1, was thinking of upgrading my 70-200 f4 to the IS version. It's about twice the cost, but from what I have read the IS is just as sharp if not sharper & the IS is a big plus towards the long focal lenths..............
The only reason I would make this switch is if you find yourself frequently shooting in situations where your shutter speed does not equal 1/focal length. If you are always outside shooting at 1/800, then you don't need the IS. If you are often inside shooting 1/100 at 200mm, then the IS may benefit you.
2, Selling my 24-105 f4 & getting a 24-70 f2.8. I seem to be doing alot of portraits lately & although the 24-105 yields very nice results, the brick seems to be the lens of choice for this kind of shooting. I have read alot of the threads between these 2 lenses, and love my 24-105, but have the itch & looking to try something different.
I wouldn't really suggest that you do this. Your gear list shows that you have the 70-200 f/4 and the 50mm f/1.4. These are both excellent portrait lenses. I also went to your gallery and looked at your portrait collection and a few others. What I saw here was alot of direct flash, red eyes, harsh shadows, and photoshopped backgrounds.
It is my opinion that you would benefit more from learning and practicing better technique than you would from buying an f/2.8 lens. Spend some time bouncing your flash, learning the rules of and experimenting with DOF, and keeping an eye out for appropriate backgrounds and portrait settings. You can do all of these things with the gear you already have and it won't cost you a thing.
I am certainly not an expert photographer, but I used to take portraits and blur the backgrounds in Photoshop just as you have done. I don't need to do that anymore and I have some of the same lenses that you do.
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