Supplementary article comparing bokeh and sharpness between two popular vintage versions of the M Series 50mm from Pentax.
Posted: 23/10/2024 - 17:53
With the latest manual focus lens review, we looked at the SMC Pentax-M 50mm f/1.4 lens and had the opportunity to attempt to compare the bokeh with that of the SMC Pentax-M 50mm f/1.7 lens already looked at. The "received wisdom" is deeply seated and tells us that the f/1.4 version is contrastier, grittier and more suited to reportage but at the expense of detailed resolution. The f/1.7 version is pictorially more pleasant but loses out on absolute speed.
This of course is fine as far as it goes, but it applies to a world where the use was on film, and even then mainly in black and white so far as the amateur photographer was concerned. Now we have mainly colour, we have digital and we also have a term "bokeh" that is delightfully vague and usually described in colourful and exotic phrasology that reflects its lack of scientific precision.
Read the full reviews:
In our lens reviews we define bokeh as being the quality of the gradation of the out of focus areas in an image. This usually means the background and when the bokeh is good it makes an unobtrusive but smooth backdrop to, say, a portrait of perhaps a person or perhaps a flower. Highlights will be rendered smoothly with no doughnut effects or ragged edges, the current fashion being for rounded aperture blades rather than sharp edged hexagons.
The Results
Having decided then that our experiment is not totally objective or scientific, we can nonetheless see what we have, draw conclusions and see if the bokeh of the two lenses is pleasing to ourselves or not. To this end Rick has introduced a slider for the images and we can seamlessly move from the f/1.4 to the f/1.7 to see how the effect changes at each aperture. The 8-bladed diaphragm of the f/1.4 clearly gives a more rounded highlight than the 6-bladed f/1.7 but that is a matter of taste, not a technical measurement.
For all the comparison frames the left side is the SMC Pentax-M 50mm f/1.4 and the right side the SMC Pentax-M 50mm f/1.7
f/1.4 versus f/1.7 (wide open)
Aperture at f/2
Aperture at f/2.8
Aperture at f/4
Aperture at f/5.6
Aperture at f/8
Aperture at f/11
MTF Chart
So which do we prefer? Frankly, on digital it is a moot point as the effects are different rather than better or worse, but after very careful examination then probably it still holds that the f/1.7 lens has the most attractive out of focus effects. As always, beauty is in the eye of the beholder.
Let us know your thoughts in the comments below.
Have fun with the f/1.2!
It was an interesting exercise to do, but the possibilities for comparisons like this are endless, there are not enough hours in the day! There may be a difference between the K1 and K10D, but we don't know for sure without experimenting. That's part of the problem with modern testing - the "film" (sensor) we use varies over the years, so the results really need constantly repeating. If we did use a standard film, at one time in black and white that would be Kodak Technical Pan (ISO 16) and it would be the same for all lenses tested. There are modules available that test lenses digitally without needing a sensor but that is way outside what is affordable to use.
Have fun with the f/1.2!
Thank you for the explanations
Perhaps I can scoop up a 1.4 & 1.7 somewhere down the road and do some comparisons with the 1.2.
Will keep you posted - and thanks again for sharing all these valuable & inspirational insights.
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72 posts
1 years
Copenhagen,
Denmark
I ordered a 50mm 1.2 yesterday and came across this post and analysis shortly afterwards.
An interesting to read, the slider is a great way to illustrate the differences.
I was surprised by the difference in saturation—I expected the color representation to be more similar.
How do you think the SMC Pentax-A 50mm 1.2 compares to the 1.7 and 1.4?
I like the tonality of the 1.7 the best, but I’m guessing there will be quite a difference between using it on a K1 versus my current go-to camera, the K10D?
And thanks again for opening up this world of older lenses, coming from the 77mm 1.8 and 35mm 2.8 macro limited ones.
All the best,
Kasper