Originally posted by Isnwm Have you ever shot any type of action stuff with your Pwntax 50-135 ? I'm curious to know how well it would perform @ a little league baseball/football game, or even a high school football game
Yes, I shot "some" sports with it - it does not fare well at all with sports using AF (SDM is quite slow with this lens), CIF in MF mode is really the only way to go when shooting sports with it. Now, the sports you have listed, this focal length is too short - you need the 70~200 for this and when shooting high school football a longer focal length should be used (300'ish); you could shoot the HS football with a 70~200 and crop but once you start cropping print-res, if you are not worried about printing as a medium then a 70~200 could do for the HS football.
Originally posted by Isnwm That's my only concern. Length & focus speed.
The HS football action is fast, very very fast and 10x harder to shoot than the common kids soccer game you see pictures of scattered all over the forums here. Football (american football that is) gets really tricky to shoot and that is one of the reasons why you don't see a gazillion great pictures of football floating around the net, it's just freak'n hard to pop good clean shots. But as for your concerns quoted, one of your other concerns should be lens speed (max aperture), a 2.8 is really the must have for shooting football for two reason -> speed and subject isolation.
Originally posted by Isnwm Say the teams were playing from the right hash mark (closest side of the field to me), if I held the camera up and had it pre focused or a great QB throw picture, or the RB running around the corner towards me... Is this expecting too much from the SDM focus ?
In short, YES, you are expecting way to much from SDM to capture this. With that being said, HSM "is without a doubt" faster than SDM, but you are also expecting to much from HSM also, In all honesty, you are expecting too much from nearly all AF systems in that situation -> this is where "CIF" rules and this is why the Tamron shouldn't even be on your list at this point.
CIF Is Your Savior Originally posted by Isnwm I am constantly seeing online that the HSM sigma AF just blows the doors off the competition in AF speed. But at what cost ? How much of a dropoff on IQ is there ?
IQ is subjective as there is a ton of variables that affect it. Out of the box, Pentax lenses (stars and limited's) produce what most people think is some of the best rendering out of any lens manufacturer, and I agree - but again, there are many factors that affect IQ. As for drop off in IQ, there is none between the 70~200 FLD and the *50~135 - both lenses are top notch and produce extremely high resolution images.