CO wrote:
The lenses that have been mentioned are excellent. For an economical lens, check out the Tamron 100-400mm f/4.5-6.3. I've been impressed with it. It's fully weather sealed and sells for $799. It weights only 1115 grams which makes it hand hold able for long periods. It's compatible with Tamron's TAP-in console for AF fine tuning. Here's a photo I took with it on a Nikon D7500.