what camera? full size sensor?
I own a 24-70L and it does produce beautiful pics, but I would
sell your primes.
One simple reason is that the 24-70L is bulky and heavy, and whenever I can get away with carrying a prime instead, I do prefer it.
I have used a friend's 85/1.8 and loved it, would not seperate with it if I owned one.
The 50/1.8 I don't know, but if it is anything like my 50/1.4 (not an L either), same true for it.
On the 350D I always like the pictures from the 50mm better than the ones taken with the L @ 50mm or around. I don't miss the zoom when I don't have it.
on the 5D I haven't made the comparison.
I'd try to keep the 85mm and sell only the other two, to buy the zoom lens. You always need a lens like this one (85mm) for low light conditions.
About the weight, well yes of course, it is lighter to go with a 85mm than with a zoom like any of those you mentioned. But still, I wouldn't shoot a weeding with any of those prime lenses only, even though it would be easier in weight... Maybe because I don't know how to use them, or probably because I find more comfortable to use my zoom lens (24-105mm) for this kind of photography... Anyway, I shot around 6 hours with the zoom continuously and it wasn't that tiresome.
On the other hand it was not the same when I went to the aquarium the other day. I used my 85mm f 1.8, I shot all my pictures to 3200iso and my pictures were way much better than the ones I took the year before with my zoom.
Hope my comment helps and my ideas of what I want to say are clear...
This is a tricky subject. I have a 50mm @ 1.4 and an 85mm @ 1.8 as prime lenses but itâs my 17-55mm @ 2.8 that I leave on my camera for general work. At the time these were bought you couldnât buy long-range zoom lenses to match them but whoâs to say that technology canât advance that far? Of course these lenses are going to be improved on eventually but as far as Iâm concerned I am so used to using them I donât think I would want to change. Yes they are bulky and heavy but to me that means rugged and reliable (I am rather âold schoolâ when it comes to quality and am suspicious of anything invented just to save weight). Although my gear is Nikon and not Cannon I think the same rules apply. I have always seen lenses as long-term investments despite whichever body they happen to be on.
The 24 and the 50 are average primes. Certainly the 85 is a great lens. I agree with Irma especially as the 85 extends your range a little over the 24-70. That said - the 85 is worth the most out of the three and would get you the biggest return if you sell it.
If you had only one or the other I would go with the 24-70. It is a killer lens on the 5D and doubles as a macro.
I'm told that there aren't enough primes for my system, but it's hard for me to judge as I wouldn't buy wide primes even if they were offered. Telephoto zooms are another matter -- I'd love to get my hands on a 150f/2 -- but I've never quite "gotten" the point of the WA stuff. It's been intriguing to see how the other half (okay, 93%) lives.
I recently took the plunge myself and got a 24-70L f/2.8. It's a wonderful piece of glass but certainly bulky for a standard zoom.
Since owning it I've barely touched my Sigma 28mm f/1.8 (which is comparable in many ways to both your Canon 24mm f/2.8 and your 50mm f/1.8 Mk1, not just in specs but also in IQ, features, and usability - or lack thereof). I keep meaning to dig out my 28mm to use, but considering it doesn't get sharp until f/2.2 there is only a 2/3 stop advantage over the 24-70 which is much more user-friendly and flexible.
I have happily kept using my Canon 50mm f/1.4 however because it's IQ is exceptional (even wide-open) and it's a full 2 stops faster than the 24-70. Until they put IS into the 24-70, you'll still need something to use for low-light. In my experience the 50mm f/1.8 just doesn't cut it, but the f/1.4 does nicely. It's also nice to have a compact 50mm prime handy because the 24-70 is not a discreet lens.
I haven't really used the 85mm f/1.8, but certainly it has a good reputation.
It sounds to me like the advice given by the others is very sound; You might not miss the 24mm and 50mm lenses, but it could be worth keeping the 85.
1. Consider your final output size..this might sway one to sell primes...
2. do not sell your primes...but...
3. if you do...let me have first dabs on the wideangle(that'll give me just the reason I need to get a 5D body then!)
4. build a shed in the back garden, rent it out to some eastern europeans= keep the primes, then get the L zoom...then shoot a photo-doc about Polish ghettoes in Redditch.
If you only remember one of the above, let it be number 3.