SMC Pentax DA* 55mm f/1.4 on Sony A7R
This classic 55mm f/1.4 lens is supposedly for APS-C, how does it do on full frame?
The DA* 55mm f/1.4 is slightly larger than the FA 50mm f/1.4, but it adds an internal autofocus motor, weather sealing, and fixed rear element extension focus for good imaging performance at all focal distances.
The lens barrel is built out of high quality composites, with a covered focus scale and hard infinity stop. The focus ring will slip once it hits the hard stop at infinity or minimum focus due to the direct manual focus operation. The hood is high quality plastic and flocked with anti-glare velvet, has polarizer access port, and nice rubber ring around the front (aesthetic and acts as a grip point). Operation of the hood is very easy, and I wish other manufacturers used such easy to use hoods.
The lens is fairly dense, weighing in at 375 g. It has 9 aperture blades making a circle at large apertures, and a standard for the class minimum focus distance of 0.45 m, providing a maximum magnification of 0.17x. It has a 9 elements in 8 groups, with no specialized aspherics or ED, although it does have Aero Bright coating which is a broadband nanostructure antireflective coating. It has 58mm filter threads, which is a bit out of place for Pentax, but common enough.
Lens curtesy of Lloyd Shell. Check out his great work at: http://lloydshell.zenfolio.com/.
- MTF 50
- MTF 20
- Lat CA
- Axial CA
- Axial 5.6
- Corner Crop f/1.4
- Flare f/1.4 -2EV in post
Note: 4k video is 2160 LW/PH
Note: HD video is 1080 LW/PH
Comments on the Results
The sharpness is a bit low wide open across the frame, but the resolving power is quite high in the center wide open. Sharpness improves rapidly on stepping down and resolution improves steadily to about f/4.5, where it maxes out the sensor. The corners lag behind and max out at about f/7.1. This is fairly classic lens performance.
Distortion is 1.3% barrel, which is pretty typical for a large aperture 50mm.
Lateral CA is minor. Longitudinal CA is fairly strong at large apertures, but typical for the class, which will cause some purple fringing at large apertures.
Vignetting is pretty severe at f/1.4 and 2 (as typical for a full frame 50mm class lens), and is pretty good by f/2.8. This lens is definitely corrected for full frame since CA is so minor, distortion is typical, and there is no vignetting at small apertures (hood vignettes a bit so need different/modified hood for full frame).
Flare resistance: Good for class, but expect some. Not many element ghosts visible, likely due to impressive coating. They are there, just very faint. I am using an adapter which could impact flare. Not going to get much for starbursts without stopping down to f/11 or more.
Measured Focal length is 59mm at 1:35 magnification. If used on APS-C, this equates to almost 90mm on full frame, which is close to what most 85mm lenses measure at with similar magnification.
Pros and Cons
- Build Quality
- Close focus IQ
- Wide open performance
- Corners until f/4 or f/5.6
The colors are selected based on overall MP, don’t compare the colors between systems. So relative to max sensor resolution a lens doesn’t do as well on the A7R as it would on the A7 relative to its (lower) sensor resolution, but it still resolves more detail on the A7R then it does on the A7.
Characteristically, this lens is almost the same as the $1700 Nikkor 58mm f/1.4G, and before you say “but that is a full frame lens”, I will answer with “So is the DA* 55mm f/1.4”. The DA* 55mm lens completely covers a full frame image circle with a high level of correction.
The lens has fairly classic lens performance in that it is pretty decent in the center wide open (MTF20) and improves dramatically across the frame as it is stopped down. It isn’t meant to be bitingly sharp wide open, simply put: this lens has character. That might not be good depending on how you view it, but I think it is very usable for what it is, and people are willing to pay a lot more for a similar Nikon lens so it can’t be all bad.
On the A7/R I wouldn’t go buy this lens just for the camera, since it is bulky and has no diaphragm control (make sure your adapter has diaphragm control for DA lenses). However, if you already own the lens it will work great on the A7/R. This lens would be perfect if Pentax releases a full frame K mount SLR, but the hood would have to be modified slightly for full frame since it causes very slight vignetting in the extreme corner.
The Bokeh can be a bit busy wide open in certain situations, but pretty typical for a large aperture 50mm lens. The best way to improve the bokeh wide open is to avoid small things in the background like leaves and to put light sources well out of focus. If they aren’t out of focus enough you will get some rings around any specular highlights.
I would skip this lens if you want bitingly sharp wide open, but instead get it for nice character, great full frame or APS-C performance, and smooth bokeh especially when stepped down a stop. If shooting the A7/R I would recommend getting the Canon FDn 50mm f/1.4 instead since it is a bit smaller and easier to deal with on the A7/R and rendering is very similar.
Consider donating, it is about $50 a lens to rent.
Photos are all © Eric Tastad, 2013-2014. and may only be used for personal evaluation of the lenses. Download full sizes by clicking on image which will take you to Zenfolio. Hover over the image, in the upper left of the image click on the menu, Download, and Original (or all available).
Example of fair resolution but low contrast
|Near 100% off center crop, wide open no processing|
|CA removal, sharpening, clarity|