Some time ago I compared the EF and FD versions of the Canon 50mm f/1.8 lens. It wasn’t exactly a fair test because the EF lens fits natively on my DSLR, while the FD lens needs an adapter with an optic. Now I am fortunate enough to own a Canon EOS M mirrorless digital camera which can make use of FD lenses with a glassless adapter. I also acquired an FD 50mm f/1.4 and an FL 50mm f/1.4, so I shall compare them to the EF and FD 50mm f/1.8 specimens.
First of all, what are the differences? In most aspects these three lenses are the same. I’ve emboldened rows where they differ.
|FL 50mm f/1.4||FD 50mm f/1.4||FD 50mm f/1.8||EF 50mm f/1.8 II|
|Angle of view||46°||46°||46°||46°|
There really isn’t much difference. The only difference we really care about is the larger maximum aperture. But what does that actually get us?
Well, it gets us an extra two-thirds of a stop of light. If you are wanting to shoot handheld in a place with poor lighting, this is your lens. I recently used it for exactly this purpose inside a church where flash was not permitted. There are other side benefits too. The faster aperture means your viewfinder will be brighter, your split-circle focusing more precise, and the in-camera metering will be more accurate. Happiness all round!
Confusingly, f/1.8 is not a “standard” aperture. f/1.4 and f/2.0 are “whole” f-numbers, and f/1.8 lies about two-thirds between them. I’m not sure why so many manufacturers use f/1.8 as a common lens – clearly it’s cheaper to make than f/1.4, but why not f/2.0? Maybe it’s considered to be too slow. There are several f/1.7 lenses around, too. Who knows.
Depth of field
The aperture also affects the depth of field. DoF depends on not only the aperture setting you’ve chosen, but also the distance to your subject. Let’s assume, if you are using the maximum aperture of your lens, that you are looking at a nearby object – say, 2m away.
|50mm f/1.4||50mm f/1.8|
|2m||Distance to subject||2m|
|0.13m||Total depth of field||0.17m|
|0.06m||In front of subject||0.08m|
By opening up another half a stop, you can decrease your DoF by a few centimetres. Not really anything to write home about, but possibly what you need for an arty shot.
Most likely, the strong point of the f/1.4 over the f/1.8 is image quality at the same aperture, for any given aperture. I mean if we set both lenses to f/8 and take a picture, which lens produces the best image? Let’s find out 🙂
For this test, I will be using the ISO 12233 test chart. Just in case you haven’t seen one before, here it is.
Here’s what I did.
- I had a large version of this chart printed on rigid board about 90x55cm in size
- I hung it on my wall and illuminated it with a 500W halogen lamp
- I placed the camera on a tripod so that the chart fills the frame
- I set the camera to ISO400 in aperture priority mode
- I set the camera to Tungsten white balance
- I focused the camera manually (even the autofocus EF lens) using magnified live view
- I varied the aperture and took a shot for each aperture setting using the self timer to avoid camera shake
Ideally I would perform MTF measurements but the software is complicated and frankly I can’t be bothered. Instead I’m going to qualitatively assess these images by looking at 100% crops in the centre and in the corner.
Centre crop, lens wide open
First, let’s look at the centre of the chart with each lens wide open.
- As expected, the FL lens performed most poorly here. This is unsurprising because it is the oldest lens, 13 years older than the FD lenses and made at a time when lens technology was less sophisticated.
- The two FD lenses showed surprisingly little difference wide open.
- The EF lens showed the sharpest image quality, unsurprising given that it was designed and manufactured with the aid of computers.
Corner crop, lens wide open
These corner crops are taken from the same source image as the centre crops above. Usually, lens defects are more apparent in the corners of the image.
- The FL lens really showed its weakness in the corner. There is a real loss of sharpness.
- The FD f/1.4 is noticeably sharper than the FD f/1.8, but both are acceptable.
- Once again, the EF lens performed the best and there is hardly any chromatic aberration.
Corner crop, lens stopped down to f/8
These corner crops were all shot at f/8 – an aperture at which all these lenses should perform really well.
- It is basically impossible to tell these four lenses apart when stopped down to f/8. I can’t really make any further comment to distinguish them.
- The lenses introduce a different colour cast. The two FD lenses offer a slightly pink cast while the FL and EF lenses offer a slightly blue cast.
- I didn’t have the willpower to process every single test image, but having observed that the lenses differed quite a lot at f/1.4 and were basically identical at f/8, I wondered at what aperture they start to become similar in quality. By f/4 they were similar, and by f/5.6 they were more-or-less indistinguishable.
- People often say that the f/1.4 is unconditionally better than the f/1.8 of any given series (FD, EF, etc). For most real-world applications, this isn’t necessarily true.
- This test does not take into account flare characteristics. The results are similar in a carefully controlled, front-lit test chart but all bets are off when the sun shines into the lens. The FL flares quite badly.
Of course, no lens test would be complete without some sample images. Here are a few of my favourites taken with these lenses.