how can I see the difference in DOF between an f5.6 and f4 lens?

[richard plumb]

I have a 70-300IS,which has a max aperture of f5.6 at the long end. I am constantly wondering about the 70-200f4IS, which is f4 (naturally), but shorter.

Is there any simple way to see the difference in DOF and therefore separation that the f4 would give me compared to the f5.6? I can use DOFcalculators to calculate what it should be, but that doesn't help me visualise how the background might look. Likewise looking on flickr doesn't let me easily compare like for like - subject/background distances will vary etc.

Does anyone have the 70-200f4 (IS or not) and has some simlar zoom shots at both f4 and 5.6?


the only thing I'd be really concerned about is that if I go 70-200 I'd probably use that as a walkaround companion to the 24-105, then be tempted for something like the 100-300 for longer stuff

[salubrious_k]

Have you considered getting a prime?

The 135 f/2 is meant to be the sharpest lens Canon produce, and that way you could see what 3 stops of extra aperture give you, that would be a massive difference DOF-wise.

It costs about the same as the 70-200 f4 IS.

If think the 200 f/2.8 costs the same too, if you want the extra reach.

[hot-fuzz]

I know its not ideal, but compare the F/4 to the f/5.6 at teh long end of your 24-105mm

might give you an idea (again not ideal).
Or if someone is kind enough they might post some test pics for you.

[Brammers]

DoF at a given aperture varies with focal length. So what you should do is zoom the 70-300 to 200mm, open it as close to f4 as you can (I reckon you should be at 4.5 at 200mm) - then go down the range, shooting at f4 and f5.6. Then compare that DoF with 300mm wide open

What this won't show you is the quality of the bokkeh, which will change from lens to lens.

If this helps, at a guess, I'd say that 300mm @ f5.6 will give shallower DoF then 200mm @ f4.

[T0MAT01]

I'm not doing an awful lot atthe moment, so I'll see if I can go and take the same scene at f/4 and f/5.6 for you and post them up here later.

Any particular camera to subject distance you would like?

[danburbridge]

http://www.dofmaster.com/dofjs.html

Just select the focal length, aperture and distance and it will show you the depth of field in feet/meters/cm etc

just seen that you have already mentioned the calculators... doh

It is however worth bearing in mind that longer focal lengths often will not focus as close as shorter ones.

[richard plumb]

Originally Posted by T0MAT01

I'm not doing an awful lot atthe moment, so I'll see if I can go and take the same scene at f/4 and f/5.6 for you and post them up here later.

Any particular camera to subject distance you would like?

hi. thanks for the offer. I don't have anythign in mind really, was just pointing out that flickr searches will be vague on this so makes 1:1 comparisons difficult.

Just wondering what real world differences I'll see - shutter speed possibilities notwithstanding.

[T0MAT01]

OK I've taken a few shots, hope they're of some help to you.
They were all uploaded straight off of the memory card.

These were roughly 1.5m camera to subject (200mm):

f/4:

f/5.6:

These were roughly 2.5m camera to subject (200mm):

f/4:

f/5.6:

These were roughly 7m camera to subject (200mm):
f/4:

f/5.6:

And these were taken at 7m with 70mm focal length:
f/4:

f/5.6:

HTH.

[T0MAT01]

Oops I forgot these 2!

200mm at about 10m:

f/4:

f/5.6:

[richard plumb]

thanks Tomato1. I'll try and do something similar with the 70-300

[senu]

Thanks tomato1 for that effort.
I think it reinforces Brammers correct surmising that the Focal length and distance to subject are variables to consider in addition to the aperture and it may be that for some subjects you see less difference in DOF than others
I tried in the past with the 70-300 (Canon and Sigma) but got bored halfway as I couldnt see a huge difference. With hindsight it may be I didn't persevere enough