Originally posted by remark13 Thanks, think I got your point. Would love to have the sigma 150-500mm but I guess being overly optimistic I was hoping for a while I save option -- doesn't happen in photography I gather. Guess I will continue to implement the always free use of my legs to get me as close as I can and continue to search out new sites.
Just to give you a little guidance, do some simple math
Image size = subject size x focal length / distance
Let's think about what you are shooting
Although birds come I all sizes or shapes, you can think of them really as large wading birds up to 1 meter tall, medium hawks etc at 0.5 meters, large birds at 0.25 meters and tiny ones at 0.1 meters tall
If you are shooting even at a modest distance, let's say 25 meters, even with a 500 mm lens here is what you get
Large wading birds = 20mm
Medium hawk = 10mm
Large birds= 5mm
Small birds = 2mm
Considering a pentax DSLR frame is 16 x 24 mm you would get a good shot and virtually fill the frame with something like a big heron or egret, you would be cropping to about 25% of the frame for a medium hawk on a branch, you would use at best 10% of the frame for a large bird like a robin or grackle, and a small bird at best will be a record shot. If you want to do birds on the cheap, look at a pentax Q. The sensor is a crop factor of 5.5 from a 35mm film camera, and is about 6.17x 4.55 mm so even a small bird at 25mm will fill the frame with the same 500mm lens. You can pick up shorter lenses, in then200mm range that would be equal to about 1100mm on film or 750-800 mm compared to your pentax DSLR quite cheap. And you don't need the arms of a gorilla to hold the lens