[GLXLR]

Full stops are F1.4, F2.0, F2.8 and F4.0
So the FA 50mm is 2 stops faster with a very shallow DOF when wide open (a plus IMO for some situations) and the 50-135 is one stop faster which with a camera like the K20 or K-7 could be compensated much of the time by an ISO boost. But size and weight are going to be factors as Wheatfield says.

These are very different beasts and it's either size and length vs speed and shorter FL. You really have to determine which is most important for your shooting style.

My bad i thought he was talking bout differece of 50-135mm and 60-250mm

[melander]

I would recomend the 50-135 so that you get one fast lens to use when light isnt enough.

Mina 2 ören

[calicojack]

I think the 50-135 is better. If you really need the longer focal length, after you buy the 50-135, you'll still have enough left over to pick up a used Sigma 135-400 (or similar). That's what I did.

[MikePerham]

Well, I had the Sigma EX 100-300 F4 lens already so I went with the 50-135. I have to admit I like the smaller lighter 50-135 focal length and faster f2.8 lens and use it a lot more than I did the 100-300 back in my 35mm days. Today, I use the 100-300 at the long end only and so I am thinking I will trade that off for the DA* 300 F4, however, would prefer something even longer so waiting to see if we get a 400 F4. If that happens, I will get the 200 F2.8 and 400 F4.

[bentax]

i cant imagine my photography without the 50-135