The best 50mm for A7RII

After testing the Sony Carl Zeiss 55mm f/1.8 FE in 2014, I was less than impressed. I may have had a decentred example (it happened to dPreview and at least one photographer I trust to know his lens performance expectations). It was, certainly, pin-sharp on a test chart or a brick wall but the moment three-dimensional subjects were involved at wide aperture the defocused detail could be very untidy. The clip below from trees behind a building which was sharply focused is at f/1.8 and 1/2500th (a suggestion that it could be caused by camera shake is easily ruled out). See my additional notes at the end!

cz55mm1p8distance

It’s worth saying that when I had this lens I made some tests of the bokeh using very strong defocus which looked good. Many examples I’ve seen, which true believers put forward, show a figure (from full length to portrait) centre of a horizontal frame at f/1.8 with a pleasant enough looking distant background. My gripe has been with what happens when your subject is further away, or the background is not all very distant. This is an expensive lens but it seems to me to have fussy bokeh with too much CA fringe and also more focus-related colour shift than desirable.

Here is a full size example with EXIF. Honestly, the best standard lens around? //www.pbase.com/davidkilpatrick/image/162847304

Now I’ve got a fair collection of 50, 55 and 58mm lenses and also the little Canon 40mm f/2.8 STM which is my alternative to having a 35mm and a 55mm. No matter what the lens – Pentax, Minolta, Sony 50mm f/1.4, Helios, Zenitar, Nikon, CZ Jena – the full aperture between f/2 and f/1.4 always proves to be a touch soft. They all have residual aberrations that the CZ 55mm f/1.8 design has eliminated. While they can have a smoother bokeh, they also have marked colour shifts and uncorrected CA. Generally, they also all perform extremely well once stopped down to f/8 and most designs are great by f/4.

Despite the advantage of full AF functions, the CZ 55mm does not have a particularly good close focus or maximum image scale. In use I often found myself framing up closer than 50cm. That’s half a metre – it’s even further than the old 55 and 58mm lenses of the 1960s, which generally manage 45cm. I find this limitation hard to understand. 50 years ago CZ Jena started to put helicoids on their standard 50mm lenses which enabled focus down to 35cm. We have gone backwards since then.

And then I realised I’ve already got a lens which is free from all vices, gives me AF and manual focus options using adaptors I already own, which cost me about a third of the price of a CZ 55mm – and I was not being used on my A7RII. We bought a good used example of the Sony SAL 50mm f/2.8 Macro to use with our Alpha DSLR.

First of all, I compared this with the idea of buying a Zeiss Loxia 50mm f/2, by fitting it to the LA-EA3. Although the focusing ring does not communicate to the camera to invoke magnified manual focus, the lens has a Focus Hold button which can be set to this. The focusing throw is steep but in practice very accurate focus is easily set. At f/2.8, the lens is already perfectly sharp with some contrast improvement at f/4. The lack of vignetting and distortion, the flatness of field and generally very attractive smooth defocusing without CA issues make the lens better than typical fast standard designs.

On the LA-EA4 with autofocus, a limited set of AF functions ends up activated and there’s always the issue of the slight delay and sound caused by mechanical aperture operation. AF-C is of limited use, along with this video functions. However, I don’t generally use this type of lens for action or for video.

I made plenty of non-image tests by defocusing bright edges, both ways, and could find no hint of colour problems. I then set up a small food shot using the close focus – exactly the reason I find a lack of close focus restricting – and made tests at f/2.8, f/5.6, f/11 and f/22 to look at the bokeh. My conclusion is that I will be hard pressed to find anything technically better, or with a more pleasant character to the background defocus, in the c.50mm focal length. The series covers all four apertures.

I am aware that one comment will be that f/2.8 simply isn’t wide enough. There’s no significant differential focus and you’d need 50mm f/1.0 to get what many photographers want. However, this is all to do with viewing size. We all tend to see pictures on smartphone screens, on Facebook, or even on our own camera three-inch screens. In fact, at f/2.8 there isn’t enough depth of field for a typical real-world use of a full page reproduction and f/5.6 is just about right. For a poster, f/11 would be good. At f/22 the whole image is slightly softened as expected and it’s just there to complete the set.

For the moment – at least until a Batis version of the 50mm f/2 Makro Planar appears and answers all my demands perfectly – I think this Minolta-derived 50mm macro will do fine as my ‘standard’ lens.

