Don't understand why anyone would sell an EF 24-70 f/2.8L II to get a 35 f/1.4L II. Save $$$ and have both. They are different enough. I really wish I could have both.
Don't understand that a zoom makes one lazy and inhibits shot planning or forces one to do anything. Crop sensor cameras don't make us lazy do they?
If one must be forced by a lens to do something then one is already lazy. Just set the 24-70 @ 35mm, slap on a piece of gaffers tape, and force oneself to pretend there is a prime 35mm attached. You are a photographer. If one feels forced into having to do something just because one has a zoom or prime attached, one has a personal problem, not a lens problem.
I really don't understand the lazy part (I read that statement a lot in zoom vs prime discussions.). Every shot should be planned. I have no idea how a zoom takes any of that away. No idea at all. We don't plan where to stand or which focal length to use? Please. When one chooses to shoot at 35mm he has chosen a focal length to shoot at. Same with a zoom. Depth of field is affected by focal length, aperture, and distance to the subject. It seems a zoom has a distinct advantage here with its much better variability.
Pro for zoom?
1. Far more versatility.
2. Fewer lens changes.
3. Cost: $1,799 (B&H) (Same price as the single prime.)
Con for zoom?
1. Weight? (24-70 II = 28.4 oz.) (1.68 oz heavier. Non-issue)
2. Smaller aperture: f/2.8
3. No IS.
4. Makes one lazy (Personal problem, not a lens problem.)
Pro for Prime (35mm f/1.4L II)
1. Weight 26.72 oz (1.68 oz lighter. Non-issue)
2. Larger Aperture: f/1.4 Possible benefit for portraits, but not if one is stopping down to f/2.8 anyway. For low light? I don't know. Very thin depth of field may outweigh wide aperture difference. I might have to rent one since I've never used it.
3. Keeps one from being lazy (No it doesn't.)
4. Forces one to plan shots more better (No it doesn't.).
5. I can zoom with my feet. (Not always, you can't.).
Con for Prime
1. Cost: $1,799 (B&H) (Same price as the zoom.) Cost for two primes? About double... close to $3,600.
2. Far less versatile. One will be forced to buy more primes. The weight advantage (1.68 oz), in the long run, is a complete myth. One will have to carry another lens at least sometimes.
3. No IS.
4. "I can zoom with my feet." Not always you can't.
5. More lens changes.
So really the choice is aperture (Valid consideration), and your financial tolerance for buying more primes to fill in the gaps (Another valid consideration). Laziness, weight, and one to one costs are non-issues. Weight becomes a very real issue if you are having to carry more primes. 35mm alone doesn't always cut it.
Cost advantage goes to the zoom for sure.
Laziness? Not being careful planning a shot or the proper focal length for the shot? A lens can't fix that.
Sharpness? It is very hard to beat the EF 24-70 f/2.8L II in the sharpness dept. I'd like to see a real world comparison between the two.
I think that if you want the 35 f/1.4 II you should get it, but don't look at it as a replacement for the 24-70 f/2.8L II. It isn't.
The 35mm isn't going to make you a better photographer, help you lose weight, make you less lazy, or turn your feet into a zoom lens motor. It is a great lens, but your costs for the shorter end of things will at least double and possibly triple.
It is all personal choice. Good luck to you!