It's not long enough. 70-200 with extender gives you 280mm, just a touch shorter than what you have now. You'd have more latitude to crop, but would need to be close for acceptable results. If wildlife is your goal then you probably want 400mm.
If you want to get to 300mm without spending a bunch of money, there are a lot of people who like the Tamron 70-300 VC. It looks terrible on the site's image comparison tool, but users seem to like it and many get pretty good results with it.
All that said... if you're trying to match the IQ of many of the posters here it could cost you a huge amount of money. Many of the wildlife shots posted are taken with a pro grade body ($3500+) and a 400mm ($1200+) or 500mm ($7000) lenses.
In my opinion, there's something to enjoying the best you can get. Truth told, the 75-300 USM III isn't that great of a lens, but depending upon your budget you can get a better 300mm lens for not a ton of money using either the Tamron, the Canon 70-300 IS, or 70-200 f/4 plus extender. If you can extend your budget to around $1200 you can get the 400mm f/5.6 which is outstanding.
Dave
Last edited by Dave Throgmartin; 07-04-2013 at 12:13 AM.
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http://www.flickr.com/photos/dthrog00/
I wanted to 2nd that thought. I just bought the 70-300 4/5.6 IS on Friday from Adorama. It's the first non-L lens I ever tried and I have to say it is pretty amazing for the price. Yes it's slow glass no doubt but as long as I don't try shooting things it wasn't designed for (fast-action sports) I get really great images.
I've only had it a few days but I don't see a *huge* difference in the IQ compared to my 70-200 2.8IS. There's some, esp at 300mm wide open. But if I'm shooting wide open at 300mm on a 4/5.6 lens I only have myself to blame for soft images. Shooting f/8 or f/11 and lo and behold center and mid-frame IQ is great, a little less than great in the corners. For under $400 I think it was a steal. It's a Canon refurb so it's in great shape, none of the zoom creep this lens is famous for. So far I love it.
That's what the 70-300mm L is for... shooting wide open at 300mm, on a 4-5.6 lens, and it being sharp at the pixel level.
On a crop camera, I recommend the EF-S 55-250mm if on a budget - best value for the money. The 70-300 non-L is not really an upgrade in terms of IQ in my opinion and not worth the extra money over the EF-S. Even if IQ is ok when stopped down - I rarely had use cases for shooting at 200mm or longer at f8 or f11. It probably depends on what you shoot, but for me that rarely happens. AF is not much better, if at all, than the EF-S lens.
So for a real upgrade in terms of IQ and AF, it is one of the 70-200s or the 70-300L (cannot speak to the Tamron)
Arnt
The OP is trying to get better pics without spending a large sum of $$$, as nice as the 70-300L is, it is a large amount of cash more than 70-300 IS or Tamron 70-300.
Arnt's suggestion of the 55-250 is a lost cost way to get there, but 250 can still be kind of short...
Dave
See my photos:
http://www.flickr.com/photos/dthrog00/
I wasn't suggesting the L, but referring to canoli's comment about expecting a variable aperture lens at 300mm to be sharp wide open... it's a valid expectation, given good enough glass. I'd have quoted him, but it's painful on a SurfaceRT.
That's true. I just would not expect a significant improvement with the 70-300 non-L (Unfortunately the Canon EF 75-300mm f/4-5.6 III USM is not available in the image quality comparison tool). Bryan recommends the 70-200 f/4L as an upgrade http://www.the-digital-picture.com/R...ns-Review.aspx. Even with an extender, it will be better than the 75-300, so sedwards already had the right idea asking about this lens.
To add to that point: I would not recommend replacing the current lens with the EF-S 55-250. Instead, I would stick it out until I have the funds available for one of the 70-200 options, maybe with an extender if more focal length is needed.
EF-S 55-250 is great if you don't have any tele zoom yet, and if you are not sure if you want or can spend the money for one of the better options (it was my gateway drug )
Arnt
See my photos:
http://www.flickr.com/photos/dthrog00/