Founder of Lensrentals, Roger Cicala, has run Modultation Transfer Function (MTF) tests on the new Sony FE 135mm f1.8 GM lens and declared it the sharpest he’s ever tested.
Cicala is a self-confessed optics nerd and runs independent MTF tests of various lenses to measure the image sharpness and detail.
MTF testing is the preferred method for studying optical performance, as it uses scientific theory to provide clear results on how lenses perform.
Several grids, starting with 10 lines per millimetre, are used to measure the level of detail a lens can capture. The red line represents 10 lines/mm, while the blue line is 50 lines/mm. The more lines per millimetre, the finer the detail, the more difficult for a lens to capture the lines with high levels of sharpness.
A score of 1.0, the top of a chart, is perfect clarity and sharpness.
The centre of the chart represents the middle of an image, while the edges represent the corners. An MTF chart has two different coloured lines – solid is tangential MTF and dotted is sagittal MTF.
‘I mounted the first one (lens), sipped my coffee and then lost my mind and started shouting various expletives, enough to bring Aaron running in from the other room to see what I’d broken,’ Cicala writes in a blog post. ‘I hadn’t broken anything; I just saw MTF curves higher than anything I’d ever seen in a normal-range lens. Lenses like 400mm f2.8 super telephotos, are about this high. But those are super telephotos and f2.8.
Cicala has tested over 300 lenses and admits Sony’s glass rarely impresses him, but the FE 135mm f1.8 GM is an exception.
‘Let’s make this simple and straightforward. In the center, that’s the highest MTF I’ve seen on a non-supertelephoto lens. The highest. Let’s put particular emphasis on the purple line, which is 50 lp/mm. That’s a higher frequency than any manufacturer tests (that we know of), appropriate for fine detail on the highest resolution cameras. We would consider an MTF of 0.5 at 50 lp/mm to be very acceptable. This is hugely better, nearly 0.8 in the center. We’ve never seen that kind of resolution before.’
The MTF benchmark test was conducted on 10 pre-release copies direct from Sony, and Cicala says he’ll do it again with 10 other copies from shop shelves – although he doesn’t suspect Sony sent him 10 ‘special’ versions.
Comparisons were made with the Sigma 135mm f1.8, which was the sharpest 135mm lens tested until now. While the outer half of the image was relatively even, the Sony GM is ‘dramatically better’ in the center half, particularly at higher resolutions.
‘No lens we’ve ever tested has resolved 100 lp/mm this well at any aperture,’ Cicala says. ‘What does this mean for you? Well, in a couple of years if you are shooting a 90-megapixel camera, this lens will be the one that wrings the most detail out of that sensor. Right now it looks at your 43 megapixels and goes, “that’s cute”.’