Originally posted by alamo5000 tamron 70-200 f2.8 which would take care of my indoors lower light stuff...but doesn't have a whole lot of stretch to it when it comes right down to it.
The 70-200 2.8 zooms are really the work horses of many pro sport/wedding photogs from what I understand. Good IQ and relatively fast max aperture.
Originally posted by alamo5000 also find very attractive is the sigma 50-500
I personally have the 150-500 OS HMS it is a really nice lens, for the price, but fast it is not! I have difficulties using it on my K-7 as I limit my ISO to about ISO1200 due to high noise (IMO) when I am out birding. The K-5 I have heard is a whole different kettle of fish with good ISO up to 6400. Currently your options are quite limited other than the sigmas when using k-mount at the super-telephoto end (except when collecting legacy glass which is hard to find)
Most pro sports shooters when shooting indoor/night football matches will have something in the 400 F2.8 or F4 ballpark if that gives you an idea of what gets used. IE very expensive lenses.
Originally posted by alamo5000 I am wondering what kind of shutter speeds you can realistically get with a sigma 50-500 lets say at full zoom in various lighting situations... (bright sunshine all the way to say indoor baseball games)
Some examples from shots I have taken with 150-500 OS @500mm
Bright sunshine = ISO 1250 1/1000s F10
Shade = ISO 1600 1/500 F8
Dull Overcast = ISO 2000 1/160s F8
Indoors Good light = ISO 1250 1/60 F6.3
Indoors Poor Light = ISO 6400 1/10 F7.1
But this is going to be pretty much Identical for any lens you get. the only difference is that when using longer lenses camera shake is amplified.
As for the trigonometry basically you just need to substitute appropriate values in for X,Y or Theta(FOV) then solve for the unknown. I have attached a bit of a maths lesson for this type of question.