Originally posted by justplainpaints Hello,
I am new to photography and Pentax. I have a Pentax K20D and recently purchased a Sigma 70mm-200mm F1.3(I think that is what it is, it is at home and I am at work)anyway, I am shooting pictures at a rodeo. So there is fast action. The lens is great as long as it is daylight but as night moves in it is a problem. Can you help me? What setting do I need to have on my camera. I have it on shutter speed prioity during the day but as night set in I had to move it to Sensitivity with a higher ISO but I lose my fast shutter speed to capture the action. Is there something else I can do?
Thanks,
Lydia
Exposure depends on the following three factors:
1. Shutter speed (this influences how long the sensor/film is exposed to light).
2. Aperture (this influences how much light the sensor/film is exposed to in any given instant).
3. The medium's sensitivity to light.
Your lens has a maximum aperture of f2.8. The general rule for hand holding and shutter speed is 1/x, where x is the focal length of your lens. With a crop camera, like yours, it is 1/x(1.5). Assuming your shooting at 200mm, your minimum shutter should be 1/350s. Your camera has built-in vibration reduction of the sensor shifting sort. I'm not certain to what degree it can compensate. However, if you're reaching the f2.8 and 1/350s bottleneck, your only choice is to raise the sensor's sensitivity and turn on the vibration reduction feature. There is no other way out unless you can add additional light to the scene, via a flash or some 10Ks... but you likely don't have a budget for 10Ks... and I'm talking about a few.
One last note though, vibration reduction will not reduce subject blur, only motion blur induced by unsteady hands. If subject motion is not a factor, and you can do less than 1/200s, then I would recommend you look into a monopod. They are not as stable as tripods, but they reduce two of the six possible vectors of motion (up and down). The other motion vectors are left, right, forward, and backward.