Minolta *50mm Bokeh Compared

TeemÅ · Joined: 07 Apr 2016 Posts: 586 Location: Australia

I was inspired to do my own test as in my usage I had replaced the MC-I 58/1.4 with the MC-X 50/1.4 believing it to be much sharper and with better coatings. My first lens was actually an MC-II 55/1.7 which I noticed immediately had a smooth bokeh while being sharp stopped down. Lastly I have the Super Rokkor 5cm F1.8 for Leica Thread Mount.
The camera was focused roughly using focus peaking, around 1.2m/4ft on the centre post for each lens. It's shot at an oblique angle as a tree would otherwise obstruct the interesting background, and cheap Chinese adapters (which do not sit flush) were used which explains why some lenses are inconsistently only sharp on one side of the fence.
In my opinion the centre focus is enough to draw conclusions however this isn't the focus of this test, and with a 2x crop on 16MP, the lenses are really pushed beyond their limit.
Having said that, with the full resolution files I make the following judgements.

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The 58/1.4 is perhaps a bit sharper than the 55/1.7 in the centre, but does also have a lot more CA. (Focus seems to be on a different paling for each). It's clear that the bokeh is very smooth wide open, without a bright edge. At F2, the 58/1.4 gains a bit of microcontrast but CA is exacerbated further. Bokeh becomes as smooth as the 1.7 but is in fact slightly larger owing to to the 58 being closer to 60mm in true FL.
The slightly curved aperture blades make for round-enough bokeh at F2, as well. Moreso, it's the orientation of the aperture blades with the corners vertical, such that horizontal details in the background just blend better. For example, the venting on the digger is still less defined at F2.8 on the 58mm compared to the MC 50/1.4 at F2!
Detail and contrast for the 58 and 55 are about the same at F2.8. Bokeh is just slightly better on the 1.4 still.

The centre detail between 58mm and MC 50mm is difficult to judge as the lighting is different. If the MC 50mm does have one major flaw, it is the amount of veiling flare wide open compared to most other Minolta lenses. Just take some images of the stars with it and you will see what I mean. Wink

The bokeh of the 50mm definitely has harder edges and more CA, however lateral CA is very well controlled and is only beginning to be apparent at F2.8, however by this time the image is much sharper than the 58/1.4. Despite being in the shade, it actually manages to turn out more micro-contrast on the timber and less veiling flare (edge/global contrast).

Lastly, the Super Rokkor 5cm F1.8. This lens is quite sharp wide open with good contrast similar to the earlier Rokkors, as it is multicoated, but when the subject is not well-lit, resolution falls dramatically. Even though the paling is shaded more compared to the 55/1.7, detail is not very impressive. Don't bother going outside of the centre with a lens this old, too, there's nothing good to see.
However, edge contrast is good and there seems to be a touch less CA. The next aperture stop on this lens is F2, and now the centre micro-contrast has already improved and edges are even better. At F2 the hard edges are mostly gone from the bokeh and it is slightly nicer than the 50/1.4 at F2. The global contrast is also a bit better than the 55mm despite much older coatings. Wide open, it just has less bokeh fringing than the 50/1.4.

These are all great lenses, but they do have their differences. If you want a compromise between all of them then the 55/1.7 is the best value. Not only is it very cheap, but it's lightweight and compact.
It is told that the MC-II 58/1.4 performs even better than the MC-I, but I've not seen any examples. The MC-I does have some weird field curvature/astigmatism issues when stopped down around F5.6 at short to medium distances and the coatings cannot handle reflections in high contrast scenes, leading to a very fuzzy look over details. Those were the main reasons I stopped using it, but it's circumstantial. It may have just been vibration from the mirror as one of my SRTs works quite violently. Razz

I still made nice portraits with the 58/1.4 and the hard edges of the bokeh are not always a problem depending on the background, particularly if you're shooting in black and white.

(Click image for full resolution)

fiftyonepointsix · Joined: 30 Apr 2017 Posts: 292

" Super Rokkor 5cm F1.8. This lens is quite sharp wide open with good contrast similar to the earlier Rokkors, as it is multicoated, "

I recently picked up the 5cm F1.8 in Leica mount, it is a single-coated lens. It has higher contrast that the earlier 5cm F2, but most likely through the use of newer glass and optical formula. The 5cm F2 is unusual in that it uses the same optical configuration of the Leica Summitar, 7 elements in 4 groups.

I converted my Minolta MC 501/.4 to Leica mount. I need to do a comparison with the native Leica mount lenses.

y · Joined: 11 Aug 2013 Posts: 308 Location: EU

The 55/1.7 holds up to its promise. It really produces very pleasing bokeh.

TeemÅ · Joined: 07 Apr 2016 Posts: 586 Location: Australia

I should add that these images were shot in RAW, and the only edit was to set the white balance to the same value for all. And, a hood was used on each lens. In terms of flare and contrast control, the Super Rokkor performs much closer to the MC 50mm than the MC 58 or 55. However many layers they used, it is very effective on this particular lens.

TeemÅ · Joined: 07 Apr 2016 Posts: 586 Location: Australia

fiftyonepointsix · Joined: 30 Apr 2017 Posts: 292

I converted the 50/1.4 MC to RF coupled M-Mount, made a coupling and use a Minolta-Leica adapter. RF Coupled Focus is down to 0.65m.

I've seen the 5cm F2 referred to as a 7/4, and have noted that some lenses such as the Nikkor 5.8cm F1.4 considered air-spaced elements as a group. Take the lens apart, and they are clearly not cemented groups. I did not know the front elements of the 5cm F2 were air-spaced. I have a 5/4 Xenar, discovered only when taking part. Also converted to Leica M mount.

Pentax is generally credited with having the first multi-coated consumer lenses, Nikon started in 1969 with multi-coating the rear elements of the 55/1.2 Nikkor-S. Looking at the 5cm F1.8: the color of the reflections of the coatings used on the front elements are different from the rear, which would be used to balance color rendition. The scheme is the same as the 50/1.4 lens, much later vintage- but still single-coated (Single-Layer coating). The amount of light being reflected seems more consistent with single coated optics. Compared with the SMC Pentax 55/1.7, the reflections of the Minolta 5cm F1.8 are brighter.

TeemÅ · Joined: 07 Apr 2016 Posts: 586 Location: Australia

tf · Joined: 29 Sep 2017 Posts: 162

Lightshow · Joined: 04 Nov 2011 Posts: 3666 Location: Calgary

Care should be taken with the Super Rokkor 5cm f1.8 when installing/removing that you don't force the focus ring past it's stop as it will bend parts inside(the rails), ask me how I know.

TeemÅ · Joined: 07 Apr 2016 Posts: 586 Location: Australia

jamaeolus · Expire: 2015-08-20

Thanks for sharing all the interesting info regarding the history of multi coatings!

TeemÅ · Joined: 07 Apr 2016 Posts: 586 Location: Australia

blotafton · Joined: 08 Aug 2013 Posts: 1636 Location: Sweden

Thanks for posting!