[Spodeworld]

It seems that F and FA lenses have pretty much the same capabilities:
Pentax K-Mount Lenses Explained: The differences between various Pentax lens series

so I was wondering what the difference is.

For example, if I am comparing a F 50mm f1.7 and a FA 50mm f1.7, what would I expect the differences to be?

Thanks.

Steve

[baro-nite]

For most uses, the main difference between the F and FA series is mentioned in the article you link:

While FA lenses are identical in operation to F lenses, they feature improved electronics that support the MTF program line.

Of the specific lenses you mention, optically they are essentially the same. So the only functional difference will be if you use a shooting mode that uses MTF, namely Green or P mode.

[boriscleto]

The differences between F and FA lenses is mainly build quality. Optically the F50 and the FA50 are identical.

Edit: And what baro-nite said about MTF. For some reason I thought it only applied to FA J and the FA Limiteds.

[Docrwm]

Got it covered in two posts - MTF and build quality. All other things being equal (cost, shape of the lenses, etc.) the FAs would be a first choice.

[audiobomber]

What build quality difference is there between F and FA? They look and feel pretty similar to me; good quality plastic shells and metal mounts. Is one supposed to be better built?

[boriscleto]

What build quality difference is there between F and FA? They look and feel pretty similar to me; good quality plastic shells and metal mounts. Is one supposed to be better built?

I believe the F lenses have metal barrels while the FA lenses have plastic barrels. That would account for the weight difference between the two lenses (205g vs 170g).

[Boker]

Isn't the fa version of the 100-300 said to be optically better than the f version?

[mysticcowboy]

My F 50/1.7 has a plastic barrel. Also, since some FA models are still being manufactured, the newer models have better anti-flare coatings than the older F models.

[jatrax]

The F series is simply much cooler. FA series is fine but boring.

[Just1MoreDave]

My F 50/1.7 has a plastic barrel. Also, since some FA models are still being manufactured, the newer models have better anti-flare coatings than the older F models.

The F50/1.7 is weird - plastic shell that feels cheap over mostly metal interior. The A50/1.7 feels better built, yet with more interior plastic.

[seventysixersfan]

I haven't done scientific testing on this but I subjectively feel like my F series lenses (F 28mm, F 35-70) auto-focus a bit faster than my FA lenses (FA 35, FA 50). Not that the FA lenses are slow by any means but the F series just "snap!" into focus with a quick motion.

[boriscleto]

Isn't the fa version of the 100-300 said to be optically better than the f version?

There are two different versions of the FA100-300. The first has power zoom and is F4.5-5.6, it is said to be worse than the F version. The second is F4.7-5.8 and is said to be the best of the 100-300s, the Silver version anyway. The Black version is said to have problems with DSLRs.

[boriscleto]

My F 50/1.7 has a plastic barrel.

Internal or external? All the F series lenses have plastic exteriors, it's the interior that is supposed to be metal.

[Franky2step]

I haven't done scientific testing on this but I subjectively feel like my F series lenses (F 28mm, F 35-70) auto-focus a bit faster than my FA lenses (FA 35, FA 50).
Not that the FA lenses are slow by any means but the F series just "snap!" into focus with a quick motion.

My newly acquired F35-70 literally "snaps" into focus, and so does my F50 f1.7. Both autofocus faster than SDM lenses. My FA Limiteds are slightly slower, and the build quality is second to none(except Zeiss PK).

[audiobomber]

I believe the F lenses have metal barrels while the FA lenses have plastic barrels. That would account for the weight difference between the two lenses (205g vs 170g).

I had an F 28mm, the build seemed no different than my FA lenses, and it is 5g lighter than the FA 28mm according the specs in the Lens Reviews on this site (185g vs 180g).