Is it really worth 10 times more?
I've been using my Canon new FD 35mm F2.8 lens with adapter on my Sony A7 for almost a year now. It proved to be so good that I even sent back my Samyang AF 35mm f/2.8 FE lens after reviewing because of its hesitating autofocus in low light conditions. On the other hand I love the character and the rendering of the Zeiss Loxia lenses. I own the Zeiss Loxia 21mm F2.8 Distagon and I think this is one of the best UWA prime ever made. It's especially good at the Loxia line that they are similarly built. They use the same size filters and they have the same type 10-bladed aperture. That's why I decided to try the Zeiss Loxia 35mm F2 Biogon so I bought a nice used copy from eBay. I know it's not 100% fair to compare these two and it would be better with the F2 version of the Canon FD. But between the F2 and F2.8 version there is a cca 3X price difference (£50-70 vs £150-200) so I don't consider it as cheap alternative when you can get a Samyang with autofocus for just a slighly more.
Meanwhile I upgraded my camera to the Mark II version so all the pictures were taken with my Sony A7II body. They are SOOC jpegs, the creative style was set to "Portrait" with Saturation +1 and Sharpness -1. This is my favoured basic setting.
At first, the pure specifications:
Zeiss Loxia 35mm F2 Biogon:
Diameter: 62.1 mm
Length: 65.0 mm
Filter Diameter: 52 mm
Aperture Blades: 10 - straight
Minimum Focusing Distance: 0.3 m
Mount: Sony E
Canon nFD 35mm F2.8:
Weight: 165g (xxx with adapter)
Filter Diameter: 52mm
Aperture Blades: 5 - slightly curved
Minimum Focusing Distance: 0.35 m
Mount: Canon FD
If the Canon attached to its adapter it becomes a tiny bit longer. The Loxia is much heavier thanks to its all metal and glass quality build. The Canon's body is mainly of plastic but it still feels solid enough.
The Loxia is a stop faster, F2 versus F2.8. Apart from this I don't want to spend more on technical details. I rather took the lenses with me on a walk and tried to shoot the usual scenes I do with both of them side-by-side.
The first pair of photos were taken around sunrise, aperture set to F11. Here I used a Sony app called "Sky HDR" to reduce the brightness of the sky. It works like a graduated ND filter, two shots with different exposure settings are faded into one final photo. As you can see below the one taken by the Canon FD is underexposed with cca 0.5-1 stop by the camera. Probably that is because the chipless adapter doesn't provide any data for the camera. Regarding sharpness I can't really see much difference.
Please right click on the photos for opening the full size versions on Flickr.
The next important thing for me is the shape of the sunstar created by the lens. I know that the 10 straight blades of the Loxias shine here. I wasn't disappointed. The 5 slightly curved blades of the Canon FD result in not very well defined star. I wouldn't consider it nice, but at least it also gives 10 pointed shape. The Canon FD photo is again underexposed a bit and as an extra there is a little green blotch on the left side not far from the centre thanks to the not really modern coating of the lens. Aperture was at F11 for both lenses.
These were backlit situations were I focused almost to infinity. I wanted to see how the lenses behaved in similar situation but fully opened and focused close to their minimums. First I stopped down the Loxia to F2.8 to have the same circumstances for both lenses but on the 3rd picture you can see how it performed when opened. The Canon FD photo shows a nice vintage hazy look which gives a special mood. At the bottom on the right we can see again the little green blotch. The Loxia is sharper here and has the typical Zeiss high micro contrast. But at F2.8 it already starts to show the shape of its aperture which I don't really prefer. And surprisingly a huge flare circle can be seen at the bottom. It's interesting that the photo by the Canon FD is a couple of hundreds Kelvin warmer and it's tinted a bit towards red. The Loxia's also tinted but toward green.The truth was somewhere between. I rather blame the camera's algorithms for these differences.
Here are some more backlit scenes. Generally the situation is the same. The Loxia holds the contrast perfectly but its flare control is not flawless (see the big circle on the first picture). It seems that the Biogon lens design is not that good as the Distagon in this regard. Chromatic aberrations are a bit better handled by the Loxia. Although being 30 years old the Canon FD still performs really well. The red tint and the warmer tones are there again. With the Loxia the pictures are more to the colder tones and greenish tint. Fortunately the results can be fine tuned in post-processing for both lenses. The bokeh at close distances and fully opened are really nice for both. For longer distances and stopped down it can be busy sometimes but these lenses are not really made for this purpose.
I also took landscape shots in normal situations without direct backlight. When stopped down to F8-F11 the difference in sharpness is almost negligible. What makes the Loxia seem a tad sharper is its excellent micro contrast. And again we can see the colour differences.
To see the real nature of the lenses I edited the raw files. I set the temperature, the tint and the exposure approximately to the same level for a couple of pairs. Then I exported them in screen size. Regarding sharpness I can't see differences. But now you can recognize the real colour profiles of the lenses. The Loxia creates a bit more saturated, punchier colours and has more micro contrast.
Answering the big question I would say, it depends. The Loxia has some extra features which videographers really appreciate. Possibility to switch to clickless aperture, excellent manual focus, high build quality. For them it's a no brainer. If you are only interested in stills it's more difficult to justify the huge price difference. I, myself also hasn't been able to decide yet. Regarding the Loxia, on the positive side there are the beautiful sunstars, exif data, easier handling and the Zeiss signature in colours and contrast. The negatives are the flare handling and the price tag. Logic says no, heart says yes. It will be tough, really tough! :)