Testing, testing....

Just a quick shot of my boy Rio. Trying out the FA 50mm 1.4 that I bought from forum member Colin (col55555ine)

Despite having used exclusively Pentax kit since 1979 I had never owned an autofocus 50mm. Despite there being a new one (D-FA 50mm) on the horizon, I had a hankering after this lens and I am glad i bought it. Just as the reviews say it is quite soft at 1.4 but sharpens up nicely from f2 (even 1.7 is noticeable difference). CA is also a bit of a problem wide open. It sits very nicely on the K1 and will make a nice walkabout lens when I dont have the energy for the D-FA 24-70.

Thanks again Colin

Yep, I've noticed that myself, under f2 not sharp but f2 and above then wow!

But isnt the fastness of the lens. suposedly what you pay the extra for ....?

Indeed it is, but all lenses display softness to some degree when wide open. There is also the bokeh to consider, as a lens that displays pleasant bokeh whilst delivering acceptable sharpness in the narrow focus zone will more often than not produce a better image than a technically sharper lens with poor bokeh.

The quick test shot i posted here is certainly sharp enough where I wanted it to be, and the transition to, and the rendering of the OOF is smooth. This was shot at 1.4

It's been posted many times the f/1.7 lenses are much sharper than the f/1.4 lenses at wide apertures.

An exception is the Pentax-A 50mm f/1.4 which I always find to be very close to the Pentax-A 50mm f/1.7 except that the f/1.7 has a flatter field.

Back in the film days with the 'M' Series I did some quite exhaustive tests and found that the edges on the M f/1.4 were far better than the edges on the M f/1.7 at around f/4 which was my most used aperture in bad light. So I stuck with the f/1.4 for all 50mm work.

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lovely shot Peter - seems to work well on the K1

I have often wondered about ultra fast lenses, and the fact that most are soft wide open, I just couldnt see the point in them.
This I do really like.
As Peter said, its sharp where it needs to be and the transition is just lovely.
Good combo for me anyway.
Nice shooting.

Other advantages of fast lenses are the ability to use a faster shutter speed or a lower ISO, and of course the brighter view you get looking through the viewfinder. Can make a big difference expecially if manually focussing in low light. 1.4 versus 2.8 (typical of a general zoom) is two stops. That is four times as much light.