50-135mm telephoto zoom
I have been using a 20 year old film-type 35-105mm ƒ3.5-4.5 macro/zoom that my sister lent me just after I bought my K20D camera. This was one of the prime reasons I bought a Pentax ... I can use lenses made for older (sometimes much older) Pentax film cameras. This lens was only made from 1988-89. Anne wanted to get close shots of her children as the grew, without having to be so close as to interfere with the shot. The best pictures of children are taken when they are not aware of the camera and act naturally ... particularly in the case of my nephew. It was very well suited for my sisters needs. While it has been instructive, I have found this older lens limiting in terms of reach and the amount of light needed to get a relatively noise free image.
I wanted to be able to get closer ... much closer, particularly to some of the wildlife around Lost Lagoon. So a couple of weekends back, I rented a telephoto zoom 55-135mm ƒ2.8 lens from Leo's Cameras on Granville St. in Vancouver. For $30.00, I was able to try this lens out for two days. And what a treat! Because the K20D has a ¾ size APS-C sensor, 55-135mm becomes 75-180mm, which allowed me to get this nicely detailed shot of two sunning turtles that were about 50 feet away. This is closer to the type of photography I want to persue, and I am quite happy with my first attempts.
A telephoto zoom allows you to have a tight depth of field, which I use to keep my subject in focus while blurring the background and foreground, further heightening the subject. I had a lot of fun, learned a lot, and have published some of the more interesting shots in this special gallery on my main website.
But what I liked more than anything was the fast glass! Going from ƒ3.5-4.5 to ƒ2.8 made a huge difference on the amount of flexibility I had with light levels. It allowed me to use a much lower ISO setting, significantly reducing the amount of noise in the image.
Most significantly, there is much more leeway with two of the three main creative elements of photography ... shutter speed and aperture size, the third (and probably the most important) being composition.
What was the biggest lesson? Any telephoto zoom lens that I buy will be at least 350mm and no slower than ƒ3.5-4.0. Anything else would, in the longer run, be a waste of money.