[Designosophy]

I have the FA 50/1.7 and the M 50/1.4. The M 50/1.4 isn't really relevant to this discussion, but I can say that, being accustomed to the bokeh of the f/1.4 lens, I am very happy with the 1.7. Here is a sample at f/2.0:




And here is a sample at 1.7. I took this photo specifically to examine bokeh/sharpness.



...with a 100% crop:



Caveat: My copy of the FA 50/1.7 has some fungus, so I imagine it could be sharper.

[Pentaxor]

I have the FA 50/1.7 and the M 50/1.4. The M 50/1.4 isn't really relevant to this discussion, but I can say that, being accustomed to the bokeh of the f/1.4 lens, I am very happy with the 1.7. Here is a sample at f/2.0:




And here is a sample at 1.7. I took this photo specifically to examine bokeh/sharpness.



...with a 100% crop:



Caveat: My copy of the FA 50/1.7 has some fungus, so I imagine it could be sharper.

to each his own and I do in fact prefer the 50/1.7's rendering.

[CEWren]

And here is a sample at 1.7. I took this photo specifically to examine bokeh/sharpness.

drool worthy bokeh there

[alphanerd]

If you had to choose between these two lenses which one would you prefer?

I recently bought a F1.7, because it's cheaper, and everyone says they're both great. Also, I had a M1.7 that I liked; so I figured I'd like the F1.7. So far, I do.

[RioRico]

Another way to look at it, and this applies to other focal lengths and apertures too: If within a certain lens line and at the same focal length, the slightly slower lens is about the same price as the faster one, then the faster one is probably the better value. If the slower lens costs notably less than the faster, then the slower may be the better value.

I emphasize 'value' -- faster glass is generally valued higher than slower glass. Lensmakers are reputed to put more effort into making faster vs slower lenses. A number I seem to recall is that every 1/3 f-stop requires 3x the design and construction resources. Something like that. Faster primes are more likely to be a maker's 'flagship' glass, as in: NOTHING is better than a K or A 50/1.2!! If an A50/1.2 and an A50/1.7 are within US$100 of each other, the f/1.2 is quite the better value. Pentax 50/1.7's are common and quite good. 50/1.2's are uncommon and great. And IMHO 50/1.4's are asymmetrically in-between: common and pretty great. And many others seem to agree, hence the usual price differential between these.

Everyone has their own preferences. And even mine vary. The Fifty that is *always* in my bag is a CZJ Tessar 50/2.8 (12 iris blades) that cost me all of US$7 shipped. There's nothing else quite like it, just as there's nothing else quite like my K50/1.2, but for totally different reasons. If I didn't have faster and odder 50-55's, I might carry the f/1.7-1.8's more often. (I'm a perv; I'll sometimes carry four different Fifty's at once.) And so it goes...

[ChopperCharles]

For me, it was a no brainer. I like very sharp lenses, and I found a *mint* copy of the F50 1.7 for $160, which is notably less than the normal going price. So far I've been shooting quite a bit wide open, and I'm very pleased with the lens. VERY pleased. I would however be interested in seeing comparison shots of the same subject between the 1.4 and 1.7 -- both lenses at f1.7.

Charles.

[danielchtong]

My big problem with the 1.7 is the bokeh. It's pretty harsh compared to the 1.4. ......The 1.7 is sharp, but the colour leaves something to be desired and I find the backgrounds rather harsh. Harsher, even, then my K 55 f1.8.

Would you call the background harsh?

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Last edited by danielchtong; 12-17-2011 at 04:18 PM.

[PentaxDK]

Just posting examples of the sharpness and bokeh using SMC Pentax-M at F/1.7 and K10d. No, image is not sharp at this stop, but the bokeh is glorious.

[civiletti]

Sharpness is a bourgeois conceit.
--Henri Cartier-Bresson

Cartier-Bresson's photos are fuzzy.
--Ansel Adams

[civiletti]

And the F 50/1.4 is allegedly the best of the Quartet in sharpness etc.

Photodo scored the MTF of the F 50/1.4 at 4.6 tied with the F 50/2.8 macro and the F 50/1. at 4.4 and the FA 50/1.4 at 4.2. Those are good scores as were the specific scores. However, the also scored the A 50/2 at 4.0 which was a bit of a surprise. I would have guessed it to come in at 3.6 or 3.7.

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Keep in mind though that most tests are from single lens samples and is hardly statistical.

According to: http://www.takinami.com/yoshihiko/photo/lens_test/pentax_normal.html

the 50/2.8 is capable of considerably more resolution.