David Kilpatrick, aka ‘some random blogger’ (©SAR comments March 2016)

Added August 30th 2016: Sony has announced an E-mount 50mm f/2.8 Macro focusing to 1:1 with a stated RRP of $500 – really, they must have read this article in March. In the meantime, during the Brexit fiasco I caved in and bought a 55mm f/1.8 CZ, suspecting the price would be 20% higher soon enough (and sure, it was). My new example is no better than those I originally tested but it has its uses and in a flat plane – no defocused image to screw the results up with an ugly mess – it’s the sharpest 50-55mm I have used. I’m still using the 50mm macro and recently spend a month using the Samyang 50mm f/1.4, which is not as sharp as the CZ but handles blur and bokeh more elegantly. Both lenses don’t really excel at suppressing Longitudinal CA, one of the strengths of the A-mount macro. Hopefully the new SEL FE 50mm macro will also give clean, colour-shift free foreground and background bokeh.

Added July 29th 2017: I have now bought the 50mm f/2.8 Sony FE Macro, and put my A-mount macro lenses up for sale. The E-mount focuses to 1:1 rather closer than I would like, at 16cm which indicates its internal focusing changes the focal length to something more like 37mm to 1:1 (16cm is a pure 40mm at 1:1 assuming no optical thickness to the lens). It’s an extremely sharp lens with bokeh as good as the A-mount 50mm and no trace of CA.

Mapping the planes

Samsung has a patent and a plan for using two lenses with triangulation (image offset) depth detection between two images in what is roughly a stereo pair. Here’s a link:

http://www.photographybay.com/2011/07/19/samsung-working-on-dslr-like-bokeh-for-compact-cameras/

Pentax also have a system on the new Q range which takes more than one exposure, changes the focus point between them, and uses this to evaluate the focus map and create bokeh-like effects. Or so the pre-launch claims for this system indicate, though the process is not described. It’s almost certain to be a rapid multishot method, and it could equally well involve blending a sharp image with a defocused one.

In theory, the sweep panorama function of Sony and some other cameras can be used to do exactly the same thing – instead of creating a 3D 16:9 shot it could create a depth mapped focus effect in a single shot. 3D is possible with sweep pans by simply taking two frames from the multi-shot pan separated by a certain amount, so the lens positions for the frames are separated enough to be stereographic. 3D ‘moving’ pans (scrolling on the TV screen) can be compared to delaying the playback of the left eye view and shifting the position of subject detail to match the right. But like 16:9 pans, they are just two JPEGs.

All these methods including the Samsung concept can do something else which is not yet common – they can alter any other parameter, not just focus blur. They could for example change the colour balance or saturation so that the focused subject stands out against a monochrome scene, or so the background to a shot is made darker or lighter than the focused plane, or warmer in tone or cooler – etc. Blur is just a filter, in digital image terms. Think of all the filters available from watercolour or scraperboard effects to noise reduction, sharpening, blurring, tone mapping, masking – digital camera makers have already shown that the processors in their tiny cameras can handle such things pretty well.

Once a depth map exists there’s almost no limit to the manipulation possible. Samsung only scratches the surface by proposing this is used for the esoteric and popular bokeh enhancement (a peculiarly Japanese obsession which ended up going viral and infecting the entire world of images). I can easily image a distance-mapped filter turning your background scene into a Monet or a van Gogh, while applying a portrait skin smoothing process to your subjects.

Any camera with two lenses in stereo configuration should also, in theory, be able to focus using a completely different method to existing off-sensor AF – using the two lenses exactly like a rangefinder with two windows. So far this has not been implemented.

Way back – 40 years ago – I devised a rangefinder optical design under which you can see nothing at all at the focus point unless the lens was correctly focused. It works well enough for a single spot, the image detail being the usual double coincident effect when widely out of focus, but blacking out when nearly in focus and suddenly becoming visible only when focus is perfect. I had the idea of making a chequerboard pattern covering an entire image, so that the viewfinder would reveal the focused subject and blank out the rest of the scene, but a little work with a pencil and paper quickly shows why it wouldn’t work like that. The subject plane would have integrity, other planes would not all black out, they’d create an interestingly chaotic mess with phase-related black holes.

Samsung’s concept, in contrast, could isolate the subject entirely – almost as effectively as green screen techniques. It would be able to map the outline of a foreground subject like a newsreader by distance, instead of relying on the colour matte effect of green or blue screen technology. This would free film makers and TV studios from the restraints of chroma-keyed matting (not that you really want the newsreader wearing a green tie).

The sensitivity of the masking could be controlled by detecting the degree of matched image detail offset and its direction (the basic principle of stereographic 3D) – or perhaps more easily by detecting exactly coincident detail, in the focused plane. Photoshop’s snap-to for layers works by detecting a match and so do the stitching functions used for sweep and multi shot in-camera panorama assembly. Snap-to alignment of image data is a very mature function.

Just when you think digital photography has rung all the bells and blown all the whistles, the tones of an approaching caliope can be heard rolling down the river…

– David Kilpatrick