rakesh wrote in post #8324545
My prime use for going to prime is that it should be easy holdable
and sharp and can shoot both birds and mammals but not in Zoo environment but in open forest areas.
So, please advise on this basis. The 2X TC I've was never used because I did not have compatible lens till now.
In terms of hand holding, I'd recommend the 300/2.8 with 1.4X and/or 2X. I think you are heading in that direction anyway, but here's one more person's opinions.
I have to disagree with a lot of the responses you've gotten, while agreeing with some others.
Yes, with small animals and birds you will never think you have a long enough lens. There will always be a little critter just out of range that you wish you could capture in an image. If you have a 300mm, you'll sometimes wish you had a 500mm. If you have a 500mm, you'll sometimes wish you had an 800mm. If you ever getan 800mm, you'll occasionally wish they made an affordable, Image Stabilized 1200mm! If they ever do, rest assured there will be times you'll still want something longer! Especially if photographing birds (read Art Morris' articles at www.birdsasart.com).
But, a longer lens actually isn't necessarily the only choice or always the correct answer. There are times to just sit back and enjoy the show, to be patient and wait for nature to come to you and within range of your lens.
I have used both the lenses you're considering for about eight years. The 300mm is far more hand holdable. I still use it on a tripod with a Wimberley Sidekick most of the time. It's more portable, fits into a much smaller backpack and leaves more room for other lenses and accessories.
Most people considering one of these lenses really should budget for a high quality tripod as well. That can be upwards of $1000 additional cost. I'd rank it as "practically essential" for the 500mm, and "very highly desirable" for the 300mm. I use a Gitzo (an older model 1325 CF which has no center column, three section legs, and is rated to probably 25+ lbs) with a leveller (Gitzo, it's fast to set up), a heavy duty ballhead (Kirk BH-1) and the gimbal mount (Sidekick, it has several advantages over a full gimbal head as far as I'm concerned). Occasionally I'll use a monopod with either lens. And only very rarely I'll hand hold or use a beanbag, tree stump, fence post, car hood, or similar. I'd guess 90%+ of the time, my 300mm is used on a tripod. With the 500mm, make that 99% of the time. If you truly want a hand holdable lens, you might be better off looking at the 300/4 IS or 100-400 IS zoom.
Eventually you may want both lenses as they tend to serve different purposes and compliment each other well. The 500mm is in some ways more difficult to use, another reason I'd recommend most people start with the 300mm and then add or graduate to the 500mm later, after mastering the shorter lens. I probably use the 300mm about 4X as much as the 500mm, but I might use the 500mm more often if shooting more wildlife photos, and less sports/events.
Speaking from lots of personal experience, I can assure you that on 5D, 5D Mk II, 10D, 30D, 50D and EOS-3 the 300mm is noticeably faster auto focusing than the 500mm. (I've used both lenses on some other film and digitalbodies, too, but it's been a while and/or only briefly, so I won't try to compare.)
Both lenses really are plenty fast focusing. The AF on the 300mm is just about instantaneous, while there's a tiny lag with the 500mm. With the 500mm it's harder to find your subject initially, easier to lose them when tracking and it's AF is more likely to hunt. None of this is at all surprising for a longer tele with a smaller max aperture. And, please don't get me wrong, the 500mm has exceptional AF capabilities. Just not quite as great as the 300mm. They both slow down a little bit with teleconverter or extension tubes attached. Again, no surprises there.
The 500mm, as an f4 lens generally *will not* auto focus with 2X TC (making for an effective f8 ) attached to it, on any camera *other than* a 1-Series camera or EOS-3 (all of which have the 45 point AF system). Even on those cameras the 500/2X combo will only focus with center AF point. With a 1.4X on it (effective f5.6), you'll be pretty much limited to using just the center point on any of the cameras that don't have the 45 point AF system. There are some kluges you can use to try to get it to auto focus, and some third party teleconverters may not be recognized by the camera and might still give some AF, but it will be slower and might be less accurate.
The 300/2.8 will AF with either TC attached, but you'll be limited to center AF point only on most bodies when using it with a 2X. It slows a bit, but not a lot (varies depending upon camera model).
Oh, and "Lens Work III" is full of typos, errors and omissions. No kidding. I think I must have noticed 25 or more the first time I read it. And I've looked for specific info that it doesn't - but should - contain (what tripod mounting ring fits the 200/2.8 II lens, for example). I've seriously considered offering my editing services to Canon, if and when they get around to "Lens Work IV".
The 300mm is slightly sharper, rendering incredible detail. The 500mm is phenomenal, too... for a 500mm. But the 300mm is even sharper. Both have great color rendition. The 500mm softens a little and tends to get warmer with the Canon 2X II attached. This is not as noticeable with the 1.4X II, or with either TC on the 300mm. I haven't really experimented much with the third party TCs, some of which I've heard are great, and will leave it up to others to advise about those.
I'd strongly suggest starting out with the 300mm and a couple TCs, then adding the 500mm later, if you still wish to do so. Learn stalking skills, use hides and blinds, use attractants to get your subjects in closer, within range of whatever lenses you have. If you were using a full frame camera, I'd suggest you consider getting a cropper for the extra "reach". But you already have a cropper, so be aware that a full framer really utilizes the 300mm's (or 500mm's) optical capabilities to their fullest.
Niall Benvie, a well known wildlife photographer based in Europe, used a 300/2.8 with 1.4X as his longest lens setup for the first ten years of his professional career. And that was all on film cameras (i.e., full frame).
That's just my two cents worth.
Oh, and you might consider renting and trying out either or both lenses. They are pretty widely available for rent and a "test drive" might help answer all your questions.