dof/bokeh: 55mm F2.8 vs 105mm F4?

i have a 17-55 f2.8 and am considering selling it for a 24-105, i rarely shoot wide and if i do its usually a panorama where i'm taking multiple shots anyways but i often find myself shooting at 55mm wishing i had more reach. i also noticed i rarely shoot at f2.8 except for those odd times where i really want subject isolation, i'd rather not give that up if i can so i'm wondering, if i'm shooting at 55mm and f2.8, would i be able to get similar dof and bokeh by shooting at 105mm and f4 on the 24-105? if anyone has the two lenses and could post examples that would be great, or if you have a 24-70 f2.8 it should be close enough. thanks!

Google DOF calculator to get the figures; bokeh is another matter, though!

Find out for yourself .

http://www.dofmaster.c​om/dofjs.html

As for bokeh quality, I'm not sure. They should all be pretty good. But I dunno, I don't use silly things like zoom lenses.

Here's an example at f/4 from the 24-70 @ 70.

matthew blake wrote in post #5185617
i have a 17-55 f2.8 and am considering selling it for a 24-105, i rarely shoot wide and if i do its usually a panorama where i'm taking multiple shots anyways but i often find myself shooting at 55mm wishing i had more reach. i also noticed i rarely shoot at f2.8 except for those odd times where i really want subject isolation, i'd rather not give that up if i can so i'm wondering, if i'm shooting at 55mm and f2.8, would i be able to get similar dof and bokeh by shooting at 105mm and f4 on the 24-105? if anyone has the two lenses and could post examples that would be great, or if you have a 24-70 f2.8 it should be close enough. thanks!

This is, of course, my own opinion. Questions like this make my head hurt. I'm a die-hard fan of the 17-55 f/2.8 IS lens because it's a unique combination of qualities that no other lens has, either for crop or full-frame bodies -- wide-normal zoom, f/2.8, IS. I would not dream of trading it for a 24-105 on a crop body.

I use the 24-105 on a 5D -- that's what this lens is designed for. Sad for us, there is no wide-angle f/2.8 IS lens for a ff body, but the 24-105 still works nicely as a walk-around lens. But, to get the type of shots that the 17-55 is capable with a crop body, you need a faster lens. Maybe the 24-70 f/2.8 will do, but more likely a fast prime. So, you can't just replace the 17-55 f/2.8 IS with one lens, but you will need two lenses or more -- one when you need IS, one when you need the f/2.8 or wider aperture.

If you really want to swap one fantastically versatile lens for two or three great lenses then more power to ya. My advice, though, would be to hang on to the 17-55 and build a collection from there, including two or three primes, one of the 70-200 series, and the 10-22. I say keep looking up!

And, as far as Perry goes, just realize that he's a "prime basket case"!

well ive had my 17-55 for a year and i really don't shoot at 17mm or f2.8 very often, indoors i prefer using flash and i can count on one hand the number of times i shot something at 17mm where there was no more room to backup had i been limited to 24mm.. i have a 70-200 f4 is as well.

matthew blake wrote in post #5185681
well ive had my 17-55 for a year and i really don't shoot at 17mm or f2.8 very often, indoors i prefer using flash and i can count on one hand the number of times i shot something at 17mm where there was no more room to backup had i been limited to 24mm.. i have a 70-200 f4 is as well.

To each his own! I personally like to be able to shoot with available light. I don't avoid using flash, but sometimes the natural light is best for the shot I want, and that f/2.8 IS really lets me grab it. Or, with my 5D, it would have to be the 85L or the 50 1.4. Sometimes I can get it with the 24-105, sometimes not.

tonylong wrote in post #5185703
To each his own! I personally like to be able to shoot with available light. I don't avoid using flash, but sometimes the natural light is best for the shot I want, and that f/2.8 IS really lets me grab it. Or, with my 5D, it would have to be the 85L or the 50 1.4. Sometimes I can get it with the 24-105, sometimes not.

i just get such sharp detiled results shooting indoors with flash that its really hard for me to shoot available light unless there's really nice daylight streaming through the windows or something which is rare and usually in those cases i shoot at iso400 and 1/30th to get a fair amount of it in the picture. outside there's rarely so little light that i can't shoot at F4 or just increase the iso to 200.. the only time i need fast glass is when i'm shooting indoor sports or events and if i was serious about either i'd get fast primes.. can you post some examples of when you really use f2.8? i wanna know what i'm missing out on

matthew blake wrote in post #5187383
i just get such sharp detiled results shooting indoors with flash that its really hard for me to shoot available light unless there's really nice daylight streaming through the windows or something which is rare and usually in those cases i shoot at iso400 and 1/30th to get a fair amount of it in the picture. outside there's rarely so little light that i can't shoot at F4 or just increase the iso to 200.. the only time i need fast glass is when i'm shooting indoor sports or events and if i was serious about either i'd get fast primes.. can you post some examples of when you really use f2.8? i wanna know what i'm missing out on

Well, off hand here is an example: a simple portrait of my grandson taken with the 17-55 at f/2.8:

Here's another indoor, available light shot at f/2.8 (all of these hand-held). This was with the 85L:

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the prime is nice what iso are those? i just find when shooting indoors i'm usually shooting my nieces and nephews who rarely remain still so even at f2.8 i end up needing high iso and with flash i don't plus the picture is as crisp as can be. what do you do at night indoors? at f2.8 to get a decent shutter speed i'd need to shoot at iso 3200 and that probably still wouldn't be enough.. with a flash the difference is night and day in terms of detail and clarity. im just wondering if i'm too dependant on my flash indoors i'll have to try without again just to see

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I'm not saying you can't get good shots with the 24-105. I do use this lens and have gotten some good indoor shots with it even, but when it comes to available-light shooting, every stop helps!

it sure would be nice to have f1.2 though whats a full stop less than f2? f1.4? and is f1.2 a full stop lower or half stop?

matthew blake wrote in post #5187598
it sure would be nice to have f1.2 though whats a full stop less than f2? f1.4? and is f1.2 a full stop lower or half stop?

1.4 is a stop wider than 2.0, but I think 1.2 is only a third of a stop wider than 1.4 (1 stop wider than 1.8 ).