I know pretty little about photography and am hoping some of you pros don't mind sharing some advice. I've read a lot of previous reports and have a good idea but still have some questions.
I have a canon eos 300D and broke my cosina 100-400 lens and need to replace it. The main question being do I need to spend $1600 to achieve what i want? I am mainly a spotter and don't need the photo's to be to of any amazing standards. However one thing I am using the camera for a lot more know is for taking photo's of aircraft at a large distance and then zooming in to obtain the registraion such as out of the plane window on arrival and overflights of Davis Monthan and Marana. With my previous lens there was a gradual deterioration until the point where I was unable to take any photo's in AF mode. It would focus but not take and I had to switch to manual by which time it was usually to late. Trying to get the focus perfect in manual was very difficult and there was a definate loss of quality the further towards 400mm you got.
So I need a lens that will still AF and take at 400 or 500m that will be of good enough quality to zoom in and get regs. The photo's themselves don't have to be amazingly sharp or anything. I'm sure they will be good enough for me.
The obvious choice seems to be the canon 100-400 from what I read although the bigma's range is better for me as I won't need a smaller lens. However I would like opinions on cheaper lenses. There are some sigma and canon lenses upto 300mm for only $200 to $300. If I put a teleconverter on one of these will I be able to get results good enough for what I want or am I likely to get similar problems to my previous lens? Does anyone have any experience using these.
The other lens that came up in previous discussions was a sigma 100-300 for $1200 and using a teleconverter ($300). Firstly will this provide the same or better results as the bigma or canon 100-400 as the price difference is $100. Secondly can anyone justify paying $900 or more for this 100-300mm lens than the cheaper ones for what I need it to do.
My next question is about the teleconverters. Discussions seem to say the 1.4X is better than the 2X. In what way? Will the 2X be just as good upto 1.4 but then lose quality after that or is it just completely not as good at any magnification.
Appreciate your help