photograph, moire is the interference pattern shown below. Moire can show in clothing and material, not ideal if you photograph fashion!
The solution is to use an anti aliasing filter of the sensor, ie an extra filter over the colour filters. The anti-aliasing filter is also known as an optical low pass filter or blur filter. That’s right it blurs the image slightly!
Fuji X-trans sensor as in the XT1 (16mp, 23.6mm x 15.6mm)
The Fuji sensor is similar to the Bayer sensor ,but it uses colour filters differently, in a random layout.
The advantage of this array is that the X-trans sensor does not need an anti-aliasing filter so no blurring of the pixels.
There are other factors which have an effect on image quality;
Lens quality, as I am comparing Canon to Fuji this is not a big issue as both make the highest quality lenses.
Front and back focussing.
Because of variations in manufacturing (mirror minutely misaligned with the sensor) when using a DSLR what you see in the viewfinder when focusing is not necessarily what the sensor sees. Which is why Canon and Nikon pro cameras have micro adjustment options to correctly focus the image. Consumer cameras do not have this option.
With the EVF, electronic viewfinder, in the XT1 you see the image from the sensor so what you see when focusing will be accurate.
I have seen photographers complain about a camera or a lens because it does not produce the image quality that they expect, very often the fault is the photographer not the kit and usually camera shake is the culprit, A tiny amount of camera movement can produce a tiny amount of blur only seen when a large print is made. Of course the worse the movement the more obvious the blur. I mostly work with a sturdy tripod and a cable release.
Another cause of movement can be caused by the mirror slapping when the exposure is made, mainly an issue when using long lenses. This can be minimised by locking the mirror up out of the way, but that is a pain with my Canon because despite pros pleading with Canon for many years the mirror lock is hidden in the menus not a separate button on the camera body. Comparing my Full Frame Canon to the Fuji XT1, the Fuji has no mirror.
Jabbing at the shutter release instead of a gentle, steady pressure can cause shake. Which is why I usually use a remote release.
Another variable in image quality is the use of cheap filters on the front of the lens. Why anyone would pay a £1000 for a top quality lens, lovingly designed and built to the highest standards with quality materials and then put a cheap filter on it baffles me.
I have now sold my Canon kit and have a Fuji XT1 kit and I am so pleased with it. It is getting a lot of use and the image quality still makes me smile. High iso performance is exceptional and I recently shot a fast moving commission at iso 1600 and no tripod which is very very rare for me. I have achieved what I intended, I am a more agile photographer.
This is a screen grab from Adobe lightroom showing retention of fine detail, Fuji XT1 test image. Click on picture to englarge.